Friction stir welding of high tensile strength steel plate using SiAlON tool

Abstract

Friction stir welding (FSW) of high tensile strength steel plate formed by cold-rolling (SPFC980) was conducted by using SiAlON tools. Characteristics of SPFC980 work-pieces after FSW tests and durability of the SiAlON tools were evaluated. FSW tests were done under various tool rotation speed (VR) and traveling one (VT) to search appropriate FSW conditions. Sound joint conditions were found when temperature measured at the shoulder part of the tool ranged from 686 to 1080°C. The durability of SiAlON tools was strongly influenced by the measured shoulder temperatures. The wear of the shoulder progressed rapidly with increasing travel distance when the measured shoulder temperature reached more than 1080°C. On the other hand, the wear progress was hardly observed in the case when the average measured shoulder temperature was less than 700°C. The most likely mechanism of the tool wear was elimination of grain clusters due to softening of glass phases contained in the SiAlON tool at high temperatures. It was concluded that the measured shoulder temperatures ranging from 680 to 800°C were effective for SiAlON tools to be used for FSW of SPFC980.