Research on the Microstructures and Mechanical Properties of Cold Rolled Hot-Dip Galvanizing CP980 Steel

In this study, cold rolled hot-dip CP980 steel was designed and effects of galvanizing parameters on microstructures and mechanical properties of the steel were also investigated. The results show that microstructures of the experimental steel consist of ferrite, bainite and martensite. Mechanical properties of the steel mainly depend on the phase fraction which may be affected by the galvanizing process. Heating and slow cooling parameters play important roles in the phase fraction evolution. Moreover, there are a lot of fine micro-alloy precipitates distributed in the matrix which is useful to increase the yield strength and also refine the grain size. Excellent mechanical properties of the CP980 steel can be gained with 997MPa (TS), 751MPa (YS) and 11.0% (A50 EL). In addition, the hole expansion test results show that CP980 steel has a better hole expansion ratio compared to DP980 steel.