Effect of nitrogen content on the environmentally-assisted cracking susceptibility of duplex stainless steels

The effect of nitrogen content on the stress corrosion cracking (SCC) behavior of 22 pct Cr duplex stainless steel (DSS) in chloride solutions was investigated in this study. Slow strain rate testing (SSRT) was employed to evaluate the SCC susceptibility. The experimental results showed that the tensile strength and ductility of 22 pct Cr DSS increased with increasing amount of nitrogen (in the range of 0.103 to 0.195 wt pct). Slow strain rate testing results indicated that 22 pct Cr DSSs were resistant to SCC in 3.5 wt pct NaCl solution at 80 °C. However, environmentally assisted cracking occurred in 40 wt pct CaCl₂ solution at 100 °C and in boiling 45 wt pct MgCl₂ solution at 155 °C, respectively. The effects of environment and nitrogen content in DSS on the cracking susceptibility are discussed in this article. Selective dissolution of ferrite phase was found to participate in the SCC process for tests in CaCl₂ solution. At temperatures above 80 °C, dynamic strain aging was found to occur in various environments at a strain beyond plastic deformation.