Effect of Pre-tempering Process on Microstructure and Properties of H13 Steel

Quenched H13 steel was pre-tempered at 620, 640, 660, 680 ℃ for 10, 20, 40 min and tempered at 600 ℃ for 120 min. By comparing with those of the steel after conventional tempering (tempering at 600 ℃ for 120 min, twice), the effect of pre-tempering process on the microstructure and properties of H13 steel was studied. The results show that with the increase of pre-tempering temperature and the extension of holding time, the degree of martensitic decomposition in H13 steel increased, the amount of residual austenite decreased, the size of precipitated carbide increased, and the dislocation density decreased; the hardness of H13 steel decreased, and the impact absorption work increased, Compared with that after conventional tempering at 600 ℃, the dislocation density of H13 steel was higher after pre-tempering at 620, 640 ℃ for 10–20 min and tempering at 600 ℃, and lower after pre-tempering at 660, 680 ℃ for 10–40 min and tempering at 600 ℃. Pre-tempering at 660 ℃ for 10–40 min and tempering treatment could improve both hardness and impact toughness, which was due to the combined effect of lower dislocation density and smaller tempered precipitated phase.