Thermal stability of primary elongated V-rich carbonitrides in H13 tool steel

摘要

Thermal stability of primary V-rich carbonitrides in H13 as-cast ingot was analyzed combining with equilibrium calculation through Thermo-Calc software. A large number of elongated V-rich carbonitrides exist in H13 ingot the size of which could be up to tens of microns. The equilibrium solution temperature for V-rich carbonitride is estimated at 1190 degrees C from thermodynamic calculations. The thermal stability of V-rich carbonitride was then assessed by quenching from 1150 degrees C and 1250 degrees C after holding different times. The fracture of elongated V-rich carbonitride is observed after 0.5 h, and the shape changes from slender to spindle-like or spherical with the increase of time. V-rich carbonitrides are still observed after 6 h at 1150 degrees C, while no carbonitrides are left after 6 h at 1250 degrees C. However, the austenite grain coarsens at high temperature with size reaching hundreds of microns after 6 h. An optimal temperature and time in view of the size of carbonitrides and grains is important when carrying out homogenization treatment to control the primary carbonitrides.