Abstract The long-term embrittlement effects of tritium and decay helium on the structural properties of stainless steels have been studied for years at Savannah River National Laboratory (Savannah River) to provide required data for establishing safe operating conditions and the lifetimes of the pressure vessels used to contain tritium gas. In this study, the fracture toughness properties of the longest-aged tritium-precharged stainless steel base metals and weldments tested at Savannah River were measured and compared to earlier results. The fracture toughness values were the lowest recorded here for tritium-exposed stainless steel. As-forged and as-welded specimens were thermally precharged with tritium gas at 34.5 MPa and 623 K, then aged for up to 17 years to build in decay helium prior to testing. American Society for Testing and Materials J-integral fracture mechanics analyses, transmission electron microscopy (TEM), and small-angle neutron scattering (SANS) examinations were conducted to characterize the effects of tritium and its radioactive decay product 3He. Results show that the fracture toughness values were reduced to less than 2% to 4% of the as-forged values for specimens with more than 1300 atomic parts per million helium from tritium decay. The trend of decreasing fracture toughness values with increasing helium content was consistent with earlier observations, and the data show that Type 304L stainless steel is more resistant to tritium-induced cracking than Type 21-6-9 stainless steel at similar decay helium levels. The fracture toughness properties of long-aged weldments were also affected, but the reductions were not as severe over time because the weldments did not retain as much tritium as did the base metals. TEM observations were used to characterize the effects of decay helium bubbles on the deformation substructures, but nanometer-sized helium bubbles were not easily resolved because of high dislocation densities within the forged microstructures. SANS results are presented that suggest the technique can provide information on decay helium bubble size, spacing, and distribution in these steels.

中文翻译：

---

氚时效对不锈钢焊件断裂韧性的影响

摘要 萨凡纳河国家实验室 (Savannah River) 多年来一直在研究氚和衰变氦对不锈钢结构性能的长期脆化效应，为建立安全操作条件和使用的压力容器的寿命提供所需的数据。含有氚气。在这项研究中，测量了在萨凡纳河测试的老化时间最长的氚预充不锈钢母材和焊件的断裂韧性特性，并与早期结果进行了比较。此处记录的氚暴露不锈钢的断裂韧性值是最低的。锻造和焊接后的样品在 34.5 MPa 和 623 K 下用氚气进行热预充，然后在测试前老化长达 17 年以建立衰变氦气。美国材料与试验协会进行了 J 积分断裂力学分析、透射电子显微镜 (TEM) 和小角度中子散射 (SANS) 检查，以表征氚及其放射性衰变产物 3He 的影响。结果表明，对于来自氚衰变的氦原子数超过百万分之 1300 的试样，断裂韧性值降低到锻造值的 2% 到 4% 以下。随着氦含量增加，断裂韧性值降低的趋势与之前的观察结果一致，数据表明，在类似的衰变氦水平下，304L 型不锈钢比 21-6-9 型不锈钢更能抵抗氚引起的开裂。长时效焊件的断裂韧性性能也受到影响，但随着时间的推移，减少并不严重，因为焊件保留的氚不如母材多。TEM 观察被用来表征衰变氦气泡对变形亚结构的影响，但由于锻造微结构内的高位错密度，纳米氦气泡不容易分辨。SANS 结果表明该技术可以提供有关这些钢中衰变氦气泡大小、间距和分布的信息。