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为了研究S31042试验用钢短时高温拉伸塑性波动大的原因，采用体视显微镜、金相显微镜、扫描电镜、透射电镜进行了断口形貌和微观组织观察分析，用X射线衍射分析了相应状态试样的萃取粉末。用Thermo-Calc热力学软件进行了相图计算。结果表明：大块簇状的含铌相颗粒分布在晶界和晶内时，固溶态S31042试验钢短时高温（700℃）拉伸塑性较低，伸长率仅28％，而且断裂试样的表面严重龟裂。当钢中的含铌相颗粒细小、独立分布时，短时高温（700℃）拉伸塑性较高，伸长率高达50％，断裂试样的表面没有龟裂。含铌相的形态是固溶态S31042钢塑性波动的原因。因此，改善含铌相颗粒的形态，有益于提高固溶态S31042钢的短时高温拉伸塑性。

In order to analyze the reasons which cause big fluctuation in elevated temperature ductility of S31042 steel, the fracture morphologies, surface and microstructure of specimens were observed by stereomicroscope, metallographic microscope, scanning electron microscope(SEM), transmission electron microscope. Extracts powder from specimens at corresponding condition were analyzed by X-ray diffraction. Phase diagram of S31042 steel were calculated using Thermo-Calc software. The results show that the big particle of NbCrN in cluster distributing on grain boundaries and in grains is the reason which leads to low short-term elevated temperature (at 700℃) tensile ductility (elongation only be 28%) of S31042 steel and serious surface checking. However, the specimen of S31042 steel with fine Nb-precipitation particles distributing dispersedly in grain have relatively high short-term elevated temperature (at 700℃) tensile ductility (elongation reaching 50%) and no surface checking on the surface of fracture specimens. The major reason which causes fluctuation in elevated temperature ductility of S31042 steel is morphologies of Nb-bearing phase. Therefore, improving the morphologies of niobium precipitation particles is beneficial to enhance the short-term elevated temperature tensile ductility for solution treatment S31042 steel.