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Microstructure and wear property of Fe–Mn–Cr–Mo–V alloy cladding by submerged arc welding
Journal of Materials Processing Technology 147 (2004) 191–196
Microstructure and wear property of Fe–Mn–Cr–Mo–V alloy cladding by submerged arc welding Shan-Ping Lu a,b,∗ , Oh-Yang Kwon a , Tae-Bum Kim a , Kwon-Hu Kim a a
Department of Mechanical Engineering, Inha University, 253 Yonghyun-dong, Inchon 402-751, South Korea b Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, PR China Received 20 November 2002; accepted 16 December 2003
Abstract A wear resistant Fe–Mn–Cr–Mo–V alloy cladding was deposited on SM45C (equivalent to AISI1045) substrate by automatic submerged arc welding using stoody 105 alloy wire. Microstructure and surface hardness of the cladding were investigated and measured on samples prepared under different welding conditions. The results showed that the retained austenite in the cladding increases with the increased welding current and reduced travel speed. The wear behavior of the clad was studied using ball-on-disk tribometer. Wear mechanism was analyzed based on the analysis of the worn surfaces both the clad and ball by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The scanning electron microscopic examination of the worn surface shows that a layer of oxide film forms on the worn surface. Oxidation wear mechanism controls the wear process. The spalling of the oxide was caused by the repeated rubbing fatigue mechanism. © 2004 Elsevier B.V. All rights reserved. Keywords: Ladding; Microstructure; Ball-on-disk wear; Stoody alloy
1. Introduction Surface condition of structural components has been a persistent problem in modern engineering application. Some components stop functioning due to only the minor damage on the surface. Using cladding techniques, it is possible to improve surface properties, such as the wear, the corrosion and oxidation resistances, and to take advantage of a longer service life and the consequent reduction of total cost. Cladding is defined as the deposition of dissimilar material on the surface of substrate to obtain desired properties, which the substrate initially does not possess, using special heat source such as arc, flame, induction heat and high energy beams. Submerged arc cladding has been used in modern industries, especially for the heavy section steels and for a large structure surfaces needing to be modified. Comparing with other welding process, submerged arc cladding offer higher deposition rate, higher layering capacity and better bead characteristic with less-sophisticated automatic equipment. ∗ Corresponding author. Present address: Materials Diagnosis and Life Assessment Laboratory, Joining and Welding Institute, Osaka University, 11-1 Mihogaoka Ibaraki, Osaka 567-0047, Japan. Tel.: +81-6-6879-8663; fax: +81-6-6879-8663. E-mail address: [email protected] (S.-P. Lu).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2003.12.016
In the past 20 years, many literatures on submerged arc welding and cladding have been published. The available research papers are focused on three areas: (1) microstructures and properties of bead and HAZ [1–7]; (2) bead characteristics in function of process variables [5,8–11]; (3) gas/metal/slag reactions in welding process [12–14]. However, there are limited literatures showing the relation of welding parameters, cladding microstructure and wear behavior. In this paper, a Fe–Mn–Cr–Mo–V alloy (Stoody 105 alloy wire) was selected as cladding material, which is often used as a cladding material on rollers, idlers, mine car wheels and similar equipments involving severe metal to metal wear, to investigate the effect of welding parameters on the microstructure and wear behavior of the cladding. Based on the results, the ball-on-disk wear mechanism of the clad was analyzed.
2. Materials and experimental procedure The substrate material used was commercial carbon steel SM45C (equivalent to AISI1045), which was cut into plates with the size 300 mm × 300 mm × 25 mm. Ferric base alloy steel wire, Stoody 105 with a diameter of 3.2 mm, was chosen as the cladding material. Stoody 105 alloy has very good resistance in metal to metal wear. In the submerged
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Table 1 Compositions of wire, substrate and mate ball (wt.%) Element
Wire SM45C Mate ball
C
Si
Mn
P
S
Cr
0.2 0.43–0.50 0.95–1.10
1.3 – 0.15–0.35
2.0 0.6–0.9 <0.50
– <0.04 <0.025
– <0.05 <0.025
2.8 – 1.30–1.60
Mo 0.4 – <0.08
V
Fe
0.15 – –
Balance Balance Balance
arc welding process, the area between the wire and the substrate is shielded in a blanket of granular fusible flux, which protects the molten filler metal. Different wires need different flux. Here commercial Stoody “S” flux was selected to match the Stoody 105 wire. During the ball-on-disk wear test, the cladding sample was machined into disk with the size Ø30 mm × 10 mm and a commercial Ø6.0 mm bearing ball (JIS SUJ2) was used as the mate material with the normalized hardness, HRc 62–65. Table 1 shows the chemical compositions of the wire, substrate and mate ball. Fe–Mn–Cr–Mo–V cladding was manufactured by automatic DC submerged arc welding machine (DSM-800). Samples were made under different welding currents (300, 360, 420 and 500 A) and travel speeds (3.23, 5.00, 5.88, 7.14 and 9.52 mm/s) to show the effect of welding parameters on the wear property. One double-layer and one three-layer sample were also prepared for the wear test. Surface hardness and microstructures of the cladding made under different welding parameters were measured and investigated by digital microhardness tester (HVS-1000), Rockwell hardness tester and SEM. Wear test was conducted with a ball-on-disk wear test machine at room temperature without lubrication shown in Fig. 1. The test samples were cut to Ø30 mm × 10 mm, the cladding surface of which was ground to a surface finish of Ra = 0.2 m. Wear tests were conducted under four different load (5, 8, 12 and 16 N), four different tangential sliding speed (8, 15, 25 and 35 cm/s) and four sliding distance (500, 1000, 1500
and 2000 m). Before and after the wear tests the disk specimens were ultrasonically cleaned in acetone solution and their weight was determined on a precision balance with accuracy of ±0.0001 g, and then the weight loss was calculated. The morphology of the worn surface was investigated through SEM.
Fig. 1. Schematic of ball-on-disk wear test.
Fig. 2. Effect of welding current on the surface hardness.
3. Results and discussion 3.1. Surface hardness and microstructure The Rockwell hardness and microhardness for the cladding surface were measured to determine the effect of welding parameters on them as shown in Figs. 2 and 3, and Table 2. The surface hardness decreases with increased welding current, reduced travel speed and increased layer number. Cladding surface hardness under different welding parameters depends to large extent on the microstructures of the cladding. Fig. 4 shows the microstructures of the cladding prepared at different parameters. The microstructure of the cladding is composed of martensite (white lath) with some retained austenite (black area). For the submerge arc cladding, the solidification process of the small pool is like that of metal mode casting process. The cooling speed is so high that the microstructure is different from the equilibrium structure. The factors influencing the final microstructure of the clad metal include the compositions of the clad and the welding parameters. The
S.-P. Lu et al. / Journal of Materials Processing Technology 147 (2004) 191–196
193
Table 2 Effect of layer number on the surface hardness and wear weight loss Wear condition
Sample
Microhardness (Hv)
Rockwell hardness (HRc)
Weight loss (mg)
12 N 25 cm/s 1500 m
Single layer Double layer Triple layer
604 516 536
43.0 41.9 41.2
5.2 6.45 5.55
Cladding parameters: 360 A and 5.88 mm/s.
such as thermal conductivity. While the heat flux is related with welding parameters. The relation between welding parameters and the cooling time t8–5 is given as following [15]: ηVI/v t8–5 = 2πλ 1
Fig. 3. Effect of travel speed on the surface hardness.
microstructures of the clad metal and HAZ are depended significantly on the cooling speed. Generally, the cooling time form 800 to 500 ◦ C, t8–5 , is decided by the heat flux from the arc source and the material thermophysical properties,
where V is the welding voltage; I the welding current; η the efficiency of the arc; v the travel speed; λ the thermal conductivity of the substrate; and T0 the pre-heat temperature of the substrate. As the welding current increased, the t8–5 will increase and the cooling rate is decreased, so the austenite to martensite transformation was partially prevented and the retained austenite is increased as shown in Fig. 4b. The more is the retained austenite, the lower is the cladding hardness. And hence the cladding hardness decreased with the increasing of the welding current in Fig. 2. As the travel speed increased, the t8–5 decreased and the cooling speed is increased which is benefit for the austenite to martensite phase transformation and made the lath martensite finer as shown
Fig. 4. Microstructures of the cladding prepared at different parameters: (a) 360 A, 5.00 mm/s, single layer; (b) 500 A, 5.00 mm/s, single layer; (c) 360 A, 9.52 mm/s, single layer; (d) 360 A, 5.88 mm/s, double-layer cladding.
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in Fig. 4c. So the cladding hardness is increased weakly with the travel speed. Considering to the thermal conductivity of the substrate, the carbon steel thermal conductivity is higher than that of alloy steel. Generally, the carbon steel thermal conductivity is around 41.0 J m−1 s−1 K−1 , while the alloy steel’s thermal conductivity is around 32 J m−1 s−1 K−1 [16]. The lower is the thermal conductivity, the longer is the cooling time and the lower is the cooling speed, which is prevent the austenite to martensite phase transformation. For the double-layer cladding, the second layer is deposited on the first layer and the first alloy layer becomes the substrate of the second layer. Since the alloy layer thermal conductivity is lower than the carbon steel, the cooling speed of multilayer is slower than
Fig. 5. Effect of wear condition on the weight loss: (a) weight loss vs. wear load; (b) weight loss vs. sliding speed; (c) weight loss vs. sliding distance.
single layer and there are more retained austenite existing in the multilayers as shown in Fig. 4d. The more the retained austenite, the lower is the cladding hardness in Table 2. 3.2. Ball-on-disk wear test Ball-on-disk wear test was conducted to the cladding samples under different wear conditions. The wear resistance of the cladding was evaluated by means of weigh loss. Fig. 5 shows the results. The weight loss increases with the wear load, sliding speed and sliding distance. Fig. 6 shows the effect of welding parameters on the wear weight loss. The wear weight loss decreased a little with the increasing of the welding current. And the weight loss is not sensitive to the travel speed. Also the wear weigh loss is not sensitive to the cladding layer numbers as shown in Table 2. The typical scanning electron morphology of the worn surface is shown in Fig. 7. It is clear to find that the worn surface is covered by an oxide film, but the film has spalled somewhere. The composition on the worn surface was analyzed using EDS as shown in Table 3. The white area (marked A in picture) consisting high oxygen is the oxide and the gray area is the fresh area as the oxide spalling off. Based on the observations above, the mild ball-on-disk wear
Fig. 6. Effect of welding parameters on the weight loss: (a) weight loss vs. welding current; (b) weight loss vs. travel speed.
S.-P. Lu et al. / Journal of Materials Processing Technology 147 (2004) 191–196
195
Fig. 7. Morphology of worn surface: (a) worn disk; (b) worn ball. Table 3 Worn surface compositions Location
Content
O
Si
Cr
Mn
Fe
White area (point A in Fig. 7a)
wt.% at.%
8.13 25.24
1.09 1.75
2.05 1.79
1.49 1.22
86.44 70.00
Gray area (point B in Fig. 7a)
wt.% at.%
0.00 0.00
1.13 2.21
2.47 2.62
2.03 2.03
94.38 93.14
White area (point A in Fig. 7b)
wt.% at.%
4.73 14.74
– –
1.72 1.66
– –
93.55 83.60
Gray area (point B in Fig. 7b)
wt.% at.%
0.00 0.00
– –
1.88 2.02
– –
98.12 97.98
is controlled by oxidation wear mechanism. The wear rate is dependant on the oxidation process and the spalling rate of the oxide film from the rubbed surface. The spalling of the oxide is a fatigue mechanism due to repeated rubbing action. The oxidation of the worn surface depends on the flash temperature during the wear process, which, on the other hand, depends upon the normal wear load and sliding speed. As usual, the surface temperature increases as normal load or sliding speed increases [17]. As the wear load and sliding speed increased, the flash temperature increased and the oxidation was accelerated. So the weight loss is increased and with the wear load and siding speed as shown in Fig. 5.
In the Fe–Mn–Cr–Mo–V alloy cladding here, the surface hardness of the cladding is related with the microstructure, which is affected by the welding parameters, such as welding current and speed. However, the ball-on-disk wear properties is not very sensitive to the welding parameters.
4. Conclusions The microstructure of the stoody alloy cladding is composed of martensite and retained austenite, which was influenced by the cladding parameters. The retained austenite
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increases with the increased welding current, and reduced travel speed. The more is the retained austenite, the lower is the surface hardness. The ball-on-disk wear process of the stoody alloy cladding is dependant to large extent on the combination of the clad oxidation and the spalling of the oxide film caused by the fatigue mechanism. The ball-on-disk wear property is not very sensitive to the welding conditions.
Acknowledgements This work was supported by Korean Research Foundation Grant (KRF-99-005-E00006).
References [1] A. Joarder, S.C. Saha, A.K. Ghose, Study of submerged arc weld metal and heat-affected zone microstructures of plain carbon steel, Weld. J. 70 (6) (1991) 141s–146s. [2] N. Bailey, Submerged arc welding ferrite steels with alloyed metal powder, Weld. J. 70 (8) (1991) 187s–206s. [3] A.O. Kluken, T.A. Siewert, R. Smith, Effects of copper, nickel and boron on mechanical properties of low-alloy steel weld metals deposited at high heat input, Weld. J. 73 (8) (1994) 193s–199s. [4] U.D. Mallya, H.S. Srinivas, Effect of magnetic steering of the arc on clad quality in submerged arc strip cladding, Weld. J. 72 (7) (1993) 289s–293s.
[5] G.N. Heintze, R. Mc Pherson, Solidification control of submerged arc welds in steels by inoculation with Ti, Weld. J. 65 (3) (1986) 71s–82s. [6] N.A. Fleck, Ö. Grong, G.R. Edwards, D.K. Matlock, The role of filler metal wire and flux composition in submerged arc weld metal transformation kinetics, Weld. J. 65 (5) (1986) 113s–121s. [7] J.A. Gianetto, N.J. Smith, J.T. Mcgrath, J.T. Bowker, Effect of composition and energy input on structure and properties of high-strength weld metal, Weld. J. 71 (11) (1992) 407s–419s. [8] R.S. Chandel, S.R. Bala, Cooling time and features of submerged arc weld beads, Weld. J. 64 (7) (1985) 201s–208s. [9] R.S. Chandel, Mathematical modeling of melting rates for submerged arc welding, Weld. J. 66 (5) (1987) 135s–140s. [10] L.J. Yang, R.S. Chandel, M.J. Bibby, The effects of process variables on the weld deposit area of submerged arc welds, Weld. J. 72 (1) (1993) 11s–18s. [11] U.D. Mallya, H.S. Srinivas, Bead characteristics in submerged arc strip cladding, Weld. J. 68 (12) (1989) 30–35. [12] T. Lau, G.C. Weatherly, A.M. Lean, Gas/metal/slag reactions in submerged arc welding using CaO–Al2 O3 based fluxes, Weld. J. 65 (2) (1986) 31s–38s. [13] P.A. Burck, J.E. Indacochea, D.L. Olson, Effects of welding flux additions on 4340 steel weld metal composition, Weld. J. 69 (3) (1990) 115s–122s. [14] N.N. Potapov, Oxygen effect on low-alloy steel weld metal properties, Weld. J. 72 (8) (1993) 367s–370s. [15] K. Easterling, Introduction to the Physical Metallurgy of Welding, Butterworths, London, 1983, p. 17. [16] Y.S. Touloukian, Thermophysical Properties of High Temperature Solid Materials, vol. 3, Ferrous Alloys, Thermophysical Properties Research Center, Purdue University, 1967, p. 81. [17] H. So, C.T. Chen, Y.A. Chen, Wear behaviours of laser-clad stellite alloy 6, Wear 192 (1996) 78–84.
Microstructure and wear property of Fe–Mn–Cr–Mo–V alloy cladding by submerged arc welding Shan-Ping Lu a,b,∗ , Oh-Yang Kwon a , Tae-Bum Kim a , Kwon-Hu Kim a a
Department of Mechanical Engineering, Inha University, 253 Yonghyun-dong, Inchon 402-751, South Korea b Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, PR China Received 20 November 2002; accepted 16 December 2003
Abstract A wear resistant Fe–Mn–Cr–Mo–V alloy cladding was deposited on SM45C (equivalent to AISI1045) substrate by automatic submerged arc welding using stoody 105 alloy wire. Microstructure and surface hardness of the cladding were investigated and measured on samples prepared under different welding conditions. The results showed that the retained austenite in the cladding increases with the increased welding current and reduced travel speed. The wear behavior of the clad was studied using ball-on-disk tribometer. Wear mechanism was analyzed based on the analysis of the worn surfaces both the clad and ball by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The scanning electron microscopic examination of the worn surface shows that a layer of oxide film forms on the worn surface. Oxidation wear mechanism controls the wear process. The spalling of the oxide was caused by the repeated rubbing fatigue mechanism. © 2004 Elsevier B.V. All rights reserved. Keywords: Ladding; Microstructure; Ball-on-disk wear; Stoody alloy
1. Introduction Surface condition of structural components has been a persistent problem in modern engineering application. Some components stop functioning due to only the minor damage on the surface. Using cladding techniques, it is possible to improve surface properties, such as the wear, the corrosion and oxidation resistances, and to take advantage of a longer service life and the consequent reduction of total cost. Cladding is defined as the deposition of dissimilar material on the surface of substrate to obtain desired properties, which the substrate initially does not possess, using special heat source such as arc, flame, induction heat and high energy beams. Submerged arc cladding has been used in modern industries, especially for the heavy section steels and for a large structure surfaces needing to be modified. Comparing with other welding process, submerged arc cladding offer higher deposition rate, higher layering capacity and better bead characteristic with less-sophisticated automatic equipment. ∗ Corresponding author. Present address: Materials Diagnosis and Life Assessment Laboratory, Joining and Welding Institute, Osaka University, 11-1 Mihogaoka Ibaraki, Osaka 567-0047, Japan. Tel.: +81-6-6879-8663; fax: +81-6-6879-8663. E-mail address: [email protected] (S.-P. Lu).
0924-0136/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2003.12.016
In the past 20 years, many literatures on submerged arc welding and cladding have been published. The available research papers are focused on three areas: (1) microstructures and properties of bead and HAZ [1–7]; (2) bead characteristics in function of process variables [5,8–11]; (3) gas/metal/slag reactions in welding process [12–14]. However, there are limited literatures showing the relation of welding parameters, cladding microstructure and wear behavior. In this paper, a Fe–Mn–Cr–Mo–V alloy (Stoody 105 alloy wire) was selected as cladding material, which is often used as a cladding material on rollers, idlers, mine car wheels and similar equipments involving severe metal to metal wear, to investigate the effect of welding parameters on the microstructure and wear behavior of the cladding. Based on the results, the ball-on-disk wear mechanism of the clad was analyzed.
2. Materials and experimental procedure The substrate material used was commercial carbon steel SM45C (equivalent to AISI1045), which was cut into plates with the size 300 mm × 300 mm × 25 mm. Ferric base alloy steel wire, Stoody 105 with a diameter of 3.2 mm, was chosen as the cladding material. Stoody 105 alloy has very good resistance in metal to metal wear. In the submerged
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Table 1 Compositions of wire, substrate and mate ball (wt.%) Element
Wire SM45C Mate ball
C
Si
Mn
P
S
Cr
0.2 0.43–0.50 0.95–1.10
1.3 – 0.15–0.35
2.0 0.6–0.9 <0.50
– <0.04 <0.025
– <0.05 <0.025
2.8 – 1.30–1.60
Mo 0.4 – <0.08
V
Fe
0.15 – –
Balance Balance Balance
arc welding process, the area between the wire and the substrate is shielded in a blanket of granular fusible flux, which protects the molten filler metal. Different wires need different flux. Here commercial Stoody “S” flux was selected to match the Stoody 105 wire. During the ball-on-disk wear test, the cladding sample was machined into disk with the size Ø30 mm × 10 mm and a commercial Ø6.0 mm bearing ball (JIS SUJ2) was used as the mate material with the normalized hardness, HRc 62–65. Table 1 shows the chemical compositions of the wire, substrate and mate ball. Fe–Mn–Cr–Mo–V cladding was manufactured by automatic DC submerged arc welding machine (DSM-800). Samples were made under different welding currents (300, 360, 420 and 500 A) and travel speeds (3.23, 5.00, 5.88, 7.14 and 9.52 mm/s) to show the effect of welding parameters on the wear property. One double-layer and one three-layer sample were also prepared for the wear test. Surface hardness and microstructures of the cladding made under different welding parameters were measured and investigated by digital microhardness tester (HVS-1000), Rockwell hardness tester and SEM. Wear test was conducted with a ball-on-disk wear test machine at room temperature without lubrication shown in Fig. 1. The test samples were cut to Ø30 mm × 10 mm, the cladding surface of which was ground to a surface finish of Ra = 0.2 m. Wear tests were conducted under four different load (5, 8, 12 and 16 N), four different tangential sliding speed (8, 15, 25 and 35 cm/s) and four sliding distance (500, 1000, 1500
and 2000 m). Before and after the wear tests the disk specimens were ultrasonically cleaned in acetone solution and their weight was determined on a precision balance with accuracy of ±0.0001 g, and then the weight loss was calculated. The morphology of the worn surface was investigated through SEM.
Fig. 1. Schematic of ball-on-disk wear test.
Fig. 2. Effect of welding current on the surface hardness.
3. Results and discussion 3.1. Surface hardness and microstructure The Rockwell hardness and microhardness for the cladding surface were measured to determine the effect of welding parameters on them as shown in Figs. 2 and 3, and Table 2. The surface hardness decreases with increased welding current, reduced travel speed and increased layer number. Cladding surface hardness under different welding parameters depends to large extent on the microstructures of the cladding. Fig. 4 shows the microstructures of the cladding prepared at different parameters. The microstructure of the cladding is composed of martensite (white lath) with some retained austenite (black area). For the submerge arc cladding, the solidification process of the small pool is like that of metal mode casting process. The cooling speed is so high that the microstructure is different from the equilibrium structure. The factors influencing the final microstructure of the clad metal include the compositions of the clad and the welding parameters. The
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193
Table 2 Effect of layer number on the surface hardness and wear weight loss Wear condition
Sample
Microhardness (Hv)
Rockwell hardness (HRc)
Weight loss (mg)
12 N 25 cm/s 1500 m
Single layer Double layer Triple layer
604 516 536
43.0 41.9 41.2
5.2 6.45 5.55
Cladding parameters: 360 A and 5.88 mm/s.
such as thermal conductivity. While the heat flux is related with welding parameters. The relation between welding parameters and the cooling time t8–5 is given as following [15]: ηVI/v t8–5 = 2πλ 1
Fig. 3. Effect of travel speed on the surface hardness.
microstructures of the clad metal and HAZ are depended significantly on the cooling speed. Generally, the cooling time form 800 to 500 ◦ C, t8–5 , is decided by the heat flux from the arc source and the material thermophysical properties,
where V is the welding voltage; I the welding current; η the efficiency of the arc; v the travel speed; λ the thermal conductivity of the substrate; and T0 the pre-heat temperature of the substrate. As the welding current increased, the t8–5 will increase and the cooling rate is decreased, so the austenite to martensite transformation was partially prevented and the retained austenite is increased as shown in Fig. 4b. The more is the retained austenite, the lower is the cladding hardness. And hence the cladding hardness decreased with the increasing of the welding current in Fig. 2. As the travel speed increased, the t8–5 decreased and the cooling speed is increased which is benefit for the austenite to martensite phase transformation and made the lath martensite finer as shown
Fig. 4. Microstructures of the cladding prepared at different parameters: (a) 360 A, 5.00 mm/s, single layer; (b) 500 A, 5.00 mm/s, single layer; (c) 360 A, 9.52 mm/s, single layer; (d) 360 A, 5.88 mm/s, double-layer cladding.
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in Fig. 4c. So the cladding hardness is increased weakly with the travel speed. Considering to the thermal conductivity of the substrate, the carbon steel thermal conductivity is higher than that of alloy steel. Generally, the carbon steel thermal conductivity is around 41.0 J m−1 s−1 K−1 , while the alloy steel’s thermal conductivity is around 32 J m−1 s−1 K−1 [16]. The lower is the thermal conductivity, the longer is the cooling time and the lower is the cooling speed, which is prevent the austenite to martensite phase transformation. For the double-layer cladding, the second layer is deposited on the first layer and the first alloy layer becomes the substrate of the second layer. Since the alloy layer thermal conductivity is lower than the carbon steel, the cooling speed of multilayer is slower than
Fig. 5. Effect of wear condition on the weight loss: (a) weight loss vs. wear load; (b) weight loss vs. sliding speed; (c) weight loss vs. sliding distance.
single layer and there are more retained austenite existing in the multilayers as shown in Fig. 4d. The more the retained austenite, the lower is the cladding hardness in Table 2. 3.2. Ball-on-disk wear test Ball-on-disk wear test was conducted to the cladding samples under different wear conditions. The wear resistance of the cladding was evaluated by means of weigh loss. Fig. 5 shows the results. The weight loss increases with the wear load, sliding speed and sliding distance. Fig. 6 shows the effect of welding parameters on the wear weight loss. The wear weight loss decreased a little with the increasing of the welding current. And the weight loss is not sensitive to the travel speed. Also the wear weigh loss is not sensitive to the cladding layer numbers as shown in Table 2. The typical scanning electron morphology of the worn surface is shown in Fig. 7. It is clear to find that the worn surface is covered by an oxide film, but the film has spalled somewhere. The composition on the worn surface was analyzed using EDS as shown in Table 3. The white area (marked A in picture) consisting high oxygen is the oxide and the gray area is the fresh area as the oxide spalling off. Based on the observations above, the mild ball-on-disk wear
Fig. 6. Effect of welding parameters on the weight loss: (a) weight loss vs. welding current; (b) weight loss vs. travel speed.
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195
Fig. 7. Morphology of worn surface: (a) worn disk; (b) worn ball. Table 3 Worn surface compositions Location
Content
O
Si
Cr
Mn
Fe
White area (point A in Fig. 7a)
wt.% at.%
8.13 25.24
1.09 1.75
2.05 1.79
1.49 1.22
86.44 70.00
Gray area (point B in Fig. 7a)
wt.% at.%
0.00 0.00
1.13 2.21
2.47 2.62
2.03 2.03
94.38 93.14
White area (point A in Fig. 7b)
wt.% at.%
4.73 14.74
– –
1.72 1.66
– –
93.55 83.60
Gray area (point B in Fig. 7b)
wt.% at.%
0.00 0.00
– –
1.88 2.02
– –
98.12 97.98
is controlled by oxidation wear mechanism. The wear rate is dependant on the oxidation process and the spalling rate of the oxide film from the rubbed surface. The spalling of the oxide is a fatigue mechanism due to repeated rubbing action. The oxidation of the worn surface depends on the flash temperature during the wear process, which, on the other hand, depends upon the normal wear load and sliding speed. As usual, the surface temperature increases as normal load or sliding speed increases [17]. As the wear load and sliding speed increased, the flash temperature increased and the oxidation was accelerated. So the weight loss is increased and with the wear load and siding speed as shown in Fig. 5.
In the Fe–Mn–Cr–Mo–V alloy cladding here, the surface hardness of the cladding is related with the microstructure, which is affected by the welding parameters, such as welding current and speed. However, the ball-on-disk wear properties is not very sensitive to the welding parameters.
4. Conclusions The microstructure of the stoody alloy cladding is composed of martensite and retained austenite, which was influenced by the cladding parameters. The retained austenite
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increases with the increased welding current, and reduced travel speed. The more is the retained austenite, the lower is the surface hardness. The ball-on-disk wear process of the stoody alloy cladding is dependant to large extent on the combination of the clad oxidation and the spalling of the oxide film caused by the fatigue mechanism. The ball-on-disk wear property is not very sensitive to the welding conditions.
Acknowledgements This work was supported by Korean Research Foundation Grant (KRF-99-005-E00006).
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