MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED AISI 304 STAINLESS STEEL

Abstract

Friction stir welding of AISI 304 stainless-steel sheets was successfully carried out with a tungsten-alloy (W+La2O3) tool and the effect of the tool rotational speed on the microstructure and mechanical properties of the joints were evaluated. 3-mm-thick plates were friction-stir welded at various rotational speeds of 600–1000 min–1 and a constant welding speed of 40 mm/min with a constant axial load of 15 kN. Defect-free joints were produced at 800 min–1 and 900 min–1, indicating a proper plastic flow of the material and ensuring adequate heat generation during welding. Tensile, Charpy impact, compression and microhardness tests were performed to evaluate the joint mechanical properties. The microstructural behavior of the welded and base-metal samples was examined with optical microscopy and scanning electron microscopy. According to the mechanical results, the welded material has a higher yield strength than the base metal due to the grain refinement and work hardening effect in the stir zone. FSW welds have a higher hardness than the base metal due to the high density of dislocations and continuous dynamic recrystallization. The joints also exhibit acceptable impact toughness. Finally, the EDS analysis confirms that there is no secondary-phase formation in the weld zone of the fabricated material.