Abstract
This paper describes an X-ray study of low-cycle fatigue damage of SUS 304 stainless steel at 873K under a total strain range controlled condition. The micro Laue method of back reflection was used as an X-ray diffraction technique and the damages at two parts of the specimen were measured by intermitting the low-cycle fatigue tests. One was the notched or cracked part and the other was the non-cracked part. From these tests, the following conclusions were obtained.
(1) Misorientation at the non-cracked zone increased monotonously with an increase in number of cycles and it correlated well with the cumulative plastic strain range of the material. Dislocation and imperfection densities, calculated from misorientation, increased rapidly in the initial stage of low-cycle fatigue, and after becoming almost constant in the middle stage, they increased rapidly again in the final stage of low-cycle fatigue, which agrees well with the observation by TEM.
(2) Misorientation at the crack tip correlated well with COD and the crack propagation rate, but the correlation between misorientation and cyclic J-integral was not so good.
