Effect of Tempering Condition on Microstructure, Mechanical Properties and Precipitates in AISI H13 Steel

The mechanical properties and microstructures, in particular precipitation in the AISI H13 steel, quenched and tempered from 773 K to 973 K for different periods, were systematically investigated by scanning electron microscopy, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results indicate a sharp decrease in hardness at temperatures > 863 K during the first 2 h of tempering. Ultimate tensile strength and yield strength decrease, while elongation and impact energy increase with the increase of tempering temperature. The volume fraction of static recrystallization increases from the EBSD result. Regarding precipitates, the coarsening rate of M23C6 was much faster than that of MC and M2C and was verified by using the Ostwald ripening model. In addition, kinetic modeling of the softening of H13 during tempering from 863 K to 973 K was performed. This model was also applied successfully to predict the hardness of double-tempered H13 steel samples.