Analysis of the hysteresis loop in stainless steels I. Austenitic and ferritic steels

In constant amplitude cyclic straining the hysteresis loops of an austenitic and a ferritic steel were recorded and their shape was analysed. The generalised statistical theory of the hysteresis loop based on the Masing hypothesis that considers the effective stress and the distribution of the critical internal stresses of the elementary volumes was employed. The second derivative of the hysteresis half-loop yields information on the effective stress and the probability density function of the critical internal stresses and its evolution in cyclic straining and in dependence on the strain amplitude. The changes of the effective modulus are also reported. The total cyclic stress can be separated into the effective and internal stress components. The high effective stress in ferritic steel is connected with the difficult motion of screw dislocations in the b.c.c. structure. The evolution of the probability density function of the austenitic and ferritic steels during cyclic straining is discussed in terms of changes of the internal dislocation arrangement.