Plastic strain characteristics of butt-welded ultra-high strength steel (UHSS)

This paper investigates the mechanical properties of direct quenched (DQ) ultra-high strength steel (UHSS) joints in butt-welded configuration. Experimental and numerical investigation of the monotonic behavior of heat-treated and welded UHSS is undertaken. The tensile tests in the study investigate the effects of three different parameters on the plastic strain capacity of UHSS, namely: size of the heat affected zone (HAZ), matching between the filler material and the BM, and welding and post welding treatments such as TIG-dressing and high frequency mechanical impact (HMFI) treatment. Laser welding with a narrow HAZ was also performed without filler material and with zero air gap. A digital image correlation technique was utilized to monitor the plastic behavior of the specimens under tensile loading. The results indicate that the strain capacity of the joint is highly sensitive to heat input (HI); even a small HAZ leads to a considerable drop in the strain capacity. A strong constraint at the boundaries of the HAZ with the surrounding material generates a hydrostatic stress component, and thus an increase in both the ductility and strength of the joint can be expected.