Research On Q-P-T And Deep Cryogenic Treatment Process Of 30CrMo Steel

How to further improve the strength and plasticity of steel materials by improving heat treatment process has been a research hotspot in the steel industry.In order to further improve the microstructure and mechanical properties of the steel,the cryogenic treatment technology was applied to 30CrMo steel on the basis of the Q-P-T heat treatment technology proposed by the academician Xu Zuyao of Shanghai Jiao Tong University.The mechanical properties of 30CrMo steel are studied by mechanical properties test.The microstructure of the steel is characterized by optical microscope?OM?,scanning electron microscope?SEM?,transmission electron microscope?TEM?and X ray diffractometer.The main contents are as follows:?1?Measured the thermal expansion of the 30CrMo steel under different load curve,obtained the thermal expansion coefficient of the steel grade of each phase,and according to the K-M formula,obtained the phase transformation kinetics of coefficients of the steel grade,??28?.920365e^-8???10?.001664,and then adopt the method of phase separation,the coefficient of phase transformation plasticity is 0.00145,perfect the basic physical parameters of 30CrMo steel material database,provide the basis physical parameters for subsequent heat treatment process.?2?The effects of different Q-P-T process parameters on Microstructure and mechanical properties of 30CrMo steel were studied,such as the quenching temperature,the partition temperature and carbon tempering time of 30CrMo steel and more,The optimum Q-P-T heat treatment process was as follows:Heat preservation 5 min at 920?,then quenching at 260?,and heat preservation 60 s at 400?,finally water quenching to room temperature.After Q-P-T heat treatment,the tensile strength of 30CrMo steel is1425MPa,the elongation is 13.5%,and the hardness is 413HV,the microstructure is the lath martensite and the thin slice retained austenite between the martensite and the martensite.This structure has high strength and good plasticity.?3?The effects of deep cryogenic temperature,times of deep cryogenic and deep cryogenic preservation time on the mechanical properties and microstructure of 30CrMo steel after Q-P-T heat treatment were studied.The best deep cryogenic treatment process was as follows:the temperature of deep cryogenic was-100?and the number of cryogenic times were once and deep cryogenic preservation time was 1h.The tensile strength of Q-P-T+samples after cryogenic treatment is 1629MPa,the elongation is10.6%,and the hardness is 482Hv.The comprehensive mechanical properties were greatly improved compared with those after Q-P-T heat treatment,and the microstructure distribution was more uniform and reasonable.Compared with the traditional Q-P-T heat treatment process,the mechanical properties of 30CrMo steel are greatly improved after Q-P-T+deep cryogenic treatment.The microhardness,tensile strength and strength of the material are increased 16.7%,13.5%,6.7%,respectively,but the elongation is reduced 3.4%,the retained austenite content is reduced 1.6%,and the decrease is less in the acceptable range.This treatment could expand the application range of the steel grade,provides reference for further research and practical production.