Effect of Ferrite Content in HAZ of Welded Duplex Stainless Steels on the Environmental Assisted Cracking and Corrosion Resistance

Abstract This paper examines how ferrite content in welds influences the in-service properties of a 22%Cr duplex stainless steel grade. Using a Dynamic Thermal-Mechanical (DTM) machine, laboratory experiments replicated Heat-Affected Zone (HAZ) microstructures with varying ferrite contents, which were subsequently tested to evaluate their in-service performance. The findings were validated through tests conducted on actual welds. The study considered various forms of corrosion, including pitting, chloride stress cracking at 100°C, sulfide stress cracking at 25 and 90°C, environmentally assisted cracking in an alkaline environment simulating refinery conditions, and hydrogen induced stress cracking (HISC). In most of the laboratory heat treatments of reals welds, achieving the upper ferrite limit of 65% was challenging with the selected “one-pass welding process”. However, the results indicate that the primary property impacted by the increased ferrite content is the resistance to H2S-assisted cracking, with significant effects observed at ferrite levels exceeding 70%.