Failures due to hydrogen embrittlement

The effect of hydrogen in metals and alloys are discussed. The various trapping and cracking processes by which hydrogen affects the behaviour of materials are summarized. Hydrogen may be introduced during melting and entrapped during solidification or it may be picked up during heat treatment, electroplating, acid pickling ,or welding. Hydrogen also can be introduced by cathodic reaction during corrosion. Embrittlement mechanisms have been described by highlighting the models such as: (i) planar pressure, (ii) cohesive energy, (iii) surface energy, (iv) dislocation, (v) hydride formation and (vi) methanation. Unlike most embrittlement phenomena, hydrogen embrittlement is enhanced by slow strain rates. The strain rate sensitivity, temperature dependence and susceptibility to delayed fracture are main characteristics of hydro¬gen embrittlment. Two case studies of failure analysis of high C steel wire products are presented. The tools and techniques for such analysis have been pointed out. It has been shown that planar pressure model and cohesive energy model can explain well the failures observed in those two cases.