Environmental fatigue behaviors of CF8M stainless steel in 310 °C deoxygenated water - Effects of hydrogen and microstructure

Abstract

The effects of environment and microstructure on low cycle fatigue (LCF) behaviors of CF8M stainless steels containing 11% of ferrites were investigated in a 310 °C deoxygenated water environment. The reduction of LCF life of CF8M in a 310 °C deoxygenated water was smaller than 316LN stainless steels. Based on the microstructure and fatigue surface analyses, it was confirmed that the hydrogen induced cracking contributed to the reduction in LCF life for CF8M as well as for 316LN. However, many secondary cracks were found on the boundaries of ferrite phases in CF8M, which effectively reduced the stress concentration at the crack tip. Because of the reduced stress concentration, the accelerated fatigue crack growth by hydrogen induced cracking was less significant, which resulted in the smaller environmental effects for CF8M than 316LN in a 310 °C deoxygenated water.