Abstract: Samples with gradient layer thicknesses of 600 μm (GS600) and 1000 μm (GS1000) were prepared by high-frequency induction quenching on 45 steel surface. And the GS600 sample was tempered at 300℃. The results show that the surface hardness of 45 steel in quenched state increases from 187 HV of the matrix to 674 HV-699 HV, which is more than 3.6 times that of the initial state. After tempering treatment, the gradient structure layer remains intact, albeit with a reduction in the hardness of the outer layer from 700 HV to about 430 HV. Compared to the initial hot rolled sample, the yield strength and tensile strength increase from 420 MPa and 680 MPa to 700 MPa and 930 MPa, respectively. After surface induction quenching, the microstructure of the sample surface transforms from initial ferrite and pearlite to martensite, while the core structure of the sample remains unchanged. The formation of martensite is a key factor in improving hardness. Due to the formation of martensite phase in the surface layer of quenched 45 steel, the fracture morphology exhibits a smooth quasi-cleavage fracture, and the center exhibits a dimple-like morphology.