In situ heat treatment in laser beam welding: a study on high-temperature processing of low-carbon steels

Pre- or post-heating is commonly employed during welding. Inducing heat to the joint prior to welding is known to be an efficient way of reducing susceptibility to cracks and improving the toughness of the weld metal. In laser beam welding (LBW), the use of pre- or post-heating is less common, mainly because of the high productivity and restrictions on access to the small molten pool. However, in situ heat treatments during LBW are very common in the steel industry when joining hot-rolled sheets before coiling. Nevertheless, the implications of heating and cooling routines during LBW are still not fully understood, and studying them is important for industrial applications. This study intends to contribute to this discussion by reviewing some phenomena associated with high-temperature laser beam welding (HTLBW) and examining a case study of low-carbon steels. Sheets of low-carbon enhanced-plasticity steel were subjected to in situ LBW heat treatment in accordance with their chemical composition, thermomechanical treatment, and proposed use. Because this steel required rolling after welding, a ferritic microconstituent instead of martensite provided superior workability to the product. For some other classes of steels, there is an advantage in processing flat products at high temperatures, depending on the case, which was reviewed in this study.