The influence of austenitization temperature on phase transformations of supercooled austenite in low-alloy steels with high resistance to abrasion wear

The paper presents continuous cooling transformation (CCT) diagram of selected low-alloy steel with high resistance to abrasion. Samples were prepared from examined material in as delivered conditions, then were austenitized at 900, 1000, 1100 and 1200 °C for 20 min, and then cooled with the rates of V800-500 = 50, 10, 5, 1, 0.5, 0.1 °C/s. During the dilatometric research, the critical temperatures were defined as well as the critical points specified for different cooling rates were designated. In addition, metallographic documentation of received microstructures after dilatometric investigations was prepared and hardness measurement was performed. The increase in the austenitizing temperature caused changes in the temperature of MS and in the size of the martensite laths. What is more, the increase in the austenitizing temperature in the case of the analyzed steel caused a displacement of the bainitic and diffusion transformations to longer times. During the analysis using the TEM and SEM it was found that the size of the austenite grains is largely controlled by precipitates of the nitrides of AlN, TiN and carbides, mainly Cr7C3 and M23C6.