Effect of Sigma Phase Precipitation on Mechanical Behavior and Pitting Corrosion of Duplex Stainless Steel

Abstract

The main purpose of this work is to investigate the pitting corrosion behavior of sigmatized duplex stainless steel (DSS) exposed to two different chloride environments: simulated seawater solution and produced water solution. Specimens taken from a commercial DSS (UNS 31803) have been subjected to aging treatments at 850°C for different holding times to achieve different amounts of sigma phase. Metallographic examinations combined with X-ray diffraction technique were employed to follow the microstructure evolution. The pitting potential of the aged samples were determined in simulated seawater solution and produced water solution. It was established that solution treated DSS shows a high pitting corrosion resistance in both test solutions, while serious deterioration of corrosion properties occurs in presence of sigma phase. It was concluded that both sigma phase amount and chloride concentration worsen the pitting potential, the higher sigma content, the lower pitting potential and the higher chloride concentration, the lower pitting potential. SEM observation showed that pitting nucleation occurs preferentially at sigma phase interfaces due to the development of Cr- and Mo-depleted regions around sigma phase. It was also confirmed that the hardness behavior is only affected for long term aged samples.

Incidence of Heat Treatment on the Corrosive Behavior of Aisi 316l Austenitic Stainless Steel

“…Once sigma phase is formed, it is difficult to restore the optimal microstructure [17]. The detrimental effect of sigma phase on corrosion resistance is usually attributed to DOI: 10.36547/ams.29.3.1803 the formation of chromium-molybdenum-depleted regions adjacent to this phase [18]. While the study of corrosion phenomena in stainless steels is still ongoing due to the wide range of steel grades available, current publications primarily focus on the degradation of mechanical properties caused by corrosion.…”