采用国产核级E316L焊条对20 mm厚奥氏体不锈钢板进行多层多道填充焊接，之后对焊缝进行610℃×16 h热处理和400℃下不同时间（400，2 000，3 500 h）的加速热老化处理，研究了在热老化过程中焊态和热处理态焊缝中铁素体及析出相的演变。结果表明：焊态和热处理态焊缝的组织均由奥氏体、铁素体和析出相组成；随着热老化时间的延长，焊缝中铁素体的数量呈先增多后减少的趋势，铁素体形貌由断续网状变为较连续网状，再变为断续网状；焊态焊缝中铁素体的含量高于热处理态的；在热老化过程中，焊缝中的析出相主要为Cr₂₃C₆相和σ相，热处理态焊缝比焊态的更容易形成析出相；随着热老化时间的延长，Cr₂₃C₆相和σ相优先在晶界处析出并聚集，随后铁素体晶内也有Cr₂₃C₆和σ相的析出和聚集。

Multi-layer and multi-pass filling welding was carried out on austenitic stainless steel plates with thickness of 20 mm with domestic nuclear grade E316L electrode. Then the welds were heat treated at 610℃ for 16 h and accelerated thermal aged at 400℃ for different times (400,2 000,3 500 h), and the evolution of ferrite and precipitated phases in the as-welded and heat-treated weld during thermal aging was studied. The results show that the microstructure of as-welded weld and heat-treated weld both consisted of austenite, ferrite and precipitated phases. With the increase of thermal aging time, the amount of ferrite in the weld increased first and then decreased, and the morphology of ferrite changed from discontinuous mesh to relatively continuous mesh and then to discontinuous mesh. The content of ferrite in the as-welded weld was higher than that in the heat-treated weld. During thermal aging, the precipitated phases in the weld were mainly composed of Cr₂₃C₆ phase and σ phase, and the precipitated phases in heat-treated weld was formed more easily than those in the as-welded weld. With the prolongation of thermal aging time, Cr₂₃C₆ phase and σ phase preferentially precipitated and aggregated at the grain boundaries, and then in ferrite crystals.