High-strength steel is divided into traditional high-strength steel and advanced high-strength steel. Traditional high-strength steels are mostly strengthened by solid solution strengthening, precipitation strengthening, and grain refinement. Advanced high-strength steels are steels with enhanced phase transformation. The strength and plasticity of advanced high-strength steels are superior to ordinary high-strength steels, and they have high strength and good formability. Therefore, their application in the automotive industry has rapidly expanded. According to the metallurgical structure, there are four types of steels: dual phase steel (DP steel), phase change induced plasticity steel (TRIP steel), multiple phase steel (CP steel), and martensitic steel.

1, dual phase steel (DP steel)

Dual-phase steel is the most used type of steel in automobile manufacturing. Its main organization is ferrite and martensite. Dual-phase steels have strength levels of 400-1180 MPa. At present, 780 MPa, 980 MPa, and 1180 MPa are high-end products for dual-phase steels, and the market demand is at an increasing stage. It is expected to become the mainstream steel for lightweight vehicles in the future.

Performance: Dual phase steel has lower yield ratio, higher work hardening index and bake hardenability. In addition to the expansion in the automotive field, it should have a higher hole expansion rate and lower carbon equivalent.

2. Transformation induced plasticity steel (TRIP steel)

The main organization of TRIP steel is ferrite, bainite and retained austenite. The commonly used grades of TRIP steel are 600MPa and 800MPa grades, and perhaps 980MPa and 1180MPa TRIP steels will be used gradually in the future.

Performance: TRIP steel generally has a high carbon content and requires the addition of elements such as Si and Al that inhibit the precipitation of carbides. The characteristics of TRIP steel are very prominent, the main advantage is the high elongation.

3, complex phase steel (CP steel)

The microstructure of CP steel consists of ferrite, bainite, and martensite. The demand for CP steel mainly comes from the introduction of models in Europe. Currently, there is very little domestic consumption. The performance characteristics of CP steel are high yield ratio and good hole expansion rate.

4. Martensitic steel Martensitic steel is obtained by rapid quenching after austenitizing at high temperature. During rapid quenching, austenite transforms into lath martensite, and the structure may contain a certain amount of ferrite, but As the intensity level increases, the tissue consists almost entirely of martensite. Martensitic steel is currently the highest class of automotive steel grades, strength levels from 900-1500MPa.