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1

The diagnostics and ways heat treatment optimization of a railway wheels steel

Vira Volodymyr, Kulyk Volodymyr, Chepil Roman, Kharchenko Yevhen, Duriagina Zoia

Diagnostyka

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2019

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Vol. 20, No. 2

105--111

EN

A high resolution sensor of linear displacements has been elaborated for diagnosing the size of the crack tip opening in standard test specimens. Based on the data measured during fatigue crack growth resistance tests of a wheel steel heat treated after various modes, calculations of the strain and energy parameters of local fracture were performed for the corresponding variants of treatment, and fatigue crack growth rate diagrams were constructed using different approaches of fatigue fracture mechanics. It was established that the diagrams obtained using the strain and energy approaches are more sensitive to material microstructure and its mechanical properties than the traditional diagrams obtained using the stress approach. Based on the parameters of the fatigue crack growth resistance estimated using the strain and energy approaches, the effective diagnostics and the best heat treatment mode for the wheel steel was developed. It comprises the stages of isothermal quenching and tempering at a temperature of 500 °С, providing the highest fatigue fracture toughness of the steel.

PL

Opracowano czujnik przemieszczeń liniowych o podwyższonej czułości dla diagnozowania rozwartości szczeliny na podstawie określenia odkształceń i energetycznych parametrów uszkodzenia lokalnego. W oparciu o różne podejścia mechaniki zniszczenia zmęczeniowego zostały skonstruowane diagramy prędkości propagacji pęknięć zmęczeniowych w stali koła kolejowego po różnych rodzajach obróbki cieplnej. Ustalono, że diagramy odporności na pękanie, otrzymane według odkształceniowego lub energetycznego podejścia, są bardziej wrażliwe do strukturalnych i mechanicznych własności materiałów w porównaniu z tradycyjnymi diagramami otrzymanymi według podejścia siłowego. Pokazano zalety odkształceniowego i energetycznego podejścia w porównaniu z podejściem siłowym w zakresie optymalizacji charakterystyk odporności materiałów na pękanie. Dokonano skutecznej diagnostyki stanu technicznego materiału oraz optymalizacji obróbki cieplnej stali kół kolejowych. Ustalono, że hartowanie izotermiczne z odpuszczaniem przy temperaturze 500°C zapewnia najwyższą odporność stali na pękanie.

2

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

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2019

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Vol. 95, nr 2

49--54

EN

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.

3

The joint effect of vanadium and nitrogen on the mechanical behavior of railroad wheels steel

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

Journal of Achievements in Materials and Manufacturing Engineering

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2018

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Vol. 89, nr 2

56--63

EN

Purpose: The aim of the proposed research is to investigate the regularities of the microstructure change, fracture micromechanism and mechanical service characteristics of the high-strength wheel steel with a lowered carbon content under static, impact and cyclic loading depending on the total content of vanadium and nitrogen and also the steel heat treatment modes. Design/methodology/approach: Alloying with vanadium was carried out in the range of 0.09-0.23% and nitrogen in the range of 0.006-0.018%. All steels were heat treated by normalizing and subsequent tempering at different temperatures in the range of 450-650°C. Steels microstructure was investigated by the optical metallography methods on the microscope EPITIP-2 (Carl Zeiss Jena). Scanning electron microscope Zeiss-EVO40XVP was also used for microstructural and microfractography investigations. Static strength (UTS), relative elongation (TEL), impact toughness tests (KCV) and fatigue crack growth resistance characteristics (fatigue threshold ΔKth, cyclic fatigue fracture toughness ΔKfc) were determined on standard specimens. Rolling contact fatigue testing was carried out on the model specimens. Findings: The regularities of the change of microstructure, fracture micromechanism and mechanical characteristics of the high-strength wheel steel with a lowered carbon content under static, impact and cyclic loading depending on the total content of vanadium and nitrogen and also the steel heat treatment modes are studied. Research limitations/implications: The results obtained on laboratory samples should be tested during a real railway wheels investigation. Practical implications: The steel with the optimal parameter [V∙N]∙104 = 22.1% provides high tread surface damaging resistance established on the model wheels. Originality/value: It was established that after normalization at 950°C and tempering at 550°C the increase of ultimate strength UTS and cyclic fracture toughness ΔKfc by 4% and 19%, respectively; impact toughness at room (KCV+20) and low temperature (KCV-40) in 1.5 and 3.3 times, respectively, when parameter [V∙N]∙104 changes from 7.8 to 22.1% and carbon content from 0.63 to 0.57%.