황산 수용액 내 듀플렉스 스테인리스강 (UNS S32205)의 부식거동에 미치는 용접프로세스 및 필거압연 공정의 영향
Corrosion Behavior of Duplex Stainless Steel (UNS S32205) in Sulfuric Acid Solutions: Effects of Welding Process and Pilgering
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This study investigated the corrosion behavior of duplex stainless steel (S32205) fabricated using plasma arc welding (PAW) and laser beam welding (LBW), followed by post-weld heat treatment (PWHT) and pilgering processes. We evaluated the impact of sulfuric acid concentrations (5% and 50%) on corrosion resistance using potentiodynamic polarization, immersion tests, and critical pitting temperature (CPT) measurements. Microstruc- tural analysis showed that LBW produced narrower, deeper welds with finer grains and significantly lower oxide inclusion fractions compared to PAW. In 50% sulfuric acid, LBW demonstrated lower passive current densities and more stable passivation, attributed to its reduced inclusion content and suppression of local anodic dissolution. PWHT restored the δ/γ phase balance to approximately 50:50, enhancing corrosion resistance, while pilgering introduced high residual stress and caused a γ→ε transformation, resulting in decreased CPT and increased local- ized attack. Weight loss in 5% sulfuric acid was negligible across all conditions, whereas in 50% acid, it increased significantly for pilgered samples. These findings suggest that LBW, particularly with optimized PWHT, provides superior corrosion performance and strong potential for applications in heat recovery steam generator (HRSG) components of combined-cycle power plants.
Abstract
This study investigated the corrosion behavior of duplex stainless steel (S32205) fabricated using plasma arc welding (PAW) and laser beam welding (LBW), followed by post-weld heat treatment (PWHT) and pilgering processes. We evaluated the impact of sulfuric acid concentrations (5% and 50%) on corrosion resistance using potentiodynamic polarization, immersion tests, and critical pitting temperature (CPT) measurements. Microstruc- tural analysis showed that LBW produced narrower, deeper welds with finer grains and significantly lower oxide inclusion fractions compared to PAW. In 50% sulfuric acid, LBW demonstrated lower passive current densities and more stable passivation, attributed to its reduced inclusion content and suppression of local anodic dissolution. PWHT restored the δ/γ phase balance to approximately 50:50, enhancing corrosion resistance, while pilgering introduced high residual stress and caused a γ→ε transformation, resulting in decreased CPT and increased local- ized attack. Weight loss in 5% sulfuric acid was negligible across all conditions, whereas in 50% acid, it increased significantly for pilgered samples. These findings suggest that LBW, particularly with optimized PWHT, provides superior corrosion performance and strong potential for applications in heat recovery steam generator (HRSG) components of combined-cycle power plants.