针对超超临界机组 P92 钢管道焊缝在安装过程中经历反复回火的问题，系统探讨了回火次数对焊缝显微组织与力学性能的影响规律。 通过 OM、SEM、EBSD 和 TEM 等表征手段，重点分析了 P92 钢焊缝的晶粒形貌演变及析出相分布特征。 研究发现，P92 钢焊缝组织主要由回火马氏体、板条界 M23C6 碳化物和弥散 δ-Fe 相构成。 随着回火次数增加，M23C6 碳化物沿马氏体板条界显著聚集，并优先在 δ- 铁素体晶界处形核生长，最终形成连续碳化物网络。 分析结果表明，多次回火通过调控碳化物析出行为和位错亚结构重组，使焊缝显微硬度呈下降趋势，而冲击韧性则逐步提升。值得注意的是，经过 4 次回火处理后，部分亚晶粒转变为等轴晶，同时 M23C6 碳化物在晶界处发生粗化偏聚。 该现象不仅导致焊缝中大角度晶界数量急剧增加，还显著弱化了固溶强化效果，最终造成显微硬度出现快速下降。

To address the issue of repeated tempering during the installation of P92 steel welded joints in ultra-supercritical units, the influence of tempering cycles on the microstructure and mechanical properties of a weld was systematically investigated. The evolution of the grain morphology and the distribution of precipitates in the P92 steel welds were analysed via OM, SEM, EBSD, and TEM characterization techniques. The results reveal that the weld microstructure primarily consists of tempered martensite, M23C6 carbides along lath boundaries, and dispersed δ-Fe phases. With increasing tempering cycles, M23C6 carbides significantly aggregate along martensite lath boundaries and preferentially nucleate and grow at δ-ferrite grain boundaries, eventually forming a continuous carbide network. These findings indicate that multiple tempering treatments regulate carbide precipitation and dislocation substructure rearrangement, leading to a gradual decrease in the microhardness and an improvement in the impact toughness. Notably, after four tempering cycles, some subgrains transform into equiaxed grains, whereas the M23C6 carbides coarsen and segregate at the grain boundaries. This phenomenon not only induces a rapid increase in high-angle grain boundaries but also significantly weakens the solid solution strengthening effect, ultimately resulting in a sharp decline in the microhardness.