Effect of Dissolved Oxygen Content on Environment Assisted Fatigue Life of 316LN Stainless Steel of Domestic Forged Main Pipes

The fatigue tests of 316LN stainless steel used for domestic forged main pipes was carried out in simulated high temperature and high pressure water environment of nuclear power plant primary circuit. The effects of strain rate and dissolved oxygen (DO) content on the environmental assisted fatigue (EAF) life of stainless steel were analyzed. The results showed that under different DO contents, the EAF fracture of the samples showed typical multi-crack source fatigue cracking characteristics, and the fatigue striation was obvious. The corrosion products covered on the fracture were mainly spinel oxides riched in Fe, Cr and Ni. With the increase of DO content, the number and size of oxide particles increased. The deviation of EAF life under different DO contents was less than 30%, and there was no significant statistical difference. Combined with different statistical models, it could be seen that the effect of DO content on EAF life of 316LN stainless steel was obvious only at low strain rate (0.1×10^-4-0.1×10^-3 s^-1). When establishing a more accurate statistical model, it was necessary to subdivide the strain rate range and consider the influence of DO content.