Effects of the weld microstructure and inclusions on brittle fracture initiation are investigated in a thermally aged ferritic high-nickel weld of a reactor pressure vessel head from a decommissioned nuclear power plant. As-welded and reheated regions mainly consist of acicular and polygonal ferrite, respectively. Fractographic examination of Charpy V-notch impact toughness specimens reveals large inclusions (0.5–2.5 µm) at the brittle fracture primary initiation sites. High impact energies were measured for the specimens in which brittle fracture was initiated from a small inclusion or an inclusion away from the V-notch. The density, geometry, and chemical composition of the primary initiation inclusions were investigated. A brittle fracture crack initiates as a microcrack either within the multiphase oxide inclusions or from the de-bonded interfaces between the uncracked inclusions and weld metal matrix. Primary fracture sites can be determined in all the specimens tested in the lower part of the transition curve at and below the 41-J reference impact toughness energy but not above the mentioned value because of the changes in the fracture mechanism and resulting changes in the fracture appearance.

在退役核电站的反应堆压力容器头的热时效铁素体高镍焊缝中，研究了焊缝微观结构和夹杂物对脆性断裂萌生的影响。焊接区和再加热区分别主要由针状和多边形铁素体组成。夏比V形缺口冲击韧性试样的分形检查​​显示，脆性断裂的主要起爆点处存在大量夹杂物（0.5–2.5 µm）。对于从小夹杂物或远离V形缺口的夹杂物引发脆性断裂的样品，测量了高冲击能量。研究了初始引发夹杂物的密度，几何形状和化学组成。脆性断裂裂纹在多相氧化物夹杂物内部或从未裂纹的夹杂物与焊接金属基体之间的脱粘界面开始，作为微裂纹而开始。由于断裂机理的改变以及由此引起的断裂变化，可以在过渡曲线下部的41-J参考冲击韧性能及以下确定所有测试的试样的原始断裂部位，但不能超过上述数值。外貌。