Precipitation Behavior of Long Term Creep-Rupture in Low Carbon-Medium Nitrogen Type 16Cr-8Ni-2Mo Weld Metal
Hiromichi HONGO, Masayoshi YAMAZAKI, Takashi WATANABE, Tatsuhiko TANABE and Yoshio MONMA
Abstract:In the past the microstructural observation was mostly applied to understand the materials behavior qualitatively in the R&D of new materials and life prediction for the fast breeder reactor components. However, the correlation between the changes in properties and microstructures must be clarified quantitatively to ensure the structural integrity. Particularly we are interested in the method to correlate the long-term properties with microstructural changes at high temperatures. The current research is to quantify the changes in microstructure of the weld metal for the welded structure of the reactor vessel. In this research we have conducted creep testing of a 16Cr-8Ni-2Mo weld metals at 823, 873 and 923K up to 76,320h. Based on the change in area fraction of the precipitates, the evaluation of creep-rupture properties with time and temperature was attempted. Correlation between ferrite content and the area fraction of the precipitates was not recognized. It was possible to correlate linearly the amount of the precipitates to log(creep exposure time) with the Larson-Miller parameter. Key Words:Creep rupture properties, Weld metal, 316FR, Stainless steel, Precipitation