Study On Microstructure And Properties Of Cr-Ni-Si-N Series Low Carbon Martensitic Stainless Steel

13Cr martensitic stainless steel has been used widely because of its excellent properties such as low cost, high strength, while it has poor corrosion resistance, ductility and toughness. 13-5 Cr-Ni martensitic stainless steel had been developed based on 13Cr martensitic stainless steel. Although the plasticity and toughness and corrosion resistance are greatly improved, the material cost improves seriously because the strength decreased significantly. In recent years, N as cheap alloying element is widely used in austenitic and duplex stainless steel to replace Ni, not only increasing the strength notably, but also improving the corrosion resistance effectively. Recently quenching and partitioning(Q&P) technique which rised suddenly at carbon steel field provided ideas to improve the strength and toughness of martensite stainless steel.Based on 10Cr13NiN,10Cr13NiSiN and 10Cr13NiSi2N as tested steel. Through the different Q&P heat treatment system on the sample, we studied the content, the distribution and the morphology of retained austenite and phase composition were investigated by charactering the tested steel samples using laser scanning confocal microscope (LSCM), X-ray diffraction (XRD) and transmission electron microscope (TEM).The influence of different Q&P heat treatment system on mechanical properties of tested steel was examined by conducting tensile and toughness impact, by which determined the relationships of component-process-microstructure-properties, then laid the foundation for the development of Cr-Ni-Si-N series of Q&P martensitic stainless steel. The conclusion was obtained as follows:1. After Q&P process, the microstructure of tested steel 10Cr13NiN,10Cr13NiSiN and 10Cr13NiSi2N can all consist of lath martensite and retained austenite dual phase structure. In the Q&P process of tested steel, the volume fraction of retained austenite of tested steels reached their peaks when the quenching temperature were 180℃,165℃,150℃, both of increasing or decreasing of quenching temperature falls down the volume fraction of retained austenite. The volume fraction of retained austenite when the partitioning temperature is 450 ℃ is more than the volume fraction of retained austenite when the partitioning temperature is 400℃.2. Quenching temperature has great influence on the comprehensive mechanical properties of experimental steel, the yield strength decreases gradually with the quenching temperature’s increasing when the quenching temperature increases from 120℃ to 180℃, the amplitude of variation of the yield strength is as high as 300MPa; the tensile strength increases with the quenching temperature increases significantly, but the amplitude is less than 100MPa; the elongation and impact toughness increases firstly and then decreases as the quenching temperature increases, the extreme temperature decreases with the increasing of Si content.3. The yield strengths of tested steel 10Cr13NiN,10Cr13NiSiN and 10Cr13NiSi2N have small difference, change from 750MPa to 1050MPa with the quenching temperature’s changing; the tensile strength of 10Cr13NiSi2N steel is about 1400MPa, significantly higher than the tensile strength of 10Cr13NiN steel and 10Cr13NiSiN steel (approximately 1300MPa); the best elongation of 10Cr13NiN,10Cr13NiSiN and 10Cr13NiSi2N steel are all above 20%, increase with the increasing content of Si; while the elongation and impact toughness increases firstly till a maximum then decrease again with the increasing of QT. The best impact toughness of 10Cr13NiN,10Cr13NiSiN and 10Cr13NiSi2N steel ranges from 40J to 70J, and increases with the increasing content of Si.4. After Q&P process, the best mechanical properties of 10Cr13NiSi2N steel: Rp0.2=1010MPa, Rm=1440MPa, A=24%, Akv=70J.