sign in sign up
<<
Home , Carburizing, Tempering (metallurgy), Wrought iron

Journal of Basic & Applied Sciences, 2012, 8, 319-324 319 Effects of Process Variables on Mechanical and Chemical Properties of Carburized Mild

A. Oyetunji*,1 and S.O. Adeosun*,2

1Dept of Metallurgical and Materials The Federal University of Technology, Akure Ondo State Nigeria 2Dept of Metallurgical and Materials Engineering University of Lagos, Akoka Lagos Nigeria Abstract: This work evaluates the suitability of using palm kernel shell, animal bone (mammalian bones from cattle) and sea shell (oyster shell) materials as carburizers for case of 0.078%C mild steel. The mild steel sample used in this study sourced from universal steel company, Ikeja Lagos Nigeria was cut into suitable sizes using hacksaw machine for tensile and tests. The carburizing media used were milled into fine powder while Barium trioxo (iv) carbonate (VI) (BaCO3) was used as an energizer in the carburizing process. Three rectangular plate boxes were fabricated to accommodate each of the steel samples and carburized.

A calculated amount of each carburizer was weighed into each of the stainless steel boxes and 20 wt % of BaC03 was mixed with each of them. Mild steel samples were covered completely in each of the boxes with the mixture of the carburizer and energizer placed in the furnace chamber. The carburizing temperatures varied between 700 - 1100oC while the holding time varied between 1-5 hrs. The boxes and its contents were allowed to cool down to room temperature in the furnace after carburization. All samples were heated to 850oC after been soaked for 30 minutes at this temperature and oil quenched. This was to increase the hardness of the case. Fifteen (15) of these samples were further tempered at 350oC for 2hrs to relieve the stress built up during . Hardness test, tensile strength tests and chemical analysis were carried out on the samples. It was observed that the hardness values of the untempered samples are superior to the tempered ones at carburizing temperatures of 7000C, 8000C and 9000C. On the other hand, the tensile strengths of the tempered samples are higher relative to the untempered samples at carburizing temperatures of 7000C, 10000C and 11000C. The results of the analysis show that palm kernel shell and animal bone are potentially suitable to be used as a carburizing media than the sea shell at high temperatures (above 10000C) with holding time above 1 hr. Keywords: Carburizers, hardness, tensile, carburizing time and temperature, pack carburizing, quenching and properties.

INTRODUCTION The service condition of many steel components such as cams, gears and shafts make it necessary for Many different types of heat treatment processes them to possess both hard and -resistant surfaces are used to modify the surface and structural properties at the same time with tough and shock-resistant cores. of engineering components as reported by Child [1]. In plain carbon , these two different sets of The engineering of surfaces of components to improve properties exist only in steels. Higgins [2] reported the life and performance of parts used in automobiles that low , containing approximately 0.1 and aerospace is an active area of research. Suitable %C, will be tough and soft, whilst a high carbon steel of thermal / mechanical / thermo mechanical surface 0.8%C or more will be hard and brittle. engineering treatments are known to produce extensive re-arrangements of atoms in and Case carburizing involved the diffusion of carbon alloys and a corresponding marked variation in into the surface layers of low carbon steel by heating it physical, chemical and mechanical properties. Among in contact with a carbonaceous material. The principle the more important of these treatments are heat of case hardening was used centuries ago in the treatment processes such as immersion hardening, conversion of wrought to steel by 'the cementation and case carburizing as studied by process. This ancient case hardening process make Child [1]. use of the fact that carbon will diffuse into the iron provided the iron is in the Face Centered Cubic (FCC) gamma form which exists above 910°C.

*Address corresponding to these authors at the Dept of Metallurgical and Prime, et al., [3] reported that carburizing is one of Materials Engineering The Federal University of Technology, Akure Ondo State Nigeria; Tel: +2348035795336; E-mail: [email protected] the most commonly performed steel heat treatments. Department of Metallurgical and Materials Engineering University of Lagos, Akoka Lagos Nigeria; Tel: +2348036126987; Over the years it was performed by packing the low E-mail: [email protected] carbon parts in , then raising the

temperature of the pack to red heat for several hours.

ISSN: 1814-8085 / E-ISSN: 1927-5129/12 © 2012 Lifescience Global 320 Journal of Basic & Applied Sciences, 2012 Volume 8 Oyetunji and Adeosun

The entire pack, charcoal and iron parts, was then reported by Xu and Kuang [15] since controlling dumped into water to quench it. The surface became parameters in carburization is a complex problem as very hard, while the interior or “core” of the part re- stated by Aramide, et al., [17]. The major influencing tained the of low carbon steel. parameters in carburization are the holding time, carburizing temperature, carbon potential and the Craig [4] defined carburizing as a diffusion- quench time in oil as reported by Shewmon [18]. controlled process, so the longer the steel is held in the carbon-rich environment, the greater the carbon Locally produced steel does not often meet the penetration will be and the higher the carbon content. requirement for manufacturing spare parts due to their The carburized section will have carbon content high low carbon content. When there is need for high carbon enough so that it can be hardened again through flame steel case for special purposes, production of high or induction hardening. The objective is to produce a carbon steel cases locally using abundant local hard, wear-resistant case which will be resistant to both materials becomes imperative. This will reduce the bending and contact whilst still maintaining its burden on foreign reserves and create employment toughness and of the low carbon core as opportunities. The present work focused on the effects studied by Stephen and Edward [5]. of carburizing process variables (carburizers, carburizing temperature and holding time) on the Surface hardening processes are influenced by heat mechanical and chemical properties of carburized mild treatment temperature, rate of heating and cooling, steel. The study is aimed at determining the potential of heat treatment period, quenching media and materials such as seashell, palm kernel shell and temperature as investigated by Schimizu and Tamura animal bone as steel carburizers with results [6]. Post heat treatment and pre-heat treatment comparable to other commonly used carbonaceous processes are the major influential parameters, which materials. affect the quality of the part surface hardened. is essentially the ease of EXPERIMENTAL METHODOLOGY and reflects the ability of a steel to be hardened to a specified depth as found in prior’s works The as-received mild steel rod of 16 mm diameter of Kirkaldy and Feldman, [7]; and Rudnev et al, [8]. was analyzed using spectrometric analyzer and it While Rakhit [9]; Rudnev et al., [8]; Smith [10], studied chemical composition is shown in Table 1. The various the factors that increase hardenability and they found carburizing media – palmkernel shell, animal bone and those factors as dissolved elements in sea shell were obtained and pulverized in ball milling (except CO), coarse grains of austenite, and machine into fine powder to increase the surface area. homogeneity of austenite. Three stainless steel boxes were fabricated to accommodate the carburizing media, as-received mild

Automobile components such as rack and pinion, steel rod samples, and the energizer (BaCO3) of 65% gears, cam, valve, rocker, shafts and axles, which purity level. require high fatigue resistance, are normally case hardened by carburizing. The carburizing furnaces are These mild steel rods were cut and machined into either gas fired or electrically heated. The carburizing tensile and hardness tests pieces. The surfaces of the temperature varies from 870 to 940 °C while the gas samples were polished into mirror-like before the atmosphere for carburizing is produced from liquid or carburization process began. gaseous hydrocarbons such as , butane or The fabricated stainless steel boxes have its density as reported by Rajan, et al., [11]. The study of as 700g/cm3. The weight of the carburizer was process parameters in metals during heat treatment calculated from the volume of the container used and a studied by Denis, [12], Leblond [13], Wang, et al., [14]; known weight of each of the carburizer was packed into Liu, et al., [15] has been of considerable interest for some years but there has been relatively little work on the stainless steel box with 20 wt % of Barium trioxocarbonate (iv) salt (BaCO ). The 20 wt % BaCO process variables during the surface hardening process 3 3

Table 1: Chemical Composition of Mild Steel Rod

Element C Ca Zn Si S P Mn Ni Cr Mo V Cu W As Sn Al Co Fe

% comp 0.078 0.0001 0.005 0.15 0.06 0.05 0.58 0.13 0.11 0.02 0.001 0.38 0.007 0.005 0.04 0.003 0.01 98.24 Effeects of Carburizing Process Variables on Mechanical Journal of Basic & Applied Sciences, 2012 Volume 8 321 is 140g and was thoroughly mixed with each carburizer Table 3: Typical Characteristics of the Quenching Oil in each of the boxes. (As Specified by the Producer: Petro-Canada)

Characteristics Values The BaCO3 act as energizer and also promotes the formation of carbon (iv) (CO2) gas, which in turns Viscosity of cSt @ 40 °C 14.0 react with the excess carbon in the media to produce Viscosity of cSt @ 100 °C 3.2 carbon (ii) oxide (CO). This CO reacts with the low Viscosity of SUS @ 100 °F 74 carbon steel surface to form atomic carbon which Viscosity of SUS @ 210 °F 37 diffuses into the steel. Then the prepared samples were buried completely in the palm kernel shell, animal Flash Point, °C/ °F 173/343 bone and seashell powder in the respective boxes. Ramsbottom Carbon Residue, Mass% 0.2 Quench Time, seconds The three boxes contained the carburizing powder Ball 16 and the steel samples were placed in the heat treatment chamber of the heat treatment furnace show Chromized Nickel Ball 19 in (1a). where they were heated to predetermined temperatures and held at these temperatures for a Chemical Analysis predetermined time as shown in Table 2. At each temperature and holding time, the furnace was allowed The chemical analysis of the as-received mild steel to cool down before the samples were all removed. samples and after carburizing processes were carried Hardening treatment was carried out on all the samples on the carburized mild steel by sparking using by heating them to a temperature of 850 oC for 30 spectrometric analyser. The results were shown in minutes and then quenched in oil. The oil quenchant Tables 1 and 4. physical properties are shown in Table 3. Table 4: % Carbon at Various Tempering Temperatures

% Carbon at Various Tempering Temperatures (OC) S/No Carburizer 700 800 900 1000 1100

1 SS 0.074 0.073 0.079 0.0094 0.0062 2 PKS 0.004 0.066 0.101 0.151 0.53 3 AB 0.078 0.084 0.128 0.131 0.426

As received : 0.078%C

SS=Sea Shell (Oyster Shell), PKS-Palm Kernel Shell; AB-Animal Bone (Mammilian Bone from Cattle).

Mechanical Test

In each case, test was conducted on three test samples and the mean value was taken.

(1a). . The tensile tests were performed on various tensile Table 2: Pack Carburizing Processes Done At Different samples using Monsanto tensometer. The load Temperatures and Times for each sample was noted as well as the diameter at the point of fracture and the final gauge length. The Treatment 700 800 900 1000 1100 initial diameter and initial gauge length for each sample temperature (oC) was noted before applying load. The sample was Holding time (hrs) 5 4 3 2 1 subjected to uniaxial load, at a fixed crosshead speed of 10 mm/min. This test was performed in accordance Fifteen (15) of these quenched samples were with standard used by Aramide et al., [17]. tempered at 350 o C for 2 hours to relieve internal stresses built up during quenching and to increase the Rockwell hardness test was carried out on toughness of the specimens while the remaining 15 carburized, tempered mild steel samples. For each of samples were untempered after hardening. the sample case the test was conducted 3 times and 322 Journal of Basic & Applied Sciences, 2012 Volume 8 Oyetunji and Adeosun the average value was taken. The test was performed 9000C. This is because tempering reduces the in line with Oyetunji and Alaneme [19] previous work hardness and increases the toughness of the samples. The tensile strength results shown in Figures 3 and 4 RESULTS revealed that samples carburized at 7000C, 10000C and 11000C in palm kernel shell carburizer have the The mechanical tests results are as presented in tensile strength values for the tempered samples which Figures (1-4). are higher than the untempered ones due to increase DISCUSSION in toughness resulting from tempering. While for animal bone carburizer, the steel samples show improved 0 From the hardness responses shown in Figures 1 tensile strengths at 700 C over untempered samples. and 2 the tempered samples have values which are Thus at higher temperature the tensile strengths of inferior to the untempered ones at 7000C, 8000C and samples in the animal bone carburizer declines. For samples carburized in sea shell, tensile strengths are

Figure 1: Hardness responses of quenched and tempered samples with carburizing temperature.

Figure 2: Hardness responses of quenched and untempered samples with carburizing temperature.

Figure 3: Tensile strengths of carburized, quenched and tempered steel samples with carburized temperature. Effeects of Carburizing Process Variables on Mechanical Journal of Basic & Applied Sciences, 2012 Volume 8 323

Figure 4: Tensile strengths of carburized and quenched steel samples with carburizing temperature. Definition: SS=Sea Shell (Oyster Shell), PKS-Palm Kernel Shell; AB-Animal Bone (Mammilian Bone from Cattle). improved for tempered samples at 8000C, 9000C and determined by the size, shape, composition and 10000C in similar pattern as reported by (Aramide et distribution of the that forms with a relatively al.; [17]). minor contribution from the solid solutions hardening of the ferrite. These changes in microstructure usually The result of the chemical analysis shown in Table decrease hardness, tensile strength and strength 4 indicates that only palm kernel shell and animal bone but increase ductility and toughness (Stephen and have the potential to be used as carburizing media. Edward) [5]. These carburizers show considerable increase in percentage carbon released into the steel sample CONCLUSIONS matrix at 9000C, 10000C and 11000C when compared to carbon percentage of the as-receive samples. The In this study, pack carburization of mild steel rod seashell does not have good carbon-release potential using palm kernel shell, animal bone, and seashell as for use as a carburizer as it decarburizes the steel carburizers were examined at 700-1100oC. And from samples in the process. The presence of martensite in the results obtained, the following deductions can be quenched steel, while greatly increasing its hardness made: and tensile strength, causes the material to be brittle as its formation is accompanied by severe matrix 1. The hardness of the untempered samples distortions. The hardness and strength of martensite carburized in palm kernel shell and animal bone structure increased sharply with increase in carbon showed higher values than the tempered content. Contribution to the strength arises from the samples. carbon in , precipitated during the quench, introduced during the 2. The tensile strengths of the samples carburized 0 transformation, and the grain size (Stephen and in powdered palm kernel shell at 1000 C and 0 Edward) [5]. 1100 C and tempered showed higher values than the untempered ones. Through careful controlled tempering treatment, the quenching stresses can be relieved and some of the 3. For the samples carburized using powdered carbon can precipitate from the super saturated solid palm kernel shell and animal bone, the carbon solution to a finely dispersed carbide phase. In this content in solid solution increases as 0 0 way, the toughness of the steel can be vastly improved temperatures increased from 800 C-1100 C. with very little detriment to its hardness and tensile 4. Palm kernel shell and animal bone carburizers properties. In steel quenched to a microstructure have good potential to be used as a carburizer consisting essentially of martensite, the iron lattice is for mild steel, while seashell has decline strained by the carbon atoms, producing the high propensity to be used as a carburizer. hardness of quenched steels and upon heating, the carbon atom diffuse and react in a series of distinct ACKNOWLEDGMENT steps that eventually form Fe3C or alloy carbide in a ferrite matrix of gradually decreasing stress level. The Alhassan Ogwu of The Department of Metallurgical properties of the tempered steel are primarily and Materials Engineering of The Federal University of 324 Journal of Basic & Applied Sciences, 2012 Volume 8 Oyetunji and Adeosun

Technology, Akure Nigeria contribution in the area of [12] Denis S. Coupled temperature stress, phase transformation calculation model numerical illustration of the internal data collection is highly appreciated. stresses evolution during cooling of a eutectoid carbon steel cylinder. Metallurgical Transaction A; 1987; 18A: 1203-87. REFERENCES http://dx.doi.org/10.1007/BF02647190 [13] Leblond JB. Mathematical modeling of transformation [1] Child HC. Surface Hardening of Steel. Oxford University in steels II: Coupling with strain hardening Press. UK 1980; pp.10-24 phenomena. Int J Plast 1989; 5(6): 573-1. http://dx.doi.org/10.1016/0749-6419(89)90002-8 [2] Higgins RA. Engineering Metallurgy. (part 1, Applied physical metallurgy).5th ed. Kent: ELBS; Edward Arnold Publishers [14] Wang KF, Chandrasekar S, Yang HTY. Experimental and Ltd. 1991; pp. 40-162. computational study of the quenching of carbon steel. Intl Jl Manufact Sci Eng 1997; 119(3): 257-65. [3] Prime MB, Prantil VC, Rangaswamy P, García FP. In: http://dx.doi.org/10.1115/1.2831102 Böttger AJ, Delhez R, Mittemeijer EJ, Eds. Measurement and Prediction in a Ring. [15] Liu CC, Xu X, Liu ZA. FEM modeling of quenching and Materials Science Forum; Residual Stress ECRS 5. tempering and its application in industrial engineering. Finite Stamford: Thomson Scientific; 2006; pp. 223-228. Elements in Analysis and Design 2003; 39(11): 1053-70. http://dx.doi.org/10.1016/S0168-874X(02)00156-7 [4] Craig F. Case hardening In a Home Garage. 2006. [16] Xu DH, Kuang ZB. A study on the distribution of residual [5] Stephen MC, Edward LL. ASM Handbook- , stress due to surface induction hardening. Int J Eng Mater 1991; Vol. 4. Technol 1996; 118(2): 571-75. [6] Schimizu N, Tamura I. (1997) An examination of the relation http://dx.doi.org/10.1115/1.2805958 between quench-hardening behaviour of steel and cooling [17] Aramide FO, Ibitoye SA, Oladele IO, Borode JO. Effects of curve in oil. Trans ISIJ 1978; 18: pp. 445-50. Carburization Time and Temperature on the Mechanical [7] Kirkaldy JS, Feldman SE. J Heat Treating 1989; 7(1): 57-64. Properties of Carburized Mild Steel, Using Activated Carbon http://dx.doi.org/10.1007/BF02833188 as Carburizer. Mater Res 2009; 12(4): 483-87. [8] Rudnev VD. Loveless RC, Black M. Handbook of Induction http://dx.doi.org/10.1590/S1516-14392009000400018 Heating, Marcel Dekker, Inc., , 2003; pp. 39-43. [18] Shewmon GP. Diffusion in solids, series in material science [9] Rakhit AK. Heat Treatment of Gears: A Practical Guide for and Engineering. Tokyo: McGraw Hill; 1963. Engineers, ASM International, Metals Park, OH, 2000; pp. [19] Oyetunji A, Alaneme KK. Influence of the Content and 44-50, 86-90. Matrix Structure on the Mechanical Properties of Al-Si Alloy. [10] Smith WF. Structure and Properties of Engineering Alloys, West Indian J Eng 2005; 28(1): 36-44. 2nd ed., McGraw-Hill, Inc., New York, 1993; pp. 132-141. [11] Rajan TV, Sharma CP, Sharma A. Heat Treatment Principles and Techniques. New Delhi: Prentice Hall 1994.

Received on 02-04-2012 Accepted on 12-05-2012 Published on 05-06-2012 http://dx.doi.org/10.6000/1927-5129.2012.08.02.11

2012 Oyetunji and Adeosun; Licensee Lifescience Global. This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.