Research On Deep Cryogenic Processing For Adjusting Residual Stress Of 42CrMo And 35MnB Alloy Steel

Residual stress directly affects the strength,fatigue and dimensional stability of mechanical parts,which in turn affects the service life of the workpiece.Residual stress is the result of various stresses,and the state is highly susceptible to external environmental factors.Cryogenic treatment can regulate residual stress to a certain extent.Therefore,it is important to study the regulation of residual stress by cryogenic treatment.Considering the cutting tooth material in the market today,42 CrMo and35 MnB alloy steel materials are taken as research objects.Through the numerical simulation and experimental verification methods,the process of controlling the residual stress of 42 CrMo and 35 MnB alloy steel by cryogenic treatment is studied.The cryogenic parameters of the surface residual stress state,the main research contents and conclusions are as follows:(1)Research on the influence of temperature field and tissue field on stress field distribution under different heat treatment processes.In the temperature field,the thermal stress caused by the uneven temperature distribution of the sample during quenching is more obvious than that of the cryogenic process;in the microstructure field,the retained austenite is non-simultaneous to the martensite structure;in the stress field,The residual stress of the workpiece decreases after cryogenic treatment and is converted from residual tensile stress to residual compressive stress.(2)Research on the influence of cryogenic temperature,cryogenic time and number of alternating times on the residual stress of materials.Using the range analysis method,the influencing factors of the cryogenic process parameters on the residual stress of 42 CrMo alloy steel specimens are as follows: deep cooling time> cryogenic temperature> alternating number,and the optimized process is obtained: the cryogenic temperature is-80 °C,deep The cold time is 12 h and the number of alternating times are 2 times.The factors affecting the residual stress of 35 MnB alloy steel sample are as follows: cryogenic temperature> alternating number> deep cooling time.The optimized process is obtained: the cryogenictemperature is-196 °C,the cryogenic time is 12 h,the number of alternating times are 2 times.(3)Exploring the mechanism of residual stress regulation from a microscopic perspective.After cryogenic treatment,most of the microstructures change from austenite to martensite,and martensite increases.The retained austenite distributed at the martensite crystal boundary can relax the dislocation accumulation at the martensite interface.The resulting stress concentration reduces the residual stress inside the tissue.