Evaluation of Low-Cycle Fatigue, Creep and Creep-Fatigue Strengths for FBR Weldment

Abstract

To establish an evaluation method of elevated temperature strength for weldments, a series of investigations^1)-5) had been performed on the low-cycle fatigue strength. In this study, the suitable evaluation methods of creep and creep-fatigue strengths for weldments were proposed and were applied to the life prediction of FBR weldments.
The following results were obtained.
(1) In the evaluation of low-cycle fatigue strength for the weldments, the accuracy of life prediction by the Method (I), Method (II) and FEM was determined mainly by the difference in cyclic deformation resistance between the base metal and the weld metal. The Method (I), Method (II) and FEM were effective for the weldments which have small difference in cyclic deformation resistance such as stainless steel and 21/4 Cr-1 Mo steel with PWHT. But for the weldments which have large difference in cyclic deformation resistance such as the 21/4 Cr-1 Mo steel without PWHT, the Method (I) predicted the life overconservatively and FEM overestimated the life inversely.
(2) In the evaluation of creep strength for the weldments, the minimum creep strain rate of the 21/4 Cr-1 Mo steel weldment was predicted by the Independent Method which paid attention to only the weakest part of the weldment and also by the Interaction Method which considered the interaction between the base metal and the weld metal. Both of them were found to be effective for the 21/4 Cr-1 Mo steel weldments.
(3) In the evaluation of creep-fatigue strength for the weldments, a new method was proposed which was an extension of the fatigue evaluation method (I) based on the linear damage summation rule. It could predict the life of the 21/4 Cr-1 Mo steel weldments within a factor of two on life.