The rapidly developing automobile industry has brought huge challenges to the country's energy conservation and emission reduction, environmental protection and energy security. As China enters the automobile society, the number of passenger cars has greatly increased. Automobile lightweighting has become an important way to save energy and reduce emissions. Among the optional lightweight materials, high-strength steel plates have certain advantages in terms of performance, cost, energy saving and emission reduction, except for their slightly lower lightweight effect. High-strength steel has high strength and high collision energy absorption, which can effectively improve the safety of cars. Compared with traditional mild steel, it can significantly reduce the weight of the car while meeting the same automotive safety regulations. It is the optimal lightweight material solution to achieve both lightweight and safety requirements for the car. As automobile safety regulations become increasingly strict, the application of high-strength steel plates in passenger cars has been rapidly developed. At the same time, because high-strength steel plates can be optimized in composition and process on existing steel plate production lines, the increase in material costs is also smaller.
Currently, commonly used automotive steel plates for passenger cars include carbon-manganese mild steel, interstitial-free steel (IF), high-strength low alloy steel (HSLA), isotropic steel (IS), dual-phase steel (DP), phase change induced steel Plastic steel (TRIP), twin induced plasticity steel (TWIP), complex phase steel (CP), martensitic steel (MS), ferritic bainitic steel (FB steel), hot formed steel, etc. High-strength steel plates have advantages in performance and cost, which determine that they are still the most popular lightweight material on the market and the first choice for lightweight materials for mid- to low-end passenger cars. The proportion of high-strength steel plates in typical foreign steel car bodies generally reaches 50% to 60%, and some models even exceed 70%. Some of the latest models have high-strength steel plates as high as 73%. As domestic automobile safety regulations and fuel consumption regulations become increasingly strict, high-strength steel plates have also received more and more attention. The amount and strength level of high-strength steel plates for self-owned brand passenger cars have also increased significantly. The proportion of high-strength steel plates in the body of FAW passenger cars reaches more than 50%. The application proportion of high-strength steel plates in Chery's car bodies has also reached more than 50%, and the proportion of newly developed models has reached 60%. Great Wall Motors uses a large amount of high-strength steel plates, with the highest usage in single vehicles reaching 62.9%. In addition, the application level of high-strength steel plates in newly developed models of self-owned brands such as Geely, Changan, Dongfeng, SAIC and BAIC is basically 50%.
The factors restricting the application of domestic ultra-high-strength cold-formed steel are mainly in forming and welding technology; while the application of hot-formed steel is mainly a cost issue. The future application direction of high-strength steel plates is mainly to further expand its application on the basis of existing body structures, safety parts, and chassis parts; new application growth points are in body coverings and seat systems. It is expected that in the next 3 to 5 years, the consumption of high-strength steel plates for car bodies will reach 65% to 70%, and the proportion of ultra-high-strength steel and hot-formed steel will further increase. To realize the application of such a large number of high-strength steel plates, the biggest technical problem in the application of existing high-strength steel plates must be solved - the stamping forming problem. Therefore, the future technological development route of high-strength steel mainly has two aspects: 1. Develop a new generation of high-strength steel cold stamping steel grades, and achieve cold-formed ultra-high-strength steel above 1GPa level through stamping or rolling processes; 2. Improve the properties of hot formed steel and hot stamping process, and develop new low-cost hot stamping process technology.
