Changing of microstructure and impact toughness of welded metal of Super 304H steel aged at（600 ℃-700 ℃）×500 h was investigated using optical microscopy,scanning electron microscopy,energy dispersive spectroscopy,X-ray diffractometer and impact test.Results show that microstructure of the welded metal comprises γ phase and precipitates.In the as-received welded metal,precipitates mainly consists of Nb（C,N） and copper-rich phase and after aging treatment M23C6 presents as well.With the increase of aging temperature,amount of precipitates increases accordingly while amount of Nb（C,N） shows a slow increasing trend.The amount of M23C6 increases rapidly at the initial stage and becomes stable later.After aging treatment,impact energy of the welded metal decreases obviously.Occurrence of aging brittleness is attributed to the precipitation of M23C6 along grain boundaries and it is found that the amount of precipitates is a determinate factor.%采用光学显微镜、扫描电子显微镜、能谱仪、X射线衍射分析等方法并通过冲击试验,研究了时效温度600~700℃,500 h时效条件下Super 304H钢焊缝金属的组织和冲击韧性变化.结果表明,焊缝金属组织均为γ＋析出相,焊态焊缝组织中主要析出相种类为Nb（C,N）和富铜相,时效组织中析出相种类又新增加了M23C6;随时效温度升高,析出相数量不断增加,但Nb（C,N）的数量呈缓慢增加趋势,而M23C6的数量先快速析出后处于稳定;时效后焊缝金属的冲击功出现了显著降低,造成时效脆化的主要原因是时效过程中M23C6
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