Influence of temperature and carbon content on the cyclic deformation and fatigue behaviour of alpha -iron. I. Cyclic deformation and stress behaviour

The cyclic deformation and stress-strain behavior of pure alpha -iron polycrystals has been investigated in tests with small to intermediate plastic strain ranges Delta epsilon sub pl in the temperature range from 220-537K. An analysis of the maximum stress amplitudes yields a high effective stress component sigma exp * at low temperatures and a maximum of the hardening at the transition temperature of approx340K. In cyclic deformation with small Delta epsilon sub pl inverse cyclic stress-strain behavior (i.e., increasing stress amplitude with decreasing Delta epsilon sub pl ) is observed and can be explained by an increase of sigma exp * with decreasing Delta epsilon sub pl caused by a decrease of the fraction of plastically deforming grains. Different effects of small carbon contents up to 74 wt. ppm on the cyclic deformation behavior and on the corresponding microstructures were noted and characterized in tests at intermediate Delta epsilon sub pl in dependence on temperature.