Grain Growth Kinetics in Steels

Project Number: RDS 21381

Grain Growth Kinetics in Steels A Major Qualifying Project Report Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE In partial fulfillment of the requirements for the Degree of Bachelor of Science in Mechanical Engineering

Submitted by: Erik Khzouz ______

Date: April 28, 2011 Approved:

______Professor Richard D. Sisson Jr.

Abstract

The effects of temperature and time on the grain growth kinetics of selected steels have been experimentally determined. The steels examined are 1045, 4140, 4340, 8620, 9310 and 52100. Samples were heat treated at temperatures ranging from 850°C to 1050°C in increments of 50°C and held for 30 minutes, 2, 4, and 9 hours. Using the standard ASTM test methods to measure grain size it was found that grain growth exhibited parabolic behavior and the activation energy for grain growth ranged from 175.2 to 353.4 KJ/mol.

Acknowledgements I would like to thank Professor Richard D. Sisson Jr. for his advice and guidance throughout the duration of this project. I would also like to thank Dr. Boquan Li, Adam Sears for their assistance in ensuring that I had the necessary equipment and training to complete this project. In addition I would like to thank George F. Vander Vort for his assistance with the etchant for revealing prior austenite grain boundaries. Lastly, I would like to thank the following graduate research students: Danielle Belsito, Chun-Min Chou, Guannan Guo, Zhijia Jin, Wendi Liu, Sidath Wijesooriya and Lei Zhang for their experimental and analytical support.

III

Table of Contents

Abstract ...... II Acknowledgements ...... III List of Figures ...... VII List of Tables ...... VIII List of Equations ...... IX 1 Introduction ...... 1 2 Literature Review ...... 2 2.1 Heat Treatment ...... 2 2.1.1 Austenitizing...... 2 2.1.2 Tempering ...... 4 2.2 Grain Size and Growth ...... 5 2.2.1 What is Grain Growth?...... 5 2.2.2 Factors Affecting Grain Growth ...... 6 2.3 Materials ...... 7 2.3.1 AISI 1045 ...... 7 2.3.2 AISI 4140 ...... 7 2.3.3 AISI 4340 ...... 8 2.3.4 AISI 8620 Steel...... 8 2.3.5 AISI 9310 Steel ...... 8 2.3.6 AISI 52100 ...... 8 2.3.7 Material Composition ...... 8 3 Methodology ...... 10 3.1 Furnace Calibration ...... 10 3.1.1 Temperature Mapping ...... 10 3.1.2 Temperature Calibration ...... 10 3.2 Heat Treatment Procedure ...... 11 3.3 Sample Preparation ...... 13 3.4 Optical Microscopy Measurements ...... 13 3.4.1 Hyen Intercept Method ...... 13

3.4.2 Jefferies Method ...... 14 4 Results and Discussion ...... 17 4.1 Gain Size Evolution ...... 17 4.2 Average Grain Diameters ...... 18 4.3 ASTM Grain Size ...... 19 4.4 Effective Time ...... 19 4.5 Ideal Grain Growth ...... 21

4.5.1 Evaluating K and D0 ...... 21 4.5.2 Evaluating Activation Energy ...... 23 5 Conclusions & Recommendations ...... 25 5.1 Heat Treatment ...... 25 5.2 Sample Preparation ...... 25 5.3 Average Grain Size Measurements ...... 25 5.4 Growth Kinetics ...... 26 Works Cited ...... 27 Appendix 1: Isothermal Transformation Diagrams ...... 29 Appendix 2: Sample Grinding & Polishing Procedures ...... 32 Mark V CS600 - Sectioning ...... 32 Beuhler Simplimet II – Mounting ...... 33 Appendix 3: Sample Etching Procedures ...... 34 Appendix 4: Jefferies Planimetric Method Calibration Studies ...... 35 Calibration Study #1 ...... 35 Calibration Study #2 ...... 37 Appendix 5: Average Grain Diameters ...... 39 Appendix 6: Effective Time Results ...... 44 Appendix 7: D2 vs. Effective Time Graphs ...... 60 AISI 1045 ...... 60 AISI 4140 ...... 63 AISI 4340 ...... 66 AISI 8620 ...... 69 AISI 9310 ...... 72 V

AISI 52100 ...... 75 Appendix 8: Log(K) vs. 1/T Graphs ...... 78 Appendix 9: Micrographs ...... 81 AISI 1045 ...... 81 AISI 4140 ...... 92 AISI 4340 ...... 103 AISI 8620 ...... 114 AISI 9310 ...... 125 AISI 52100 ...... 134

List of Figures

Figure 1 - Temperature vs. Time Plot of Solution and Precipitation Heat Treatments [4] ...... 2

Figure 2 – Fe3C Phase Diagram [2] ...... 3 Figure 3 - Isothermal Transformation Diagram Fe-C Alloy of Eutectiod Composition [1] ...... 4 Figure 4 - Comparison of Thermocouple Connections [12] ...... 11 Figure 5 - Heating Rate of 8620 to 900C ...... 12 Figure 6 Time-Temperature Graph of 900C Heat Treatment ...... 12 Figure 7 - Heyn Intercept Method at 200x Magnification: 1045 850C 9Hr ...... 14 Figure 8 - Jefferies Method at 200x Magnification: 1045 850C 4Hr ...... 15 Figure 9: Variation in Grain Size of AISI 4140 with Time at 1050°C ...... 17 Figure 10: Variation of Grain Size of AISI 4140 with Temperature at 2 Hours ...... 18 Figure 11: Plot of Average Grain Diameter squared vs. Effective Time ...... 21 Figure 12 - Log(Kp) vs. 1/T Comparison ...... 23

VII

List of Tables

Table 1 - Material Composition Obtained via OES ...... 9 Table 2: Functions of Alloying Elements [12] ...... 9 Table 3: Average Grain Diameter (mm) for AISI 8620 Steel ...... 19

Table 4: Comparison of K and D0 for Various Alloys ...... 22 Table 5 - Comparison of Activation Energy and Pre-exponential constant ...... 24

VIII

List of Equations

Equation 1- Hall-Petch Equation ...... 5 Equation 2 - Ideal Grain Growth Law ...... 5 Equation 3 - General Grain Growth Law ...... 6 Equation 4 - Relationship between K and Heating Temperature T ...... 6 Equation 5: Zener Equation [10] ...... 7 Equation 6: ASTM Grain Size Equation ...... 19 Equation 7: Heating Time Equation ...... 20 Equation 8: Effective Time Equation ...... 20

1 Introduction

Steels are utilized in a wide variety of applications ranging from automobiles, bolts, to structural components, etc. The addition of alloying elements within low, medium and high carbon steels leads to enhanced mechanical properties over traditional plain carbon steel. Alloying elements that are added within the steel can include: chromium, manganese, molybdenum, nickel, phosphorous, sulfur and silicon. [1] In the past, researchers have noted significant changes in the microstructure of steels that undergo alloy element addition to enhance the desired mechanical properties. As grain size increases, the strength, hardness and fatigue life of the steel decrease. [3] It was observed that the prior austenite grain size is directly influenced by the temperatures and the various time durations of exposure. Austenite grains grow at elevated temperatures which can affect mechanical properties. Grain growth is dependent upon heat treatment time and temperature as well pinning effects of second phase precipitates within the steel.

The goal of this project is to investigate the effect of temperature and time upon the grain growth kinetics of selected steels. The steels examined included 1045, 4140, 4340, 8620, 9310 and 52100. Heat treatment temperature and time were varied ranging from 850°C to 1050°C in increments of 50°C and held for 30 minutes, 2, 4, and 9 hours. Utilizing the standard ASTM test methods, average grain size measurements could be determined using the Jefferies Planimetric Method to further examine the growth kinetics.

2 Literature Review

2.1 Heat Treatment Heat Treatment is a process commonly utilized to obtain desired properties within steels. [4] This is done by controlling the heat treatment temperature, its holding time and the rate at which it is cooled. A typical temperature vs. time plot for a heat treatment schedule can be seen in Figure 1. In most cases, a process consists of a two-part heat treatment, Solution Heat Treating or Austenitizing and Tempering or Precipitation Heat Treating.

Figure 1 - Temperature vs. Time Plot of Solution and Precipitation Heat Treatments [4]

2.1.1 Austenitizing Austenitizing is the first step heat treatment and involves transforming the initial microstructure to an austenitic structure. [3] By observing the Fe-C phase diagram in Figure 2 the phase transformation can be seen.

Figure 2 – Fe3C Phase Diagram [2]

To transform the microstructure to austenite, the sample is heated above the eutectoid temperature (727°C). If the material is a hypoeutectoid alloy (contains less than 0.76 weight % C), the ferrite will start to transform into austenite and continue to do so as the temperature rises above the eutectoid temperature. If the material is a hypereutectoid alloy (contains between 0.76 and 2.14 weight % C), the cementite will transform into austenite and continue to do so as the temperature increases. The temperature at which the microstructure is completely austenite depends upon the amount of carbon within the alloy. [4]

After being held for the desired time, the steel can be rapidly quenched from the austenitic region. The resulting microstructure is dependent on the rate of cooling as well as the concentration of alloying elements within the steel. The Isothermal Transformation Diagram for a steel with a eutectoid composition is presented in Figure 3, additional ITT diagrams for each steel examined within this study can be seen within Appendix 1.

Figure 3 - Isothermal Transformation Diagram Fe-C Alloy of Eutectiod Composition [1]

By referencing the appropriate ITT diagrams, the final microstructure can be controlled to produce desired microstructures and properties. A rapid quench may avoid the formation of Pearlite or Bainite and allow martensite to form.

2.1.2 Tempering Generally the microstructure of steel in its post-quenched state is undesirable due to internal stresses, brittleness and hardness. . Tempering is generally utilized for martensitic steels as their ductility and toughness are not optimal for most applications. [1] The process of tempering steel is utilized to relieve the internal stresses and remove other undesirable properties that may have arisen in previous heat treatment. The microstructure of tempered martensite consists of carbide particles embedded within a ferrite matrix leading to a substantially enhanced ductility and toughness.

Martensite (BCT, single phase) → Tempered Martensite (α +Fe3C and other carbides)

Tempering is normally carried out at temperatures between 250 and 650°C, but stress relief can be accomplished at temperatures as low as 200°C. [4]

2.2 Grain Size and Growth The grain size within steels largely contributes to bulk material properties such as strength, creep, and fatigue resistance, electrical and magnetic properties.[5] The Hall-Petch equation relates yield strength, σ, to the average grain diameter, d, where σ0 and k are constants as seen in the equation below. [7]

Equation 1- Hall-Petch Equation

The relationship introduced in Equation 1 can be explained via dislocation theory which assumes that grain boundaries act as obstacles to slip dislocations, causing dislocations to pile up on their slip planes behind the grain boundaries. Dislocations that attempt to pass from one grain to the adjacent grain will have to change its direction of motion due to crystallographic misorientation. [4] An increase in the number of dislocations is assumed with increasing grain size and magnitude of applied stress. [3] Thus a fine grained material possess a higher yield strength compared to a coarse grained material as a greater applied stress would be needed to cause slip to pass through the boundary. In order to estimate material properties as a function of heat treatment, the kinetics of grain growth must be understood.

2.2.1 What is Grain Growth? The driving force for grain growth is the surface energy of the grain boundaries. As growth occurs at elevated temperatures the number overall number of grains decreases as larger grains consume smaller grains. As some grains begin to shrink, their area diminishes and the total surface energy is lowered. [2] It has been generally recognized that the decrease of surface energy as a result of grain growth is the driving force for grain growth. [7] As grains are continually growing and shrinking over time, the mean grain size increases. The mean grain diameter is utilized as a measure of the grain size of an alloy. The Ideal Grain Growth Law relates average grain diameter to initial grain size, and time as seen below.

Equation 2 - Ideal Grain Growth Law

D is the average grain diameter, D0 is the initial grain size, K is a constant of proportionality that relates heating temperature and activation energy for grain growth, and t is the holding time. The Ideal Grain Growth Law is commonly written in a more general form by substituting the exponent as the variable m.

Equation 3 - General Grain Growth Law

Equation 4 - Relationship between K and Heating Temperature T

Early theories of grain growth are based upon the proportionality of the growth rate to the interfacial free energy per unit volume or based on the inverse proportionality of the rate of boundary migration to the boundary curvature predict a value of m to be 2. [8] Experimentally it has been shown that values of m lie within the range of 2 to 5. The kinetic exponent, m, within an ideal system controlled by diffusion, has a value of 2, meaning that the system has no defects or precipitates. A value of 3 indicates several phenomena such as precipitate phases with diffusion in the produced grains. If a value of 4 is determined, it means there is an effect of the precipitate with diffusion along the grain boundary. [9]

2.2.2 Factors Affecting Grain Growth

2.2.2.1 Heating Rate The heating rate of the steel has been determined to have a significant influence upon the growth kinetics in Equation 3. Slower heating rates have been shown to result in a larger initial grain size, D0. Experimentally A36 steel has shown to possess varying initial grain sizes based upon the rate of heating. Slowly heated specimens were heated to 1100°C at 100°C/s reveals initial grain sizes of 47μm. Rapidly heated specimens were heated in a stepped heating cycle and were heated initially at 5°C/s to 900°C and held for 120 seconds, then heated at 100°C/s to 1100°C. The initial grain size of the rapidly heated samples was 88μm in size. [9] The difference in initial grain size can be explained by grain growth during heating. As the sample is heated from its austenite transition temperature to the target temperature grains are growing; the sample with a slower heating rate took more time to reach the target temperature compared to the faster heating rate and thus had more time for grain growth.

2.2.2.2 Zener Pinning Grain growth can be inhibited in the presence of second phase particles which pin grain boundaries in place. The restraining forces exerted on grain boundaries are called Zener forces. [9] A grain of critical radius Rcr is the radius where the driving force is equivalent to the pinning force exerted by second phase particles on grain boundaries. The limiting size for which grain growth can occur can be seen in the Zener Equation. [10]

Equation 5: Zener Equation [10]

A is a constant, r is the mean second phase particle radius, and f is the volume fraction of second phase particles. Second phase particles which can inhibit grain growth include very small oxide, sulfide, carbide or silicate particles. [2] Zener pining can be observed at lower temperatures where second phase particles are present, but not at elevated temperatures the particles dissolve. [11]

2.3 Materials The following steels were used throughout the duration of this project. Each of the steels utilized have distinct chemical and physical properties which allow them to be used in a variety of applications.

2.3.1 AISI 1045 AISI 1045 steel is a widely used medium carbon steel with various engineering applications ranging from bolts, gears, axels spindles, crankshafts, connecting rods and guide rods. [13] This steel has a carbon content generally within the range of 0.43 to 0.5 wt% which results in increased strength in the steel. [15]

2.3.2 AISI 4140 AISI 4140 is a low cost chromium-molybdenum alloy with uses in the oil and gas sector. [9] This steel possesses desirable properties such as wear resistance, toughness and ductility in the quenched and tempered conditions. Additionally it is easy to machine in the heat treated condition allowing for use in a variety of applications such as axels and structural applications. [17] AISI 4140 typically possesses a carbon content in the range of 0.38 to 0.43 wt%. [15]

2.3.3 AISI 4340 AISI 4340 is a nickel chromium-molybdenum steel alloy known for its toughness and ability of developing a high strength in the heat treated condition while retaining good fatigue strength. This alloy is utilized in structural applications such as aircraft landing gear, power transmission gears and shafts. AISI 4340 possesses a carbon content generally within the range of 0.38 to 0.43 wt%. [18]

2.3.4 AISI 8620 Steel AISI 8620 is a Chromium-Molybdenum-Nickel low alloy steel, often used in carburizing to develop a hard case resulting in good wear resistance. Applications of this steel include transmission components in a wide variety of vehicles as well gears, ring gears, shafts and crankshafts. [14] Typical carbon content within this steel is within the range of 0.18 to 0.23 wt% carbon. [15]

2.3.5 AISI 9310 Steel AISI 9310 is a Nickel-Chromium-Molybdenum steel utilized widely in vehicle transmission gears, track rod pins, roller bearing rings and small arms parts. [14] Typical carbon content for this steel is in the range of 0.08 to 0.13 wt% carbon. [14]

2.3.6 AISI 52100 AISI 52100 is a high carbon chromium alloy steel utilized for ball bearings. This alloy is a tool steel which is capable of cutting a wide range of materials due to its combination of toughness, wear resistance and hardness. Low quantities of manganese and chromium are utilized to improve hardening characteristics. AISI 52100 possesses a low corrosion resistance compared to other chromium steels due to low chromium levels. This steel typically has a carbon concentration within the range of 0.95 to 1.05 wt%. [19]

2.3.7 Material Composition

Optical Emission Spectrometry (OES) was used to determine the chemical composition of the steels. The average readings of three measurements are shown in Table 1. The addition of each element within the steel provides a specified role in determining the properties of the alloy. The function of each element can be seen within Table 2. [1]

Table 1 - Material Composition Obtained via OES

C Cr Fe Mn Mo Ni P S Si 1045 0.484 0.1195 Bal. 0.745 0.0225 0.081 0.00435 0.0135 0.215 4140 0.377 1.025 Bal. 0.695 0.1505 0.1565 0.0071 0.011 0.2265 4340 0.417 0.79 Bal. 0.76 0.2283 1.71 0.00893 0.021 0.241 8620 0.2135 0.56 Bal. 0.805 0.1535 0.4525 0.00645 0.014 0.2355 9310 0.121 1.3 Bal. 0.605 0.141 3.49 0.0053 0.0098 0.2405 52100 0.975 1.57 Bal. 0.316 0.029 0.102 0.00625 0.0075 0.2045

Table 2: Functions of Alloying Elements [1]

Alloying Element Function

C To Control Strength Level and Hardenability

Cr Hardenability & Oxidation Resistance

Mn Hardenability

Mo Hardenability & to Improve Creep Strength

Hardenability & to Improve Notch Toughness at Ni Low Temperatures

Ferrite Strengthening & to Improve Corrosion P Resistance

S To Improve Machinability

As a Deoxidizer or to Reduce Core Losses in Si Electrical Sheets

By observing the chemical composition of each element in relation to the function of the element grain growth rates can be compared due to Zenner Pinning Effects.

3 Methodology Steels were received from Peterson Steel Corporation and A.M. Castle Metals in a rod stock form. With assistance from the machinists at WPI’s Haas Technical Education Center, these rods were turned down to 46, 1cm thick disks. The process of furnace calibration, heat treatment, sample preparation, and analysis are outlined within this chapter.

3.1 Furnace Calibration In order to ensure the entire sample reached a specified temperature, the temperature of both the furnace and the core of the sample were monitored closely. The process of temperature mapping was utilized to view the temperature variation profile of the furnace. By temperature mapping the furnace as well as measuring the sample’s core temperature, uniform heating can be achieved.

3.1.1 Temperature Mapping The furnace initially utilized for heat treatment was a Thermolyne 1300 Furnace. This furnace was utilized for lower temperature heat treatments, while the Thermolyne 48000 Furnace, model number F48015 was utilized for temperatures exceeding 1000°C. Temperature variation profiles from a number of locations inside the furnace chamber were monitored in a process called temperature mapping, to identify potential ‘cold or hot spots’ that can cause deviations from the anticipated uniform heating of the samples.

The temperature of each furnace was mapped using an Omega brand K-type thermocouple and an Omega HH111 data-logger. To ensure the thermocouple and the datalogger were functioning within specifications, a container of water was set to boil on a hotplate, and the temperature was measured. The furnace was heated to a set temperature, and held for several minutes. The thermocouple was then placed within the furnace at set locations to determine if a variance in temperature existed with respect to location within the chamber.

3.1.2 Temperature Calibration To monitor the core temperature of the samples, a 1 cm deep hole was drilled into the side of each sample with a 1.6 mm drill bit. An Omega K-type grounded thermocouple was press fit into the hole. A grounded thermocouple was utilized since the wires are physically attached to the interior of the sheathing, thus eliminating possible air-gaps produced by ungrounded thermocouples. Exposed

thermocouples were not utilized as the bead of the bimetal could become easily damaged resulting in inaccurate readings as seen in Figure 4 below.

Figure 4 - Comparison of Thermocouple Connections [12]

The core temperature of the disks was measured at fifteen minute intervals to ensure the samples did not deviate from the specified heat treatment temperature.

3.2 Heat Treatment Procedure The samples were heat treated in 50°C increments from 850°C to 1050°C and held for 0.5 to 9 hours. The temperature and time values were chosen through consideration of the austenitizing temperatures for medium carbon steels. Two identical samples were heat treated under identical conditions to ensure redundancy.

The furnace was heated to the desired temperature; once this temperature was achieved the samples were placed within the furnace. One of these samples contained the thermocouple, which would monitor the internal core temperature. The time – temperature curve for the heating rates can be observed by recording the temperatures at 10 second intervals until the samples are within 10 °C of the target temperature. Once the core temperatures reached 10°C of the target temperature, the heat treatment process began with temperature measurements at 15 minute intervals to ensure thermal stability. A time-temperature curve can be seen in Figure 5 & Figure 6.

8620 Heating Rate to 900C 1000 900

800 700 600 500 400 300 Temperature(C) 200 100 0 0 100 200 300 400 500 Time (s)

Figure 5 - Heating Rate of 8620 to 900C

Heat Treatment: 900C 2 Hours 1000 900

800 700 600 500 400 300 Temperature(C) 200 100 0 0 2000 4000 6000 8000 10000 Time (S)

Figure 6 Time-Temperature Graph of 900C Heat Treatment

Once the samples reached the prescribed length of heat treatment, they were immediately quenched within a bath of ice water which was vigorously stirred.

3.3 Sample Preparation Once the samples were quenched, they were sectioned and mounted via standard metallographic procedures using a Mark V CS600 cutting wheel and a Buehler Simplimet II mounting press. The samples underwent a grinding process using a Buehler Metaserv 2000 grinding wheel with progressively finer grits of sandpaper. After achieving uniform directional wear with 600 grit sandpaper, the samples were finely polished via a combination of the Buehler Vibromet I polisher and Century E- plus polishers to produce a mirror finish. A Picric Acid Etchant was used in order to observe the microstructure of the samples. Detailed instructions regarding sample preparation can be seen within Appendix 2 and 3.

3.4 Optical Microscopy Measurements Once the samples were etched, digital optical micrographs were taken using a Nikon Epiphot Optical Microscope attached to a Nikon Digital Sight DS-U1 image acquisition system. Average grain size measurements were conducted manually using the Hyen Intercept Method and Jefferies Planimetric Method for each sample. While there are a number of image analysis software packages available to measure the grain sizes, there have been a number of occasions where the level of accuracy of the analysis was questioned. Hence, the analysis was conducted manually. The image processing program ImageJ was utilized to overlay necessary features upon the micrographs for analysis.

3.4.1 Hyen Intercept Method The first widely used methodology for measuring the average grain size is the Hyen Intercept Method. The Intercept method utilizes a randomly positioned line of a known length that is overlaid on the micrograph. In order to ensure accuracy the line must be long enough that it produces 50 to 150 intersections or interceptions at the micrograph’s magnification. Once the line is drawn, a set of rules are utilized to count the intercepts along the line. [8] Seen below in Figure 7 is an example of the Intercept Method for one of the samples with a line length of 0.23 mm. By calibrating the software ImageJ with the micrograph’s scale bar, the line length can be measured within the program.

Figure 7 - Heyn Intercept Method at 200x Magnification: 1045 850C 9Hr

A set of rules are utilized to count the number of intersections and interceptions across the length of the line. “If the ends of the line end within a grain boundary, each end is counted as one-half interception. Grain boundary intersections are counted as one point, triple-point intersections are counted as 1.5 points and tangent hits are counted as one-half point.” [8] Once the intersections along the line have been tallied up, the mean intercept length, L3, can be determined:

[ ] where NL is the tallied intercept count. With the mean intercept length, the ASTM grain size, G, can be determined and further correlated to the average grain diameter via ASTM E112. [9]

3.4.2 Jefferies Method The second methodology widely utilized to determine grain size is the Jefferies Planimetric Method. The Jefferies Method has become the preferred methodology for measuring grain with industry size due to its ease of use. This methodology utilizes a circle or rectangle of known area that has been overlaid on top of the micrograph. The number of full grain boundaries within the area and partial grain boundaries intersected by the shape are tallied and used to calculate the average grain diameter.

During this analysis, it is suggested that a standard circle of 79.8 mm in diameter (5000 mm2) be drawn on the micrograph obtained at 100x. Figure 8 shows an example of the Jefferies Method on one of the samples. By calibrating the software ImageJ with the micrograph’s scale bar, an accurate value of the circle’s area can be determined for non-standardized sizes.

Figure 8 - Jefferies Method at 200x Magnification: 1045 850C 4Hr

A set of rules are also utilized for the Jefferies Method, but are much simpler in comparison to the Heyn Intercept Method. A grain that is within the area of interest counts as a full point, where a grain that intersects the boundary counts as a half point. [8] The grain area and diameter can be determined via the following equations:

While the Jefferies Method provides slower results, the results were observed to be more accurate. This was seen when multiple measurements were taken along the same micrograph, consistent values were observed via the Jefferies Method, but a spread could be seen using the Heyn Intercept Method.

To achieve a more representative value for the average grain diameter, it was decided that the Jefferies Method would be utilized with a total of fifteen measurements per sample. To remove bias 15

within the measurements, several graduate students assisted in calculating the grain sizes. A calibration study was performed on a known sample to further measure the bias of each individual with results seen in Appendix 4. Each individual performed three distinct measurements at different locations within the sample. Outlying data was discarded by utilizing the Inter-Quartile Range (IQR) and the average of the remaining data was taken as the representative average grain diameter for the sample.

4 Results and Discussion

4.1 Gain Size Evolution

By utilizing the Nikon Epiphot Optical Microscope, digital optical micrographs could be obtained. By observing samples with respect to time and temperature, a visual indication of grain growth can be seen. The following series of micrographs of AISIS 4140 were held at 0.5, 2, 4, and 9 hours at 1050°C as well as 850, 900, 950, 1000 and 1050°C for 2 hours. All micrographs are at 100x magnification. These micrographs visually indicate in average grain size with both heat treating time and temperature.

0.5 Hours 2 Hours

4 Hours 9 Hours

Figure 9: Variation in Grain Size of AISI 4140 with Time at 1050°C

850°C 900°C

950°C 1000°C

1050°C

Figure 10: Variation of Grain Size of AISI 4140 with Temperature at 2 Hours

4.2 Average Grain Diameters

The average grain diameter for each of the samples was determined using the procedure outlined in Section 4.4.2. Fifteen measurements were taken per sample and the Inter-Quartile Range (IQR) was utilized to filter out the outlying results. [19] The IQR calculation method, a representative average of the grain diameter can be taken for each sample. Average grain diameters (mm) for AISI 8620 with respect to holding temperature and time can be seen within Table 3, additional steels can be seen within Appendix 5.

Table 3: Average Grain Diameter (mm) for AISI 8620 Steel

0.5 Hours 2 Hours 4 Hours 9 Hours 850°C 0.0112 0.0108 0.0106 0.0118 900°C 0.0121 0.0142 0.0145 0.0157 950°C 0.0140 0.0167 0.0165 0.0244 1000°C 0.0172 0.0204 0.0219 0.0313 1050°C 0.0230 0.0345 0.0382 0.0515

From observed values of the average grain diameter, grain size increased with both holding temperature as well as time. Variance within measurements at lower temperatures can be attributed to minimal grain growth resulting in consistent diameters.

4.3 ASTM Grain Size

Different methodologies can be utilized to calculate the ASTM Grain Size Number including use of an eyepiece graticules for optical microscopes and conversion from either the Hyen Linear Intercept Method or Jefferies Planimetric Method. As data was collected via the Jefferies Method, a conversion was utilized.

[ ]

Equation 6: ASTM Grain Size Equation

Equation 6 was utilized to calculate the ASTM Grain Size Number for each sample where NA is the number of grains per square millimeter. Calculated ASTM Grain Size Numbers for each steel can be seen within Appendix 5.

4.4 Effective Time

It has been shown through previous work that the heating rate affects the grain size of steels. To account for this within the results the effective heating time had to be determined by observing the recorded heating rates.

∫

Equation 7: Heating Time Equation

Equation 8: Effective Time Equation

Through the use of Equation 7 and Equation 8, the effective heating time and time grains were allowed to grow can be calculated. The effective heating time was taken to be the amount of time the steel took to go from the eutectoid temperature of 727°C, where austenite initially forms to the lower extreme of the holding temperature tolerance, 10°C from the holding temperature. Detailed as well as tabulated calculations for the total heating time each steel can be seen in Appendix 6.

4.5 Ideal Grain Growth

4.5.1 Evaluating K and D0

The grain growth kinetics of Equation 3 can be observed for each steel by plotting values of average grain diameter squared vs. effective time. In doing so an assumption is made that ideal grain growth is present, thus the value of the exponent m is 2.

A comparison of D2 vs. time for 8620 can be seen within Figure 11. At lower temperatures grain growth is minimal; at elevated temperatures substantial growth can be seen. Plots of each steel can be seen in Appendix 7.

8620 Comparison

0.003

)

2 0.0025 (mm

850C

2 0.002 900C 0.0015 950C 0.001 1000C

0.0005 Average Average GrainDiameter 1050C

0 0.00 100.00 200.00 300.00 400.00 500.00 600.00 Effective Time (min)

Figure 11: Plot of Average Grain Diameter squared vs. Effective Time

The proportionality constant, K, and initial grain size D0 were determined from the slope and intercept

of the trend line. Calculated values of K and D0 for each steel can be seen within Table 4.

Table 4: Comparison of K and D0 for Various Alloys

Alloy Temperature K (mm2/min) D0 (mm) (°C) 850 6.65E-08 0.0107

900 2.31E-07 0.0116 950 2.58E-07 0.0148 1045 1000 2.19E-06 0.0312 1050 3.73E-06 0.0401 850 2.73E-08 0.0109

900 6.61E-08 0.0125 950 5.64E-08 0.0136 4140 1000 1.28E-07 0.0173 1050 7.26E-07 0.0341 850 3.13E-08 0.0107

900 4.55E-08 0.0114 950 1.28E-07 0.0133 4340 1000 2.82E-07 0.0184 1050 9.90E-07 0.0304 850 3.39E-08 0.0107

900 1.65E-07 0.0128 950 7.65E-07 0.0124 8620 1000 1.33E-06 0.0147 1050 3.95E-06 0.0221

900 7.62E-08 0.0111

950 8.75E-08 0.0125

9310 1000 5.47E-07 0.0163 1050 1.46E-06 0.0346

900 2.49E-08 0.0139 950 1.28E-07 0.0133

1000 3.96E-07 0.0221 52100 1050 1.65E-06 0.0270

An increase in initial grain size, D0, as well as the constant K can be seen with increasing temperature as growth occurs at an accelerated rate at elevated temperatures.

4.5.2 Evaluating Activation Energy

For grain growth to occur, a number of barriers must be surpassed, one of which is the necessary activation energy must be supplied to the steel. The activation energy, Q, is related to grain growth via Equation 4.

By plotting the inverse of absolute temperature against the proportionality constant K, the activation energy was determined from the slope of a linear trend line.

Comparison of Alloys

-10.5 1045 -11 4140 -11.5 4340 -12 8620

Log(Kp) -12.5

9310 -13

-13.5 52100

-14 0.00074 0.00076 0.00078 0.0008 0.00082 0.00084 0.00086 0.00088 0.0009 1/T

Figure 12 - Log(Kp) vs. 1/T Comparison

The relation between the slope of the trend line and the activation energy needed for grain growth can be seen below where R is the gas constant. Plots of individual alloys with accompanying linear trend lines can be seen within Appendix 8.

Values obtained for the activation energy as well as the pre-exponential constant, k0 for each alloy can be seen in Table 5 below:

Table 5 - Comparison of Activation Energy and Pre-exponential constant

Steel Q (KJ/mol) K0

1045 253.3 6.165E-04

4140 175.2 5.409E-08

4340 213.7 3.392E-06

8620 287.9 1.747E-02

9310 273.4 1.352E-03

52100 353.4 4.061E-01

5 Conclusions & Recommendations

5.1 Heat Treatment

The rate of heat treatment of samples was significantly improved through the use of the Thermolyne 48000 due to its large chamber size. The presence of a larger chamber allowed for all samples at a prescribed holding temperature to be heat treated simultaneously in single batch. This significantly decreased the amount of time spent heat treating as 0.5, 2, 4 and 9 hour samples could undergo this process within a single day.

Recommendations for further heat treatment include the use of a Data Acquisition System (DAQ) to record temperature measurements over time. Without the use of a DAQ, measurements had to be recorded by hand for the course of the heat treatment cycle. Implementation of such a system would provide an accurate temperature profile during quenching to ensure a martensitic microstructure was obtained.

5.2 Sample Preparation

The process of sample preparation faced minimal challenges in terms of cutting and mounting samples. Grinding and polishing proved to be a challenging process at first as it required producing a mirror finish, free from scratches. A completely flat samples is critical to obtain high quality micrographs with the optical microscope. In order to achieve a flat surface, pressure must be applied uniformly on the sample’s surface during the grinding and polishing procedures.

Etching the grain boundaries proved to be the most challenging portion of this project. Due to the varying chemical composition between each of the steels, they had to be immersed within the etchant for varying amounts of time. In addition, each batch of etchant provided varying grain boundary visibility as the etchant concentration changed over time on the hot plate. Additionally, samples behaved differently to the etchant within clear grain boundaries outlined in all steels but 1045.

5.3 Average Grain Size Measurements

Average grain size measurements were calculated utilizing the Jefferies Planimetric Method as it proved to be a more reliable methodology compared to the Hyen Intercept Method. While measurements did take substantially longer it was much easier to distinguish between a full and partial

grain of Jefferies Method compared to an intersection, triple point and tangent in the Intercept Method. Even though the Jefferies Method proved to produce more reliable results, the quality of the etchant strongly impacted visibility of the grain boundaries. If grain boundaries are not well defined, it is recommended to outline the boundaries on the micrograph to aid in further analysis.

By performing an IQR analysis of a total of fifteen measurements between five individuals at different locations within the sample provided a representative average grain diameter for each sample. To ensure grains were being counted correctly, a calibration study was performed and the numbers of grains within a known sample were counted and compared. Determining grain boundaries proved difficult if they were not well defined through the etchant process which led to multiple iterations of measurements.

As expected, average grain sizes increased with both holding time and temperature, as predicted from the grain growth equations. An increase in temperature was found to have a larger effect on grain size than an increase in holding time as temperature is exponentially dependent compared to time’s linear dependence. At lower temperatures, grain growth was minimal or severely restricted due to grain pinning effects. By utilizing the Energy Dispersive Spectroscopy (EDS) function of an SEM, the chemical composition of the grain boundaries can be analyzed indicating if carbides or other inclusions are present within the sample. The addition of pinning mechanisms within the sample alter the growth kinetics as the growth exponent, m, is no longer equal to 2. In order to predict a value of m for non-ideal growth, an iterative algorithm would have to be developed which solves for values of m, k and d0.

5.4 Growth Kinetics

In determining the grain growth kinetics of each of the steels, the average grain size (squared) was plotted against time. In doing so, values of K and D0 can be determined and utilized to find the activation energy for grain growth; Q. Values of K and D0 were specific to each steel and temperature, while Q is specific to each steel. The calculated activation energy for grain growth was compared to the activation energy for diffusion of iron in iron, 284 KJ/mol. [4] Observed values of activation energy lie within the range of 175 to 353 KJ/mol. While the calculated values for Q, K and D0 pertain to ideal grain growth, further work must be done to determine if pinning effects are present and how they affect growth kinetics.

Works Cited [1] Seco / Warwick, Heat Treating Data Book, 10th ed. Meadville, PA: Seco / Warwick Corporation, 2011.

[2] Reza Abbaschian, Lara Abbaschian, and Robert E. Reed-Hill, Physical Metallurgy Principles. Stamford, CT: Cengage Learning, 2009.

[3] William D. Callister Jr., Materials Science and Engineering an Introduction. York: Wiley, 2007.

[4] Advanced Cast Products. The Austempering Process. [Online]. http://www.advancedcast.com/austempering-process.htm

[5] A.K. Giumelli, M. Militzer, and E.B Hawbolt, "Analysis of the Austenite Grain Size Distribution in Plain Carbon Steels," The Iron and Steel Institute of Japan, vol. 39, no. 3, pp. 271-280, 1998.

[6] J. W. Morris, Jr., "The Influence of Grain Size on the Mechanical Properties of Steel," Berkeley, 2001.

[7] Chongxiang Yue, Liwen Zhang, Shulun Liao, and Huiju Gao, "Kinetic Analysis of the Austenite Grain Growth in GCr15 Steel," Journal of Materials Engineering and Performance, vol. 19, no. 1, pp. 112- 115, February 2009.

[8] S. Illescas, J. Fernandez, and J.M. Guilemany, "Kinetic Analysis of the Austenitic Grain Growth in HSLA Steel with a Low Carbon Content," Materials Letters, vol. 62, pp. 3478 - 3480, March 2008.

[9] Alan Giumelli, "Austenite Grain Growth Kinetics and the Grain Size Distribution," University of British Columbia, Vancouver, M.A.Sc. Thesis 601896139, 1995.

[10] J Rudnizki, B Zeislmair, U Prahl, and W Bleck, "Prediction of Abnormal Grain Growth During High Temperature Treatment," Computational Materials Science, vol. 47, pp. 209-216, April 2010.

[11] P. A. Manohar, D. P. Dunne, T. Chandra, and C. R. Killmore, "Grain Growth Predictions in Microalloyed Steels," The Iron and Steel Institute of Japan, vol. 36, no. 2, pp. 194-200, September 1995.

[12] P. A. Beck, M. L. Holzworth, and P. Sperry, "Effect of a Dispersed Phase on Grain Growth in Al-Mn Alloys," AIME Transactions, vol. 180, no. 163, 1949.

[13] Tata Steel International Ltd. Medium Tensile Steel - AISI 1045. [Online]. http://www.corusnz.com/downloads/MeduimTens_AISI1045.pdf

[14] Granta Design. (2010) CES EduPack - Low Alloy Steel, AISI 9310. Software v. 5.2.0.

[15] West Yorkshire Steel Company Ltd. West Yorkshire Steel: UK Special Steel Stockholders. [Online]. http://www.westyorkssteel.com/AISI_4140.html

[16] Short Run Pro: Custom Machines Parts. [Online]. http://www.shortrunpro.com/Machining/General_eng_guidelines.aspx

[17] Metal Suppliers. (2009) Material Property Data Alloy Steels 4340. [Online]. http://www.suppliersonline.com/propertypages/4340.asp

[18] Metal Suppliers Online. (2009) Alloy Steels 8620. [Online]. http://www.suppliersonline.com/propertypages/8620.asp

[19] Sullivan Steel Service. Applications of 52100 Alloy Steel Tubing. [Online]. http://www.52100steel.com/about.html

[20] Omega. Introduction to Thermocouples. [Online]. http://www.omega.com/techref/themointro.html

[21] George F Vander Voort, Metallography: Principles and Practice. New York: ASM International, 2004.

[22] ASTM International, ASTM E112 - 10: Standard Test Methods for Determining Average Grain Size.: ASTM International, 2010.

[23] Joseph D Petruccelli, Applied Statistics for Engineers and Scientists. Upper Saddle River, N.J., United States of America: Prentice Hall, 1999.

[24] American Society for Metals, Atlas of Isothermal Transformation and Cooling Transformation Diagrams.: ASM, Metals Park, Ohio, 1977.

[25] Key to Metals: The World's Most Comprehensive METALS Database. [Online]. http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=62

[26] Mike Meier. (2004, September) UC Davis: Department of Chemical Engineering and Materials Science. [Online]. http://chms.engineering.ucdavis.edu/students/undergraduates/labs/files/HT- Steel.pdf

[27] C.S Smith,. Cleveland, United States of America: ASM International, 1952, p. 65.

[28] Mid-Atlantic Casting Services. (2005, Feburary) A Guide to Mechanical Properties of Cast Carbon and Low Alloy Steels. [Online]. http://www.mid-atlanticcasting.com/cast-steel-guide_FEB05.pdf

Appendix 1: Isothermal Transformation Diagrams

Isothermal Transformation Diagram for AISI 1045 Steel [4]

Isothermal Transformation Diagram for AISI 4140 Steel

Isothermal Transformation Diagram for AISI 4340 Steel

Isothermal Transformation Diagram for AISI 8620 Steel

Isothermal Transformation Diagram for AISI 52100 Steel

Appendix 2: Sample Grinding & Polishing Procedures

The following details instructions on how to section and mount a sample utilizing the Mark V CS600 cutting wheel and Buehler Simplimet II mounting press.

Mark V CS600 - Sectioning 1) Select the appropriate blade based on the hardness of your sample, a chart is posted within the lab. An incorrect choice of blade will lead to damage of the blade and or sample. a. If the blade is damaged, it must be replaced. Utilize the correct combination of wrenches within the supply drawers to remove and replace the blade. 2) Check lubricating fluid levels within the fluid bay, refill if necessary. 3) Secure the sample within the vice on the cutting table. 4) Rotate the stop to allow for the cutting table to pivot. 5) Press On/Off, followed by Start to start the Mark V. Slowly lower the cutting table until contact is made with the sample. 6) Allow for the weight of the sample to drive the sectioning process, do not apply pressure to the sample as it leads to a non-uniform cutting face and could damage the blade. 7) Once the sample is bisected, press the On/Off button to power down the Mark V. Raise the protective enclosure, replace the stop and remove the sample. 8) Utilize a paper towel to remove chips, powder or excess fluid that has deposited within the machine.

Mark V CS600

Beuhler Simplimet II – Mounting 1) Power on the Mounting Press via the On button located on the display panel. 2) Turn on the water from the flow control valve located on the wall behind the press. 3) Ensure both the metallic stopper on the underside of the handle as well as the ram are clear of debris. 4) Place the desired sample on the center of the ram with the face of interest faced down. 5) Lower the ram via the down arrow on the display. Pour/place the mounting powder or disk on top of the sample. 6) Once the sample has been lowered to the bottom of the chamber, press the metallic stopper into the chamber and lock by rotating. 7) To start the mounting process, press “Start” on the display panel. Once completed, the press will beep. 8) Unlock the stopper and press the Up arrow to raise the ram. Remove the sample as well as any present residual polymer flakes on the ram or stopper. 9) Lower the ram to just below the top of the machine, stop the flow of water, and power off the machine.

Beuhler Simplimet II Mounting Press

Appendix 3: Sample Etching Procedures The following details the procedure for creating the Picric Acid etchant utilized to reveal the microstructure of 1045 samples. The following dictates how to prepare 300 mL of etchant.

1. Measure 12g of Picric Acid into a beaker and mix with 300mL of water to create an aqueous solution. 2. Place a magnetic stir rod within the beaker and utilize a stirring plate to dissolve the majority of the Picric Acid, creating a saturated solution. 3. Add two tablespoons of Nacconal 90G, a wetting agent made of sodium dodecyl benzene sulfonate. 4. Excess Picric Acid and wetting agent are filtered out via a funnel and wetted cotton to create a seal. 5. The filtered solution is heated between 80 and 90C underneath a hood. 6. If the samples to be etched contain > 0.5% Cr, 18 drops of HCl are added to the solution (6 drops per 100mL). 7. Samples are submerged within the etchant sample facing up for initially 30 seconds. 8. Once the time has elapsed, samples are washed under running warm water, rinsed with acetone and blown dry. 9. The quality of the procedure is observed via an Optical Microscope, if the grains are faint further time within the etchant is required. If the sample is dark, it has been over-etched and must be back- polished with figure eight motions to remove smut build up. 10. A blue hue will be visible on the sample’s surface, providing a visual clue that it has been etched sufficiently.

Appendix 4: Jefferies Planimetric Method Calibration Studies The following details the calibration methods utilized for the Jefferies Planimetric Method. The Jefferies method was performed on known micrographs in order to compare measured values of inscribed and partial grains. The calibration studies were also utilized to determine the impact of the number of full and partial grains on calculated grain size.

Calibration Study #1 The first micrograph utilized below is of an austenitic manganese steel that was solution annealed at 1038C and aged at 621C. The micrograph is taken at 100x magnification and the area is approximately 5000 mm2. [8]

Value of both the inscribed and partial grains were counted by each individual and compared to the known values. As seen in the following tables, a discrepancy of 12.27% in determining full and partial grains results in a 1.34% difference in average grain diameter.

Results: Calibration Study #1

Measured Actual % Difference

Full Grains 43 44 -2.27 Chunmin Partial Grains 23 25 -8.00

Full Grains 43 44 -2.27 Erik Partial Grains 25 25 0.00

Full Grains 44 44 0.00 Lei Partial Grains 22 25 -12.00

Full Grains 44 44 0.00 Sidath Partial Grains 22 25 -12.00

Full Grains 44 44 0.00 Zhijia Partial Grains 24 25 -4.00

Average Grain Measured Actual ASTM % Difference Diameter (mm) ASTM Grain # Grain #

Chunmin 0.01354 3.818 3.87 -1.34

Erik 0.01342 3.845 3.87 -0.66

Lei 0.01348 3.832 3.87 -0.99

Sidath 0.01348 3.8315 3.87 -0.99

Zhijia 0.01336 3.8575 3.87 -0.32

Calibration Study #2 The second micrograph utilized below is of low-carbon sheet steel taken at 500x magnification and an area of approximately 5000 mm2. [8]

Value of both the inscribed and partial grains were counted by each individual and compared to the known values. The second calibration study is a closer representation to micrographs of 1045 steel due to the faint grain boundaries. As seen in the following tables, a discrepancy of 18.15% in determining full and partial grains results in a 1.77% difference in average grain diameter.

Results: Calibration Study #2

Measured Actual % Difference

Full Grains 57 61 -6.56 Chunmin Partial Grains 28 30 -6.67

Full Grains 55 61 -9.84 Erik Partial Grains 33 30 10.00

Full Grains 56 61 -8.20 Lei Partial Grains 27 30 -10.00

Full Grains 54 61 -11.48 Sidath Partial Grains 28 30 -6.67

Full Grains 58 61 -4.92 Zhijia Partial Grains 28 30 -6.67

Average Grain Measured Actual ASTM % Difference Diameter (mm) ASTM Grain # Grain #

Chunmin 0.00237 8.844 8.94 -1.08

Erik 0.00236 8.854 8.94 -0.96

Lei 0.00239 8.813 8.94 -1.42

Sidath 0.00242 8.7816 8.94 -1.77

Zhijia 0.00235 8.8640 8.94 -0.85

Appendix 5: Average Grain Diameters

AISI 1045

Temperature Effective Time ASTM Grain Size Avg Grain Diameter Kp (mm^2 / D0 (°C) (min) # (mm) min) (mm) 850 34 10.263 0.0103 6.65E-08 0.0107 850 124 9.815 0.0120 6.65E-08 0.0107 850 244 10.090 0.0109 6.65E-08 0.0107 850 544 9.743 0.0123 6.65E-08 0.0107 900 34.67 9.905 0.0116 2.31E-07 0.0116 900 124.67 9.560 0.0131 2.31E-07 0.0116 900 244.67 9.418 0.0138 2.31E-07 0.0116 900 544.67 8.968 0.0161 2.31E-07 0.0116 950 35.42 9.130 0.0152 2.58E-07 0.0148 950 125.42 8.895 0.0165 2.58E-07 0.0148 950 245.42 9.025 0.0158 2.58E-07 0.0148 950 545.42 8.450 0.0192 2.58E-07 0.0148 1000 44.92 7.226 0.0294 2.19E-06 0.0311 1000 134.92 6.590 0.0367 2.19E-06 0.0311 1000 254.92 6.200 0.0420 2.19E-06 0.0311 1000 554.92 5.963 0.0456 2.19E-06 0.0311 1050 42.08 6.645 0.0360 3.73E-06 0.0400 1050 132.08 5.951 0.0457 3.73E-06 0.0400 1050 252.08 5.279 0.0577 3.73E-06 0.0400 1050 552.08 5.279 0.0577 3.73E-06 0.0400

AISI 4140

Temperature Effective ASTM Grain Size Avg Grain Diameter Kp (mm^2 / min) D0 (°C) Time (min) # (mm) (mm) 850 33.33 10.188 0.0105 2.73E-08 0.0109 850 123.33 10.027 0.0111 2.73E-08 0.0109 850 243.33 9.893 0.0117 2.73E-08 0.0109 850 543.33 9.978 0.0113 2.73E-08 0.0109 900 33.83 9.768 0.0122 6.61E-08 0.0125 900 123.83 9.658 0.0127 6.61E-08 0.0125 900 243.83 9.351 0.0141 6.61E-08 0.0125 900 543.83 9.462 0.0135 6.61E-08 0.0125 950 35.83 9.511 0.0133 5.64E-08 0.0136 950 125.83 9.428 0.0137 5.64E-08 0.0136 950 245.83 9.160 0.0150 5.64E-08 0.0136 950 545.83 9.287 0.0144 5.64E-08 0.0136 1000 43.83 8.824 0.0169 1.28E-07 0.0173 1000 133.83 8.584 0.0184 1.28E-07 0.0173 1000 253.83 8.471 0.0191 1.28E-07 0.0173 1000 553.83 8.597 0.0183 1.28E-07 0.0173 1050 42.83 6.784 0.0343 7.26E-07 0.0341 1050 132.83 6.375 0.0395 7.26E-07 0.0341 1050 252.83 6.658 0.0358 7.26E-07 0.0341 1050 552.83 6.576 0.0368 7.26E-07 0.0341

AISI 4340

Temperature Effective ASTM Grain Size Avg Grain Diameter Kp (mm^2 / min) D0 (°C) Time (min) # (mm) (mm) 850 33.33 10.126 0.0108 3.13E-08 0.0107 850 123.33 10.044 0.0111 3.13E-08 0.0107 850 243.33 10.112 0.0108 3.13E-08 0.0107 850 543.33 9.923 0.0115 3.13E-08 0.0107 900 32.33 9.924 0.0115 4.55E-08 0.0114 900 122.33 10.127 0.0108 4.55E-08 0.0114 900 242.33 9.614 0.0128 4.55E-08 0.0114 900 542.33 9.772 0.0122 4.55E-08 0.0114 950 35.67 9.318 0.0142 1.28E-07 0.0133 950 125.67 9.626 0.0128 1.28E-07 0.0133 950 245.67 9.225 0.0147 1.28E-07 0.0133 950 545.67 9.017 0.0158 1.28E-07 0.0133 1000 40.58 8.542 0.0186 2.82E-07 0.0184 1000 130.58 8.529 0.0187 2.82E-07 0.0184 1000 250.58 8.068 0.0220 2.82E-07 0.0184 1000 550.58 8.187 0.0211 2.82E-07 0.0184 1050 43.58 7.364 0.0280 9.90E-07 0.0304 1050 133.58 6.739 0.0348 9.90E-07 0.0304 1050 253.58 6.670 0.0357 9.90E-07 0.0304 1050 553.58 6.523 0.0375 9.90E-07 0.0304

AISI 8620

Temperature Effective ASTM Grain Size Avg Grain Diameter Kp (mm^2 / min) D0 (°C) Time (min) # (mm) (mm) 850 34.25 10.008 0.0112 3.39E-08 0.0107 850 124.25 10.122 0.0108 3.39E-08 0.0107 850 244.25 10.161 0.0106 3.39E-08 0.0107 850 544.25 9.864 0.0118 3.39E-08 0.0107 900 33.75 9.782 0.0121 1.65E-07 0.0128 900 123.75 9.320 0.0142 1.65E-07 0.0128 900 243.75 9.257 0.0145 1.65E-07 0.0128 900 543.75 9.044 0.0157 1.65E-07 0.0128 950 34.50 9.364 0.0140 7.65E-07 0.0124 950 124.50 8.864 0.0167 7.65E-07 0.0124 950 244.50 8.887 0.0165 7.65E-07 0.0124 950 544.50 7.770 0.0244 7.65E-07 0.0124 1000 44.42 8.768 0.0172 1.33E-06 0.0146 1000 134.42 8.282 0.0204 1.33E-06 0.0146 1000 254.42 8.082 0.0219 1.33E-06 0.0146 1000 554.42 7.050 0.0313 1.33E-06 0.0146 1050 43.75 7.931 0.0230 3.95E-06 0.0220 1050 133.75 6.768 0.0345 3.95E-06 0.0220 1050 253.75 6.474 0.0382 3.95E-06 0.0220 1050 553.75 5.610 0.0515 3.95E-06 0.0220

AISI 9310

Temperature Effective ASTM Grain Size Avg Grain Diameter Kp (mm^2 / min) D0 (°C) Time (min) # (mm) (mm) 900 33.00 10.135 0.0107 7.62E-08 0.0111 900 123.00 10.322 0.0101 7.62E-08 0.0111 900 243.00 9.320 0.0142 7.62E-08 0.0111 900 543.00 9.806 0.0120 7.62E-08 0.0111 950 35.25 9.683 0.0125 8.74E-08 0.0125 950 125.25 9.590 0.0130 8.74E-08 0.0125 950 245.25 9.469 0.0135 8.74E-08 0.0125 950 545.25 9.317 0.0142 8.74E-08 0.0125 1000 41.50 9.012 0.0158 5.47E-07 0.0163 1000 131.50 8.511 0.0188 5.47E-07 0.0163 1000 251.50 8.193 0.0210 5.47E-07 0.0163 1000 551.50 7.884 0.0234 5.47E-07 0.0163 1050 38.58 7.131 0.0304 1.46E-06 0.0346 1050 128.58 6.406 0.0391 1.46E-06 0.0346 1050 248.58 6.067 0.0439 1.46E-06 0.0346 1050 548.58 6.151 0.0427 1.46E-06 0.0346

AISI 52100

Temperature Effective ASTM Grain Size Avg Grain Diameter Kp (mm^2 / D0 (°C) Time (min) # (mm) min) (mm) 850 33.85 9.564 0.0131 -7.90E-08 0.0119 850 123.85 10.478 0.0095 -7.90E-08 0.0119 850 243.85 10.050 0.0110 -7.90E-08 0.0119 850 543.85 10.270 0.0102 -7.90E-08 0.0119 900 35.58 9.162 0.0150 2.49E-08 0.0139 900 125.58 9.554 0.0131 2.49E-08 0.0139 900 245.58 9.485 0.0134 2.49E-08 0.0139 900 545.58 9.204 0.0148 2.49E-08 0.0139 950 35.67 9.318 0.0142 1.28E-07 0.0133 950 125.67 9.626 0.0128 1.28E-07 0.0133 950 245.67 9.225 0.0147 1.28E-07 0.0133 950 545.67 9.017 0.0158 1.28E-07 0.0133 1000 41.50 7.999 0.0225 3.96E-07 0.0221 1000 131.50 7.913 0.0232 3.96E-07 0.0221 1000 251.50 7.518 0.0266 3.96E-07 0.0221 1000 551.50 7.765 0.0244 3.96E-07 0.0221 1050 44.83 7.599 0.0258 1.65E-06 0.0268 1050 134.83 7.145 0.0302 1.65E-06 0.0268 1050 254.83 6.398 0.0392 1.65E-06 0.0268 1050 554.83 6.551 0.0371 1.65E-06 0.0268

Appendix 6: Effective Time Results

The effective time was calculated via Equation 7 & Equation 8 to determine the total amount of time that austenite grains were allowed to grow. Tabulated results are listed below for both effective heating time as well as the effective time that grains were allowed to grow. Following the tabulated results are the accompanying Mathcad calculations.

Tabulated Effective Time for AISI 1045

Sample Temperature Holding Time Heating Time # °C (min) (min) Effective Time (min) 131 850 30 3.74 33.74 112 850 120 3.74 123.74 111 850 240 3.74 243.74 114 850 540 3.74 543.74 132 900 30 4.60 34.60 105 900 120 4.60 124.60 106 900 240 4.60 244.60 109 900 540 4.60 544.60 133 950 30 5.00 35.00 118 950 120 5.00 125.00 117 950 240 5.00 245.00 120 950 540 5.00 545.00 123 1000 30 13.48 43.48 124 1000 120 13.48 133.48 125 1000 240 13.48 253.48 126 1000 540 13.48 553.48 127 1050 30 11.01 41.01 128 1050 120 11.01 131.01 129 1050 240 11.01 251.01 130 1050 540 11.01 551.01

Tabulated Effective Time for AISI 4140

Temperature Holding Time Heating Time Sample # °C (min) (min) Effective Time (min) 234 850 30 3.04 33.04 215 850 120 3.04 123.04 214 850 240 3.04 243.04 217 850 540 3.04 543.04 235 900 30 3.39 33.39 208 900 120 3.39 123.39 209 900 240 3.39 243.39 212 900 540 3.39 543.39 236 950 30 5.37 35.37 221 950 120 5.37 125.37 220 950 240 5.37 245.37 224 950 540 5.37 545.37 226 1000 30 12.49 42.49 227 1000 120 12.49 132.49 229 1000 240 12.49 252.49 228 1000 540 12.49 552.49 230 1050 30 11.78 41.78 231 1050 120 11.78 131.78 232 1050 240 11.78 251.78 233 1050 540 11.78 551.78

Tabulated Effective Time for AISI 4340

Sample Temperature Holding Time Heating Time # °C (min) (min) Effective Time (min) 610 850 30 3.01 33.01 611 850 120 3.01 123.01 612 850 240 3.01 243.01 613 850 540 3.01 543.01 614 900 30 1.57 31.57 615 900 120 1.57 121.57 616 900 240 1.57 241.57 617 900 540 1.57 541.57 618 950 30 5.21 35.21 619 950 120 5.21 125.21 620 950 240 5.21 245.21 621 950 540 5.21 545.21 601 1000 30 9.68 39.68 602 1000 120 9.68 129.68 604 1000 240 9.68 249.68 603 1000 540 9.68 549.68 605 1050 30 12.37 42.37 606 1050 120 12.37 132.37 609 1050 240 12.37 252.37 608 1050 540 12.37 552.37

Tabulated Effective Time for AISI 8620

Sample Temperature Holding Time Heating Time # °C (min) (min) Effective Time (min) 331 850 30 4.00 34.00 317 850 120 4.00 124.00 319 850 240 4.00 244.00 321 850 540 4.00 544.00 332 900 30 3.46 33.46 310 900 120 3.46 123.46 313 900 240 3.46 243.46 314 900 540 3.46 543.46 333 950 30 4.15 34.15 304 950 120 4.15 124.15 306 950 240 4.15 244.15 308 950 540 4.15 544.15 323 1000 30 13.54 43.54 324 1000 120 13.54 133.54 325 1000 240 13.54 253.54 326 1000 540 13.54 553.54 327 1050 30 12.71 42.71 328 1050 120 12.71 132.71 329 1050 240 12.71 252.71 330 1050 540 12.71 552.71

Tabulated Effective Time for AISI 9310

Sample Temperature Holding Time Heating Time # °C (min) (min) Effective Time (min) 423 900 30 2.70 32.70 406 900 120 2.70 122.70 411 900 240 2.70 242.70 408 900 540 2.70 542.70 424 950 30 4.94 34.94 401 950 120 4.94 124.94 403 950 240 4.94 244.94 405 950 540 4.94 544.94 413 1000 30 10.55 40.55 414 1000 120 10.55 130.55 416 1000 240 10.55 250.55 415 1000 540 10.55 550.55 417 1050 30 7.83 37.83 422 1050 120 7.83 127.83 421 1050 240 7.83 247.83 420 1050 540 7.83 547.83 *Note AISI 9310 was not heat treated at 850°C as the selected temperature was to close in proximity to the austenitizing temperature for this steel.

Tabulated Effective Time for AISI 52100

Temperature Holding Time Heating Time °C (min) (min) Effective Time (min) 850 30 3.36 33.36 850 120 3.36 123.36 850 240 3.36 243.36 850 540 3.36 543.36 900 30 5.22 35.22 900 120 5.22 125.22 900 240 5.22 245.22 900 540 5.22 545.22 950 30 5.16 35.16 950 120 5.16 125.16 950 240 5.16 245.16 950 540 5.16 545.16 1000 30 11.67 41.67 1000 120 11.67 131.67 1000 240 11.67 251.67 1000 540 11.67 551.67 1050 30 7.61 37.61 1050 120 7.61 127.61 1050 240 7.61 247.61 1050 540 7.61 547.61 *Note AISI 52100 did not possess sample numbers as they could not be engraved via the Haas MiniMill, instead a methodology of sample bags was adopted to differentiate between samples.

At T = 850 Celsius Ttarget  850  10 1045 Steel

2 6.73 10 4 x x  240 x  480 f(x)  6.1610 e min max

xmax  5 Area  f (x) dx  1.886 10  xmin

Area effective   224.494 Ttarget

4140 Steel

2 7.43 10 4 x x  190 x  385 f(x)  6.3410 e min max

xmax  5 Area  f (x) dx  1.532 10  xmin

Area effective   182.388 Ttarget

4340 Steel

0.0008  x f (x)  622.9e xmin  180 xmax  375

xmax  5 Area  f (x) dx  1.518 10  xmin

Area effective   180.729 Ttarget

8620 Steel

2 5.76 10 4 x x  185 x  440 f(x)  6.6010 e min max

xmax  5 Area  f (x) dx  2.017 10  xmin

Area effective   240.087 Ttarget 50

9310 Steel

2 8.96 10 4 x x  165 x  340 f(x)  6.2910 e min max

xmax  5 Area  f (x) dx  1.382 10  xmin

Area effective   164.478 Ttarget

52100 Steel

2 6.84 10 4 x f(x)  6.3110 e xmin  215 xmax  430

xmax  5 Area  f (x) dx  1.693 10  xmin

Area effective   201.549 Ttarget

At T = 900 Celsius Ttarget  900  10 1045 Steel

2 9.05 10 4 x x  165 x  450 f(x)  6.5110 e min max

xmax  5 Area  f (x) dx  2.457 10  xmin

Area effective   276.12 Ttarget

4140 Steel

2 7.43 10 4 x x  150 x  380 f(x)  6.4610 e min max

xmax  5 Area  f (x) dx  1.811 10  xmin

Area effective   203.521 Ttarget

4340 Steel

2 1.62 10 4 x f(x)  5.8010 e xmin  140 xmax  280

xmax  4 Area  f (x) dx  8.401 10  xmin

Area effective   94.395 Ttarget

8620 Steel

2 9.52 10 4 x x  180 x  405 f(x)  6.2110 e min max

xmax  5 Area  f (x) dx  1.849 10  xmin

Area effective   207.801 Ttarget 52

9310 Steel

2 1.20 10 3 x x  140 x  315 f(x)  6.2710 e min max

xmax  5 Area  f (x) dx  1.444 10  xmin

Area effective   162.284 Ttarget

52100 Steel

2 6.32 10 4 x f(x)  6.7710 e xmin  155 xmax  490

xmax  5 Area  f (x) dx  2.786 10  xmin

Area effective   313.02 Ttarget

At T = 950 Celsius Ttarget  950  10 1045 Steel

2 8.20 10 4 x x  145 x  470 f(x)  6.7210 e min max

xmax  5 Area  f (x) dx  2.819 10  xmin

Area effective   299.859 Ttarget

4140 Steel

2 7.16 10 4 x x  155 x  505 f(x)  6.8210 e min max

xmax  5 Area  f (x) dx  3.031 10  xmin

Area effective   322.46 Ttarget

4340 Steel

2 7.46 10 4 x f(x)  6.6310 e xmin  205 xmax  540

xmax  5 Area   f (x) dx  2.94  10  xmin

Area effective   312.784 Ttarget

8620 Steel

2 9.47 10 4 x x  195 x  465 f(x)  6.3310 e min max

xmax  5 Area  f (x) dx  2.342 10  xmin

Area effective   249.197 Ttarget 54

9310 Steel

2 7.78 10 4 x x  120 x  440 f(x)  6.9810 e min max

xmax  5 Area  f (x) dx  2.784 10  xmin

Area effective   296.214 Ttarget

52100 Steel

2 7.62 10 4 x f(x)  6.9310 e xmin  125 xmax  460

xmax  5 Area  f (x) dx  2.909 10  xmin

Area effective   309.476 Ttarget

At T = 1000 Celsius Ttarget  1000  10 1045 Steel

2 3.17 10 4 x x  185 x  1070 f(x)  7.3910 e min max

xmax  5 Area  f (x) dx  8.006 10  xmin

Area effective   808.657 Ttarget

4140 Steel

2 3.48 10 4 x x  200 x  1020 f(x)  7.2910 e min max

xmax  5 Area  f (x) dx  7.417 10  xmin

Area effective   749.153 Ttarget

4340 Steel

2 4.47 10 4 x f(x)  7.3410 e xmin  145 xmax  780

xmax  5 Area  f (x) dx  5.751 10  xmin

Area effective   580.867 Ttarget

8620 Steel

2 2.63 10 4 x x  125 x  990 f (x)  8.0110 e min max

xmax  5 Area   f (x) dx  8.04  10  xmin

Area effective   812.132 Ttarget 56

9310 Steel

2 3.97 10 4 x x  180 x  870 f (x)  7.3510 e min max

xmax  5 Area  f (x) dx  6.266 10  xmin

Area effective   632.96 Ttarget

52100 Steel

2 3.75 10 4 x f (x)  7.0710 e xmin  250 xmax  1020

xmax  5 Area  f (x) dx  6.932 10  xmin

Area effective   700.163 Ttarget

At T = 1050 Celsius Ttarget 1050  10 1045 Steel

2 4.25 10 4 x x  145 x  870 f (x)  7.6110 e min max

xmax  5 Area  f (x) dx  6.872 10  xmin

Area effective   660.812 Ttarget

4140 Steel

0.0004  x x  160 x  930 f (x)  765.41e min max

xmax  5 Area  f (x) dx  7.358 10  xmin

Area effective   707.527 Ttarget

4340 Steel

2 3.77 10 4 x f(x)  7.3210 e xmin  265 xmax  1080

xmax  5 Area  f (x) dx  7.718 10  xmin

Area effective   742.079 Ttarget

8620 Steel

2 3.30 10 4 x x  115 x  940 f(x)  8.0510 e min max

xmax  5 Area  f (x) dx  7.928 10  xmin

Area effective   762.354 Ttarget 58

9310 Steel

2 5.96 10 4 x x  135 x  650 f(x)  7.4810 e min max

xmax  5 Area  f (x) dx  4.887 10  xmin

Area effective   469.865 Ttarget

52100 Steel

2 5.89 10 4 x f(x)  6.6810 e xmin  190 xmax  730

xmax  5 Area  f (x) dx  4.75 10  xmin

Area effective   456.703 Ttarget

Appendix 7: D2 vs. Effective Time Graphs

AISI 1045 1045 Comparison

4.00E-03

) 3.50E-03 2 850C

(mm 3.00E-03

2 2.50E-03 900C

2.00E-03 950C

1.50E-03 1000C

1.00E-03 1050C

Average Average GrainDiameter 5.00E-04

0.00E+00 0 100 200 300 400 500 600 Effective Time (min)

1045 850C

1.60E-04

) 2

1.40E-04

(mm

2 1.20E-04 1.00E-04 8.00E-05 y = 6.65E-08x + 1.14E-04 6.00E-05 R² = 4.79E-01 4.00E-05 2.00E-05

0.00E+00 Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

1045 900C

3.00E-04

) 2

2.50E-04

(mm

2 2.00E-04

1.50E-04 y = 2.312E-07x + 1.337E-04 1.00E-04 R² = 9.843E-01 5.00E-05

0.00E+00 Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

1045 950C

4.00E-04

) 2

3.50E-04

(mm

2 3.00E-04 2.50E-04 2.00E-04 y = 2.583E-07x + 2.190E-04 1.50E-04 R² = 8.544E-01 1.00E-04 5.00E-05 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

1045 1000C

2.50E-03

) 2

(mm 2.00E-03

2 1.50E-03 y = 2.192E-06x + 9.717E-04 1.00E-03 R² = 8.624E-01

5.00E-04

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

1045 1050C

4.00E-03

) 2

3.50E-03

(mm

2 3.00E-03 2.50E-03 2.00E-03 1.50E-03 y = 3.728E-06x + 1.605E-03 R² = 6.849E-01 1.00E-03 5.00E-04 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

AISI 4140 4140 Comparison 1.80E-03

1.60E-03

) 2

1.40E-03 850C

(mm

2 1.20E-03 900C 1.00E-03

8.00E-04 950C

6.00E-04 1000C 4.00E-04 1050C Average Average GrainDiameter 2.00E-04

0.00E+00 0 100 200 300 400 500 600 Effective Time (min)

4140 850C

1.60E-04

) 2

1.40E-04

(mm

2 1.20E-04 1.00E-04 8.00E-05 y = 2.733E-08x + 1.184E-04 6.00E-05 R² = 3.324E-01 4.00E-05 2.00E-05 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4140 900C

2.50E-04

) 2

(mm 2.00E-04

2 1.50E-04 y = 6.612E-08x + 1.570E-04 1.00E-04 R² = 4.300E-01 5.00E-05

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4140 950C

2.50E-04

) 2

(mm 2.00E-04

2 1.50E-04 y = 5.639E-08x + 1.863E-04 R² = 3.365E-01 1.00E-04

5.00E-05

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4140 1000C

4.00E-04

) 2

3.50E-04

(mm

2 3.00E-04 2.50E-04 2.00E-04 1.50E-04 y = 1.275E-07x + 2.992E-04 R² = 7.413E-01 1.00E-04 5.00E-05 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4140 1050C

1.80E-03 )

2 1.60E-03 (mm

1.40E-03 2 1.20E-03 1.00E-03 8.00E-04 y = 7.257E-07x + 1.166E-03 R² = 9.872E-01 6.00E-04 4.00E-04 2.00E-04 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

AISI 4340 4340 Comparison

1.60E-03

) 1.40E-03 2 850C

(mm 1.20E-03

2 1.00E-03 900C

8.00E-04 950C

6.00E-04 1000C 4.00E-04 1050C Average Average GrainDiameter 2.00E-04

0.00E+00 0 100 200 300 400 500 600 Effective Time (min)

4340 850C

1.35E-04

) 2

(mm 1.30E-04

2 1.25E-04

1.20E-04 y = 3.128E-08x + 1.148E-04 R² = 7.527E-01 1.15E-04

1.10E-04

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4340 900C

1.80E-04 )

2 1.60E-04 (mm

1.40E-04 2 1.20E-04 1.00E-04 8.00E-05 y = 4.552E-08x + 1.299E-04 6.00E-05 R² = 2.316E-01 4.00E-05 2.00E-05 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4340 950C

3.00E-04

) 2

2.50E-04

(mm

2 2.00E-04

1.50E-04 y = 1.277E-07x + 1.778E-04 1.00E-04 R² = 6.374E-01 5.00E-05

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4340 1000C

6.00E-04

) 2

5.00E-04

(mm

2 4.00E-04 3.00E-04 y = 2.822E-07x + 3.376E-04 2.00E-04 R² = 8.566E-01 1.00E-04 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

4340 1050C

1.60E-03

) 2

1.40E-03

(mm

2 1.20E-03 1.00E-03 8.00E-04 y = 9.897E-07x + 9.267E-04 R² = 6.731E-01 6.00E-04 4.00E-04 2.00E-04 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

AISI 8620

3.00E-03 8620 Comparison

) 2

2.50E-03

(mm

2 850C 2.00E-03 900C 1.50E-03 950C 1.00E-03 1000C

5.00E-04 1050C Average Average GrainDiameter 0.00E+00 0 100 200 300 400 500 600 Effective Time (min)

8620 850C

1.60E-04

) 2

1.40E-04

(mm

2 1.20E-04 1.00E-04 8.00E-05 y = 3.394E-08x + 1.154E-04 6.00E-05 R² = 4.216E-01 4.00E-05 2.00E-05 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

8620 900C

3.00E-04

) 2

2.50E-04

(mm

2 2.00E-04

1.50E-04 y = 1.647E-07x + 1.626E-04 1.00E-04 R² = 8.082E-01 5.00E-05

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

8620 950C

7.00E-04

) 2

6.00E-04

(mm

2 5.00E-04 4.00E-04 3.00E-04 y = 7.647E-07x + 1.542E-04 2.00E-04 R² = 9.339E-01 1.00E-04 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

8620 1000C

1.20E-03

) 2

1.00E-03

(mm

2 8.00E-04

6.00E-04

4.00E-04 y = 1.329E-06x + 2.148E-04 R² = 9.728E-01 2.00E-04

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

8620 1050C

3.00E-03

) 2

2.50E-03

(mm

2 2.00E-03

1.50E-03

1.00E-03 y = 3.945E-06x + 4.889E-04 R² = 9.796E-01 5.00E-04

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

AISI 9310

9310 Comparison

2.50E-03

) 2 2.00E-03

900C

(mm

1.50E-03 950C

1.00E-03 1000C

5.00E-04 1050C Average Average GrainDiameter

0.00E+00 0 100 200 300 400 500 600 Effective Time (min)

9310 900C

2.50E-04

) 2

(mm 2.00E-04

2 1.50E-04

1.00E-04 y = 7.622E-08x + 1.229E-04 R² = 1.424E-01 5.00E-05

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

9310 950C

2.50E-04

) 2

(mm 2.00E-04

2 1.50E-04

1.00E-04 y = 8.745E-08x + 1.570E-04 5.00E-05 R² = 9.764E-01

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

9310 1000C

6.00E-04

) 2

5.00E-04

(mm

2 4.00E-04

3.00E-04 y = 5.473E-07x + 2.659E-04 2.00E-04 R² = 9.249E-01 1.00E-04

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

9310 1050C

2.50E-03

) 2

(mm 2.00E-03

2 1.50E-03

1.00E-03 y = 1.457E-06x + 1.200E-03 R² = 5.142E-01 5.00E-04

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

AISI 52100

52100 Comparison 0.0018

0.0016

) 2

0.0014 850C

(mm

2 0.0012 900C 0.001 950C 0.0008

0.0006 1000C

0.0004 1050C Average Average GrainDiameter 0.0002

0 0.00 100.00 200.00 300.00 400.00 500.00 600.00 Effective Time (min)

52100 850C

1.80E-04 )

2 1.60E-04 (mm

1.40E-04 2 1.20E-04 1.00E-04 8.00E-05 6.00E-05 y = -7.897E-08x + 1.408E-04 4.00E-05 R² = 2.515E-01 2.00E-05 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

52100 900C

2.50E-04

) 2

(mm 2.00E-04

2 1.50E-04

1.00E-04 y = 2.490E-08x + 1.936E-04 5.00E-05 R² = 4.175E-02

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

52100 950C

3.00E-04

) 2

2.50E-04

(mm

2 2.00E-04

1.50E-04

1.00E-04 y = 1.277E-07x + 1.778E-04 R² = 6.374E-01 5.00E-05

0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

52100 1000C

8.00E-04

) 2

7.00E-04

(mm

2 6.00E-04 5.00E-04 4.00E-04 y = 3.956E-07x + 4.894E-04 3.00E-04 R² = 9.974E-01 2.00E-04 1.00E-04 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

52100 1050C

1.80E-03 )

2 1.60E-03 (mm

1.40E-03 2 1.20E-03 1.00E-03 8.00E-04 y = 1.648E-06x + 7.286E-04 R² = 8.271E-01 6.00E-04 4.00E-04 2.00E-04 0.00E+00

Average Average GrainDiameter 0 100 200 300 400 500 600 Effective Time (min)

Appendix 8: Log(K) vs. 1/T Graphs

y = -13244x - 3.2101 1045 R² = 0.9307 -13

-13.5

-14

Log(Kp) -14.5

-15

-15.5 0.00072 0.00076 0.0008 0.00084 0.00088 0.00092 1/T

4140 y = -9161.7x - 7.2669 R² = 0.8173 -13.8 -14 -14.2

-14.4 -14.6 -14.8 Log(Kp) -15 -15.2 -15.4 -15.6 0.00072 0.00076 0.0008 0.00084 0.00088 0.00092 1/T

y = -11174x - 5.4695 4340 R² = 0.9576 -13.5

-14

-14.5

Log(Kp) -15

-15.5

-16 0.00072 0.00076 0.0008 0.00084 0.00088 0.00092 1/T

y = -15054x - 1.7578 8620 R² = 0.9828 -13

-13.5

-14

Log(Kp) -14.5

-15

-15.5 0.00072 0.00076 0.0008 0.00084 0.00088 0.00092 1/T

y = -14295x - 2.8691 9310 R² = 0.9059 -13.4 -13.6 -13.8

-14 -14.2 -14.4 Log(Kp) -14.6 -14.8 -15 -15.2 0.00074 0.00076 0.00078 0.0008 0.00082 0.00084 0.00086 1/T

y = -18483x - 0.3912 52100 R² = 0.9967 -13

-13.5

-14

Log(Kp) -14.5

-15

-15.5 0.00074 0.00076 0.00078 0.0008 0.00082 0.00084 0.00086 1/T

Appendix 9: Micrographs

AISI 1045

Micrograph 1-1

Microstructure of AISI 1045 Steel, austenized at 850°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-2

Microstructure of AISI 1045 Steel, austenized at 850°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-3

Microstructure of AISI 1045 Steel, austenized at 850°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-4

Microstructure of AISI 1045 Steel, austenized at 850°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-5

Microstructure of AISI 1045 Steel, austenized at 900°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 83

Micrograph 1-6

Microstructure of AISI 1045 Steel, austenized at 900°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-7

Microstructure of AISI 1045 Steel, austenized at 900°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 84

Micrograph 1-8

Microstructure of AISI 1045 Steel, austenized at 900°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-9

Microstructure of AISI 1045 Steel, austenized at 950°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 85

Micrograph 1-10

Microstructure of AISI 1045 Steel, austenized at 950°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-11

Microstructure of AISI 1045 Steel, austenized at 950°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 86

Micrograph 1-12

Microstructure of AISI 1045 Steel, austenized at 950°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 1-13

Microstructure of AISI 1045 Steel, austenized at 1000°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 87

Micrograph 1-14

Microstructure of AISI 1045 Steel, austenized at 1000°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x.

Micrograph 1-15

Microstructure of AISI 1045 Steel, austenized at 1000°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x. 88

Micrograph 1-16

Microstructure of AISI 1045 Steel, austenized at 1000°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x.

Micrograph 1-17

Microstructure of AISI 1045 Steel, austenized at 1050°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x. 89

Micrograph 1-18

Microstructure of AISI 1045 Steel, austenized at 1050°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x.

Micrograph 1-19

Microstructure of AISI 1045 Steel, austenized at 1050°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x. 90

Micrograph 1-20

Microstructure of AISI 1045 Steel, austenized at 1050°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x.

AISI 4140

Micrograph 2-1

Microstructure of AISI 4140 Steel, austenized at 850°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-2

Microstructure of AISI 4140 Steel, austenized at 850°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-3

Microstructure of AISI 4140 Steel, austenized at 850°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 93

Micrograph 2-4

Microstructure of AISI 4140 Steel, austenized at 850°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-5

Microstructure of AISI 4140 Steel, austenized at 900°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 94

Micrograph 2-6

Microstructure of AISI 4140 Steel, austenized at 900°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-7

Microstructure of AISI 4140 Steel, austenized at 900°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 95

Micrograph 2-8

Microstructure of AISI 4140 Steel, austenized at 900°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-9

Microstructure of AISI 4140 Steel, austenized at 950°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 96

Micrograph 2-10

Microstructure of AISI 4140 Steel, austenized at 950°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-11

Microstructure of AISI 4140 Steel, austenized at 950°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 97

Micrograph 2-12

Microstructure of AISI 4140 Steel, austenized at 950°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-13

Microstructure of AISI 4140 Steel, austenized at 1000°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 98

Micrograph 2-14

Microstructure of AISI 4140 Steel, austenized at 1000°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-15

Microstructure of AISI 4140 Steel, austenized at 1000°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 99

Micrograph 2-16

Microstructure of AISI 4140 Steel, austenized at 1000°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 2-17

Microstructure of AISI 4140 Steel, austenized at 1050°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 100

Micrograph 2-18

Microstructure of AISI 4140 Steel, austenized at 1050°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

Micrograph 2-19

Microstructure of AISI 4140 Steel, austenized at 1050°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 101

Micrograph 2-20

Microstructure of AISI 4140 Steel, austenized at 1050°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

102

AISI 4340

Micrograph 3-1

Microstructure of AISI 4340 Steel, austenized at 850°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

103

Micrograph 3-2

Microstructure of AISI 4340 Steel, austenized at 850°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-3

Microstructure of AISI 4340 Steel, austenized at 850°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 104

Micrograph 3-4

Microstructure of AISI 4340 Steel, austenized at 850°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-5

Microstructure of AISI 4340 Steel, austenized at 900°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 105

Micrograph 3-6

Microstructure of AISI 4340 Steel, austenized at 900°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-7

Microstructure of AISI 4340 Steel, austenized at 900°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 106

Micrograph 3-8

Microstructure of AISI 4340 Steel, austenized at 900°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-9

Microstructure of AISI 4340 Steel, austenized at 950°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 107

Micrograph 3-10

Microstructure of AISI 4340 Steel, austenized at 950°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-11

Microstructure of AISI 4340 Steel, austenized at 950°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 108

Micrograph 3-12

Microstructure of AISI 4340 Steel, austenized at 950°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-13

Microstructure of AISI 4340 Steel, austenized at 1000°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 109

Micrograph 3-14

Microstructure of AISI 4340 Steel, austenized at 1000°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-15

Microstructure of AISI 4340 Steel, austenized at 1000°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 110

Micrograph 3-16

Microstructure of AISI 4340 Steel, austenized at 1000°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 3-17

Microstructure of AISI 4340 Steel, austenized at 1050°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 111

Micrograph 3-18

Microstructure of AISI 4340 Steel, austenized at 1050°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

Micrograph 3-19

Microstructure of AISI 4340 Steel, austenized at 1050°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 112

Micrograph 3-20

Microstructure of AISI 4340 Steel, austenized at 1050°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

113

AISI 8620

Micrograph 4-1

Microstructure of AISI 8620 Steel, austenized at 850°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

114

Micrograph 4-2

Microstructure of AISI 8620 Steel, austenized at 850°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 4-3

Microstructure of AISI 8620 Steel, austenized at 850°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x. 115

Micrograph 4-4

Microstructure of AISI 8620 Steel, austenized at 850°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 4-5

Microstructure of AISI 8620 Steel, austenized at 900°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 116

Micrograph 4-6

Microstructure of AISI 8620 Steel, austenized at 900°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 4-7

Microstructure of AISI 8620 Steel, austenized at 900°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 117

Micrograph 4-8

Microstructure of AISI 8620 Steel, austenized at 900°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 4-9

Microstructure of AISI 8620 Steel, austenized at 950°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 118

Micrograph 4-10

Microstructure of AISI 8620 Steel, austenized at 950°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 4-11

Microstructure of AISI 8620 Steel, austenized at 950°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 119

Micrograph 4-12

Microstructure of AISI 8620 Steel, austenized at 950°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

Micrograph 4-13

Microstructure of AISI 8620 Steel, austenized at 1000°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 120

Micrograph 4-14

Microstructure of AISI 8620 Steel, austenized at 1000°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 4-15

Microstructure of AISI 8620 Steel, austenized at 1000°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 121

Micrograph 4-16

Microstructure of AISI 8620 Steel, austenized at 1000°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

Micrograph 4-17

Microstructure of AISI 8620 Steel, austenized at 1050°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 122

Micrograph 4-18

Microstructure of AISI 8620 Steel, austenized at 1050°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

Micrograph 4-19

Microstructure of AISI 8620 Steel, austenized at 1050°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 123

Micrograph 4-20

Microstructure of AISI 8620 Steel, austenized at 1050°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 50x.

124

AISI 9310

Micrograph 5-1

Microstructure of AISI 9310 Steel, austenized at 900°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

125

Micrograph 5-2

Microstructure of AISI 9310 Steel, austenized at 900°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 5-3

Microstructure of AISI 9310 Steel, austenized at 900°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 126

Micrograph 5-4

Microstructure of AISI 9310 Steel, austenized at 900°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 5-5

Microstructure of AISI 9310 Steel, austenized at 950°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 127

Micrograph 5-6

Microstructure of AISI 9310 Steel, austenized at 950°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 5-7

Microstructure of AISI 9310 Steel, austenized at 950°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 128

Micrograph 5-8

Microstructure of AISI 9310 Steel, austenized at 950°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 5-9

Microstructure of AISI 9310 Steel, austenized at 1000°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 129

Micrograph 5-10

Microstructure of AISI 9310 Steel, austenized at 1000°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 5-11

Microstructure of AISI 9310 Steel, austenized at 1000°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 130

Micrograph 5-12

Microstructure of AISI 9310 Steel, austenized at 1000°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 5-13

Microstructure of AISI 9310 Steel, austenized at 1050°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 131

Micrograph 5-14

Microstructure of AISI 9310 Steel, austenized at 1050°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

Micrograph 5-15

Microstructure of AISI 9310 Steel, austenized at 1050°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 132

Micrograph 5-16

Microstructure of AISI 9310 Steel, austenized at 1050°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

133

AISI 52100

Micrograph 6-1

Microstructure of AISI 52100 Steel, austenized at 850°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

134

Micrograph 6-2

Microstructure of AISI 52100 Steel, austenized at 850°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 6-3

Microstructure of AISI 52100 Steel, austenized at 850°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x. 135

Micrograph 6-4

Microstructure of AISI 52100 Steel, austenized at 850°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 6-5

Microstructure of AISI 52100 Steel, austenized at 900°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 136

Micrograph 6-6

Microstructure of AISI 52100 Steel, austenized at 900°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 6-7

Microstructure of AISI 52100 Steel, austenized at 900°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x. 137

Micrograph 6-8

Microstructure of AISI 52100 Steel, austenized at 900°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 500x.

Micrograph 6-9

Microstructure of AISI 52100 Steel, austenized at 950°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 138

Micrograph 6-10

Microstructure of AISI 52100 Steel, austenized at 950°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 6-11

Microstructure of AISI 52100 Steel, austenized at 950°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 139

Micrograph 6-12

Microstructure of AISI 52100 Steel, austenized at 950°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 6-13

Microstructure of AISI 52100 Steel, austenized at 1000°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 140

Micrograph 6-14

Microstructure of AISI 52100 Steel, austenized at 1000°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 6-15

Microstructure of AISI 52100 Steel, austenized at 1000°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 141

Micrograph 6-16

Microstructure of AISI 52100 Steel, austenized at 1000°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 6-17

Microstructure of AISI 52100 Steel, austenized at 1050°C for 0.5 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x. 142

Micrograph 6-18

Microstructure of AISI 52100 Steel, austenized at 1050°C for 2 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 200x.

Micrograph 6-19

Microstructure of AISI 52100 Steel, austenized at 1050°C for 4 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x. 143

Micrograph 6-20

Microstructure of AISI 52100 Steel, austenized at 1050°C for 9 Hours then water quenched. Etchant utilized is an aqueous HCl- Picral Acid solution. Magnification is 100x.

144