Abstract
Strain-controlled fatigue tests using a flexural resonant vibration were performed on miniature specimens of the solution treated 316 stainless steel with the total strain amplitude εt≤12×10−4 at temperatures between 293 K and 573 K. From the investigations of in situ changes in the resonant period, P, and in the drive force, DF, applied to the specimens during the fatigue tests, the following results were obtained. (1) Overlapped on general changes in P and DF, small and step-like changes in P and DF were observed for εt larger than the fatigue limit and were considered to be associated with the proceeding of fatigue damages. (2) General changes of P at the middle stage during the fatigue tests were a slight increase (softening) at T=333 K but a strong decrease (hardening) at T=573 K. From the detailed study of the above mentioned phenomena, it was concluded that the fatigue test with εt above the fatigue limit induced an age hardening at T=573 K. The age hardening became to be revealed above T=473 K and increased in magnitude with increasing εt.
