On the role of molybdenum on the microstructural, mechanical and corrosion properties of the GTAW AISI 316 stainless steel welds

A comparative study was carried out on GTAW AISI 316 welds fabricated by three different filler metals including ER-317M, ER-316 and ER-308. Filler metals were selected in a way to induce varying Molybdenum (Mo) concentrations in the weld metal, so that the effect of Mo on the microstructural, mechanical and corrosion behavior of the welds was investigated. Microstructural studies revealed that as Mo concentration increased in the weld metal, the dendritic morphology of this zone gradually was changed from cellular dendritic to columnar dendritic and a noticeable amount of austenitic phase and precipitations were formed. Mo-containing ER-316 and ER-317M welds showed appreciable amount of Mo- and Cr-rich carbides such as (Fe,Cr)23C6 which formed at the grain boundaries of δ-ferrite phase resulting in increased the hardness and strength of welded samples. The highest microhardness value of 188 HV and yield strength of 330 MPa belonged to ER-317M welds containing the highest Mo concentration. Also, corrosion resistance of the welds significantly improved by increasing Mo concentration and a minimum corrosion rate of 4.178 mm/year was accounted for ER-317M welds in which, the formation of passive film was more facilitated due to the higher concentration of Mo.