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Mechanical behavior of wheel steels with solid solution and precipitation hardening

Kulyk V. V., Shipitsyn S. Ya., Ostash O. P., Duriagina Z. A., Vira V. V.

Archives of Materials Science and Engineering

2019

Vol. 95, nr 2

49--54

Purpose: The aim of the proposed research is to investigate operational properties of a wheel steel treated with simultaneous solid solution and precipitation hardening at various carbon content, in comparison with the standard wheel grade T steel. Design/methodology/approach: The mechanical behaviour of wheel steels with increased content of silicon, manganese, vanadium, and nitrogen at various carbon content has been investigated and compared to that of the standard high-strength wheel grade T steel. The steels were undergo thermal treatment due to austenitic heating up to a temperature of 950.C with cooling down in water to 550.C followed by intense blowing of blanks in the air. After that, a tempering was performed at a temperature in the range of 450-650.C. Static strength (UTS), relative elongation (TEL), impact toughness tests (KCV) were determined on standard specimens. The characteristics of Mode I fatigue crack growth resistance of steel were determined on the basis of fatigue macrocrack growth rate diagrams da/dN–ΔKI, obtained by the standard method on compact specimens with the thickness of 10 mm at a frequency of 10-15 Hz and the stress ratio R = 0.1 and R = 0.5 of the loading cycle. The characteristics of Mode II fatigue crack growth resistance were determined on the basis of da/dN–ΔKII diagrams, obtained earlier method on edge notched specimens with the thickness 3.2 mm at a frequency of 10-15 Hz and R = -1 taking account of the crack face friction. Rolling contact fatigue testing was carried out on the model specimens. Findings: The regularities of the change of mechanical characteristics of the high-strength wheel steel with simultaneous solid solution and precipitation hardening at lowered carbon content under static, impact and cyclic loading are studied. Research limitations/implications: The results obtained using laboratory samples should be checked during a real railway wheels investigation. Practical implications: The investigated steel with simultaneous solid solution and precipitation hardening provides high wear resistance of the tread surface and damage resistance determined on the model wheels. Originality/value: A steel with solid solution hardening due to increased content of silicon (up to 0.7%) and manganese (up to 0.8%) and also with precipitation hardening (at optimal content of vanadium and nitrogen [V‧N]‧104 = 28.9%) at lowered carbon content (0.52) possesses high strength and fatigue fracture toughness in cases of Mode I and Mode II loading, causing better combination of wear and damage resistances of the tread surface of the model wheels, as compared to corresponding parameters for grade T steel.