Toshio Sakon

Exploratory research on creep and fatigue properties of 9Cr-steels for the steam generator of an FBR

Abstract Research on the applicability of 9Cr-steels to the steam generator of the demonstration fast breeder reactor was performed by the Subcommittee of the Japan Welding Engineering Society as a four-year program from 1985. In this program, exploratory tests, which included tensile, creep rupture and low-cycle fatigue tests, were conducted on three kinds of 9Cr-steels (Mod.9Cr-1Mo, 9Cr-1Mo-V-Nb, and 9Cr-2Mo) and their weldments. This paper describes the summary of results obtained in this program. Among the tested 9Cr-steels, Mod.9Cr-1Mo steel shows the best creep rupture strength and its weldment indicates almost the same level of creep rupture strength and the base metal at 500 and 550°C. The low-cycle fatigue properties of Mod.9Cr-1Mo steel is also discussed from its relation to the tensile properties.

Study on Fracture Mechanism and a Life Estimation Method for Low Cycle Creep-Fatigue Fracture of Type 316 Stainless Steels

In order to improve the accuracy of creep-fatigue life estimation method, experimental investigations were conducted focusing to the ductility exhaustion rule. At first, it was found by the tensile test for type 316 stainless steels that the ductility decreased and fracture mode changed with the decrease of strain rate. The tensile test was also performed using the creep-fatigue interruption test specimen and it was found that there was a good correlation between the decrease of residual ductility and the creep damage. From these points of view, the authors proposed the improved life estimation method based on the ductility exhaustion concept and confirmed its effectiveness.

Notch Effect on Low Cycle Fatigue in Creep-Fatigue at High Temperatures: Experiment and Finite Element Method Analysis

This paper describes the notch effect on low cycle fatigue in creep-fatigue conditions by experiments and finite element method (FEM) analysis. FEM analyses for cyclic and monotonic loadings were made, and the analytical results were compared with the measured strain at the notch root using a high temperature strain gage. The calculated strain by FEM agreed well with the measured strain if we used the proper FEM model and proper constitutive equation. In order to examine the accuracy of life prediction by FEM analysis, low cycle fatigue tests were also carried out using SUS 304 stainless steel for notched plate and notched round bar specimens. Life prediction by FEM analysis had sufficient accuracy; the applicability of other conventional life prediction methods was also discussed.