Composite microstructure of cold-drawn pearlitic steel and its role in stress corrosion behavior

This paper analyzes the microstructural evolution in a high-strength pearli tic steel subjected to progressive cold drawing in the course of manufactur ing to produce prestressing steel wires. It is seen that the material under study possesses a composite microstructure in the form of plated patterns, which evolve toward a markedly oriented arrangement. This occurs at the tw o basic microstructural levels (the pearlite colonies and the pearlitic lam ellae), which become aligned quasi-parallel to the wire axis or cold drawin g direction, thus inducing anisotropic stress corrosion behavior of the ste els. This paper offers a composites engineering approach to the modeling of this phenomenon. The approach is based on the fundamental idea of material s science: linking the microstructure of the steels (progressively oriented as a consequence of the manufacture process by cumulative cold drawing) wi th their macroscopic stress corrosion behavior (increasingly anisotropic as the degree of cold drawing increases). The special case of the most heavil y drawn steel (strongly anisotropic) is analyzed for conditions of hydrogen -assisted cracking (HAC) and localized anodic dissolution (LAD), In both si tuations, the material behaves as a fiber-reinforced composite (or as a lam inate) at the microstructural level.