Thermal Effect of Welding on Mechanical Behavior of High-Strength Steel

In this study, an experimental investigation of the thermal effect of welding on the mechanical behavior of thermomechanical control process (TMCP) high-strength steel (HSS) Q690CFD is carried out. Twenty-four specimens in four groups with different welding heat input, strength mismatch ratio of weld filler and base material, heat treatment condition [preheating (PH) and postweld heat treatment (PWHT)], as well as mechanical boundary condition during the welding process are designed and tested. The thermal history and cooling rate are monitored and analyzed. The welding residual stress near the weld toe and the microstructure of the heat-affected zone (HAZ), as well as Vickers hardness, are respectively examined with the ASTM hole-drilling method, metallurgical microscope observation, and Vickers hardness tests. The effect of heat input (q), mismatch ratio (r), heat treatment, and mechanical boundary conditions on welding residual stress, microstructure, and hardness of the HAZ is investigated. The effect of welding heat input on the tensile behavior of the TMCP HSS is studied. Results indict that different heat inputs could have varied cooling times and cooling rates and hence could produce different distributions of residual stress. When the same PH and PWHT is applied, the heat treatment could have better stress-relief effect for the specimens without mismatching. In addition, the width of the HAZ increases steadily with the increase in heat input. A good yield and ultimate strength prediction from hardness can be observed for base steel and welded connections.