Dislocation Structure Changes in Ferritic-Pearlitic Steels Caused by Low-Cycle Fatigue at Elevated Temperature

Synopsis

During low-cycle fatigue tests of ferritic-pearlitic steels a considerable reduction of their cyclic plastic properties was observed, at elevated temperature. An attempt of an explanation of the observed occurrence was made in two ways: the physical as well as metallurgical ones. Effect of strain rate and temperature on the value of saturation stress was investigated. The hypothesis was made that during low-cycle fatigue at elevated temperature a development of dislocation structures takes place in the examined steels. The new developed dislocation structures have an essential effect on locking the active slip systems and, in conseguence, it causes a reduction of cyclic plastic properties of steel, at elevated temperature. This hypothesis was examined by testing the dislocation structures in the direct proximity of the lateral surface of samples, Influence of the elevated temperature on the development of dislocation structures was observed/ particularly, on the chord size of dislocation cells and dislocation density in the cell walls.