Structure of the plastic zone at the crack tip and the endurance of steel during low-cycle loading

Abstract

From microhardness, metallographic, and also layered and sight x-ray analyses, the mechanisms controlling changes in the phase composition, structure, and size of the plastic zone at the crack tip during low-cycle loading of steels 12Kh18N10T and Kh11N10M2T have been established. These steels had various initial structures due to directional changes in their strength and ductility. It was shown that with increase in the maximum uniform elongation, there is an increase in the amount of intense structural changes in the plastic zone, an increase in the number of load cycles to failure, and a decrease in the rate of stable crack growth. These mechanical effects can be explained by the positive influence of the martensitic transformation and of dislocation mobility on the energy intensity of failure activation in the plastic zone. In particular, dislocation mobility leads to a partial relaxation of microdistortion in the crystallographic lattice of the matrix phase.