Study On Microstructure And Properties Of 20Cr15NiMoN、20Cr14MnNiMoN Martensitic Stainless Steel

30Crl3 martensitic stainless steel has widely application prospects because of its good corrosion resistance in the atmosphere,water vapor and organic acids.The traditional heat treatment process for such martensitic stainless steel is quenchingtempering,which brings high strength and hardness,but often poor plasticity toughness.Quenching-Partitioning(Q&P)process is a new heat treatment process for the martensitic steel which can obtain multiphase microstructure about martensitic and carbon-riched austenite so that to improve strength and plasticity.In addition to improving the heat treatment process,it can also improve plasticity and toughness combined with the alloying method.Based on 20Cr15NiMoN and 20Cr14MnNiMoN as the tested steels in this study,the effects of different Q&P heat treatment process on the microstructure and mechanical properties of the steels were investigated by using Laser scanning confocal microscope(LSCM)、X-ray diffraction(XRD)、Electron backscattered diffraction(EBSD)and Transmission electron microscope(TEM)and mechanical properties test.The results are as follows:1.The martensitic stainless steels must choose the appropriate austenitizing temperatu-re during Q&P process.The carbonitrides and alloying elements are not dissolved sufficiently when the austenitizing temperature is lower,the Ms is higher and the volume fraction of retained austenite is less as relusts;the carbonitrides and alloying elements are dissolved sufficiently when the austenitizing temperature is higher so that there will be more retained austenite.The austenitic grain size begin to grow up when the austenitizing temperature is high enough and it will have a negative impact about the mechanical properties.The corrosion resistance can be improved as well as the austenitizing temperature reduced by 60℃ to 80℃ with 0.1%N instead of 0.1%C.2.Different quenching temperatures have a great impact on the mechanical properties:20Cr15NiMoN steel austenitizationed at 1020 ℃ for 30min and then partitioned at 480℃ for 30min after quenching at 12～50℃.With the increasing of quenching temperature,the volume fraction of retained austenite increased from 27.3%to 37.6%and the yield strength decreased from 1123MPa to 855MPa;the elongation and impact energy first increased and then decreased and the tensile strength changed little.3.When the partitioning temperature increased from 45° to 480℃ after Q&P heat treatment of 20Cr14MnNiMoN steel,the volume fraction of retained austenite increased as well as the elongation,the tensile strength and impact energy,the hardness changed little and the change of yield strength is more stable.4.The steel of 20Cr15NiMoN austenitization at 1020℃ for 30min then quenched to 20℃ and then partitioned at 480℃ for 60min.The microstructures are the mixture structure of film-like retained austenite in lath martensite and composite structure with block retained austenite and twin martensite at room temperature.It obtain the best strength and plastic cooperation(the volume fraction of retained austenite is 27.2%):Rp0.2=1110MPa,Rm1612MPa,A=27.2%,HRC=45.6,Akv=20J,Rm×A=43.8GPa·%.5.The steel of 20Cr14MnNiMoN austenitization at 1030℃ for 30min then quenched to 40℃ and then partitioned at 480℃ for 60min obtain the best strength and plastic cooperation(the volume fraction of retained austenite is 22.5%):Rp0.2=1151MPa,Rm=1517MPa,A=27.4%,HRC=44.4,Akv=29J,Rm×A=41.6GPa·%.