Gas Metal Arc Welding of Advanced High Strength Steel - Developments for Optimized Welding Control and Weld Quality

Gas Metal Arc Welding (GMAW) is used in the automotive industry, for joining heavier gauge mild and HSLA steels, where it is recognized for its versatility and speed. The only constraints typically encountered relate to fatigue performance of the joint as a result of poor design or manufacturing fit-up. Advanced High Strength Steels, however, do not offer the same ease of welding, and process control is significantly more critical. The process window represents the range of acceptable process parameters, primarily heat inputs, to achieve an acceptable weld; which is a measure of the robustness of the process. AHSS differ from mild steels in chemical composition and thermal processing, resulting in a different microstructure; designed with a richer chemistry to have higher strength at equivalent thickness compared to mild steels. As a result, the sensitivity to heat input is greater and AHSS has a narrower process window in which acceptable welds can be achieved. Optimization of the welding process, through the understanding of the influence of the weld process parameters, has allowed the weld window to be enlarged to encompass AHSS. Empirical data generated so far has shown an excellent correlation between the weld geometric profile and one of the most critical mechanical properties, fatigue strength.