3.1 The microstructure of dual phase steels(DP) steel is ferrite and martensite, and the martensite structure is dispersed on the ferrite matrix in the form of islands. Dual-phase steel has low yield ratio and high work hardening performance. Under the same yield strength level, high strength low alloy steel has higher strength, and it is one of the preferred materials for structural parts.
3.2 Martensitic Steel martensitic steels(MS) steel has almost all martensite microstructure, and martensite steel usually has high tensile strength and high yield ratio.
3.3 The microstructure of transformation induced plasticity steel Transformation Induced Plasticity Steels (TR) is ferrite, bainite and retained austenite, and the content of retained austenite is not less than 5%. During the forming process, the retained austenite can be transformed into martensite structure. Because of its high work hardening rate, this steel has higher uniform elongation and higher tensile strength of Q/BQB 418-20212, and has higher elongation than dual-phase steel at the same tensile strength level.
3.4 The microstructure of complex phase steels(CP) steel is martensite, bainite, ferrite and a small amount of retained austenite. Its matrix structure is mainly hard martensite and bainite, with high yield strength and even elongation slightly lower than that of dual-phase steel (DP) and transformation induced plasticity steel (TRIP) with the same tensile strength. The tensile strength is usually above 600MPa, and the bending performance is excellent. 3.5 Quenching and Partitioning Steel (QP) steel is a kind of ultra-high strength steel with high formability produced by quenching-partitioning process. The microstructure of the steel is composed of martensite+ferrite+residual austenite, etc. By using the ultra-high strength brought by martensite and the transformation induced plasticity (TRIP) effect of residual austenite, the formability of the steel is superior to that of the traditional ultra-high strength steel. QP steel has medium yield ratio and high work hardening performance, and is suitable for body frame parts and safety parts with relatively complex shape and high strength requirements.
3.6 The microstructure of Dual Phase High Ductility Steels (DH) steel with high formability is mainly composed of ferrite, martensite and a small amount of retained austenite and bainite. Compared with DP steel with the same strength grade, TRIP can provide continuous work hardening ability, and obtain more excellent formability, which is suitable for forming parts with higher drawing requirements.
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