Formation of Cracks during Thermal Treatment of Martensite-Bainite Steel Parts

In this paper, we study the causes of crack formation after thermal treatment of alloyed steel parts with high resistance of overcooled austenite. A thermokinetic diagram of transformations of overcooled austenite during continuous cooling is plotted using the dilatometric method, and the temperature-time intervals for the occurrence of transformations are established. The hydrogen content in the melts of the studied steel is determined. The distribution of microstructure and hardness over the cross section of the part is analyzed. Computational modeling of the processes occurring during thermal treatment of parts is performed. Atomic emission spectral analysis reveals the presence of significant liquation of carbon in the axial zone that leads to a decrease in the temperature of the onset of martensitic transformation in the core of the part.