本文叙述了一种液氦下使用的21-6-9超低温用钢,在室温至液氦温区的力学、物理性能及组织稳定性研究结果。这种钢的特点是以氮强化而用锰改善低温磁性,因此,在液氦下它具有高强度、高韧性和较高的反铁磁转变点T_N,T_N在130～143K之间因测试方法不同略有差异,在T_N以下有优良的磁稳定性,是一个综合性能优异的超导结构用钢。在83、4K拉伸形变50、20％时发生形变诱导马氏体转变。用磁金相、透射电镜金属薄膜技术与X-射线衍射技术鉴定出这种马氏体是hcp结构ε-马氏体及bcc结构的α′马氏体。但即使冷却到液氦中也没有冷却马氏体。 This paper describes the results of a study on the mechanical, physical and microstructural properties of 21-6-9 cryogenic steel used under liquid helium at room temperature to liquid helium temperature. This steel is characterized by nitrogen to improve the use of manganese to improve the low-temperature magnetic, therefore, under liquid helium it has high strength, high toughness and high antiferromagnetic transition point T_N, T_N between 130 ~ 143K due to test methods Different slightly different, below T_N has excellent magnetic stability, is a comprehensive performance of superconducting structural steel. At 83,4K tensile deformation 50,20% deformation-induced martensitic transformation occurs. Magnetism, transmission electron microscopy and thin-film X-ray diffraction techniques to identify this martensite is hcp structure ε-martensite and bcc structure α ’martensite. But even cooling to liquid helium did not cool the martensite.