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Mechanical behavior of wheel steels with solid solution and precipitation hardening

100%

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

tom 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.

Relationships between the fatigue crack growth resistance characteristics of a steel and the tread surface damage of railway wheel

86%

Ostash O. P. , Kulyk V. V. , Lenkovskiy T. M. , Duriagina Z. A. , Vira V. V. , Tepla T. L.

tom Vol. 90, nr 2

49--55

Purpose: The aim of the proposed research is to establish experimentally the relation between damaging of the tread surface of model wheels and the characteristics of fatigue crack growth resistance of wheel steels AKh th AKh th AKh fc AKh fc), depending on its microstructure. Design/methodology/approach: Characteristics of the fatigue crack growth resistance have been determined on the specimens cut out from the hot rolled plate of thickness 10 mm of the steel which is an analogue of railway wheel steels. To obtain different steel microstructures and its strength level, test specimens were quenched (820°C, in oil) and then tempered at 400°C, 500°C, and 600°C for 2 h. The characteristics of Mode I fatigue crack growth resistance of steel were determined on the basis of fatigue macrocrack growth rate diagrams da/dN-AK, 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 of the loading cycle. The characteristics of Mode II fatigue crack growth resistance were determined on the basis of da/dN-AKH diagrams, obtained by authors 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. The hardness was measured with a TK-2 hardness meter. Zeiss-EVO40XVP scanning electron microscope was used for microstructural investigations. Rolling contact fatigue testing was carried out on the model specimens of a wheel of thickness 8 mm and diameter 40 mm in contact with a rail of length 220 mm, width 8 mm and height 16 mm. Wheels were manufactured form the above-described steel after different treatment modes. Rails were cut out from a head the full-scale rail of hardness 46 HRC. The damaging was assessed by a ratio of the area with gaps formed by pitting and spalling to the general area of the wheel tread surface using a special stand. Findings: The growth of the damage of the tread surface of the model wheels correlates uniquely with the decrease of the cyclic fracture toughness of the wheel steel AKh fc and AKh fc, determined at Mode I and Mode II fracture mechanisms. These characteristics of the wheel steel can be considered as the determining parameter of this process, in contrast to the fatigue thresholds AKh th and AKh th. Research limitations/implications: Investigations were conducted on model wheels that simulate the damage of real railway wheels tread surface. Practical implications: A relationship between the damage of tread surface of railway wheels and the strength level of wheel steels is determined. Originality/value: The damage of the tread surface of the model wheels during the rolling contact fatigue of the pair wheel-rail increases with the growth of the strength (hardness) of the wheel steel, which corresponds to the statistical data of the operation of the real railway wheels. Research limitations/implications: Investigations were; conducted on model wheels that simulate the damage of real railway wheels tread surface. Practical implications: A relationship between the damage of tread surface of railway wheels and the strength level of wheel steels is determined. Originality/value: The damage of the tread surface of the model wheels during the rolling) contact fatigue; of the pair wheel-rail increases with the growth of the strength (hardness) of the wheel steel, which corresponds to the statistical data of the operation of the real railway wheels.