Effect of austenitization temperature on structure and mechanical properties of new medium-carbon economically alloyed steel

The results of the analysis of the new economically alloyed steel 44Kh2G2S2MF are presented. The relationship “amount of austenite – heating temperature” was constructed with use a modern horizontal quenching dilatometer. In resistance furnaces with an oxidizing atmosphere, the heat treatment modes were carried out, within which heating was carried out at temperatures of complete and incomplete austenitization. It has been revealed that in the process of continuous cooling of steel, martensite/bainite and carbides of various dispersion and shape are formed from the upper range of the intercritical temperature range. The amount of martensite/austenite component does not exceed 5 % after each heat treatment mode. Impact bending tests showed that the fractures had a pitted structure, and the crack propagated along the body of the former austenite grain. Tensile tests have shown that when 44Kh2G2S2MF steel is loaded, the TRIP effect appears, as a result of which a deformation γ→α transformation occurs, leading to an increase in ductility. From the results of the study and analysis of literary sources, it follows that the range of mechanical properties of 44Kh2G2S2MF steel corresponds to different areas of the plasticity diagram of automotive steels, including the area of high-strength steels of the third generation. It has been established that to ensure the use of 44Kh2G2S2MF steel as a high-strength steel of the third generation, it is necessary to carry out heat treatment modes consisting of heating to austenitization temperatures above 800 °C, but lower than or equal to 830 °C, holding and cooling in still air.