Development of Hot-dip Galvanized Baking Hardened H220BD + Z Steel for Automobile External Application

Considering the metallurgy characteristic of baking hardening steels,the YS220 MPa grade baking hardening steel was developed by suitable alloying design and optimizing smelting,hot-rolling and galvanizing processes.The results show the steel has 220～270 MPa yield strength,320～400 MPa tensile strength,A₈₀≥32%,r-value ≥1.5,n-value ≥0.16 and BH₂ value≥30 MPa,and excellent formability and good bake-hardening behavior.The coating layer of sheet is even..After aging 150 days,the steel still has the smooth tensile curve and constant mechanical properties except decreasing r-value.The steel is well used in automobiles for exposed panels with excellent aging behavior within room temperature.