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.
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