Influence of preheating on residual stresses in ultra-high strength steel welded components

Preheating is generally required in the welding of ultra-high strength steels (UHSSs) for avoiding cold cracking. The present work systematically explores the influence of preheating on welding residual stresses (WRS) in components made of UHSS by means of both experiments and numerical simulations. The results reveal that, no matter what UHSS is with or without metallurgical phase transformation, preheating has a great influence on the magnitude of transverse residual stress (σ_T-RS). In general, the higher preheating temperature (T_PH) the lower magnitude of σ_T-RS is. Preheating would change the longitudinal residual stress (σ_L-RS) sign in the weld area and σ_L-RS amount obviously diminishes with the increase of T_PH for transforming UHSS, while that has nearly no influence on the maximum σ_L-RS but has an impact on the area of tensile σ_L-RS for non-transforming UHSS. The effect of entire preheating and partial preheating on WRS in UHSS welded components could be nearly the same. Nevertheless, T_PH in the partial preheating case (about 300°C here) should be higher than that in the entire preheating one (corresponding 100°C here) for that same effect. The weld dimensions, especially the size of the heat-affected zone (HAZ), and cooling time Δt_8/5 significantly increase with T_PH. Preheating has almost no influence on the restraint degree of welded components.