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概要

The SCC susceptibility of the weld metal was evaluated from the maximum depth and number of cracks occurring during the CBB (Creviced Bent Beam) test in high temperature pressurized water using plate specimens cut from shielded metal arc weld metals. When the specimen received a heat treatment consisting of stress relief annealing (SR) for 72 ks at 893 K and subsequent ageing (LTA) for 720 ks at 673 K, however, the significant influences of the increases in C and Nb contents on the SCC susceptibility were observed; the susceptibility of weld metals with higher C contents (~0.07mass%) decreased with increas ing the Nb content up to ~2.6mass%, but a further increase in the Nb content enhanced the SCC susceptibility remarkably. The hardness increased remarkably with the Nb content, suggesting that the higher stress was applied to the specimen during the CBB test, as the Nb content was increased. Also, the weld metal that yield stress is high could be confirmed to high stress value at grain boundary by FEM analysis. This increase in the applied stress is a possible factor that contributes to the increase in the SCC susceptibility with the Nb content in the weld metal free from the grain boundary depletion of Cr.

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