Microstructure, mechanical properties and biocorrosion behavior of dissimilar welds of AISI 904L and UNS S32750

Abstract

This article addresses the joining of 5mm thick plates of marine grade, super-austenitic (AISI 904L) and super-duplex stainless steels (UNS S32750) by pulsed current gas tungsten arc welding using duplex and austenitic stainless steel fillers. Microstructure studies revealed the segregation of Mo-rich phases in the fusion zone while employing ERNiCrMo-10. Grain coarsening was observed at the heat affected zone (HAZ) of super-duplex stainless steel in both the cases. The study attested that all the tensile failures experienced in the parent metal, AISI 904L for both the weldments. Charpy V-notch impact studies demonstrated that the weldments employing ER2553 were experienced better impact toughness than ERNiCrMo-10 weldments. Further potentiodynamic polarization test in 3.5% NaCl environment was conducted on the coupons of the weldments. The coupons of the weldments were then tested for accelerated corrosion in salt fog chamber for 300h in 3.5% NaCl environment. This accelerated corrosion test concludes that the parent metal AISI 904L experienced better corrosion resistance than the fusion zones. The investigation also deals with biocorrosion studies of the dissimilar welds of super-austenitic and super-duplex stainless steels. Microbial consortium comprising of six bacterial isolates of which four were Pseudomonas strains P. aeruginosa strain MB1, P. aeruginosa strain MB2, P. fluorescens and P. flavescens, two belonged to Bacillus strains, B. subtilis and B. cereus, for the first time. The bacterial isolates were inoculated in the medium with the presence of the metal coupons. The results were obtained after 15 and 30days interval and compared with the control to determine the rate of biocorrosion which confirms that there is an accelerated deterioration of the metal coupons by the microbial strains.