A three-dimensional heat transfer modelling and experimental study on friction stir welding of dissimilar steels

Abstract

In this research, numerical as well as experimental analysis on friction stir welding (FSW) of dissimilar steels, i.e. DH36 steel and AISI 1008 steel, was performed. A 3D heat transfer FE model based on Abaqus/CAE using Fortran code via DFLUX subroutine was developed to investigate the effect of FSW parameters (i.e. rotational speed and traverse speed) on temperature distribution during the welding. It was observed that decreasing the traverse speed, increasing the rotational speed and shoulder diameter enhanced the peak temperature due to higher heat input. Based on the experimentally obtained sound quality welding parameters, the FE model was successfully validated with a maximum percentage error of 5.57% for peak temperature. Experimental results revealed that the higher heat generation reduced the grain size by increasing the rotational speed and decreasing the traverse speed. The inhomogeneous hardness distribution was observed across the weld cross section due to grain size variation. The higher grain refinement at a rotational speed of 600 rpm with a traverse speed of 70 mm/min produced the maximum value of the hardness and impact toughness. The tensile weld samples were fractured in the base metal zone (i.e. AISI 1008 steel) and experienced the tensile strength within the range of the AISI 1008 steel. The microstructure in the SZ exhibited the Widmanstatten ferrite in AISI 1008 steel and acicular-shaped bainite ferrite in DH36 steel. EDS analysis of the fractured surface of impact specimens confirmed the embedment of tungsten carbide particles in the weld zone due to the tool wear.