Hydrogen assisted cracking paths in cold drawn pearlitic steels

Abstract

This paper analyses hydrogen assisted cracking (HAC) paths in cold drawn pearlitic steels in which progressive cold drawing produces a preferential orientation of the pearlitic microstructure in the matter of colonies and lamellae, thereby inducing strength anisotropy in the steel, and thus the resistance to HAC is a directional property that depends on the angle in relation to the drawing direction. Therefore, an initial transverse crack changes its propagation direction to approach that of the wire axis, thus producing mixed mode propagation, the deflection angle being an increasing function of the cold drawing degree. This experimental result may be explained by micro-mechanical considerations on the basis of the lamellar microstructure of the steels. A relationship is established between the microstructural angles and the deflection angles of the macroscopic HAC path, thus providing a materials science type relationship between the microstructure and the macroscopic crack.