LAUSR

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%.