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Effects of carbides on abrasive wear properties and failure behaviours of high speed steels with different alloy element content
Wear 376-377 (2017) 968–974
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Wear journal homepage: www.elsevier.com/locate/wear
Effects of carbides on abrasive wear properties and failure behaviours of high speed steels with different alloy element content Liujie Xu a,b,n, Shizhong Wei a, Fangnao Xiao b, He Zhou c, Guoshang Zhang b,c, Jiwen Li c a
Engineering Research Center of Tribology and Materials Protection, Ministry of Education, Henan University of Science and Technology, Luoyang 471003, China Henan Collaborative Innovation Centre of Non-Ferrous Generic Technology, Luoyang 471023, China c School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang 471003, China b
ar t ic l e i nf o
a b s t r a c t
Article history: Received 1 September 2016 Received in revised form 9 December 2016 Accepted 5 January 2017
High speed steels (HSSs) are effective materials applied in aggressive environments where abrasion resistances are required because they have hard carbides and relatively ductile matrix to bind carbides. But there are many kinds of carbides in HSSs, which lead to different effect on wear properties of HSSs. In this paper, three kinds of casting HSSs with VC, M6C or M2C type carbide were prepared respectively through the reasonable design of alloy elements, and then the effects of carbide type on wear behaviours were researched under different abrasive particle size and load using abrasive wear testing machine. The microstructures and failure behaviours of HSSs were analyzed by electron microscopy. The results showed the abrasive particle size and load had obvious effect on wear weight loss of high speed steel (HSS), but the carbide type decided the relative wear resistance of HSS. As the abrasive particle size or load increased, the wear weight loss of any HSS increased obviously. For the fine abrasive wear, the HSS with M6C had higher relative wear resistance than HSS with M2C. But the contrary was the case for the coarse abrasive wear. For any abrasive particle size and load, the HSS with VC had more excellent wear resistance than HSS with M6C or M2C type carbide. The relative wear resistance of HSS with VC was three times higher than that of HSS with M6C or M2C. The excellent wear resistance of HSS with VC was mainly attributed to VC characteristics, such as high hardness and good morphology, which can resist microcutting of abrasive particles efficiently. & 2017 Elsevier B.V. All rights reserved.
Keywords: High speed steel Abrasive wear Carbide Abrasive particle size Load
1. Introduction High speed steels are characterized by many high hardness carbides such as M6C, M2C and MC distributed in matrix composed of martensite and austenite with high strength and toughness, so they have excellent wear resistance under extreme wear conditions [1–4]. In recent years, HSSs have been applied for rolls. The previous research results showed that HSSs, compared with high chromium cast iron, have more excellent wear resistance because they have stiffer carbides and more excellent red hardness [1,2,5–7]. Recently, the pulverization industry develops rapidly. Large amounts of wear-resistant parts such as hammerhead, jaw plate and lining board were consumed in pulverization industry. The high n Corresponding author at: Engineering Research Center of Tribology and Materials Protection, Ministry of Education, Henan University of Science and Technology, Luoyang 471003, China. E-mail address: [email protected] (L. Xu).
http://dx.doi.org/10.1016/j.wear.2017.01.021 0043-1648/& 2017 Elsevier B.V. All rights reserved.
chromium cast iron or high manganese steel is often used to manufacture the wear-resistance parts [8,9]. However, the serving life is not satisfactory because it is difficult for the two kinds of materials to resist severe abrasive wear in the process of service. In the previous research, it was proved that HSSs with high hardness carbides can resist rolling/sliding wear effectively when they are used for rolls [2–5,10,11]. To improve the serving life of wear-resistant parts in pulverization industry, we developed HSSs enhanced by VC carbides based on the above research results, and researched on the abrasive wear property [12–14]. The results show the HSSs with VC carbides have more excellent wear resistance than high chromium cast irons and high manganese steel [15,16]. Nevertheless, there are many kinds of carbides in HSSs, such as VC, M6C and M2C. The different carbide type may have different effects on the wear properties of HSSs. In the paper, three kinds of casting high-speed steels with VC, M6C or M2C type carbide respectively were prepared through the reasonable design of alloy elements, and then the effects of carbide type on abrasive wear behaviours were researched under different abrasive particle size and load.
L. Xu et al. / Wear 376-377 (2017) 968–974
2. Experimental methods 2.1. Chemical compositions The chemical compositions of HSSs were fabricated according to conventional HSSs. In order to obtain VC, M6C and M2C carbides respectively, about 10 wt% vanadium, 10 wt% tungsten or 10 wt% molybdenum was added into three kinds of HSSs, respectively. Accordingly, the three kinds of HSSs were also named V10, W10 and Mo10, respectively. In addition, approximate 4 wt% chromium was mixed in the tested alloy to ensure the realization of a high-hardness HSS. Based on the method of definite proportion of carbon, the effect of secondary hardening is optimal when alloy elements and carbon contents meet the constant proportion of molecular formula of carbide, so the carbon contents in HSSs were designed according to the method of definite proportion of carbon [17]. The actual chemical compositions of the three kinds of materials are listed in Table 1.
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Table 1 Chemical compositions of HSSs (wt%). Materials
C
V
W
Mo
Cr
Mn
Si
S、P
RE
V10 W10 Mo10
2.95 1.30 1.43
9.96 — —
— 10.02 —
2.31 2.20 10.01
4.13 4.20 4.20
0.76 0.82 0.78
0.62 0.60 0.59
r 0.03 r 0.03 r 0.03
0.4 0.4 0.4
2.2. Preparation of samples The alloy ingots were produced by melting the raw materials in a 50 kg intermediate frequency induction melting furnace. The deoxidation was conducted by adding 0.1% pure aluminum. The melting alloys were tapped from the furnace at approximate 1500 1550 °C and casted at 1450–1480 °C. The samples were austenized at 1050 °C for 40 minutes, air quenched, and then three times tempered at 560 °C. A siliconkryptol resistance furnace (SKZ-8–13) was the quenching furnace used in this study and it was controlled with a microcomputer. A resistance furnace (SKZ-8–10) was the tempering furnace used in this study. 2.3. Mechanical properties test The macro-hardness of the specimens was measured using an HR-150A Rockwell tester. The Vickers hardness was tested using a micro-hardness tester (HVS-1000A) with a load of 200 g and a dwell time of 20 s. Five points were measured for each sample, and the last value was the average of the five values. The toughness of a 20 mm 20 mm 110 mm smooth specimen was tested on a JB300B pendulum-type impact testing machine, and the gauge length was 70 mm. 2.4. Wear performances test The wear test was conducted on a pin-on-disk (type ML-100) wear testing machine using grit alumina water proof abrasive sand paper, and the abrasive particle sizes of sand papers were 4.5 μm, 8.5 μm, 28 μm and 58 μm, respectively. This kind of machine was widely applied by many researchers in the past years, and the standard deviation of which is not more than 3% [14,18]. The diagram of testing machine is shown in Fig. 1. The samples were pins, and the specimens’ size was φ5 mm 30 mm. The disk of testing machine turned at the speed of 70 r/min when the pin moved at the speed of 5 mm/s from center of disk to brim for 70 mm with pressure at 0.50 Mpa, 0.76 Mpa, 1.27 Mpa and 2.55 Mpa, respectively. So the moving pathways of samples are helical line. Each sample repeatedly moved for 10 times, and then the wear weight loss of which was measured. For every group, three samples were selected, and the weight loss is the average result of the three repetitions. The wear resistance was specified by β with β ¼W 1. The weight loss of sample was measured using a TG328B analytical balance, which ranges from 0 to 200 g and possesses a relative accuracy of 0.1 mg. The relative wear
Fig. 1. The diagram of testing machine.
resistance was specified by
ε (ε ¼ β/β0 ¼ W0/W).
2.5. Microstructures analysis and worn surface observation The microstructure and worn surface of the HSSs were observed using JSM-5160LV type scanning electron microscope (SEM). The phase structures of carbides and matrix in HSSs were analyzed using X-ray diffraction (XRD).
3. Results 3.1. Microstructure of HSSs Fig. 2 shows the microstructures of HSSs. The HSS with high vanadium content was characterized by primary lump VC carbides evenly distributed in matrix composed of martensite and austenite [Fig. 2(a) and (b)]. However, the carbide of HSS with high tungsten content was primary fishbone-like M6C carbides, which were distributed in matrix composed of martensite and austenite [Fig. 2 (c) and (d)]. In the process of heat treatment, some fine secondary carbides precipitated from matrix. The molybdenum element in HSS with high molybdenum content mainly formed M2C-type carbide with lamellar structure [Fig. 2(e) and (f)]. The M2C-type carbides were mainly distributed at the grain boundaries of matrix composed of martensite and austenite. 3.2. Mechanical properties of HSSs Table 2 shows the hardness and impact toughness of the experimental HSSs. After heat treatment, the hardness of all the tested three HSSs was higher than 60HRC. Besides, the Mo10 has slight higher hardness than V10 and W10. The V10 had higher impact toughness than the other two kind of HSSs. Fig. 3 shows the fracture morphologies of HSSs. It can be seen from Fig. 3 that all the three kinds of HSSs were mainly brittle fracture type. The V10 had much finer grains on the fracture surface than W10 and
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Fig. 2. SEM microscopy and XRD analysis of HSSs: (a) SEM microscopy of V10; (b) XRD analysis of V10; (c) SEM microscopy of W10; (d) XRD analysis of W10; (e) SEM microscopy of Mo10; (f) XRD analysis of Mo10.
Table 2 Hardness and impact toughness of experimental materials. Materials
Hardness (HRC)
Main carbide microhardness (HV)
Microhardness of matrix(HV)
Impact toughness (J/cm2)
V10 W10 Mo10
63.5 61.0 64.6
VC:2320 M6C:1520 M2C:1680
596.5 583.8 613.2
6.8 5.2 5.7
Mo10, which may be responsible for better impact toughness. 3.3. Wear properties of HSSs 3.3.1. Effect of abrasive particle size and load on wear property Fig. 4 and Fig. 5 show the relationship of wear weight loss vs. abrasive particle size and load, respectively. For all the three kinds of HSSs, the wear weight loss rose obviously with increasing abrasive particle size under the same load (Fig. 4). Similarly, the wear weight loss increased with increasing load under the same abrasive particle size (Fig. 5). That is to say that the wear weight loss will increase whatever the abrasive particle size or load rises.
However, it can be seen from Fig. 5 that the increasing rate of wear weight loss was different, which was related to abrasive particle size. The increasing rate of wear weight loss (K) is defined by Eq. (1).
K = dW /dp
(1)
where W and p are wear weight loss and load, respectively. The bigger the abrasive particle size was, the bigger the K value was. It means that the wear weight loss increased more quickly with increasing load. The relation between increasing rate of wear weight loss and abrasive particle size (d) could be obtained after the relation of wear weight loss and load was fitted using least
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Fig. 3. Fracture morphologies of HSSs: (a) V10; (b) W10; (c) Mo10.
Fig. 4. Wear weight loss vs. abrasive particle size under different load condition: (a) V10; (b) W10; (c) Mo10.
Fig. 5. Wear weight loss vs. load under different abrasive particle size condition: (a) V10; (b) W10; (c) Mo10.
(3)
Mo 10: K = 0.3738 d + 7.7626
(4)
where K and d are the increasing rate of wear weight loss and abrasive particle size, respectively. From Fig.6 and Eqs. (2)–(4), it can be seen that the increasing rate of wear weight loss of HSS increased gradually as abrasive particle size increased, which means that the wear of HSS becomes fast with increasing of abrasive particle size. Moreover, the K values of W10 and Mo10 were much bigger than those of V10 at any abrasive particle size. It indicates that W10 and Mo10 wore faster than V10 with the increase of load at any abrasive particle size.
Fig. 6. The increasing rate of wear weight loss vs. abrasive particle size.
square method, as shown in Fig. 6. According to Fig. 6, the relation of K and d can be specified by (Figs. (2) to 4) for the three HSS after fitting using least square method.
V 10: K = 0.1697d + 1.0228
W 10: K = 0.689 d + 3.1371
(2)
3.3.2. Relative wear resistance among the three kinds of HSSs Putting Mo10 as a standard material, the relative wear resistance of V10 and W10 were obtained, as shown in Fig.7. The relative wear resistance of V10 was about 3.5 to 7.0 times that of Mo10, and the relative wear resistance slightly decreased with the
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Fig. 7. Effect of abrasive particle size on relative wear resistance of HSSs: (a) The relative wear resistance of V10 compared with Mo10; (b) The relative wear resistance of W10 compared with Mo10.
increasing of abrasive particle size [Fig. 7(a)]. The relative wear resistance of W10 was about 0.7 to 1.5 times that of Mo10 [Fig. 7 (b)]. For the fine abrasive wear (d r8.5 μm) and slightly big load (p40.75 MPa), W10 had higher relative wear resistance than Mo10. But the contrary was the case for the coarse abrasive wear (dZ28 μm). For any abrasive particle size and load, V10 had more excellent wear resistance than W10 or Mo10. 3.3.3. Wear failure analysis Figs. 8–10 show the worn surface morphologies of three kinds of HSSs. The abrasive wear of HSSs was caused by scratching of Al2O3 abrasive. So the abrasive wear form is micro-cutting. Large amounts of furrows occurred on the worn surface of HSSs. The ploughing severity was related to material, abrasive particle size and load. At the same abrasive particle size and load, the furrows on the surface of V10 were narrower and shallower than those of W10 and Mo10 (compared Fig. 8 with Figs. 9 and 10), indicating that V10 can resist micro-cutting of Al2O3 abrasive more effectively, resulting in good wear resistance of V10. For the same material, the abrasive particle size and load have obvious effect on ploughing severity. With the increase of abrasive particle size or load, the furrows on the worn surface became gradually wide and deep, indicating that the wear of HSS became severe gradually.
4. Discussion 4.1. Effect of carbide on abrasive wear properties According to above research results, HSS with VC type carbide has much more excellent wear properties at any abrasive particle size and load than HSS with M6C or M2C type carbide. The cause is mainly related to VC characteristics. Firstly, the microhardness of VC is far higher than that of M6C or M2C [19] (Table 2). So the VC in HSS can more effectively resist micro-cutting of abrasive compared with M6C or M2C in HSS. Secondly, VC has good morphology. Compared with fishbone-like M6C -type carbide and lamellar structure M2C-type carbide, the lump VC type carbide is not easy to be crushed by hard abrasive even under big load in the process of wear. For the above two reasons, VC can not only effectively resist micro-cutting of abrasive but protect the matrix of HSS in the process of abrasive wear, which results in excellent wear resistance of HSS enhanced by VC. The microhardness of M6C is close to that of M2C, just slightly lower than that of M2C. This leads to the close wear property of the two kinds of HSSs with M6C and M2C. However, there is still a little difference for the relative wear resistance of two kinds of HSSs. When the matrix microhardness of two kinds of HSSs is close, the relative wear resistance of HSS is related to morphology and
Fig. 8. Worn surface morphologies of V10: (a) d ¼ 4.5 μm, p ¼ 2.55 Mpa; (b) d¼ 28 μm, p¼ 2.55 Mpa; (c) d ¼58 μm, p ¼ 2.55 Mpa; (d) d ¼ 28 μm, p ¼ 0.75 Mpa.
L. Xu et al. / Wear 376-377 (2017) 968–974
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Fig. 9. Worn surface morphologies of W10: (a) d ¼4.5 μm, p¼ 2.55 Mpa; (b) d ¼ 28 μm, p ¼ 2.55 Mpa; (c) d¼ 58 μm, p¼ 2.55 Mpa; (d) d ¼28 μm, p ¼ 0.75 Mpa.
Fig. 10. Worn surface morphologies of Mo10: (a) d¼ 4.5 μm, p ¼ 2.55 Mpa; (b) d ¼28 μm, p ¼ 2.55 Mpa; (c) d ¼ 58 μm, p ¼ 2.55 Mpa; (d) d¼ 28 μm, p¼ 0.75 Mpa.
microhardness of carbide. For the fine abrasive wear, the morphology of carbide plays a main role. The fishbone-like M6C, compared with lamellar M2C, can bind much matrix, and therefore can protect matrix more efficiently, resulting in somewhat better wear resistance. For the coarse abrasive wear, the microhardness of carbide plays a main role. M2C has slightly higher microhardness than M6C, which leads to somewhat better wear resistance of HSS with M2C. 4.2. Effects of abrasive particle size and load on wear properties The previous research results show that the abrasive particle size and load have obvious effects on wear weight loss of materials
[20,21]. With the increase of abrasive particle size, the HSSs are more likely to become scratched, as can be seen in Figs. 8–10. The higher load can produce more penetration of abrasive particle into HSS. Sin et al. [22] reported that the extension of plastic work depends on the load and the abrasive particle size. So the wear weight loss of HSS rapidly rises as abrasive particle size or load increases. At the same time, the severe wear will lead to the desquamating of large amounts of carbides. The desquamating carbides on the worn surface will become abrasive particles with high hardness, aggravating the wear of HSSs further. Nevertheless, the affecting degree of abrasive particle size and load on wear of HSSs
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has a connection with the carbide type in HSS. For the HSS with VC type carbide, the aggravating degree of wear is relatively slight. Based on the above analysis, it can be concluded that the carbide type decides the relative wear resistance of HSS. But wear weight loss of HSS is mainly related to the abrasive particle size and load. When the cast high speed steel is used for abrasive wear, VC type carbide is the ideal wear-resistant hard phase. The HSS with M6C is suitable for fine abrasive wear, while the HSS with M2C is suitable coarse abrasive wear.
5. Conclusion
(1) The carbide type in HSS decides the relative wear resistance of HSS. But wear weight loss is mainly related to abrasive particle size and load. (2) The HSS with VC has the most excellent wear resistance compared with the HSS with M6C or M2C. The relative wear resistance of HSS with VC is three times higher than that of HSS with M2C. (3) For the fine abrasive wear, the speed steel with M6C has higher relative wear resistance than HSS with M2C. But the contrary is the case for the coarse abrasive wear. (4) The excellent wear resistance of HSS with VC is mainly attributed to VC characteristics, such as high hardness and good morphology, which can resist micro-cutting of abrasive particles efficiently.
Acknowledgments The authors greatly acknowledge the National Natural Science Foundation of China (No. 51171060) and Production-Study-Research Cooperation Project of Henan Province of China (No. 162107000062) for financial support.
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[3] G.C. Gu, R. Pesci, E. Becker, L. Langlois, R. Bigot, M. Scheel, Quantification and localization of the liquid zone of partially remelted M2 tool steel using X-ray microtomography and scanning electron microscopy, Acta Mater. 60 (2011) 948–957. [4] Anh Kiet Tieu, Qiang Zhu, Hongtao Zhu, Cheng Lu, An investigation into the tribological behaviour of a work roll material at high temperature, Wear 273 (2011) 43–48. [5] M.A.De Carvalho, R.R. Xavier, C. Da. Silva Pontes Filho, C. Morone, M. Boccallini Jr, A. Sinatora, Microstructure, mechanical properties and wear resistance of high speed steel rolls for hot rolling mills, Iron Steelmak. 29 (2002) 27–32. [6] Yikun Luan, Nannan Song, Yunlong Bai, Kang Xiuhong, Li Dianzhong, Effect of solidification rate on the morphology and distribution of eutectic carbides in centrifugal casting high-speed steel rolls, J. Mater. Process. Tech. 210 (2010) 536–541. [7] Chang Kyu Kim, Jong Il Park, Sunghak Lee, Yong Chan Kim, Nack J. Kim, Jung Seung Yang, Effects of alloying elements on microstructure, hardness, and fracture toughness of centrifugally cast high-speed steel rolls, Metall. Mater. Trans. A 36 (2005) 87–97. [8] X.-D. Du, X.-J. Yang, Y.-F. Wang, L. Wang, Impact corrosion wear properties and mechanism of lining board steels, P I Mech. Eng. J-J Eng. 223 (2009) 729–733. [9] X.H. Tang, R. Chung, C.J. Pang, D.Y. Li, B. Hinckley, K. Dolman, Microstructure of high (45 wt%) chromium cast irons and their resistances to wear and corrosion, Wear 271 (2011) 1426–1431. [10] L. Xu, S. Wei, J. Xing, R. Long, Effects of carbon content and sliding ratio on wear behavior of high-vanadium high-speed steel (HVHSS) under high-stress rolling-sliding contact, Tribol. Int. 70 (2014) 34–41. [11] Xu Liujie, Wei Shizhong, Han Mingru, Long Rui, Effect of carbides on wear characterization of high-alloy steels under high-stress rolling–sliding condition, Tribol. Trans. 57 (2014) 631–636. [12] Liujie Xu, Jiandong Xing, Shizhong Wei, Yongzhen Zhang, Rui Long, Study on relative wear resistance and wear stability of high-speed steel with high vanadium content, Wear 262 (2007) 253–261. [13] Wei shizhong, Zhu jinhua, Xu liujie, Retained austenite on performance of high-vanadium high-speed steel, Trans. Mater. Heat. Treat. 26 (2005) 44–47. [14] Wei Shizhong, Zhu Jinhua, Xu Leujue, Research on wear resistance of high speed steel with high vanadium content, Mater. Sci. Eng. A 404 (2005) 138–145. [15] Shizhong Wei, Rui Long, Development and application of high vanadium high wear-resistant alloy hammerhead, Cement 8 (2001) 31–33. [16] Liujie Xu, Shizhong Wei, Rui Long, Reach on abrasive wear behaviour of high vanadium high speed steel, Min. Process. 11 (2003) 77–79. [17] X.T. Wang, Metal Materials, Mechanical Industry Press, Beijing 1988, p. 131. [18] M.M. Khruschov, Principles of abrasive wear, Wear 28 (1974) 69–88. [19] The casting Branch of the Institute of Mechanical Engineering of China, Cast Iron Handbook, Machine industry press, Bei Jing, 2002. p. 549. [20] J.J. Coronado, A. Sinatora, Effect of abrasive size on wear of metallic materials and its relationship with microchips morphology and wear micromechanisms: part 1, Wear 271 (2011) 1794–1803. [21] N.C. Kaushik, R.N. Rao, Effect of grit size on two body abrasive wear of Al 6082 hybrid composites produced by stir casting method, Tribol. Trans. 102 (2016) 52–60. [22] H. Sin, N. Saka, N.P. Suh, Abrasive wear mechanists and the grit size effect, Wear 55 (1979) 163–190.
Contents lists available at ScienceDirect
Wear journal homepage: www.elsevier.com/locate/wear
Effects of carbides on abrasive wear properties and failure behaviours of high speed steels with different alloy element content Liujie Xu a,b,n, Shizhong Wei a, Fangnao Xiao b, He Zhou c, Guoshang Zhang b,c, Jiwen Li c a
Engineering Research Center of Tribology and Materials Protection, Ministry of Education, Henan University of Science and Technology, Luoyang 471003, China Henan Collaborative Innovation Centre of Non-Ferrous Generic Technology, Luoyang 471023, China c School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang 471003, China b
ar t ic l e i nf o
a b s t r a c t
Article history: Received 1 September 2016 Received in revised form 9 December 2016 Accepted 5 January 2017
High speed steels (HSSs) are effective materials applied in aggressive environments where abrasion resistances are required because they have hard carbides and relatively ductile matrix to bind carbides. But there are many kinds of carbides in HSSs, which lead to different effect on wear properties of HSSs. In this paper, three kinds of casting HSSs with VC, M6C or M2C type carbide were prepared respectively through the reasonable design of alloy elements, and then the effects of carbide type on wear behaviours were researched under different abrasive particle size and load using abrasive wear testing machine. The microstructures and failure behaviours of HSSs were analyzed by electron microscopy. The results showed the abrasive particle size and load had obvious effect on wear weight loss of high speed steel (HSS), but the carbide type decided the relative wear resistance of HSS. As the abrasive particle size or load increased, the wear weight loss of any HSS increased obviously. For the fine abrasive wear, the HSS with M6C had higher relative wear resistance than HSS with M2C. But the contrary was the case for the coarse abrasive wear. For any abrasive particle size and load, the HSS with VC had more excellent wear resistance than HSS with M6C or M2C type carbide. The relative wear resistance of HSS with VC was three times higher than that of HSS with M6C or M2C. The excellent wear resistance of HSS with VC was mainly attributed to VC characteristics, such as high hardness and good morphology, which can resist microcutting of abrasive particles efficiently. & 2017 Elsevier B.V. All rights reserved.
Keywords: High speed steel Abrasive wear Carbide Abrasive particle size Load
1. Introduction High speed steels are characterized by many high hardness carbides such as M6C, M2C and MC distributed in matrix composed of martensite and austenite with high strength and toughness, so they have excellent wear resistance under extreme wear conditions [1–4]. In recent years, HSSs have been applied for rolls. The previous research results showed that HSSs, compared with high chromium cast iron, have more excellent wear resistance because they have stiffer carbides and more excellent red hardness [1,2,5–7]. Recently, the pulverization industry develops rapidly. Large amounts of wear-resistant parts such as hammerhead, jaw plate and lining board were consumed in pulverization industry. The high n Corresponding author at: Engineering Research Center of Tribology and Materials Protection, Ministry of Education, Henan University of Science and Technology, Luoyang 471003, China. E-mail address: [email protected] (L. Xu).
http://dx.doi.org/10.1016/j.wear.2017.01.021 0043-1648/& 2017 Elsevier B.V. All rights reserved.
chromium cast iron or high manganese steel is often used to manufacture the wear-resistance parts [8,9]. However, the serving life is not satisfactory because it is difficult for the two kinds of materials to resist severe abrasive wear in the process of service. In the previous research, it was proved that HSSs with high hardness carbides can resist rolling/sliding wear effectively when they are used for rolls [2–5,10,11]. To improve the serving life of wear-resistant parts in pulverization industry, we developed HSSs enhanced by VC carbides based on the above research results, and researched on the abrasive wear property [12–14]. The results show the HSSs with VC carbides have more excellent wear resistance than high chromium cast irons and high manganese steel [15,16]. Nevertheless, there are many kinds of carbides in HSSs, such as VC, M6C and M2C. The different carbide type may have different effects on the wear properties of HSSs. In the paper, three kinds of casting high-speed steels with VC, M6C or M2C type carbide respectively were prepared through the reasonable design of alloy elements, and then the effects of carbide type on abrasive wear behaviours were researched under different abrasive particle size and load.
L. Xu et al. / Wear 376-377 (2017) 968–974
2. Experimental methods 2.1. Chemical compositions The chemical compositions of HSSs were fabricated according to conventional HSSs. In order to obtain VC, M6C and M2C carbides respectively, about 10 wt% vanadium, 10 wt% tungsten or 10 wt% molybdenum was added into three kinds of HSSs, respectively. Accordingly, the three kinds of HSSs were also named V10, W10 and Mo10, respectively. In addition, approximate 4 wt% chromium was mixed in the tested alloy to ensure the realization of a high-hardness HSS. Based on the method of definite proportion of carbon, the effect of secondary hardening is optimal when alloy elements and carbon contents meet the constant proportion of molecular formula of carbide, so the carbon contents in HSSs were designed according to the method of definite proportion of carbon [17]. The actual chemical compositions of the three kinds of materials are listed in Table 1.
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Table 1 Chemical compositions of HSSs (wt%). Materials
C
V
W
Mo
Cr
Mn
Si
S、P
RE
V10 W10 Mo10
2.95 1.30 1.43
9.96 — —
— 10.02 —
2.31 2.20 10.01
4.13 4.20 4.20
0.76 0.82 0.78
0.62 0.60 0.59
r 0.03 r 0.03 r 0.03
0.4 0.4 0.4
2.2. Preparation of samples The alloy ingots were produced by melting the raw materials in a 50 kg intermediate frequency induction melting furnace. The deoxidation was conducted by adding 0.1% pure aluminum. The melting alloys were tapped from the furnace at approximate 1500 1550 °C and casted at 1450–1480 °C. The samples were austenized at 1050 °C for 40 minutes, air quenched, and then three times tempered at 560 °C. A siliconkryptol resistance furnace (SKZ-8–13) was the quenching furnace used in this study and it was controlled with a microcomputer. A resistance furnace (SKZ-8–10) was the tempering furnace used in this study. 2.3. Mechanical properties test The macro-hardness of the specimens was measured using an HR-150A Rockwell tester. The Vickers hardness was tested using a micro-hardness tester (HVS-1000A) with a load of 200 g and a dwell time of 20 s. Five points were measured for each sample, and the last value was the average of the five values. The toughness of a 20 mm 20 mm 110 mm smooth specimen was tested on a JB300B pendulum-type impact testing machine, and the gauge length was 70 mm. 2.4. Wear performances test The wear test was conducted on a pin-on-disk (type ML-100) wear testing machine using grit alumina water proof abrasive sand paper, and the abrasive particle sizes of sand papers were 4.5 μm, 8.5 μm, 28 μm and 58 μm, respectively. This kind of machine was widely applied by many researchers in the past years, and the standard deviation of which is not more than 3% [14,18]. The diagram of testing machine is shown in Fig. 1. The samples were pins, and the specimens’ size was φ5 mm 30 mm. The disk of testing machine turned at the speed of 70 r/min when the pin moved at the speed of 5 mm/s from center of disk to brim for 70 mm with pressure at 0.50 Mpa, 0.76 Mpa, 1.27 Mpa and 2.55 Mpa, respectively. So the moving pathways of samples are helical line. Each sample repeatedly moved for 10 times, and then the wear weight loss of which was measured. For every group, three samples were selected, and the weight loss is the average result of the three repetitions. The wear resistance was specified by β with β ¼W 1. The weight loss of sample was measured using a TG328B analytical balance, which ranges from 0 to 200 g and possesses a relative accuracy of 0.1 mg. The relative wear
Fig. 1. The diagram of testing machine.
resistance was specified by
ε (ε ¼ β/β0 ¼ W0/W).
2.5. Microstructures analysis and worn surface observation The microstructure and worn surface of the HSSs were observed using JSM-5160LV type scanning electron microscope (SEM). The phase structures of carbides and matrix in HSSs were analyzed using X-ray diffraction (XRD).
3. Results 3.1. Microstructure of HSSs Fig. 2 shows the microstructures of HSSs. The HSS with high vanadium content was characterized by primary lump VC carbides evenly distributed in matrix composed of martensite and austenite [Fig. 2(a) and (b)]. However, the carbide of HSS with high tungsten content was primary fishbone-like M6C carbides, which were distributed in matrix composed of martensite and austenite [Fig. 2 (c) and (d)]. In the process of heat treatment, some fine secondary carbides precipitated from matrix. The molybdenum element in HSS with high molybdenum content mainly formed M2C-type carbide with lamellar structure [Fig. 2(e) and (f)]. The M2C-type carbides were mainly distributed at the grain boundaries of matrix composed of martensite and austenite. 3.2. Mechanical properties of HSSs Table 2 shows the hardness and impact toughness of the experimental HSSs. After heat treatment, the hardness of all the tested three HSSs was higher than 60HRC. Besides, the Mo10 has slight higher hardness than V10 and W10. The V10 had higher impact toughness than the other two kind of HSSs. Fig. 3 shows the fracture morphologies of HSSs. It can be seen from Fig. 3 that all the three kinds of HSSs were mainly brittle fracture type. The V10 had much finer grains on the fracture surface than W10 and
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Fig. 2. SEM microscopy and XRD analysis of HSSs: (a) SEM microscopy of V10; (b) XRD analysis of V10; (c) SEM microscopy of W10; (d) XRD analysis of W10; (e) SEM microscopy of Mo10; (f) XRD analysis of Mo10.
Table 2 Hardness and impact toughness of experimental materials. Materials
Hardness (HRC)
Main carbide microhardness (HV)
Microhardness of matrix(HV)
Impact toughness (J/cm2)
V10 W10 Mo10
63.5 61.0 64.6
VC:2320 M6C:1520 M2C:1680
596.5 583.8 613.2
6.8 5.2 5.7
Mo10, which may be responsible for better impact toughness. 3.3. Wear properties of HSSs 3.3.1. Effect of abrasive particle size and load on wear property Fig. 4 and Fig. 5 show the relationship of wear weight loss vs. abrasive particle size and load, respectively. For all the three kinds of HSSs, the wear weight loss rose obviously with increasing abrasive particle size under the same load (Fig. 4). Similarly, the wear weight loss increased with increasing load under the same abrasive particle size (Fig. 5). That is to say that the wear weight loss will increase whatever the abrasive particle size or load rises.
However, it can be seen from Fig. 5 that the increasing rate of wear weight loss was different, which was related to abrasive particle size. The increasing rate of wear weight loss (K) is defined by Eq. (1).
K = dW /dp
(1)
where W and p are wear weight loss and load, respectively. The bigger the abrasive particle size was, the bigger the K value was. It means that the wear weight loss increased more quickly with increasing load. The relation between increasing rate of wear weight loss and abrasive particle size (d) could be obtained after the relation of wear weight loss and load was fitted using least
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Fig. 3. Fracture morphologies of HSSs: (a) V10; (b) W10; (c) Mo10.
Fig. 4. Wear weight loss vs. abrasive particle size under different load condition: (a) V10; (b) W10; (c) Mo10.
Fig. 5. Wear weight loss vs. load under different abrasive particle size condition: (a) V10; (b) W10; (c) Mo10.
(3)
Mo 10: K = 0.3738 d + 7.7626
(4)
where K and d are the increasing rate of wear weight loss and abrasive particle size, respectively. From Fig.6 and Eqs. (2)–(4), it can be seen that the increasing rate of wear weight loss of HSS increased gradually as abrasive particle size increased, which means that the wear of HSS becomes fast with increasing of abrasive particle size. Moreover, the K values of W10 and Mo10 were much bigger than those of V10 at any abrasive particle size. It indicates that W10 and Mo10 wore faster than V10 with the increase of load at any abrasive particle size.
Fig. 6. The increasing rate of wear weight loss vs. abrasive particle size.
square method, as shown in Fig. 6. According to Fig. 6, the relation of K and d can be specified by (Figs. (2) to 4) for the three HSS after fitting using least square method.
V 10: K = 0.1697d + 1.0228
W 10: K = 0.689 d + 3.1371
(2)
3.3.2. Relative wear resistance among the three kinds of HSSs Putting Mo10 as a standard material, the relative wear resistance of V10 and W10 were obtained, as shown in Fig.7. The relative wear resistance of V10 was about 3.5 to 7.0 times that of Mo10, and the relative wear resistance slightly decreased with the
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Fig. 7. Effect of abrasive particle size on relative wear resistance of HSSs: (a) The relative wear resistance of V10 compared with Mo10; (b) The relative wear resistance of W10 compared with Mo10.
increasing of abrasive particle size [Fig. 7(a)]. The relative wear resistance of W10 was about 0.7 to 1.5 times that of Mo10 [Fig. 7 (b)]. For the fine abrasive wear (d r8.5 μm) and slightly big load (p40.75 MPa), W10 had higher relative wear resistance than Mo10. But the contrary was the case for the coarse abrasive wear (dZ28 μm). For any abrasive particle size and load, V10 had more excellent wear resistance than W10 or Mo10. 3.3.3. Wear failure analysis Figs. 8–10 show the worn surface morphologies of three kinds of HSSs. The abrasive wear of HSSs was caused by scratching of Al2O3 abrasive. So the abrasive wear form is micro-cutting. Large amounts of furrows occurred on the worn surface of HSSs. The ploughing severity was related to material, abrasive particle size and load. At the same abrasive particle size and load, the furrows on the surface of V10 were narrower and shallower than those of W10 and Mo10 (compared Fig. 8 with Figs. 9 and 10), indicating that V10 can resist micro-cutting of Al2O3 abrasive more effectively, resulting in good wear resistance of V10. For the same material, the abrasive particle size and load have obvious effect on ploughing severity. With the increase of abrasive particle size or load, the furrows on the worn surface became gradually wide and deep, indicating that the wear of HSS became severe gradually.
4. Discussion 4.1. Effect of carbide on abrasive wear properties According to above research results, HSS with VC type carbide has much more excellent wear properties at any abrasive particle size and load than HSS with M6C or M2C type carbide. The cause is mainly related to VC characteristics. Firstly, the microhardness of VC is far higher than that of M6C or M2C [19] (Table 2). So the VC in HSS can more effectively resist micro-cutting of abrasive compared with M6C or M2C in HSS. Secondly, VC has good morphology. Compared with fishbone-like M6C -type carbide and lamellar structure M2C-type carbide, the lump VC type carbide is not easy to be crushed by hard abrasive even under big load in the process of wear. For the above two reasons, VC can not only effectively resist micro-cutting of abrasive but protect the matrix of HSS in the process of abrasive wear, which results in excellent wear resistance of HSS enhanced by VC. The microhardness of M6C is close to that of M2C, just slightly lower than that of M2C. This leads to the close wear property of the two kinds of HSSs with M6C and M2C. However, there is still a little difference for the relative wear resistance of two kinds of HSSs. When the matrix microhardness of two kinds of HSSs is close, the relative wear resistance of HSS is related to morphology and
Fig. 8. Worn surface morphologies of V10: (a) d ¼ 4.5 μm, p ¼ 2.55 Mpa; (b) d¼ 28 μm, p¼ 2.55 Mpa; (c) d ¼58 μm, p ¼ 2.55 Mpa; (d) d ¼ 28 μm, p ¼ 0.75 Mpa.
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Fig. 9. Worn surface morphologies of W10: (a) d ¼4.5 μm, p¼ 2.55 Mpa; (b) d ¼ 28 μm, p ¼ 2.55 Mpa; (c) d¼ 58 μm, p¼ 2.55 Mpa; (d) d ¼28 μm, p ¼ 0.75 Mpa.
Fig. 10. Worn surface morphologies of Mo10: (a) d¼ 4.5 μm, p ¼ 2.55 Mpa; (b) d ¼28 μm, p ¼ 2.55 Mpa; (c) d ¼ 58 μm, p ¼ 2.55 Mpa; (d) d¼ 28 μm, p¼ 0.75 Mpa.
microhardness of carbide. For the fine abrasive wear, the morphology of carbide plays a main role. The fishbone-like M6C, compared with lamellar M2C, can bind much matrix, and therefore can protect matrix more efficiently, resulting in somewhat better wear resistance. For the coarse abrasive wear, the microhardness of carbide plays a main role. M2C has slightly higher microhardness than M6C, which leads to somewhat better wear resistance of HSS with M2C. 4.2. Effects of abrasive particle size and load on wear properties The previous research results show that the abrasive particle size and load have obvious effects on wear weight loss of materials
[20,21]. With the increase of abrasive particle size, the HSSs are more likely to become scratched, as can be seen in Figs. 8–10. The higher load can produce more penetration of abrasive particle into HSS. Sin et al. [22] reported that the extension of plastic work depends on the load and the abrasive particle size. So the wear weight loss of HSS rapidly rises as abrasive particle size or load increases. At the same time, the severe wear will lead to the desquamating of large amounts of carbides. The desquamating carbides on the worn surface will become abrasive particles with high hardness, aggravating the wear of HSSs further. Nevertheless, the affecting degree of abrasive particle size and load on wear of HSSs
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has a connection with the carbide type in HSS. For the HSS with VC type carbide, the aggravating degree of wear is relatively slight. Based on the above analysis, it can be concluded that the carbide type decides the relative wear resistance of HSS. But wear weight loss of HSS is mainly related to the abrasive particle size and load. When the cast high speed steel is used for abrasive wear, VC type carbide is the ideal wear-resistant hard phase. The HSS with M6C is suitable for fine abrasive wear, while the HSS with M2C is suitable coarse abrasive wear.
5. Conclusion
(1) The carbide type in HSS decides the relative wear resistance of HSS. But wear weight loss is mainly related to abrasive particle size and load. (2) The HSS with VC has the most excellent wear resistance compared with the HSS with M6C or M2C. The relative wear resistance of HSS with VC is three times higher than that of HSS with M2C. (3) For the fine abrasive wear, the speed steel with M6C has higher relative wear resistance than HSS with M2C. But the contrary is the case for the coarse abrasive wear. (4) The excellent wear resistance of HSS with VC is mainly attributed to VC characteristics, such as high hardness and good morphology, which can resist micro-cutting of abrasive particles efficiently.
Acknowledgments The authors greatly acknowledge the National Natural Science Foundation of China (No. 51171060) and Production-Study-Research Cooperation Project of Henan Province of China (No. 162107000062) for financial support.
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