Influence of SC-HAZ microstructure on the mechanical behavior of Si-TRIP steel welds

Transformation induced plasticity (TRIP) steel provides enormous potential for auto-body construction in the automotive sector, owing to its enhanced mechanical behavior. In this work, Si-alloyed TRIP steel is joined by employing laser beam welding (LBW) and by utilizing two arc welding processes: gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) in order to assess the effect of the net heat input on the microstructure, the uniaxial tensile properties and the forming response. Results indicate that in spite of the Si content in TRIP steel; precipitation and growth of carbides (tempering) are observed in both: the martensite islands and the retained austenite phase, thus leading to the measurable softening at the sub-critical heat affected zone (SC-HAZ) of the arc welded samples. Although the failure location was predominantly found at the sub-critical heat affected zone of the GMAW samples, the maximum stress and elongation was basically controlled by the total extension of the weldment including fusion zone and heat affected zone. While the limiting dome height upon tension-tension (T-T) and tension-compression (T-C) depended primarily on the fusion zone hardness, weld width and geometry of the sample; the fracture location was outside the weld for T-C, whereas the fracture initiated at the weld in T-T samples. LBW specimens showed optimum forming performance.