This article is about an analysis on the causes of unqualiifed low-temperature (-70℃) impact property of 09MnNiD steel for low-temperature pressure vehicle by optical microscope, scanning electron microscope and energy disperse spectroscopy. The analysis indicates that such defects as porosity and spot segregation are the main causes for the unqualiifed impact property of 09MnNiD steel at -70℃. The ifnal test has ascertained the measures to improve heat treatment.%利用光学显微镜、扫描电镜及能谱仪，对低温压力容器用钢的09MnNiD低温（-70℃）冲击性能不合格原因进行了分析。分析结果表明：疏松及点状偏析等缺陷是引起09MnNiD钢在-70℃的冲击性能不合格的主要原因。最后通过试验，确定了热处理工艺的改进措施。
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