Influence of Post-Weld Heat Treatment on Microstructural and Mechanical Properties of Dual-Phase Steel Gas Metal Arc-Welded Joints

Dual-phase (DP) steels have gained considerable attention in the automotive sector because of the remarkable strength and formability combination, owing to the complex thermomechanical treatment employed during the production of steel. Weld fabrication, which is inevitable during the production of automotive components, often results in microstructure that adversely affects the mechanical properties. A post-weld heat treatment (PWHT) can be employed to improve the formability in addition to stress relieving. The present work investigates the microstructure and mechanical properties of similar and dissimilar gas metal arc-welded (GMAW) and post-weld heat-treated (300, 400 and 500 degrees C) joints of DP590 and DP780 steels. The weldments in the as-welded condition have shown a considerable reduction in the tensile elongation (%El) (up to 60-65%) and formability (up to 50-60%) due to the microstructural modifications in various zones. Subsequent PWHT at 500 degrees C resulted in a significant (25%) increase in the formability of the weldments. However, the formability of the weldments after the PWHT is still lower than that of the corresponding base metals due to the existence of microstructural inhomogeneity across the weldment.