Effect of tempering process on microstructure and impact toughness of 35Cr16Cu3Mo2VN steel

The 35Cr16Cu3Mo2VN martensitic stainless steel was subjected to tempering treatment, and the effects of different tempering temperatures（500-650 ℃） on its microstructure and mechanical properties were systematically analyzed. The results indicated that as the tempering temperature increased, the impact toughness of the tested steel significantly rose from 2 to 17 J before reaching a stable level, while the hardness decreased monotonically. A critical transition occurred at 530 ℃, where the tested steel exhibited a notable increase in toughness while maintaining a hardness of 55HRC, achieving optimal overall performance. Within the tempering temperature range, the impact toughness of the 35Cr16Cu3Mo2VN steel is improved. On the one hand, this is due to the synergistic effect of the precipitation and growth of M₂C carbides, along with the reduction in the size of M₂₃C₆ carbides. On the other hand, the transformation of the matrix microstructure. The decrease in hardness with increasing the tempering temperature was due to carbon precipitation and agglomeration at high temperatures, which reduced the solid solution strengthening effect of carbon and thus was harmful for the material′s hardness.