Microstructure evolution and mechanical properties of PESR 55Cr17Mo1VN plastic die steel during quenching and tempering treatment

55Cr17Mo1VN high nitrogen martensitic stainless steel is usually applied to the high-quality mold, which is largely produced by the pressurized electro slag remelting process. The microstructure evolution of quenching and tempering heat treatment were investigated and an optimal heat treatment process to achieve excellent mechanical properties was found out. The main precipitates in the steel included carbon-rich type M23C6 and nitrogen-rich type M2N. With increasing austenitizing temperature, the equivalent diameter of the precipitates got fined, and retained austenite content increased significantly when the austenitizing temperature exceeded 1020 degrees C. The fracture mode gradually changed from brittle fracture to ductile fracture with increasing tempering temperature from 200 to 550 degrees C. The experimental steel tempered at 350 degrees C achieved a good combination of hardness (60.6 HRC) and strength (2299.2 MPa) to meet service requirements. Flake M23C6 precipitated along martensite lath boundaries and the secondary hardening phenomenon occurred when the tempering temperature was 450 degrees C. Due to the high nitrogen content, M2N precipitated from the inside of laths and matrix when tempered at 550 degrees C.

Automated summary

The study investigates the microstructure evolution of quenching and tempering heat treatment in high nitrogen martensitic stainless steel, finding an optimal heat treatment process for outstanding mechanical properties. The main precipitates in the steel are carbon-rich type M23C6 and nitrogen-rich type M2N. The fracture mode transitions from brittle to ductile with increasing tempering temperature.