On the Heat-Affected Zone Role for Mechanical Properties of Structural-Steel MIG and CMT-MIG Weldments

The effect of evolved heat-affected zone (HAZ) during metal inert gas (MIG) and cold metal transfer (CMT)-MIG welding of two IS2062 structural-steels, i.e. E250 and E410, was studied. The comparison of mechanical properties such as yield strength, ultimate tensile strength, tensile ductility being represented by %elongation, impact toughness at room temperature, and microhardness was done. Conventional optical and field-emission scanning electron microscopy were used for detailed examination of microstructural evolution across weldments. CMT-MIG in comparison to MIG mode was observed to produce a well-refined microstructure for both E250 and E410. Various HAZ subzones comprised of fully formed pearlite colonies in coarse-grain HAZ, pearlite in patched form in fine-grain HAZ, partially distributed pearlite in inter-critical HAZ, and fine Widmanst & auml;tten and acicular ferrite in deposited weld-metal of ER-70S6. Such microstructural manifestations particularly in HAZ subzones exhibited a positive effect leading to improved mechanical performance.