Research On Controlling Microstructure And Property Of High-strength Steel Rectangular Tube In Induction Hardening

Due to light weight, high strength, ease of assembly, beautiful appearance,rectangular tube is commonly used in the bus frame. High-strength steel can enhance strength and save material to achieve lightweight of automobile which led to saving steel, energy conservation and emission reduction. When rectangular tube is induction hardened, unhomogeneous temperature distribution caused by the limit of its shape lead to the defect of unhomogeneous microstructure and mechanical properties which seriously affect the rectangular tube’s quality. The research on controlling microstructure and property of high-strength steel rectangular tube in induction hardening is significant for environmental conservation, development of automotive manufacturing and improving vehicle safety performance.Induction heating control equation was derived by studying the basic principle of induction heating and the physical quantities that affect temperature distribution were concluded. It established equation of magnetic flux density distribution when rectangular tube was induction hardened by special-shaped coil.This paper analyzed the law how parameters of special-shaped coil and width of rectangular tube affect magnetic flux density distribution. It designed and optimized special-shaped coil assorting with different rectangular tube aiming that optimal coil produce homogeneous magnetic flux density distribution at surface around the tube. Compared with the rectangular coil, special-shaped coil can effectively improve the distribution of rectangular tube’s magnetic flux density to make it homogeneous.Numeral simulation of induction heating for rectangular tube was carried out to study the influence law that parameters of special-shaped coil and width of rectangular tube affect temperature distribution, and obtain special-shaped coil which make temperature distribute uniformly. Nnumeral simulation of induction hardening was conducted by using the optimized special-shaped coil so that we obtain homogeneous microstructure and mechanical properties.This paper produced special-shaped coil with optimal parameters and built induction hardening testing system. We carried out experiment on the rectangular tube’s induction hardening test with different running speed and make tensile strength above 1500 MPa. Hardness test and microstructure test were carried out to verify that rectangular tube’s microstructure and mechanical properties distributed uniformly, when it was induction hardened by using special-shaped coil, which was consistent with the conclusion of coil optimization and numerical simulation.