FRICTION STIR WELDING OF DUAL PHASE STEEL

Friction stir welding (FSW) of a dual phase (DP590) steel was evaluated with a cemented carbide tool. Different tool traverse speeds at 1000 rpm tool rotation rate were employed to compare the microstructural changes (phase transformation, grain morphology, and grain size) and mechanical properties in the nugget region. Mechanical properties of the parent material and nugget regions were characterized by mini-tensile and microhardness tests. The yield strength and ductility increased in the nugget region after FSW. The weld efficiency was about 83% for a 1 inch per minute (ipm) run and over 90% for 2 ipm and 4 ipm runs. Microhardness was higher in the nugget than the base material, and the heat affected zone was the softest region. Detailed microstructural evolution and corresponding thermal history of various regions are compared and discussed.