The rupture behavior of the modified 10Cr–1Mo steel multi-layer welded joint is determined by the fine-grain zones of the weld metal adjacent to the fusion line during the long-term creep test at 620 °C. The microstructures of multi-layer weld metal before and after the creep tests were characterized in detail, and its role in creep behavior was systematically investigated. Most grain boundaries of subgrains represented the low-angle boundaries in the weld metal adjacent to the fusion line both before and after the creep test. The widths of grains in the fine-grain zones were about 0.5–1 μm. The fracture morphology appeared as “wave” structure due to the cracking initiating from multi-layer grain boundaries in the fine-grain zones. Some W elements that melted into weld metal adjacent to the fusion line altered the thermodynamic and kinetic conditions of the Laves phase formation during long-term creep exposure. Laves phase particles mainly distributed along the grain boundaries due to the faster diffusion and segregation of Mo, W, and Si elements. Moreover, higher-density grain boundaries in the fine-grain zones led to easier nucleation and growth of Laves phase particles. Compared with other areas in the welded joint, the size of Laves phase particles in the fine-grain zones of the weld metal adjacent to the fusion line was the largest ones. The interface between Laves phase particles and the matrix acted as the nucleation site of creep micro-cavities. The creep micro-cavities grew up at the expense of fine-grain boundaries and even grew across the grain boundary deeply into adjacent grains, and then developed to cracks in the fine-grain zones.

中文翻译：

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多层焊接金属的特性和改性10Cr-1Mo焊接接头的蠕变断裂行为

改进的10Cr-1Mo钢多层焊接接头的断裂行为由在620°C的长期蠕变试验期间与熔合线相邻的焊接金属的细晶粒区域确定。详细描述了蠕变试验前后多层焊接金属的微观结构，并系统地研究了其在蠕变行为中的作用。在蠕变测试之前和之后，大多数亚晶粒的晶界代表了与熔合线相邻的焊缝金属中的低角度边界。细粒区域的晶粒宽度约为0.5-1μm。裂纹的形态表现为“波”结构，这是由于细晶粒区域中的多层晶界引起的裂纹所致。在长期蠕变暴露过程中，一些熔化到熔合线附近的焊缝金属中熔化的W元素改变了Laves相形成的热力学和动力学条件。Laves相粒子主要由于Mo，W和Si元素的更快扩散和偏析而沿晶界分布。此外，细晶粒区域中较高密度的晶界导致Laves相颗粒更容易成核和生长。与焊接接头中的其他区域相比，熔合线附近的焊接金属细晶粒区域中的Laves相颗粒尺寸最大。Laves相颗粒与基质之间的界面充当蠕变微腔的成核位置。