Effect of air environment on creep-fatigue interaction of 316 FR stainless steel

Creep-fatigue tests were conducted using 316FR stainless steel at 650 degrees C in air under a variety of strain time programs including symmetric continuous, unsymmetric continuous and strain hold cycles. By comparison of the results with the test data obtained in vacuum, it was found that the life reduction which occurred for a slow tension - fast compression strain wave and the tensile strain holding wave was smaller in air than in vacuum, and that the symmetric continuous cycle gave the largest life reduction from the data obtained in vacuum. Following the creep-fatigue tests, failure surfaces were investigated by SEM. When time/rate-dependent life reduction occurred, the fracture mode in vacuum was intergranular, but in air, striations were observed and intergranular fracture was rarely observed.