Sigma Phase Effect on Pitting Corrosion of Super Duplex Stainless Steel UNS S32750

Abstract

The welding process on Super Duplex Stainless Steel material can cause decreased corrosion resistance of Super Duplex Stainless Steel material. This process occurs a lot in the heat treatment process piping and pipeline. This decrease in corrosion resistance occurs due to the formation of sigma phase precipitation due to heat treatment of the metal. This research will determine the relationship between the ratio of heat input cold pass: the ratio of heat input root pass to the percentage of sigma phase and the relationship between the percentage of sigma phase to the weight loss value. accompanied by the formation of pitting corrosion on UNS S32750 Super Duplex Steel. Test Coupon (TC) specimens obtained from as-welded with the ratio of heat input cold pass : ratio of heat input root pass (TC-1=74%; TC-2=70%; TC-3=68%; TC-4=61 %) which was then tested for microstructure. The percentage of sigma phase obtained is TC-1 = 13.96%, TC-2 = 8.33%, TC-3 = 8.33%, and TC-4 = 4.38%). The corrosion resistance test yielded weight loss values (TC-1 = 14.67 gr/m2, TC-2 = 11.71 gr/m2, TC-3 = 1.27 gr/m2, and TC-4 = 2.71 gr/m2). This study concludes that the formation of the sigma phase will be directly proportional to the value of the root pass heat input ratio: the cold pass heat input ratio. The higher the percentage of sigma phase, the higher the weight loss value in the corrosion test, which will cause pitting corrosion.