DUCTILE-BRITTLE TRANSITION TEMPERATURE SHIFT CONTROLLED BY GRAIN BOUNDARY DECOHESION AND THERMALLY ACTIVATED ENERGY AND HYDROGEN GB EMBRITTLEMENT

摘要

Classical structural problems of temper embrittlement are evaluated in terms of changes in the ductile-brittle transition temperature (DBTT). Experimentally, DBTT is not only strongly dependent on the effects of the type and amount of segregated solute X_(gb)~s at grain boundary (GB) but also on the hardness of the steel and strain rate. Recent first-principles calculations provide the decohesion of the GB based on the concentration of different elements on the GB. The decohesion, 2γ_(int), is difference between the energy of the fracture surfaces and the energy of the GB (2γ_(int) = 2γ_(fs) - γ_(gb)) The calculations show that the decohesion is linearly related to the concentration of metalloids on the GB. The calculations show that the embrittling potency (?e_p) of the different metalloids, Sb, Sn, and P, are ranked as follows: ?e_p~(Sb) > ?e_p~(Sn) > ?e_p~p.