Creep of TiN-dispersion strengthened stainless steels

High-precision creep curves recorded for nitrided 20% Cr/25% Ni steels, with titanium contents varying from 0.24 to 3.0 wt%, have been analysed using a new approach to creep, termed the theta Projection Concept. This envisages normal creep curves as the sum of a decaying primary and an accelerating tertiary component described by the equation derived. The theta parameters in the equation and the creep ductility are shown to vary systematically with titanium content and, for a fixed Ti level of 1.66%, with applied stress. These relationships indicate that the theta Projection Concept allows both interpolation and extrapolation of creep data. Using this new procedure for creep data extrapolation, the present analysis suggests that the TiN-dispersion strengthened 20% Cr/25% Ni steels can exhibit long-term stress-rupture properties which are considerably superior to those for type 316 stainless steel and approaching those predicted for the cast, nickel-base superalloy, IN 100. (author)