EffEct of cryogEnic trEatmEnt on WEar rEsistancE and microstructurE of 42crmo stEEl in this work, thermo-mechanically treated 42CrMo steel was subjected to cryogenic treatment conducted by means of orthogonal design method, followed by low-temperature tempering to investigate the effect of different parameters of cryogenic treatment on wear resistance of 42CrMo steel and to optimize parameters of cryogenic treatment for improving wear resistance. The results of hardness test and wear test show that cryogenic treatment significantly improves wear resistance with marginal changes in coefficient of friction and hardness. Specifically, cryogenic temperature has the largest impact on wear resistance of 42CrMo steel, holding time has medium impact, and the parameter of treatment cycles has the least impact. The optimum parameters of cryogenic treatment are −196°C for 12 hours with one cycle for improving wear resistance. The results of scanning electron microscopy (SEM) and X-ray diffractometry (XRD) analysis indicate that marginal changes in hardness and coefficient of friction may be owing to little amount of transformation of retained austenite, and the significant influence of cryogenic treatment on improving wear resistance of 42CrMo steel can be mainly attributed to segregation of carbon atoms promoted by cryogenic treatment resulting in more precipitation of carbides in subsequent tempering.
Using W6Mo5Cr4V2 HSS (High-speed steel) as a sample material, effects of cryogenic treatment on residual surface stress of ground W6Mo5Cr4V2 HSS specimens were investigated. The residual stress in the ground surface and its change caused by cryogenic treatment were analyzed using both X-ray diffraction technique and finite element method. It was demonstrated that the cryogenic treatment reduced the equivalent stress Max Mises from 248.9 MPa to 114.3 MPa, and the principal stress reduced from 124.0 MPa to 91.6 MPa. The residual stress at X direction (S11) parallel to the grinding direction was tensile stress, which was reduced from the Max. 105.8 MPa to 63.48 MPa. However, the residual stress (S22) perpendicular to the grinding direction was compressive stress, which was slightly increased from 272.6 MPa to 287.8 MPa by the cryogenic treatment. The changes in both the tensile and compressive residual stress components are beneficial to material performance, e.g., wear resistance. Results from the computational and experimental analyses are consistent.
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