The Microstructural Evolution and Wear of Weld Deposited M2 Steel Coating After Laser Spot Melting
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INTRODUCTION
ONE of the current objectives of modern technology is to extend the life of friction-coupled components, which operate under high dynamic loads and poor lubrication conditions.[1–4] Having their high hardness, red-hardness, and wear resistance, the high-speed steels remain one of the best candidates not only for making various types of cutting tools but also for manufacturing punches, matrices, mill train roller reinforcement, and friction-coupled components. The results of numerous research works[5,6] proved the superiority of the cast high-speed steels (HSS) over the wrought ones in terms of wear resistance, despite the fact that both of them possess similar chemical composition and hardness. The main factors that affect the intensity of wear on HSS are the quantity, type of distribution and size of eutectic carbides as well as the amount of the retained metastable austenite.[6,7] These parameters can be modified during primary melt crystallization, blank casting, or in coating deposition using directed heat sources such as electron or laser beam, as well as plasma torch. For instance, composite M2 high-speed steel electron beam clad multipass coatings[6] are used for hard facing the gear shaft bearing journals in heavy-duty gear reducers or inner races in needle bearings. Wear tests on the M2 coating rubbed against ball beating steel showed an inequality of the wear distribution over the worn
S.F. GNYUSOV, I.A. ISAKIN, S.YU. TARASOV, S.E. BUKHANCHENKO are with the National Research Tomsk Polytechnic University, Tomsk, Russia. Contact e-mail: [email protected] Manuscript submitted March 6, 2019. Article published online June 17, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
surface so that an extremely worn area was located between two areas of the steady-state wear.[7] The sharp increase in wear occurs as a result of thermal softening and a fi c-transformation at elevated temperatures in the sliding contact zone. The existence of steady wear areas is explained by generation of a micro-composite structured tribological layer reinforced by fragments of eutectic M6C carbide network. The thickness of the micro-composite and tribological layers is 6 and 0.7 lm, respectively. Similar effect of the micro-composite structure on improving the wear resistance was reported not only for high-speed steels[8] but also for WC-Co bulk composites.[9,10] Laser remelting of metals allows obtaining the non-equilibrium fine grain structures in the subsurface layer due to fast directed crystallization of the melted alloy.[11,12] Several papers[12–22] describe the prospects of using a laser to modify the surface of the wrought high-speed steels intended for various tribological applications. Research work in this direction is still pursued due to the variety and complexity of the structures obtained on the wrought high-speed steels subjected to laser melting.[13,14,22] Even more interesting approach in terms of obtaining the non-equilibrium structures may be applying the laser remelting to the previously clad HSS steel coating
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