Grain Refinement in Ferritic Stainless Steel Welds Through Magnetic Arc Oscillation and Its Effect on Tensile Property

Abstract

Grain size reduction in weld fusion zone confers the advantage of increased resistance to solidification cracking and improved mechanical properties. In an effort to refine the fusion zone grain structure in AISI 430 ferritic stainless steel, Gas tungsten arc welding (GTAW) was performed during which transverse oscillations of the arc were induced through the use of an alternating external magnetic field. It was observed that the structure in the as - soIidified weld was predominantly columnar in the case of the conventional (i.e. continuous current) gas tungsten arc welding process. Arc oscillation results in columnar to equiaxed transition in the grain structure; under optimum condition of arc oscillation frequency and amplitude, the grain size of the weld bead was finer than in conventional welds. This could be attributed to the factors that include enhanced fluid flow, reduced temperature gradients and continually changing weld pool size and shape due to the action of the imposed magnetic field. An oscillation variable, which resulted in maximum grain refinement in the fusion zone, was employed to evaluate longitudinal all-weld tensile properties, and residual stresses across weldments. The tensile properties of arc oscillation welds were found to be superior to those of conventional welds. Arc oscillated welds exhibited low tensile residual stresses in the fusion zone compared to conventional gas tungsten arc welds.