The first generation of automotive high-strength steel IF steel, that is, interstitial-free steel (ultra-low carbon steel), has low C and N content, and the curve changes very smoothly. Its tensile strength is about 280MPa and has good plasticity; Mars Solid steel, its microstructure is martensitic structure, and after corresponding heat treatment process, its tensile strength can reach 2100MPa. However, there are obvious problems with the first generation of high-strength steel: materials with high tensile strength have poor plastic properties, and the elongation difference reaches about 37%. The first generation of automotive steel was not suitable for the modern automobile manufacturing industry. Due to its low strength-to-plastic ratio, the second generation of steel materials was developed.
The second generation advanced automotive high-strength steel (TWIP steel) has a plastic deformation of only 20% when the tensile strength is 800MPa. As the stress gradually increases, when the stress reaches 1200MPa, the strain reaches more than 58%. , has good plastic properties, and its strong-plastic product is much higher than that of the first generation automotive steel. It can be seen that the improved second-generation automotive steel has stronger collision energy absorption capabilities and better performance than the first-generation, but the cost is relatively high.
In the third-generation advanced automotive high-strength steel Q&P steel, the carbon in the martensite state is distributed to the retained austenite during the quenching process. The retained austenite is more stable due to carbon, thereby improving the strength and toughening properties of the steel. . When the strain is about 15%, the stress of Q&P steel reaches the highest value, about 1500MPa. In other words, it has the advantages of high strength, strong plasticity, and low cost. It is considered to be a new generation of high strength steel that perfectly combines high strength with good toughness and plasticity. Strength steel.
