Corrosion fatigue crack growth behavior of duplex stainless steels with different nitrogen contents

The effect of nitrogen content on the environmentally-assisted cracking behavior of 22% Cr duplex stainless steel in chloride solutions was investigated. Slow strain rate tests and corrosion fatigue tests employing fracture mechanics specimens were conducted in chloride containing solution. The experimental results show that the strength of 22% Cr duplex stainless steel increases with increasing amount of nitrogen (in the range of 0.1 to 0.2 wt%) in the steel. Slow strain rate testing results indicate that 22% Cr duplex stainless steels with different nitrogen contents are resistant to environmentallyassisted cracking in 3.5 wt% NaCl solution at room temperature, but become susceptible in boiling 45 wt% MgCl₂ solution. The experimental results indicate that the fatigue crack growth rates of 22% Cr duplex stainless steels with different nitrogen contents are lower than that of 316L stainless steel in air at 1 Hz. But in the 3.5 wt% NaCl solution, the fatigue crack growth rates in 316L stainless steel and all duplex stainless steels are almost the same. The environmental effect is more prominent for duplex stainless steel than for 316L stainless steel. The results revealed that nitrogen in the range of 0.1 to 0.2 wt% does not affect the FCG rate of 22% Cr duplex stainless steel in air and in 3.5 wt% NaCl solution at 1 Hz.