接合自己完了型摩擦圧接した高張力鋼継手の特性とその改善

Abstract

This paper describes the joint properties and its improvement of high tensile strength steel joint by an autocompleting friction welding method, that method was developed by authors. The base metal was 800MPa class high tensile strength steel. The weld faying surface of the fixed specimen had a 10mm diameter, and the effect of the thickness and that at the bottom of the grooves (groove bottom thickness) for the insert piece on the joining phenomena and joint properties were investigated. The value of a circumferential shear fracture (CSF value) was defined and calculated by the ratio between the theoretical and the actual generated friction torques. When the CSF value was lower than 1, the insert piece had the circumferential shear fracture before the friction torque reached the initial peak. Also, when the CSF value was larger than 1, the insert piece had the circumferential shear fracture after the friction torque reached the initial peak. When the joint was made at the insert thickness of 5mm with the CSF value of nearly 1, that had 100% joint efficiency although it had the softened region at the near of the weld interfaces. The joint had cracks at the weld interface when it was made with friction pressures of 36 and 120MPa. However, the joint had no crack at the weld interface when it was made with a friction pressure of 90MPa. When the joint was made at the insert thickness of 4mm with the CSF value of nearly 1, that had also 100% joint efficiency although it had the softened region at the near of the weld interfaces. However, the softened region at the weld interface of the joint with the insert thickness of 4mm was lower than that with 5mm. Also, this joint had 90 degrees bend ductility with no crack at the weld interface. In conclusion, a joint with no cracks for high tensile strength steel was able to make by an autocompleting friction welding method.