Ductile crack growth resistance in hydrogen-charged steels

The effect of hydrogen on the shear localization and associated crack nucle ation has been investigated by means of a three point bending test of hydro gen-charged steels. The ductile crack growth resistance in terms of the slo pe of R-curve was lowered under the presence of hydrogen, the decrease bein g more pronounced in the steel with more abundant slip constraint phases al ong grain boundaries. Enlargement of size and reduction in depth/width rati o of primary dimples, occasionally associated with quasi-cleavage, were obs erved on the fracture surface of the hydrogen-charged steels. By means of a FEM calculation, the increase of the nucleation void volume fraction local ized at the crack tip with strain localization as well was shown to take pl ace in the hydrogen-charged steel in consistent with enhanced shear instabl ity. It was discussed that the evolution of vacancy-type defects, rather th an void nucleation at second phase particles. in the course of plastic stra ining was enhanced under the presence of hydrogen, reducing the ductile cra ck growth resistance.