| Abstract: | Creep equations are necessary for the design and supervision of high temperature components. To obtain a sound basis for the development of such equations, the typical results of creep rupture tests have usually to be expanded by supplementary tests. At first a creep equation is developed for an extensively tested individual material. This equation then serves as prime solution for the corresponding steel type. The creep equation of the steel type is derived from condensed creep data which are the result of a scatter band analysis of multi-heat creep data. In the analysis, a large number of values of stress to specific strain are assessed on the basis of a time temperature parameter. The result is a family of correlated curves of stress to specific creep strain against time for all temperatures, stresses and strain values covered by the original test results. From these isostrain curves, mean creep curves are derived to form the basis for the modelling of the creep equation. For the development of this equation, a formulation is recommended which contains terms for initial plastic strain and primary, secondary and tertiary creep strain. The individual terms of this equation, which generally depend on stress and temperature, are determined in a stepwise procedure. The methods how such creep equations are developed and how their limits are fixed, are demonstrated for the examples of individual steels of type 14 MoV 6 3 and X 3 CrNiMoN 17 13 and of steel type 1 %. CrMoNiV according to SEW 555. |
