Effect of hydrogenation and plastic predeformation of steel on its crack resistance

Abstract

We study the joint effect of hydrogenation and plastic predeformation of 40KhN steel of drill strings after heat treatment on its crack resistance under static and cyclic loads. In the nonhydrogenated state, plastic predeformation of steel only slightly decreases its short-term crack resistance and, owing to crack closure, significantly increases the crack-growth resistance in the near-threshold region. Hydrogenation of the material sharply decreases the short-term crack resistance of steel and intensifies the growth of fatigue cracks, especially in the middle-amplitude region of low-frequency loading. The joint action of plastic predeformation and hydrogenation results in a maximal decrease in the static and cyclic crack resistance of the steel under investigation. We also analyze possible consequences of such an effect from the viewpoint of the structural strength of a drill string.