MICROSTRUCTURE OF WELDED JOINT AND HEAT-AFFECTED ZONE OF REINFORCING PROFILES MADE OF RIMMED STEELS AFTER LASER WELDING

Abstract

The paper presents the results of studying the microstructure of the weld metal and the heat-affected zone (HAZ) of reinforcing profiles made of rimmed steels after laser welding. Laser welding is considered a promising alternative to conventional methods due to its high energy concentration, short process duration, and ability to ensure high- quality joints at elevated welding speeds. However, determining optimal process parameters requires experimental studies, which can be accelerated by applying macro- and microstructural analysis. Chemical composition analysis of the base metal and metallographic investigations were conducted. It was established that in specimens with a thickness of 1.2 mm, the fusion zone exhibits a distinct dendritic structure with a width of 2–3 mm, widening towards the outer surface of the profile. The HAZ retains a fine-grained structure without significant grain growth, owing to rapid heat dissipation. In 2 mm profiles, oxide non-metallic inclusions were detected, which reduce process stability and intensify spattering. In the absence of shielding gas, oxidation of the molten pool was found to cause crater formation and surface defects. The study demonstrates that low Si and Mn content in rimmed steels leads to an increased number of non-metallic inclusions and oxide-related imperfections. To ensure process stability and improve weld quality, it is recommended to use steels with Si ≥ 0.1 % and Mn ≥ 0.3 % at minimum sulfur and phosphorus levels. The obtained results are of practical importance for the production of profile tubes and reinforcing elements where weld integrity is critical.