Effects of heat treatment technology on microstructures and properties of 30Cr15NiMo martensitic stainless steel

As an effective approach for improving the match of strength and ductility of martensitic stainless steel， the processing of quenching and partitioning （Q&P） is seldom implemented in industrial practice of commercial steels due to two factors： the one is difficulty in accurate controlling the quenching suspending temperature， and another is large amount of carbide precipitation within martensite during partitioning. In this work， an experimental medium-carbon martensitic stainless steel of 30Cr15NiMo is designed and fabricated. The effects of processing parameters on microstructures revolution are investigated， and the mechanism of strengthening and toughening is clarified as well， through microstructure characterization and mechanical property testing conduct on Q&P treated samples. The research results show that， the martensitic start （Ms） temperature of the testing steel is approximately 200 ℃ after complete austenitization， and a compound microstructure of martensite and retained austenite can be obtained after the sample being cooled to ambient temperature. The excellent comprehensive mechanical properties of 1255 MPa in yield strength， 1631 MPa in tensile strength， 18.5% in elongation and 42% in area reduction can be achieved in the hot rolled testing steel plate subjected to tempering-assisted partitioning treatment at 480 ℃. The microstructure characterization confirms the volume fraction of retained austenite is approximately 20.2%， and small amount of cementite precipitated inside martensite， these factors improve the uniform elongation and non-uniform elongation synergistically. The research results provide fundamental basis for further optimizing in chemistry and processing.