Analysis of first order kinetics for tertiary creep in aisi 304 stainless steel

The results of constant load creep tests on AISI 304 stainless steel at 873 and 973 K for different test conditions were found to obey the first order kinetics for tertiary creep. Distinct master creep curves were obtained at 873 and 973 K with a separate set of constant values of K', epsilon(t), beta' and C-MG. A relationship between steady-state creep rate epsilon over dot(s) , time spent in tertiary creep t(t) and limiting tertiary creep strain epsilon(t) is formulated as epsilon over dot(s) . t(t)/epsilon(t) = constant and is found to be valid for all test conditions. Further, this relation is identical to the modified Monkman-Grant relation (MMGR) for the conditions satisfying f = 1/lambda; it is postulated that the validity of MMGR is a consequence of first order kinetics. Another important outcome of this study is a generalised relation of the form epsilon over dot(s) . t(r) = (epsilon(23).epsilon(f))(1/2); and this relation is compared with the relation proposed by Radhakrishnan, i.e. epsilon over dot(s) . t(r) = (epsilon(23)(2) .epsilon(f))(1/3). It is suggested that cavities act as vacancy sinks and accelerate dislocation climb controlled recovery process leading to tertiary creep. Copyright (C) 1996 Acta Metallurgica Inc