Hardfacing Welded ASTM A572-Based, High-Strength, Low-Alloy Steel: Welding, Characterization, and Surface Properties Related to the Wear Resistance

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Article Hardfacing Welded ASTM A572-Based, High-Strength, Low-Alloy Steel: Welding, Characterization, and Surface Properties Related to the Wear Resistance

Nakarin Srisuwan 1,2, Nuengruetai Kumsri 3, Trinet Yingsamphancharoen 2,3 and Attaphon Kaewvilai 3,* 1 Thai-French Innovation Institute, King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand; nakrin.s@tﬁi.kmutnb.ac.th 2 Welding Engineering and Metallurgical Inspection, Science and Technology Research Institute, King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand; [email protected] 3 Department of Welding Engineering Technology, College of Industrial Technology, King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand; [email protected] * Correspondence: [email protected]; Tel.: +66-2-555-2000 (ext. 6417)

Received: 31 December 2018; Accepted: 13 February 2019; Published: 19 February 2019

Abstract: This work presents the improvement of hardfacing welding for American Society for Testing and Materials (ASTM) A572-based high-strength, low-alloy steel by controlling the heating/cooling conditions of welding process. In the welding process, the buffer and hardfacing layers were welded onto A572-based material by a nickel–chromium electrode and chromium carbide electrode, respectively. The base metal and electrode materials were controlled by the heating/cooling process during the welding to reduce excessive stress, which could result in a crack in the specimens. The welded specimens were examined by visual and penetrant inspections for evaluating the welding quality. The macro–micro structure of the deposited layer was investigated; scanning electron microscope with an energy-dispersive X-ray spectrometer (SEM-EDS) and XRD were used to characterize structural properties, elemental compositions, and crystallite sizes of the welded specimens. The surface properties, such as hardness, impact, and abrasive wear of the welded specimens, were tested for evaluation of the wear resistance of the welded specimens.

Keywords: hardfacing; high strength low alloy steel; ASTM A572; characterization; surface property; wear resistance

1. Introduction American Society for Testing and Materials (ASTM) A572 steel plate is a kind of high-strength, low-alloy steel, which has many excellent properties, such as high strength and ductility, good corrosion resistance, and being easy to form [1–3]. Based on the excellent properties, A572 has been of interest for use in many applications, such as for a cane shredder hammer, machine tools, construction steel, etc. [3–5]. However, the surface of A572 is soft and extremely easily corroded, causing deterioration in wear conditions like abrasive and impact-based uses. Therefore, some properties, such as hardness, abrasive wear, and impact resistance of A572 still need to be improved. Hardfacing is well known as a welding process for surface improvement and material maintenance, and is done by applying ﬁller materials on the base material [6–8]. It has mostly been used in a production part of tools and machines to increase wear resistance and service life time [8,9]. In the hardfacing process, the ﬁller metal can be welded up onto the base surface by various

Metals 2019, 9, 244; doi:10.3390/met9020244 www.mdpi.com/journal/metals Metals 2019, 9, 244 2 of 12 techniques, such as shielded metal arc welding (SMAW), gas metal arc welding (GMAW), submerged arc welding (SAW), etc. [8–10]. The consumable austenitic metals can be used as a buffer layer deposited between the base metal and actual hardfacing material, increasing elemental compatibility at the fusion layer [8,9]. However, using ﬁller materials with dissimilar properties of their base materials can cause undesirable properties, such as incompatibility, low penetration weldability, and high residual stress, which ends up cracking and damaging the weld after use [8–14]. Based on this knowledge, weld quality could be improved by controlling the temperature of the welding process, such as preheating, interpass temperature, and cooling rate [8–11]. The preheating of base and ﬁller materials, which are applied before welding, can eliminate various contaminants, such as moisture, bubbles, and hydrogen gas; slow down the cooling rate; and reduce shrinkage stress for preventing defects [8–11]. The interpass temperature is the temperature of the weld between weld passes in a multi-pass weld. Controlling interpass temperature can help reduce the risk of cold cracking and prevent deterioration of the mechanical properties of materials [9,10]. Generally, the temperatures of preheating and interpass could be determined from the carbon equivalent (CE) of materials [8,11,12]. For cooling rate control, controlling interpass temperature is a general method for preventing stress cracking of the weld from distortion and residual stress [13,14]. For the above reason, heating/cooling control has been investigated for application during the hardfacing welding process, with the preheating and interpass conditions based on the calculated carbon equivalence of materials [15]. Therefore, this research presents the hardfacing welding process of A572 with heating/cooling control. The buffer and hardfacing layers were created from two types of electrode materials, which were DIN 8555: E8-UM-200-KRZ and DIN 8555: E10-UM-65-GRZ, respectively. Moreover, the relevant characteristic and surface properties of the weld were also investigated. The improving processes from these heating/cooling control conditions should increase the grain size of microstructures and weld penetration of the deposited layers, which helps enhance surface properties related to the wear resistance for some extended applications, such as the increasing durability of the hammer and shredder in sugar cane industrial equipment.

2. Materials and Methods

2.1. Materials ASTM A572 grade 50 steel plates (carbon equivalent = 0.48 calculated by the International Institute of Welding (IIW) formula [8,15]) purchased from Welding Whale Co., Ltd. (Samutprakarn, Thailand) were cut as the size of 100 × 190 × 25 mm for three duplicate tests of each techniques. The UTP S63-based nickel-chromium [16] (DIN 8555: E8-UM-200-KRZ [17]) with a diameter of 4.0 mm and UTP LEDURIT65-based chromium carbide [18] (DIN 8555: E10-UM-65-GRZ [17]) with diameter of 4.0 mm were used as buffer and hardfacing electrodes, respectively. The elemental composition and hardness of A572 grade 50 steel and welding electrodes are summarized in Table1. A vermiculite insulator was obtained from the Thai-German Institute (Chonburi, Thailand). The chemical agents obtained from NABAKEM (Chacheongsao, Thailand) were used for penetrant inspection. The 0.259 mm silica quartz purchased from Herosign Marketing Co., Ltd. (Nonthaburi, Thailand) was used for abrasive-wear testing, according to ASTM G65 [19,20].

Table 1. Elemental composition and hardness of A572 grade 50 steel and welding electrodes.

Materials % Elemental Composition (Fe Balanced) Hardness (HV) A572 grade 50 ≤0.23 C ≤1.35 Mn ≤0.40 Si ≤0.05 S ≤0.04 P 134–137 Buffer Electrode 0.10 C 19.0 Cr 8.50 Ni 5.00 Mn 0.80 Si 194–258 Hardfacing Electrode 4.50 C 23.5 Cr 6.50 Mo 5.50 Nb 1.50 V 594–834 Metals 2019, 9, 244 3 of 12

2.2. Instruments Wire cutting (JZ, DK7730, Taizhou Jiangzhou Number-Controlled Machine Tool Manufacture Co., Ltd., Jiangsu, China) was used for preparing specimens. The preheating temperature of the specimens and electrodes were controlled by oven (CARBOLITE, PF 30, Carbolite Gero Ltd., Hope Valley, UK). The arc-welding machine was acquired from Fronius, Thailand. Multi-meter (UNI-T, UT200, UNI-T, Opava, Czech Republic) and infrared thermo-sensor (PROSKIT, MT-4612, PRO’SKIT, Amelia Court House, VA, USA) were used for detecting actual current, voltage, and welding temperature. The structural properties of the hardfacing welded A572 was characterized by scanning electron microscope, with an energy-dispersive X-ray spectrometer (SEM-EDS: Philips XL 30 series, Philips, North Billerica, MA, USA) and X-ray diffractometer (Philips X-Pert-MPD X-ray diffractometer, Eindhoven, The Netherlands). The hardness at the weld surface of the specimen was tested by SONOHARD (SH-75, JFE Advantech Co., Ltd., Hyogo, Japan). The hardness at the inside of the weld and base positions was tested by a stationary hardness tester (Wilson Instruments, GWI Wilson Instruments Ltd., Campbellford, ON, Canada). The adsorption energy of specimens was tested by a model IT406 by Tinius Olsen, Horsham, PA, USA. The abrasive-wear tester was product from WEMI center, KMUTNB, Bangkok, Thailand. Weight loss of the specimen after wear testing was measured by a balancer with four decimals (OHAUS, Ranger 2000, OHAUS Instruments (Shanghai) Co., Ltd., Shanghai, China).

2.3. Hardfacing Welding, Inspection, and Macro–Micro Structure The buffer and hardfacing electrodes were re-dried before welding for 2 h at 150 ◦C and 300 ◦C, respectively [16,18]. The A572 without preheating was used as S1 and H1 specimens, while those preheated at 150 ◦C for 2 h were labeled as S2 and H2, respectively. In the hardfacing welding process, the specimen was welded by SMAW with the stringer technique, at a ﬂat position. The number of deposited layers (buffer and hardfacing), as well as the welding parameters with heating/cooling conditions are summarized in Table2. For multiple passes of welding, the interpass temperatures of buffer-based nickel–chromium (Ni–Cr) and chromium hardfacing weld were controlled at 150 ◦C and 400 ◦C, respectively [15]. After welding, the S1 and H1 specimens were cooled down in ambient conditions without controlling the cooling rate (~20 ◦C/min). In the case of S2 and H2, the specimens were embedded under a vermiculite insulator for controlling the cooling rate of 5 ◦C/min. All welded specimens were observed for the weld quality by visual and penetrant inspections. In addition, the macro–micro structure of the welded specimens at deposited layers was also investigated.

Table 2. Welding parameters.

Preheat Deposited Interpass Welding Parameters Cooling Specimen Temperature Weld Temperature Current Voltage Travel Speed Rate No. ◦ ◦ ◦ ( C) Layers ( C) (A) (V) (mm/min) ( C/min) S1 - Hardfacing - 168 26 20 20 S2 150 Hardfacing 400 168 26 20 5 Buffer - 106 24 30 H1 - 20 Hardfacing - 168 26 20 Buffer 150 106 24 30 H2 150 5 Hardfacing 400 168 26 20

2.4. Structural Characterizations by Scanning Electron Microscope with Energy-Dispersive X-ray Spectrometer and XRD The elemental composition of the welded specimens at the base, buffer, and hardfacing welding areas was characterized by SEM-EDS. The SEM-EDS with mapping technique was used for studying the compatible elements of the deposited layer. The structural phase of welded specimens was characterized by XRD using Cu-Kα as a radiation source (λ = 1.54 Å), with the 2θ ranging from 30◦ Metals 2019, 9, 244 4 of 12 to 80◦ at a scanning rate of 0.2 s−1. The crystallite size of the welded specimen was calculated by Scherrer’s equation, as follows: Metals 2019, 9, x FOR PEER REVIEW 4 of 12 D = Kλ/βcosθ (1) 80° at a scanning rate of 0.2 s−1. The crystallite size of the welded specimen was calculated by where DScherrer’sis the mean equation, size as of follows: the ordered (crystalline) domains, which may be smaller or equal to the grain size; K is a dimensionless shape factor with a value of 0.89; λ is the X-ray wavelength; β is the D = Kλ /βcosθ (1) line broadening at half the maximum intensity (FWHM) in radians, after subtracting the instrumental line broadening,where D is whichthe mean is alsosize of sometimes the ordered denoted (crystalline) as domains,∆(2θ); θ whichis the may Bragg be smaller angle of or theequal diffraction. to the grain size; K is a dimensionless shape factor with a value of 0.89; λ is the X-ray wavelength; β is the 2.5. Hardness,line broadening Impact, and at Abrasivehalf the Wearmaximum Properties intensity (FWHM) in radians, after subtracting the instrumental line broadening, which is also sometimes denoted as Δ(2θ); θ is the Bragg angle of the Thediffraction. welded specimen was cut into a cross section and tested in ﬁve positions for Vickers hardness with load 0.5 kgf. The welded specimen and base metal were prepared in the size of 70 × 25 × 10 mm and further2.5. Hardness, tested Impact, for abrasive and Abrasive wear Wear resistance Properties by dry sand rubber wheels, corresponding to the adapted ASTMThe G65welded method specimen with was the cut procedure into a cross C (load section of and 130 N,tested rotation in five rate positions of 200 for rpm, Vickers and testing time ofhardness 30 s) three with times,load 0.5 which kgf. The helps welded reduce specimen the and testing base metal time were and prepared accumulated in the size temperature of 70 × 25 [17]. × 10 mm and further tested for abrasive wear resistance by dry sand rubber wheels, corresponding The abrasive-wear resistance could be considered from weight loss after testing. The welded specimen to the adapted ASTM G65 method with the procedure C (load of 130 N, rotation rate of 200 rpm, and was preparedtesting time as aof Charpy 30 s) three V-notch times, which (type helps A) accordingreduce the testing to ASTM time and E23 accumulated [21], as shown temperature in Figure 7b, ◦ for testing[17]. adsorption The abrasive-wear impact resistance energy atcould 25 beC. considered from weight loss after testing. The welded specimen was prepared as a Charpy V-notch (type A) according to ASTM E23 [21], as shown in 3. ResultsFigure and 7b, Discussion for testing adsorption impact energy at 25 °C.

3.1. Hardfacing3. Results Welding, and Discussion Inspection, and Macro–Micro Structure

The3.1. visual Hardfacing and penetrantWelding, Inspec testingtion, and results Macro–Micro (Figure Structure1) showed the weld dimension of the specimens (S1, S2, H1, andThe visual H2) asand approximately penetrant testing 10.0 results mm (Figure width 1) andshowed 4.0 the mm weld convex. dimension From of hardfacingthe specimens welding, the obtained(S1, S2, specimens H1, and H2) without as approximately heating 10.0 (S1 andmm width H1) revealed and 4.0 mm a lotconvex. of cracks From onhardfacing the weld welding, (Figure 1a,c). This couldthe obtained be explained specimens in that without this weldingheating (S1 condition and H1) revealed caused residuala lot of cracks stress on on the the weld hardfacing (Figure weld from thermal-volumetric1a,c). This could be explained expansions in that [13 this]. welding For welding condition with caused preheating residual stress and cooling on the hardfacing conditions, the weldedweld specimens from thermal-volumetric (S2 and H2) have expansions no planar [13]. or criticalFor welding defects with on preheating the surface and (Figurecooling 1conditions,b,d). This result the welded specimens (S2 and H2) have no planar or critical defects on the surface (Figure 1b,d). clearly indicates that preheating and controlling temperature could reduce the critical defects from This result clearly indicates that preheating and controlling temperature could reduce the critical hardfacingdefects welding, from hardfacing as reported welding, elsewhere as reported [8,9 elsewhere,15]. [8,9,15].

Figure 1. Visual (upside) and penetrant (downside) testing results of hardfacing specimens: (a) S1

(without pre-heating), (b) S2 (with pre-heating), (c) H1 (without pre-heating), and (d) H2 (with pre-heating). Metals 2019, 9, x FOR PEER REVIEW 5 of 12

Figure 1. Visual (upside) and penetrant (downside) testing results of hardfacing specimens: (a) S1 Metals(without2019, 9, 244 pre-heating), (b) S2 (with pre-heating), (c) H1 (without pre-heating), and (d) H2 (with5 of 12 pre-heating).

The deposited layers layers of of hardfacing hardfacing welded welded specim specimensens (S1, (S1, S2, S2, H1, H1, and and H2) H2) were were investigated investigated by byan optical an optical microscope, microscope, as shown as shown in Figure in Figure 2 and2 and in the in theSupplementary Supplementary Materials Materials (Figure (Figure S1). S1).The Theweld weld penetration penetration on the on base the metal base metalof S1, S2, of S1,H1, S2,and H1, H2 andwas H2determined, was determined, and found and to be found 2.02, to2.86, be 2.02,1.64, 2.86,and 2.44 1.64, mm, and respectively. 2.44 mm, respectively. This implies This that implies the specimens that the specimenswithout heating/cooling without heating/cooling control (S1 controland H1) (S1 have and a H1)weld have penetration a weld penetration lower than lowerthose with than temperature those with temperature control (S2 and control H2). (S2 Moreover, and H2). Moreover,the macroscopic the macroscopic results of resultsH1 (Figure of H1 2c) (Figure clearly2c) clearlyshow the show separated the separated layers layers of base, of base,buffer, buffer, and andhardfacing, hardfacing, while while those those of H2 of H2(Figure (Figure 2d)2d) exhibit exhibit the the homogeneous homogeneous fusion fusion between bufferbuffer andand hardfacing layers. From the macroscopic results, it might be concluded that hardfacing welding with heating/cooling control control could could increase increase the the weld weld penetr penetration.ation. For For cooling cooling control, it is possible to get better stressesstresses distribution distribution and and values values in thein bufferthe buffer layer layer and meltedand melted zones betweenzones between the base the material base andmaterial buffer, and but buffer, also betweenbut also bufferbetween and buffer surface and layer. surface layer.

Figure 2. Macroscopic results and weld penetration profiles proﬁles of hardfacing welded specimens: ( a)) S1, S1, (b)) S2,S2, ((c)) H1,H1, andand ((d)) H2.H2.

As shown in Figure 3a–d, the microstructure of the base metal at the heat affect zone (HAZ), both with and without heating/cooling control, showed the mixed phases between ferrite and pearlite. It revealed that the heating/cooling control and hardfacing welding condition had no effect on the structural phase of base metal. However, it was found that the non-heating specimens (S1, H1) showed finer and smaller grains compared to those with heating/cooling control (S2, H2), as shown in the Supplementary Materials (Figure S2). This indicates that the additional heat could increase the grain size of microstructure in the HAZ zone. In the buffer layer, the microstructure of H specimens (Figure 3c,d) showed an austenitic phase, with a small dendritic structure at the grain boundaries (Supplementary Materials, Figure S3). For the hardfacing zone, the microstructure of specimens (Supplementary Materials, Figure S4) clearly showed a martensitic matrix with probably someMetals 2019small, 9, 244austenite fields at the grain boundaries. The dendrite structure (brighten) was denoted6 of 12 as chromium carbide. It revealedAt the thatfusion the line heating/cooling (interphase), the control S specimens and hardfacing showed weldinga large fusion condition line from had nothe effectassembly on the of carbonstructural elements, phase ofdue base to the metal. low diffusion However, of it carbon was found elements that into the non-heatingthe base metal. specimens In the case (S1, of H1) H specimens,showed ﬁner it andwas smallerfound that grains the compared fusion at interphase to those with was heating/cooling observed as a controltiny line, (S2, indicating H2), as shown that the in austeniticthe Supplementary buffer layer Materials could (Figurehelp combine S2). This and indicates homogenize that the the additional elemental heat components could increase at the interfacialgrain size ofregion microstructure between inbase the metal HAZ zone.and hardfa In thecing buffer material. layer, the In microstructure addition, the oforientation H specimens of (Figuredendrite3c,d) shape showed corresponded an austenitic to the phase,movement with from a small hard dendriticfacing tostructure the buffer at la theyer, grain clearly boundaries indicating (Supplementarythe dispersion and Materials, dissolution Figure of chromium S3). For thecarbide hardfacing from hardfacing zone, the to microstructure the austenitic of buffer specimens layer. (SupplementaryFrom macro-microscopic Materials, results, Figure it can S4) be clearly clearly showed concluded a martensitic that hardfacing matrix welding with probably using a buffer some withsmall heating/cooling austenite ﬁelds control at the could grain increase boundaries. the penetration The dendrite and structure diffusion (brighten) of a deposited was layer denoted to the as basechromium metal. carbide.

Figure 3. Microscopic result of hardfacing welded specimens: (a) S1, (b) S2, (c) H1, and (d) H2. At the fusion line (interphase), the S specimens showed a large fusion line from the assembly 3.2. Structural Characterization by Scanning Electron Microscope with Energy-Dispersive X-ray Spectrometer of carbon elements, due to the low diffusion of carbon elements into the base metal. In the case and XRD of H specimens, it was found that the fusion at interphase was observed as a tiny line, indicating From the SEM-EDS analysis, the EDS spectrum (Supplementary Materials, Figure S5) at the that the austenitic buffer layer could help combine and homogenize the elemental components at base metal area showed the peak position of iron (Fe), carbon (C), and manganese (Mn). The the interfacial region between base metal and hardfacing material. In addition, the orientation of spectrum of the buffer layer exhibited the signal of iron, chromium (Cr), nickel (Ni), and manganese. dendrite shape corresponded to the movement from hardfacing to the buffer layer, clearly indicating The peaks of iron, chromium, carbon, and silicon (Si) were found in the spectrum of the hardfacing the dispersion and dissolution of chromium carbide from hardfacing to the austenitic buffer layer. zone. In addition, a chromium element at the interlayer region of the S1 (welding without From macro-microscopic results, it can be clearly concluded that hardfacing welding using a buffer heating/cooling control, without buffer) and H2 specimens (welding with buffer and heating/cooling with heating/cooling control could increase the penetration and diffusion of a deposited layer to the base metal.

3.2. Structural Characterization by Scanning Electron Microscope with Energy-Dispersive X-ray Spectrometer and XRD From the SEM-EDS analysis, the EDS spectrum (Supplementary Materials, Figure S5) at the base metal area showed the peak position of iron (Fe), carbon (C), and manganese (Mn). The spectrum of the buffer layer exhibited the signal of iron, chromium (Cr), nickel (Ni), and manganese. The peaks of iron, chromium, carbon, and silicon (Si) were found in the spectrum of the hardfacing zone. In addition, a chromium element at the interlayer region of the S1 (welding without heating/cooling control, without buffer) and H2 specimens (welding with buffer and heating/cooling control) were Metals 2019, 9, x FOR PEER REVIEW 7 of 12 control) were analyzed by EDS mapping for consideration of elemental compatibility and dispersion, as shown in Figures 4 and 5, respectively. For the elemental results of the S1 specimen, it was found that the semi-quantitative amount of carbon content (4.28%) was rather high, which increases the risk of generating defects after welding. In addition, the amount of manganese in S2 (Mn, 1.16%) was in the range of A572-50 specification [1]. This indicates the incompatibility of hardfacing material and base metal, and means the manganese in the base metal could not diffuse into the hardfacing layer. For the base metals of S2 and H2, the relative carbon contents were found to be very low (0.22% and 0.21%, respectively) compared to that of S1, which indicates that the welding with heating/cooling control had no effect on the carbon composition in the base metal. In addition, the manganese in H1 (Mn, 1.56%) and H2 (Mn, 1.60%) was slightly higher than the limit of ASTM A572-50 specification [1] showing the possibility of elemental diffusion from the buffer into the base metal. From these results, it might be concluded that the buffer layer could help improve the welding quality by increasing the elemental diffusion and compatibility between buffer material and base metal. For S1, the SEM-EDS mapping (Figure 4) clearly showed chromium (Cr), the main element in hardfacing weld, which was separated from base metal. This demonstrates that the weld and base metal had low compatibility, and is related to the microscopic results, which explained that the welding without a buffer layer caused a large fusion line of carbon content and a high barrier for weldingMetals 2019 without, 9, 244 a buffer layer caused a large fusion line of carbon content and a high barrier7 offor 12 chromium carbide diffusion. Figure 5 shows the SEM-EDS mapping of H2 with the dispersion of Cr in the areas of base metal buffer and hardfacing zone. This result indicates that the buffer layer could helpanalyzed improve by EDS the mappingweldability for and consideration weld quality of elementalof the base compatibility metal by increasing and dispersion, the Cr diffusion as shown and in compatibilityFigures4 and5 between, respectively. base metal, buffer, and hardfacing layer.

Figure 4. ScanningScanning electron electron microscope microscope with with energy- energy-dispersivedispersive X-ray X-ray spectrometer (SEM-EDS) mapping with the Cr element of S1 at the interlayersinterlayers of the base metal and hardfacing.

Figure 5. SEM-EDS mapping with Cr element of H2 at the interlayers of the base metal and buffer. Figure 5. SEM-EDS mapping with Cr element of H2 at the interlayers of the base metal and buffer. For the elemental results of the S1 specimen, it was found that the semi-quantitative amount of Phase components of hardfacing welded specimens with and without heating/cooling control carbonPhase content components (4.28%) wasof hardfacing rather high, welded which specimens increases the with risk and of generatingwithout heating/cooling defects after welding. control (S1, S2, H1, and H2) were characterized by X-ray diffraction. The XRD results of H1 and H2 are (S1,In addition, S2, H1, theand amount H2) were of manganese characterized in S2 by (Mn, X-ray 1.16%) diffraction. was in theThe range XRD ofresults A572-50 of speciﬁcationH1 and H2 are [1]. showed in Figure 6c,d, respectively. The resulting XRD patterns of the hardfacing welds of H1 and showedThis indicates in Figure the incompatibility6c,d, respectively. of hardfacing The resulting material XRD andpatterns base metal,of the andhardfacing means thewelds manganese of H1 and in H2 show the peaks of chromium carbide (Cr3C2; ICDD (International Centre for Diffraction Data), H2the baseshow metal the peaks could of not chromium diffuse into carbide the hardfacing (Cr3C2; ICDD layer. For(International the base metals Centre of S2for and Diffraction H2, the relative Data), carbon contents were found to be very low (0.22% and 0.21%, respectively) compared to that of S1, which indicates that the welding with heating/cooling control had no effect on the carbon composition in the base metal. In addition, the manganese in H1 (Mn, 1.56%) and H2 (Mn, 1.60%) was slightly higher than the limit of ASTM A572-50 speciﬁcation [1] showing the possibility of elemental diffusion from the buffer into the base metal. From these results, it might be concluded that the buffer layer could help improve the welding quality by increasing the elemental diffusion and compatibility between buffer material and base metal. For S1, the SEM-EDS mapping (Figure4) clearly showed chromium (Cr), the main element in hardfacing weld, which was separated from base metal. This demonstrates that the weld and base metal had low compatibility, and is related to the microscopic results, which explained that the welding without a buffer layer caused a large fusion line of carbon content and a high barrier for chromium carbide diffusion. Figure5 shows the SEM-EDS mapping of H2 with the dispersion of Cr in the areas of base metal buffer and hardfacing zone. This result indicates that the buffer layer could help improve the weldability and weld quality of the base metal by increasing the Cr diffusion and compatibility between base metal, buffer, and hardfacing layer. Phase components of hardfacing welded specimens with and without heating/cooling control (S1, S2, H1, and H2) were characterized by X-ray diffraction. The XRD results of H1 and H2 are showed in Figure6c,d, respectively. The resulting XRD patterns of the hardfacing welds of H1 and H2 show the Metals 2019, 9, x FOR PEER REVIEW 8 of 12

No. 03-065-0897), which correspond to the orthorhombic crystal structure. In addition, the peaks at 2θ around 43° and 45° were assigned to the signals of austenite (γ-Fe-C; ICDD No. 33-0397), and martensite (Fe-C; ICDD No. 65-4899), respectively. In the case of S1 and S2, the XRD patterns (Figure 6a,b) showed the diffraction peaks that correspond to martensitite and Cr3C2; no peak of austenite Metalswas observed.2019, 9, 244 This result confirmed that the austenite peak of H1 and H2 was from the buffer 8layer. of 12 The structural phase of the hardfacing layer was Cr3C2 and martensite, while that of the austenite was obtained from the buffer layer on the base metal. The ratio of austenitic to martensitic and Cr3C2 peaks of chromium carbide (Cr3C2; ICDD (International Centre for Diffraction Data), No. 03-065-0897), whichof was correspond considered, to and the the orthorhombic results found crystal that structure.the H1 showed In addition, a lower the ratio peaks than at 2thatθ around of the 43H2◦ andspecimen. 45◦ were This assigned confirmed to the that signals the heating/coolin of austenite (γg-Fe-C; control ICDD could No. help 33-0397), combine and the martensite austenitic (Fe-C; and ICDDmartensitic No. 65-4899), phase and respectively. help improve In the the dilution case of S1of buffer and S2, and the hardfacing XRD patterns layers. (Figure Moreover,6a,b) showedthe good combination of austenitic and martensitic phase in H2 should have had an effect on the hardfacing the diffraction peaks that correspond to martensitite and Cr3C2; no peak of austenite was observed. Thiswelded result specimen,conﬁrmed and that it gave the austenite no crack peakin the of weld. H1 and H2 was from the buffer layer. The structural From crystallite size calculations at the 2θ of 43° for martensite, 45°for austenite, and 65° for phase of the hardfacing layer was Cr3C2 and martensite, while that of the austenite was obtained from Cr3C2 of the H1 specimen, the crystallite sizes were found to be 43.00, 43.19, and 47.43 nm, the buffer layer on the base metal. The ratio of austenitic to martensitic and Cr3C2 of was considered, andrespectively. the results For found the H2 that specimen, the H1 showed the crysta a lowerllite sizes ratio of than martensite, that of the austenite, H2 specimen. and Cr This3C2 were conﬁrmed found thatto be the 61.44, heating/cooling 60.37, and 64.82 control nm, respectively. could help combine The results the austeniticclearly demonstrate and martensitic that the phase crystallite and help size improveof martensite, the dilution austenite, of buffer and andCr3C hardfacing2 is in nano-range, layers. Moreover, and that theheating/cooling good combination control of during austenitic the andwelding martensitic process phase made in the H2 shouldcrystal havestructure had angrow effect toon bethe the hardfacing larger size, welded which specimen, decreases and stress it gave and noincreases crack in weldability. the weld.

FigureFigure 6.6.XRD XRD PatternPattern ofof weldedwelded specimens:specimens: ((aa)) S1,S1, ((bb)) S2,S2, ((cc)) H1,H1, andand ( (dd)) H2. H2.

◦ ◦ ◦ 3.3. Hardness,From crystallite Impact, sizeand Abrasive calculations Wear at Properties the 2θ of 43 for martensite, 45 for austenite, and 65 for Cr3C2 of the H1 specimen, the crystallite sizes were found to be 43.00, 43.19, and 47.43 nm, respectively. The average hardness of all specimens (S1, S2, H1, and H2) in five positions of each area (Figure For the H2 specimen, the crystallite sizes of martensite, austenite, and Cr3C2 were found to be 61.44, 60.37,7) were and observed 64.82 nm, and respectively. compared, The as results shown clearly in Figures demonstrate 7 and that8. In the the crystallite case of the size base of martensite, area, the hardness value of hardfacing welded specimens were found to be around 191–199 HV. This result austenite, and Cr3C2 is in nano-range, and that heating/cooling control during the welding process madeindicates the crystalthat the structure welding grow process tobe has the no larger effect size, on hardness which decreases at the base stress area. and The increases welded weldability. specimens without buffer layers S1 and S2 showed hardness at heat affected zone (HAZ) values of 323.4 and 3.3.290.8 Hardness, HV, respectively, Impact, and which Abrasive are Wear higher Properties than the hardness value (229.7–230.0 HV) of specimens with a buffer layer (H1–H2), as shown in Figure 8a. Based on this result and microstructure, it might The average hardness of all specimens (S1, S2, H1, and H2) in ﬁve positions of each area (Figure7) be explained that the buffer layer could prevent the direct diffusion of carbon from the hardfacing were observed and compared, as shown in Figures7 and8. In the case of the base area, the hardness layer to the HAZ, due to the elemental compatibility of metals such as Cr, Ni, Mn, and Si between value of hardfacing welded specimens were found to be around 191–199 HV. This result indicates the buffer and hardfacing materials, which has the effect of decreasing the hardness. Considering the that the welding process has no effect on hardness at the base area. The welded specimens without buffer layers S1 and S2 showed hardness at heat affected zone (HAZ) values of 323.4 and 290.8 HV, respectively, which are higher than the hardness value (229.7–230.0 HV) of specimens with a buffer layer (H1–H2), as shown in Figure8a. Based on this result and microstructure, it might be explained that the buffer layer could prevent the direct diffusion of carbon from the hardfacing layer to the Metals 2019, 9, 244 9 of 12

Metals 2019, 9, x FOR PEER REVIEW 9 of 12 HAZ,Metals 2019 due, 9 to, x FOR the PEER elemental REVIEW compatibility of metals such as Cr, Ni, Mn, and Si between the buffer9 of 12 hardnessand hardfacing at the materials,buffer area which of H2, has it thewas effect found of decreasingthat the buffer the hardness. welding with Considering temperature the hardness control showedathardness the buffer the at hardness areathe buffer of H2, value area it was approximately of foundH2, it thatwas theasfound 235.8 buffer that HV welding ,the which buffer withwas welding close temperature to withthe hardness temperature control of showed HAZ. control theOn thehardnessshowed other the hand, value hardness the approximately buffer value welding approximately as 235.8without HV, astemperat which 235.8 wasHVure, closewhichcontrol to was of the H1 close hardness showed to the of thehardness HAZ. hardness On of theHAZ. value other On of 273.8hand,the other theHV, bufferhand, which the welding is buffer higher without welding than temperature withoutthat of temperatthe control hardnessure of control H1 of showed HAZ. of H1 theThis showed hardness result the suggests valuehardness of 273.8that value HV,the of whichtemperature273.8 isHV, higher which control than is in that higherwelding of the than hardnesscould that better ofof HAZ. helpthe hardnessbalance This result the ofsuggests hardness HAZ. thatThis between theresult temperature the suggests HAZ and control that buffer the in weldingthantemperature welding could controlwithout better in help temperature welding balance could thecontrol. hardnessbetter help between balance the the HAZ hardness and bufferbetween than the welding HAZ and without buffer temperaturethan welding control. without temperature control.

Figure 7. ((a) The hardness testing positions and (b) the impact specimen. Figure 7. (a) The hardness testing positions and (b) the impact specimen.

Figure 8. a Figure 8. TheThe hardness hardness results results of of welded welded specimens specimens at atthe the areas areas of ofthe the (a) (base,) base, HAZ, HAZ, and and buffer; buffer; (b) (interiorFigureb) interior 8.and The and surface hardness surface of results ofthe the hard-weld; hard-weld;of welded and specimens and (c) ( cthe) the athardness hardness the areas profiles proﬁlesof the (ina in) base,various various HAZ, zones zones and ofbuffer; welded (b) specimens (•) S1, ( ) S2, ( ) H1, and (×) H2. specimensinterior and ( )surface S1, () S2,of the(N ) hard-weld;H1, and ( )and H2. (c) the hardness profiles in various zones of welded specimens () S1, () S2, () H1, and () H2. The hardness of hardfacing weld at the surface and its interior to 2 mm (Inside Hard-Weld) The hardness of hardfacing weld at the surface and its interior to 2 mm (Inside Hard-Weld) were tested, as shown in the Figure8b. The hardness of S1 and H1 specimens (non-heating/cooling were Thetested, hardness as shown of hardfacingin the Figure weld 8b. Theat the hard surfaceness ofand S1 itsand interior H1 specimens to 2 mm (non-heating/cooling (Inside Hard-Weld) condition) was found to be in the range of 630–655 HV at the inside of the weld, and found to be condition)were tested, was as found shown to in be the in theFigure range 8b. of The 630–655 hardness HV atof theS1 andinside H1 of specimens the weld, and(non-heating/cooling found to be 631– 680condition) HV at the was surface found toarea. be inFor the the range hardness of 630–655 value HV of specimens at the inside with of theheating/cooling weld, and found conditions, to be 631– it was680 foundHV at thatthe surface the hardness area. For of S2 the and hardness H2 was value found of to specimens be 410 and with 463 heating/coolingHV at the inside conditions, of the weld, it respectively,was found that and the 554 hardness and 511 of HV S2 andat the H2 surface was found area, to respectively. be 410 and 463 Figure HV at 8c the shows inside the of hardnessthe weld, respectively, and 554 and 511 HV at the surface area, respectively. Figure 8c shows the hardness

Metals 2019, 9, x FOR PEER REVIEW 10 of 12 profile of welded specimens, and finds that the H2 specimen showed the minimum rate of increasing hardness (from base to hardfacing zones). This result clearly indicates that the heating/cooling condition during welding decreased the hardness at the hardfacing weld, because the additional heating during the welding made large grain and crystal sizes, which can relieve Metalsstress2019 [22–24], 9, 244 and increase weldability at the weld of materials. In addition, the surface hardness10 of 12of H2 was lower than those of S1, S2, and H1, because the buffer could cause the dilution between buffer and hardfacing materials, resulting in increasing the grain size of microstructure, which 631–680 HV at the surface area. For the hardness value of specimens with heating/cooling conditions, reduces the hardness of hardfacing surface. it was found that the hardness of S2 and H2 was found to be 410 and 463 HV at the inside of the weld, For impact testing, the impact adsorption energy of welded specimens, S1, S2, H1, and H2, were respectively, and 554 and 511 HV at the surface area, respectively. Figure8c shows the hardness proﬁle found to be 46, 73, 59, and 151 joules, respectively, as shown in Figure 9a. It was found that the S1 of welded specimens, and ﬁnds that the H2 specimen showed the minimum rate of increasing hardness specimen without buffer and non-heating/cooling control showed an adsorption energy lower than (from base to hardfacing zones). This result clearly indicates that the heating/cooling condition during that of the welded specimen (H1) obtained from buffer hardfacing without temperature control. This welding decreased the hardness at the hardfacing weld, because the additional heating during the indicates that the buffer could improve the impact property, because the buffer material consisted of welding made large grain and crystal sizes, which can relieve stress [22–24] and increase weldability at Ni, which could improve the impact property of steels [25]. In addition, the specimens from the weld of materials. In addition, the surface hardness of H2 was lower than those of S1, S2, and H1, heating/cooling control (S2 and H2) showed the impact value higher than those S1 and H1 because the buffer could cause the dilution between buffer and hardfacing materials, resulting in specimens, because the S2 and H2 have a large grain size, which results in high ductility [21]. This increasing the grain size of microstructure, which reduces the hardness of hardfacing surface. result clearly concludes that heating/cooling control during hardfacing can improve the adsorption For impact testing, the impact adsorption energy of welded specimens, S1, S2, H1, and H2, energy of the weld, which results from decreasing the stress of the weld by increasing the size of the were found to be 46, 73, 59, and 151 joules, respectively, as shown in Figure9a. It was found that the crystal in microstructure. S1 specimen without buffer and non-heating/cooling control showed an adsorption energy lower The A572-50 and welded specimens were tested by a wear testing machine with a dry sand than that of the welded specimen (H1) obtained from buffer hardfacing without temperature control. rubber wheel. The wear resistance of all specimens could be determined from the weight loss of the This indicates that the buffer could improve the impact property, because the buffer material consisted specimen after wear testing, as shown in Figure 9b. From the testing results, it was found that the of Ni, which could improve the impact property of steels [25]. In addition, the specimens from specimen before welding showed a wear rate of 0.223 g/min, while those of hardfaced specimens heating/cooling control (S2 and H2) showed the impact value higher than those S1 and H1 specimens, exhibited a wear rate of 0.040–0.050 g/min. The results indicate that the hardfacing welding process because the S2 and H2 have a large grain size, which results in high ductility [21]. This result clearly can help improve the wear resistance of A572-50. When more layers of hardfacing were applied, concludes that heating/cooling control during hardfacing can improve the adsorption energy of greater hardness and wear resistance were obtained [10]. Therefore, the hardfacing should carry out the weld, which results from decreasing the stress of the weld by increasing the size of the crystal two or three hardfacing layers to effectively harden the welded specimen [8,10]. in microstructure.

FigureFigure 9.9.The The testingtesting resultsresults ofof weldedweldedspecimens: specimens: ((aa)) impactimpact andand ((bb)) abrasiveabrasive wear. wear. The A572-50 and welded specimens were tested by a wear testing machine with a dry sand 4. Conclusions rubber wheel. The wear resistance of all specimens could be determined from the weight loss of the specimenThe high-strength, after wear testing, low-alloy, as shown steel-based in Figure ASTM9b. From A572 the grade testing 50 results,was successfully it was found welded that theby a specimenhardfacing before welding welding process. showed For awelding wear rate with of 0.223 heating/cooling g/min, while control those ofand hardfaced buffer, the specimens welded exhibitedspecimens a wearhave rateno critical of 0.040–0.050 defects g/min.on the surface, The results which indicate indicates that thethat hardfacing preheating welding and controlling process cantemperature help improve with thea buffer wear may resistance reduce ofthe A572-50. stress in hardfacing When more welding. layers of From hardfacing the testing were results, applied, the greaterhardfacing hardness welding and wearprocess resistance with buffer-based were obtained Ni-Cr [10]. Therefore,and heating/cooling the hardfacing control should could carry help out twoimprove or three weldability, hardfacing wear layers resistance, to effectively and hardenadsorpti theon weldedenergy. specimen In addition, [8,10 the]. XRD results clearly demonstrate that the weld structure was nano-crystalline of martensite, austenite, and Cr3C2. The 4.high Conclusions austenitic–martensitic ratio might affect the hardfacing welded specimen, which had no cracks. TheseThe results high-strength, indicate that low-alloy, heating/cooling steel-based control ASTM during A572 the grade hardfacing 50 was welding successfully process welded made by a alarger hardfacing crystalline welding size, process.which affected For welding the weldability with heating/cooling of specimen. controlThe overall and results buffer, indicate the welded that specimens have no critical defects on the surface, which indicates that preheating and controlling temperature with a buffer may reduce the stress in hardfacing welding. From the testing results, the hardfacing welding process with buffer-based Ni-Cr and heating/cooling control could help improve weldability, wear resistance, and adsorption energy. In addition, the XRD results clearly Metals 2019, 9, 244 11 of 12

demonstrate that the weld structure was nano-crystalline of martensite, austenite, and Cr3C2. The high austenitic–martensitic ratio might affect the hardfacing welded specimen, which had no cracks. These results indicate that heating/cooling control during the hardfacing welding process made a larger crystalline size, which affected the weldability of specimen. The overall results indicate that the welded specimens from welding with heating/cooling control showed suitable surface properties for wear-resistant applications.

Supplementary Materials: The following are available online at http://www.mdpi.com/2075-4701/9/2/244/s1, Figure S1: Weld penetration of hardfaced specimens: (a) S1, (b) S2, (c) H1 and (d) H1; Figure S2: Microscopic result at HAZ of hardfacing welded specimens: (a) S1, (b) S2, (c) H1 and (d) H2; Figure S3: Microscopic result at buffer of hardfacing welded specimens: (a) H1 and (b) H2; Figure S4: Microscopic result at hardfacing of hardfacing welded specimens: (a) S1, (b) S2, (c) H1 and (d) H2; Figure S5: The EDS spectrum of welded specimen at (a) base, (b) buffer and (c) hardfacing weld. Author Contributions: N.S. performed research design, grant-materials provision, experiment, data analysis and revised the article. N.K. assisted in experiment and characterization. T.Y. performed materials provision, experiment data analysis and revised the article. A.K. performed research design, characterization, data analysis, wrote and revised the manuscript. Funding: This research was funded by King Mongkut’s University of Technology North Bangkok, Contract no. KMUTNB-60-ART-030. Acknowledgments: The authors are very grateful to Department of Materials Engineering, Kasetsart University for supporting X-ray diffractometer. Additional thanks to Vorakorn Thongsang (Thai-German Institute) and Thammanoon Thaweechai (Department of Chemistry, Kasetsart University) for their support of the instruments. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. ASTM A572/A572M-15: American Society for Testing and Materials (ASTM). Standard Speciﬁcation for High-Strength Low-Alloy Columbium-Vanadium Structural Steel; ASTM: West Conshohocken, PA, USA, 2015. 2. Desai, S. Plastic Design in A572 (Grade 65) Steel: Mechanical Properties of ASTM A572 Grade 65 Steel. Master’s Thesis, Lehigh University, Bethlehem, PA, USA, 1969. 3. Zhou, J.; Yang, J.; Ye, Y.; Dai, G.; Peng, X. Effect of Heat Input on Microstructure and Properties in Heat Affected Zone of ASTM A572 GR.65 Steel. Adv. Mater. Res. 2011, 148, 553–557. [CrossRef] 4. Doty, W.D. Weldability of constructional steels-USA Viewpoint. Suppl. Weld. J. 1971, 157, 49–57. 5. Shen, Y.F.; Zuo, L. High-strength low-alloy steel strengthened by multiply nanoscale microstructure, HSLA steels 2015. In Micro Alloying 2015 & Offshore Engineering Steels 2015 Conference Proceedings; Springer: Cham, Switzerland, 2015; pp. 187–193. 6. Kenchireddy, K.M.; Jayadeva, C.T.; Sreenivasan, A. Inﬂuence of material characteristics on the abrasive wear response of some hardfacing alloys. Glob. J. Eng. Sci. Res. 2014, 1, 12–21. 7. Gómez, A.L.; Cañón, C.F.; Ramírez, D.E. Hard faced welded tips in shredder hammers: Technical and economical performance. Int. Sug. J. 2008, 110, 335–340. 8. Kjellberg, O. Repair and Maintenance Welding Handbook, 2nd ed.; ESAB: Gothenburg, Sweden, 2006; p. 130. 9. O’Brien, A. Welding Processes Part 1, Welding Handbook, 9th ed.; American Welding Society (AWS): Miami, FL, USA, 2004; Volume 2, p. 680. 10. Kumsri, N.; Tippayasam, C.; Srisuwan, N.; Yingsamphancharoen, T.; Kaewvilai, A. Improvement of wear resistant properties of ASTM A572 steel by hardfacing welding process. In Proceedings of the MRS-Thailand International Conference’s E-Proceedings, Chiang Mai, Thailand, 31 October–3 November 2017; pp. 120–124. 11. Lancaster, J.F. Metallurgy of Welding, 6th ed.; Elsevier: Amsterdam, The Netherlands, 1999; p. 464. 12. Yurioka, N. Weldability of modern high strength steels. Adv. Weld. Metall. 1990, 1190, 79–100. 13. Nasir, N.S.M.; Razab, M.K.A.A.; Mamat, S.; Iqbal, M. Review on Welding Residual Stress. ARPN J. Eng. Appl. Sci. 2016, 11, 6166–6175. 14. Srivastava, B.K.; Tewari, S.P.; Prakash, J.A. Review on effect of preheating and/or post weld heat treatmemt (PWHT) on mechanical behaviour of ferrous metals. Int. J. Eng. Sci. Technol. 2010, 2, 625–631. 15. Kobewelding. Available online: http://www.kobewelding.com/SelectingConsumables/hardfacing.pdf (accessed on 7 February 2019). Metals 2019, 9, 244 12 of 12

16. Bohler-uddeholm. Available online: http://www.bohler-uddeholm.cz/media/UTP%20Maintenance_EN. pdf (accessed on 7 February 2019). 17. DIN 8555-1, Filler Metals Used for Surfacing; Filler Wires, Filler Rods, Wire Electrodes, Covered Electrodes; Designation; Technical Delivery Conditions; German Institute for Standardisation: Berlin, Germany, 1983. 18. Bohlerperu. Available online: http://www.bohlerperu.com/images/article/p37_UTP%20LEDURIT%2065. pdf (accessed on 7 February 2019). 19. Franek, F.; Badisch, E.; Kirchgaßner, M. Advanced methods for characterization of abrasion/erosion resistance of wear protection materials. FME Trans. 2009, 37, 61–70. 20. ASTM G65-16: American Society for Testing and Materials (ASTM). Standard Test Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel Apparatus; ASTM: West Conshohocken, PA, USA, 2016. 21. ASTM E23-18: American Society for Testing and Materials (ASTM). Standard Test Methods for Notched Bar Impact Testing of Metallic Materials; ASTM: West Conshohocken, PA, USA, 2018. 22. Chakrabarty, I. Surface and Heat Treatment Processes. Compr. Mater. Finish. 2017, 2, 246–287. 23. Calcagnotto, M.; Adachi, Y.; Ponge, D.; Raabe, D. Deformation and fracture mechanisms in ﬁne-and ultraﬁne-grained ferrite/martensite dual-phase steels and the effect of aging. Acta Mater. 2011, 59, 658–670. [CrossRef] 24. Equbal, M.I.; Alam1, P.; Ohdar, R.; Anand, K.A.; Alam, M.S. Effect of cooling rate on the microstructure and mechanical properties of medium carbon Steel. Int. J. Metall. Eng. 2016, 5, 21–24. 25. Gerard, B. Fundamentals of Hardfacing by Fusion Welding, Welding Alloys Group, 2018; pp. 1–37. Available online: https://www.welding-alloys.com/uploads/pdf/brochures/en/wa-consumables/WA% 20Hardfacing%20Fundamentals%20by%20arc%20welding.pdf (accessed on 7 February 2019).

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