Development Of 590MPa Grade Lightweight Commercial Vehicle Wheel Steel

Automobile make people’s life easy,at the same time,it also bring a series of other problems. Especially in recent years, the energy crisis and global warming have become more serious.Therefore, energy saving, environmental protection and safety have become the main problems facing the auto industry development.And the important way to solve this problem is automotive lightweighting technology. Automotive lightweighting is implemented through the various parts of lightweight. According to statistics, wheels of a car is under spring mass as a high-speed rotating part. The energy savings generated by its weight will be about 1.5 times than the other parts of the energy saving effect. Therefore, the wheel is an effective way to achieve lightweight automotive lightweight, and it has caused widespread concern the majority of car manufacturers.However, the domestic production of lightweight wheels compared with the same type of abroad products. There are many problems in the domestic wheels,such as,the prevalence of weight, and easy to crack forming and welding processes cause the product broken rate, fatigue performance is not ideal for a range of issues and so on. To solve these problems in the process of lightweight wheels, it is necessary to develop a new excellent formability, weldability and fatigue resistance of high-strength steel wheels.The paper mainly used the Gleeble-1500 machine, Formastor-F Ⅱ thermal dilatometer, metallographic,SEM,TEM, microhardness tester, WE-300B tensile testing machine and BUP600 forming machine.Firstly, the target microstructure of the wheel steel is determined by experiment. Secondly, the paper discuss the main chemical component on the influence of the phase transformation kinetics of test steel. Discussion on the influence of DIFT with different deformation parameters of test steels systematically, and the influence of test steels with different TMCP on microstructure. Finally, the optimization composition of wheel steel has been obtained and comfirming a best TMCP parameters, then develop a lightweight wheel steel RS590 with series products abroad.The main results of the paper are as follows:Confirmed the target microstructure of wheel steel is Ferrite+Bainite, and the main chemical component is:0.04～0.08C-1.2～1.8Mn-0.5Si-0.02～0.04NbThe CCT curve of two test steels are almost overlap, but the pearlite transformation temperature of test steel containing Nb lower than without Nb.The DIFT content of test steel is increases with the decreasing deformation temperature, the average grain size decreases. And its content increased with the increase of deformation, the average grain size increased.With different controlled rolling and cooling process parameters, both test steel microstructure mainly are the polygonal ferrite, polygonal ferrite, granular bainite and a small amount of pearlite hybrid structure.Observe two test steel microstructure, ultimately determine the parameters in the process of rolling is:the finish rolling temperature is 840±15℃, the deformation is 40%, the cooling temperature is 760 ℃, the cooling time is 5-8s, the cooling rate is 25℃/s, coiling temperature is 450±15℃.The yield strength of industrial trial production of hot rolled dual phase steel RS590 is more than 530 MPa and showed the yield ratio less than 0.9, the tensile strength is more than 590 MPa, the elongation is 36.0, the hole expanding rate is 104%.The industrial trial production indicates that the trial production of wheel steel all the indexes meet the requirements.