高張力鋼板スポット溶接継手の面内引張試験での強度と伸びに及ぼすHAZ軟化の影響

抄録

In this study, we investigated the effects of HAZ softening on the strength and elongation of resistance spot-welded joints in high-strength steel sheet in an in-plane tensile test. The fracture in the softened HAZ had a little effect on the maximum stress of the resistance spot-welded specimen; however, the fracture elongation decreased. The nugget diameter and HAZ softened width had little effect on the fracture elongation of the resistance spot-welded specimen. Also, the fracture elongation decreased slightly with the decrease in the sheet thickness. The major factor affecting the fracture elongation was the HAZ hardness ratio (= Softened HAZ /Base metal × 100%). For the resistance spot-welded specimen with a thickness of 1.6mm, when the HAZ hardness ratio decreased to less than 80%, the fracture position changed from the base metal to the softened HAZ and the fracture elongation decreased sharply. In addition, with a decrease in the hardness ratio, the fracture elongation decreased.