Ductile crack growth resistance in hydrogen-charged steels

Abstract

The effect of hydrogen on the shear localization and associated crack nucleation has been investigated by means of a three point bending test of hydrogen-charged steels. The ductile crack growth resistance in terms of the slope of R-curve was lowered under the presence of hydrogen, the decrease being more pronounced in the steel with more abundant slip constraint phases along grain boundaries. Enlargement of size and reduction in depth/width ratio of primary dimples, occasionally associated with quasi-cleavage, were observed on the fracture surface of the hydrogen-charged steels. By means of a FEM calculation, the increase of the nucleation void volume fraction localized at the crack tip with strain localization as well was shown to take place in the hydrogen-charged steel in consistent with enhanced shear instablity. It was discussed that the evolution of vacancy-type defects, rather than void nucleation at second phase particles, in the course of plastic straining was enhanced under the presence of hydrogen, reducing the ductile crack growth resistance.