The softening effect of welding on the mechanical properties of cold-worked stainless steel

Abstract

Cold-working can occur during production of flat sheet products and during fabrication of structural cross-sections. In both cases, when the material is cold-worked, plastic deformations result in material strength enhancements. These strength enhancements are particularly significant for materials such as stainless steel, which exhibit rounded stress-strain behaviour and pronounced strain hardening, and for hollow structural sections, where the strength increases arise in both the corner and flat regions of the cross-sections. Numerous studies have shown the importance of utilising this strength enhancement for efficient structural design, and predictive models have been derived for harnessing these enhancements. However, if cold-worked material is welded, some of the enhanced strength can be lost due to partial softening in the heat affected zone (HAZ). The extent of this strength loss is investigated experimentally in the present study. The experimental programme comprised ten tensile coupon tests on 1 mm thick austenitic (Grade 1.4301) stainless steel sheet material, with central welds parallel and transverse to the direction of cold-rolling, as well as twelve full cross-section tensile tests on 80×60 mm and 60×60 mm hollow sections with thicknesses varying between 2 and 4 mm. Digital image correlation was utilised to determine the local constitutive properties of the base metal, the heat affected zone, and the weld metal of each specimen. The hardness and microstructure of the welded samples, along with the widths of the weld and heat affected zone, were also characterised.