Structure, Phase Composition and Mechanical Properties of a High-Strength Steel with Transition Carbide η-Fe₂C

Abstract

Abstract—The influence of quenching and tempering on the structure, phase composition and mechanical properties of high-strength Fe–0.34 C steel with 1.77 wt % Si is considered. The tempering at temperatures up to 500°C has virtually no effect on the structural characteristics of packet martensite formed during quenching. At tempering temperatures in the range of 200–400°C, the precipitation of transition η-carbide occurs, which leads to an increase in the yield strength to 1490 MPa and impact toughness to 35 J/cm2. The determined temperature of the brittle-ductile transition after tempering at 200°C is about –50°C. A decrease in the impact toughness and a decrease in the proportion of ductile fracture with a decrease in the test temperature is accompanied by a transition from transgranular to intergranular fracture. The precipitation of cementite particles along the boundaries of laths and blocks is observed after tempering at 500°C. This leads to a decrease in the yield strength, while the impact toughness of the steel remains unchanged.