Traditional high-strength steel
Traditional high-strength steel is mainly bake hardenable steel (Bake Hardenable, BH). Improved strength is achieved during the painting process after stamping. The degree of strain hardening during the stamping process has a significant impact on the strength improvement during the subsequent baking process. Strain hardening during the forming process is mainly based on the increase in dislocation density caused by deformation. The improvement in strength during the baking process is based on the obstruction of subsequent dislocation movement caused by the diffusion of atoms in the process. The differences in the molding method and the amount of strain caused by the molding process will have a certain impact on the bake hardening effect.
Typical first-generation advanced high-strength steel and its control technology
The first generation of advanced high-strength steel is mainly based on dual phase steel (Dual Phase, DP) and transformation induced plasticity (TRIP) steel.
DP steel, hence the name, is composed of two phases, which can be ferrite + bainite or ferrite + martensite. Ferrite, as the soft phase, ensures it has certain plasticity and is easy to form; bainite/martensite, as the hard phase, ensures it has reasonable strength.
Typical second-generation advanced high-strength steel and its control technology
The second generation of advanced high-strength steel is mainly Twinning Induced Plasticity (TWIP) steel. TWIP steel is based on the mechanical crystal formation due to the change of austenite phase during the deformation process. Due to the formation of crystals, the energy during the collision can be absorbed. Its basic composition is 18%Mn-3%Si-3%Al. Of course, this composition can be adjusted appropriately depending on the different concerns of different components on the performance of each phase and the bottleneck problems in the production process.
Development of the third generation of advanced high-strength steel
The third generation of advanced high-strength steel is based on the gap between the first and second generation of high-strength steel areas to develop varieties with high strength and high plasticity and excellent comprehensive properties, such as Q&P (Quenching and Partition) steel, which is currently a hot research topic at home and abroad. .The room temperature structure of Q&P steel is ferrite, martensite and austenite. Its design principle is that after quenching to a certain temperature to form a considerable amount of martensite, there is a secondary heating process, during which the martensite is achieved. The diffusion of carbon atoms into the retained austenite improves its stability. The strength and plasticity of the high-strength steel produced by this process can far exceed that of the first and second generation advanced high-strength steel.