Effect of Microstructure on Hardness and Wear Properties of 45 Steel after Induction Hardening

Herein, the mechanical properties and microstructural evolution of 45 steel subjected to induction hardening (IH) is studied. To study the strengthening mechanism of IH on the 45 steel, the flow rate (FL) with 50, 60, and 70 L min−1 are chosen to cool the samples. The hardness distribution in the near‐surface layer is measured by a CARAT 930 Vickers hardness tester. The metallographic structures of the 45 steel with and without IH are analyzed by optical microscope (OM) and transmission electron microscopy (TEM). The phase analysis in the surface layer is determined by X‐ray diffraction (XRD). Combined with OM and hardness distribution, the results indicate that bainite is the reason for the low hardness of the raw material. Also the wear mechanism of 45 steel changes from adhesive wear and delamination to abrasive wear. Moreover, when FL increases from 50 to 70 L min−1, the surface hardness of 45 steel raises by 19.86% and the coefficient of friction reduces from 0.122 to 0.0418. Combined with TEM analysis, the determinate factors of surface hardness and tribological characteristics owes to martensite grain refinement, during the process of transforming austenite to martensite. Dislocations provide conditions for martensite nucleation, the driving force of the phase change generated by thermal deformation and FL drop provides energy for martensite nucleation. Induction hardening (IH) improves the hardness and wear performance of the 45 steel surface. During the IH process, dislocations and sufficient phase transition driving force promote the nucleation of martensite and further refine the martensite. As the flow rate (FL) increases, the grains of martensite are gradually refined, the surface hardness and wear resistance of the material are significantly improved.