A criterion of failure of steels susceptible to propagation of brittle microcracks along crystal boundaries

Abstract

1. A structural criterion of the ductile-brittle transition of structural steels for the case of weakening of the cohesion strength of the crystal (grain) boundaries was proposed. The criterion takes into account the variation of the length of free passage of the brittle microcrack and effective surface energy of failure during the appearance of intercrystalline failure on the brittle fracture surfaces. 2. The variation of the true fracture stress during propagation of the brittle crack both through the body and along the boundaries of the crystals is closely linked with the fraction of intercrystalline failure. 3. For steels with weakened crystal boundaries we proposed a structural criterion of crack resistance K1c in the region of the lower shalf of the values of this criterion which does not depend on the size of the crystals and is closely linked with the fraction of intercrystalline failure on the brittle fracture surfaces. 4. For the steels with weakened crystal boundaries, the results revealed the resistance of a close relationship between the cracking resistance characteristics K1c in the range of the lower shelf of the values of this parameter, critical brittleness temperature Tc, and true fracture stress σF.