Cold cracking of structural steel weldments as reversible hydrogen embrittlement effect

The problem of hydrogen induced cold cracking (HICC) during welding is discussed in this paper. This form of cracking is seen as the special case of the reversible hydrogen embrittlement (HE) effect. The main hypotheses for the HE are briefly analyzed. It is shown that the difficulties in understanding of HICC are caused by the uncertainty of the physical factors of hydrogen action and by the absence of a clear knowledge of metal fracture micromechanisms. The new model of HE is described. It is suggested that the microcrack occurs in dislocation cluster by a microcleavage mechanism during deformation and propagates at the initial period analogous to the Griffith’s classic scheme. The hydrogen, transported by moving dislocations, is adsorbed by new crack surfaces in the form of negatively charged atoms and lowers the surface energy promoting crack propagation. Some experimental evidence of this model is presented.