Abstract
Resistance spot weldability of high strength steel (HSS) sheets for automobiles and the quality assurance technique of joints were investigated. The suitable welding current range in spot welding of HSS sheets shifted to the lower current side compared with that of mild steel sheets and it was affected by the electrode force. Vickers hardness at the welded zone increased with an increase of base steel carbon content. Tensile shear strength (TSS) of joints increased with an increase of nugget diameter, sheet thickness, and base steel strength. The cross tension strength (CTS) of joints increased with an increase of nugget diameter and sheet thickness. However, it showed a peak for base steel strength and carbon equivalent. Fatigue strength didn’t increase with base steel strength. The suitable welding current range in spot welding of galvannealed HSS sheets shifted to the higher current side compared with that of bare HSS sheets. Electrode tip life for galvannealed HSS sheets was over 3 000 points and it was a practical use level. It’s possible to assure the joint strength by estimating the nugget diameter using current and voltage during spot welding.
Published Version
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