異強度板組の抵抗スポット溶接継手の引張せん断強さと破断位置に及ぼす材料強度の影響

Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. In general, weldability and formability of steel sheet tends to decline as steel strength increases. Hot stamping is a technique that achieves both formability and strength of steel sheet, and TS1500 MPa class hot stamped steel sheet is applied to many vehicle models. On the other hand, since the joint strength characteristics of the spot weld are dominated by the melt-solidified zone and weld heat affected zone, there is a concern that performance of spot welded joints will decline as steel strength increases. In other words, in order to further expand the application of AHSS, it is very important to have knowledge about the characteristics of spot welded joints. In this report, we investigated the TSS of the TS1500 MPa class hot stamped steel sheet, focusing on the characteristics of tensile shear joints. Then, we compared the joint strength and failure position of the same kind material joints and the dissimilar material joints with the TS1500 MPa class hot stamped steel sheet in case of the plug failure. As a result, it was found that TSS of dissimilar material joints depend on base metal strength on lower strength steel side. However, fracture occurred on the TS1500 MPa class hot stamped steel side except for joints with large difference of base metal strength. The mechanism is thought that the effect of strain concentration at the edge of nugget on the TS1500 MPa class hot stamped steel side due to the increase of rotational deformation around the nugget.