Dislocation structures, effective and internal stresses of cyclic strained ferritic stainless steel

The hysteresis loops of ferritic X10CrA124 were digitally recorded and analysed in order to separate the effective and internal. By means of the "Generalised statistical theory of the hysteresis loop" the average characteristics such as the effective elastic modulus Eeff, the saturated effective stress [sigma es] and the probability density function f(sic) in relation to the number of cycles and [epsilon ap] were determined. The cyclic plastic response of ferritic steel can be accurately described by this statistical theory (high [sigma es] = 255 MPa). As for the ferritic steel, the secon local maximum of f([sigma ic]) was revealed. This phenomenon was discussed together with an observed dislocation arrangement by TEM methods, the orientation of crystals was determined by Kikuchi lines. The dislocation structures were studied in cyclical deformed polycrystalline ferritic stainless steel X10CrA124 using transmission electron microscope (TEM). Specimens were strained in plastic strain amplitude [epsilon ap] controlled tests (symmetric tension-compression) at room temperature to failure. Thin foils were prepared from specimens cycled with plastic strain amplitudes = 1x10-5, 2x10-5, 1x10-4, 5x10-4, 1x10-3, 3x10-3, 1x10-2. In dependence on [epsilon ap] three basic dislocation structures were identified. Nevertheless space dislocation arrangements at low [epsilon ap] change into bunch dislocation loops, veins, walls (labyrinths) and cell dislocation arrangements prevail at high.