MODEL CALCULATION OF THE NELSON CURVES FOR HYDROGEN ATTACK.

A void growth model has been applied to hydrogen attack of plain carbon structural steels, and to calculation of the Nelson curves. The driving force for void growth is the methane pressure, which is not assumed to be constant, arising from the interaction between carbon and hydrogen at void surfaces. Grain boundary diffusion and creep are considered as growth processes, and void-void interactions are treated in an appropriate way. Incorporation of a failure criterion allowed a model calculation of the Nelson curves for incipient hydrogen attack. The curves were quite sensitive to the void density, but not the initial void size. With reasonable values selected for the model parameters, a semi-quantitative agreement with experimental Nelson curves was established.