The activation energy of the static fatigue (creep of steel)

In an earlier paper[1] the relation sigma(B)=sigma(infinity)+const. t(B)(-1/4) has been deduced for the time dependence of the strength decrease under a static load. In the formula sigma(infinity) means the fatigue limit and sigma(B) is the stress causing a fracture after the loading period t(B). By application of this formula the activation energy of the static fatigue of glass and of the creep of steel is calculated from experimental data at different temperatures. The activation energy determined for steel corresponds to activation energy for the diffusion of sulfur in iron but corresponds also to the half of the sublimation enthalpy for iron. Therefore, the rate limiting step of the creep of steel at elevated temperatures may be a diffusion of interstitial atoms as well as a quasi-sublimation. A theoretical model is given for the defect growth due to a quasi-sublimation.