Hydrogen embrittlement failure of hot dip galvanised high tensile wires

Abstract

A case of failure of high carbon eutectoid steel wires is investigated. During the production stage, i.e. cold drawing and subsequent coiling/stranding operations, the wires of 4.0 mm diameter failed by central splitting along longitudinal planes. Microscopic examination, fractography and mechanical tests along with acoustic emission monitoring were carried out on the wire samples. The experimental results confirm that the failure is related to hydrogen embrittlement which has been characterised by fractography, strain rate sensitivity and susceptibility to delayed fracture as indicated by acoustic activity. It has been argued that the cohesive energy model for hydrogen embrittlement, where hydrogen reduces the bond strength and cohesive strength ahead of pre-existing cracks, can explain the failures observed in the present case. It appears that improper pickling and subsequent baking processes, during the final stages of drawing operations, are responsible for the hydrogen related failures.