Mechanisms of Hardness Variation in 14Cr12Ni3Mo2VN Martensitic Stainless Steel Under Different Tempering Temperatures Following High-Frequency Induction Quenching

To investigate the effect of tempering temperature on the hardness and its underlying mechanisms in 14Cr12Ni3Mo2VN martensitic stainless steel after high-frequency induction quenching (HFIQ), the microstructure, energy-dispersive spectroscopy (EDS) of precipitated particles, residual austenite, residual stress, and microhardness of the material tempered at different temperatures were examined and analyzed. The results reveal that a secondary hardening phenomenon occurs during the tempering process in 14Cr12Ni3Mo2VN martensitic stainless steel. Overall, with increasing tempering temperature, the microhardness initially decreases slightly, then rises to a secondary hardening peak, and finally drops rapidly. The secondary hardening peak corresponds to a tempering temperature of approximately 440 °C, with a microhardness of about 483 HV0.1. The secondary hardening phenomenon is likely attributed to the dispersion strengthening caused by the precipitation of alloy carbides during tempering. The precipitation and coarsening of carbides reduce lattice distortion and solid solution strengthening, while the release of residual stress diminishes stress-induced strengthening. Additionally, the decomposition of the martensitic structure leads to the formation of ferrite and carbides. The combined effects of these factors result in a decrease in hardness.