Influence of Specimen Geometry on Creep Strength of Long-Term Used Mod.9Cr-1Mo Steel Welded Joint

Abstract

In creep damage assessment of a welded joint by a finite element analysis, it is important to characterize creep strength property of constituent materials (base metal, heat affected zone(HAZ), weld metal) in the welded joint. In order to clarify the creep strength property of a long-term used Mod.9Cr-1Mo steel welded joint, miniature specimens with 1mm diameter and 5mm parallel length were machined from the constituent materials, and creep tests of these miniature specimens were performed in inert gas atmosphere. Creep strength of the base metal and the HAZ were similar to those of the new welded joint previously reported, while the creep strength of the weld metal remarkably decreased compared to that of the new weld metal. In addition to these tests, creep tests were conducted using miniature and standard size welded joint specimens. Creep rupture time of the miniature specimens was much shorter than that of the standard size specimens. From the results of finite element creep analyses, it was indicated that creep strain at the HAZ of the miniature specimen accumulated faster than that of the standard size specimen due to lower triaxiality factor. It was demonstrated that rupture time of a standard size welded joint specimen is predicted from a miniature welded joint specimen by applying the previously proposed method for new welded joints.