Advisable Grades of High-Strength Steel Sheets and Welding Conditions for Spot-Weld Strength in Automotive Body Application

Experimental study on static strength of spot-welds for high-strength steel sheets is summarized, focusing on thicker and coated sheets. Tensile shear strength (TSS) increases with sheet strength and thickness. Cross tensile strength (CTS) also increases, but the variation with sheet strength is small. Welding with expulsion deteriorates CTS, especially for thicker or coated sheets with higher strength or carbon content. Blow-holes and shrinkage cavities are found frequently at thicker sheet welds, and their existence near nugget edge reduces CTS. Above-mentioned knowledge leads developments of galvannealed sheets with carbon content less than 0.1 % for tensile strength up to 980MPa.