Effects of heat input on strength, fatigue and corrosion characteristics of dissimilar 2507 super duplex/316 L austenitic stainless steel welds with austenitic filler metal

This research has investigated effects of heat input on strength, fatigue crack growth and corrosion characteristics of gas metal arc welded (GMAW) joints of dissimilar 2507 super duplex and AISI 316 L austenitic stainless steels. For this intention, the GMAW processes were performed using filler metal of ER309LSi austenitic stainless steel at varying heat inputs of 0.29, 0.33, 0.38 and 0.44 kJ/mm. Afterwards, several experiments were conducted including microstructural analyses (light microscopy, EBSD, FE-SEM, and XRD), mechanical characterizations (hardness, tensile, and fatigue crack growth rate tests) and corrosion tests. The results exhibited that increasing heat input caused grain coarsening and microstructural changes in weld metal from dendritic structure to skeletal and lathy ferrites. It was attained that the dissimilar metal weld having the best fatigue crack growth performance was produced at the heat input of 0.44 kJ/mm owing to fatigue crack growth inhibition by δ-ferrite. In addition, this particular weld was also proved to have excellent corrosion resistance as indicated by its low corrosion current density, i corr (0.183 µA/cm 2 ) and high pitting corrosion potential, E pit typically 743.77 mV. It seemed likely that the corrosion resistance mechanism involved passive film formation and its relationship with the weld microstructure was discussed in the present paper. Of note is that such a comprehensive study on microstructure, mechanical properties, fatigue crack growth, and corrosion behaviors of GMAW joints of dissimilar metals between 2507 super duplex stainless steel and 316 L austenitic stainless steel under varying heat inputs is limited, therefore it is a novelty of the present paper.