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 sym metric continuous, unsymmetric continuous and strain hold cycles. By c omparison of the results with the test data obtained in vacuum, it was found that the life reduction which occurred for a slow tension - fas t compression strain wave and the tensile strain holding wave was smal ler in air than in vacuum, and that the symmetric continuous cycle gav e the largest life reduction from the data obtained in vacuum. Followi ng the creep-fatigue tests, failure surfaces were investigated by SEM. When time/rate-dependent life reduction occurred, the fracture mode i n vacuum was intergranular, but in air, striations were observed and i ntergranular fracture was rarely observed.