Abstract: With the increasing maturity of induction heating technology, more and more auto parts use this energysaving and efficient heat treatment method to improve the mechanical performance of metal parts. This paper mainly introduces the study of middle frequency induction scanning hardening process of S45C. Through the hardness determination and metallographic organization analysis, the metallographic results conform to the standard of JB/T 9204—2008《Metallographic Examination of Induction hardened Steel Parts》, and the hardening layer depth is uniform and consistent. The results show that medium-frequency induction quenching can be used in the heat treatment production of double-gear racks for automobile parts.