As low yield ratio alloyed hot-dip galvanized steel sheet. Kobe Steel has previously developed 590MPa and 780MPa GA steel plates. As its design concept, in order to ensure the formability and weldability required by automobile steel plate, the idea of obtaining ferrite+martensite composite structure with low alloy composition has become a common design concept, and the technology has been established on this basis. When the strength of the steel plate is increased to 980MPa, the design of the best composition system is also based on this idea. The design idea to ensure both ductility and strength is as follows:
1) Although Mn is effective as a solid solution strengthening element, it should be added as little as possible to ensure the ductility of ferrite phase.
2) Cr and Mo are elements that improve hardenability and contribute to increasing the volume percentage of martensitic phase. In addition, C is helpful to improve the hardness of martensite phase. However, excessive addition of any element will lead to the reduction of weldability, so the amount required to increase the strength should be compounded
