Effect of Chemistry on the Heat-Affected Zone Softening during Induction Welding of Advanced High-Strength Steel Tubes

摘要

High-frequency induction welding is widely used in industry for tube making. This process is fast and effective for producing low and medium carbon steel as well as high-strength low-alloy (HSLA) steel tubes for automotive applications. Tubes made of advanced high-strength steel (AHSS) have potential applications in automotive frames and structures. However, heat-affected zone (HAZ) softening has been a major issue for welding of AHSS tubes which may reduce their formability for applications such as hydroforming. This paper presents the results of a study on seam weldability of AHSS tubes. Tube mill fabrication was simulated in laboratory using press brake forming and high-frequency induction welding. Different grades of dual-phase (DP) and transformation-induced plasticity (TRIP) steels were used for tube making. The effect of chemistry on the weld zone properties was analyzed. The study showed that softening in the HAZ was affected by the chemistry of DP and TRIP steels which was detrimental to the weld mechanical properties. A significant drop of the weld tensile strength and overall circumferential elongation was observed in the tubes made of lean chemistry steel. This HAZ softening was associated with the tempering of base metal microstructure in the grades with rich chemistry while it was more severe by the presence of reformed ferrite in the lean chemistry.