Microstructure and properties of friction stir welded 304 stainless steel using W-based alloy tool

Microstructure, and mechanical and corrosion properties were examined in 304 stainless steel friction-stir-welded using a tool made of a W-based alloy, and then these were compared with those of a weld produced by polycrystalline cubic boron nitride (PCBN) tool. Severe wear of the W-based alloy tool occurred during friction stir welding (FSW). The weld contained some tunnel-type defects in the stir zone. The microstructure in the bottom and advancing sides of the stir zone was relatively more sensitive for etching than the other regions, and it was identified as the duplex microstructure consisting of austenite and ferrite phases. W was enriched in the ferrite phase. The W-based alloy tool made the weld having roughly the same mechanical properties as the base material. The weld produced by the W-based alloy tool had the better corrosion resistance than that by the PCBN tool, although the corrosion resistance was slightly lower in the advancing side of the stir zone and heat affected zone (HAZ) than in the base material.