Effect of heat input on plastic deformation of undermatched welds

The aim of this work is to study the tensile properties of undermatch welds carried out in high strength quenched and tempered steel, RQT701 (British Steel). Two different heat inputs were used in order to obtain distinct mechanical properties in the weld metal (WM) and the heat-affected zone (HAZ) of the welds. Attention was focused on the microstructure and mechanical properties of the welded joints. Real stress–real strain curves of specimens sampling the WM, the WM in conjunction with the HAZ and the three zones altogether (WM, HAZ and BM) were analysed. The increase of heat input coarsened the microstructure and diminished the hardness in the WM and HAZ. A loss of hardness was also observed in the subcritical zone probably due to carbide precipitation. The increase of heat input increases the yield and tensile strength undermatching of the WM and also produces HAZ undermatching. The undermatch condition induces a concentration of plastic flow in the weakest zone and a loss of strength and ductility of the weld when loaded in tension.