Influence of thermal effect on the structure and properties of die steel 70Kh3G2FTR(m)

Conventional heat-resistant die ferrite-pearlite steels with carbide and mixed (carbide-intermetallic) hardening are softened very intensively after heating above 350-400 degrees C, what leads to rapid tool failure. Heat-resistant austenite steels and alloys also does not solve the problem of operating resistance of die tools, due to their tendency to cracking, poor machinability by cutting, high cost and scarcity of alloying elements included in their composition. Investigations of structural state, thermophysical properties and physical and technical characteristics of the developed die steel 70Kh3G2FTR(m) were carried out in this work under thermal exposure. Considerations about the structural stability of the alloy are confirmed by the data of X-ray diffraction analysis within the temperature range from -187 degrees C to 300 degrees C, as well as of transmission electron microscopy (TEM) at all stages of heat treatment and thermal exposure. It is shown that the developed steel 70Kh3G2FTR(m) after the proposed heat treatment procedure is characterized by thermal and structural stability within the studied temperature range up to 450 degrees C, due to influence of a microalloying complex in the form of dispersed carbide inclusions registered by TEM. The dispersion hardening mechanism in the developed alloy prevents motion of dislocations during heating, distorts and seals the atomic crystal structure, slowing down diffusion processes and migration transmissions of grain boundaries.