Microstructural Evolution and Its Correlation with Gas Metal Arc Welded Dissimilar Advanced High Strength Steels

Two dissimilar advanced high strength steels (AHSS)—ferrite-bainite (F-B) and ferrite-martensite (F-M) steel grades were joined by gas metal arc welding (GMAW) process. Microstructure of the heat-affected zone (HAZ) after welding was critically reviewed and further correlated with the performance of the welded joint. It was observed that both the steels had softening in the HAZ, particularly in the intercritical HAZ (ICHAZ) although the reasons were found to be different. For the F-B steel grade, the extent of softening was much higher and primarily attributed to the annihilation of the dislocations (which was manifested by presence of internal strain) present in the base matrix. Besides, the volume fraction of the precipitates present in the base steel was also reduced drastically and aided in the softening process. In contrast, the F-M steel inherently contained less internal strain and the softening was predominantly due to the tempering of the martensite islands distributed in the ferrite matrix during the welding process. Thus, to extract the optimum benefits from these modern AHSSs after welding, it is important to have a thorough knowledge about the steel design philosophy (i.e., base metal chemistry and transformed microstructural products).