Effect of Mn Content on Tempering Softening Resistance of Hot Forging Die Steel 3Cr4MoSiV

Tempering treatments at 550 ℃ and 650 ℃ were carried out on hot forging die steel 3Cr4MoSiV samples containing 1.20wt%,2.00wt% and 4.00wt% Mn, and the effect of Mn content on tempering softening resistance of the steel was investigated by means of transmission electron microscopy, scanning electron microscopy, hardness testing and so on. The results show that tempering softening resistance was the most excellent when Mn content was 1.2wt%. Increasing Mn content was good for improving tempering softening resistance of the steel after tempering at 550 ℃ for short time, but decreasing that after tempering at 550 ℃ for a long time and at 650 ℃. After tempering at 650 ℃, tempering softening resistance of the steel containing above 1.20wt% Mn greatly decreased mainly, this was due to the more content of Mn promoting carbide coarsening.