On the prediction of long term creep strength of creep resistant steels

Abstract

Abstract When the conventional power law creep equation is applied to rationalise the creep data of creep resistant steels, its parameters depend strongly on stress and temperature and hence cannot be used to predict long term creep properties. Here, it is shown that this problem can be resolved if it is modified to satisfy two boundary conditions, i. e. when σ (stress) = 0, ε ˙ min ${\dot \varepsilon _{{\rm{min}}}}$ (minimum creep rate) = 0, and when σ = σTS (tensile stress at creep temperature T), ε ˙ min ${\dot \varepsilon _{{\rm{min}}}}$ = ∞. This can be achieved by substituting the reference stress σ0 in the conventional equation by the term (σTS – σ). The new power law creep equation describing the stress and temperature dependence of minimum creep rate can then be applied to predict long term creep strength from data of short term measurements. This is demonstrated using the creep and tensile strength data measured for 11Cr-2W-0.4Mo-1Cu-Nb-V steel (tube).