极低温工程装备的高速发展对低温特种合金提出了更高的要求，采用传统热处理工艺制备的18Ni马氏体时效钢难以满足航空航天等领域对特种钢的性能需求，亟需探索其他热处理工艺进行优化。深冷处理可以优化钢的性能，但是针对马氏体时效钢的研究较少。本工作以18Ni(200)马氏体时效钢为研究对象，研究深冷处理温度和时间对其显微组织和力学性能的影响。结果表明，深冷处理能有效促进残余奥氏体转变为马氏体，并细化马氏体板条，从而提高马氏体时效钢的力学性能。经对比发现，在-78 ℃深冷处理12 h的马氏体时效钢表现出最佳的综合性能，其屈服强度、硬度和断后延伸率分别约为1778.9 MPa、484.9 HV和7.2%；相比于-78 ℃深冷时效样品，-196 ℃处理12 h的马氏体时效钢在时效后逆转变奥氏体体积分数降低，同时，较低的深冷温度在马氏体内引发晶格应变，使得试样内部积累了大量势能，在时效处理时迅速释放，诱导组织回复，基体位错密度和析出相的密度和尺寸均降低，导致其强塑性均低于-78 ℃深冷时效样品。此外，在-78 ℃下，随深冷时间延长，时效样品中逆转变奥氏体含量逐渐降低、马氏体板条细化，同时小角度晶界比例逐渐增加且析出相尺寸减小，细晶强化与析出强化的协同作用逐渐增强，显著提升材料强度。

With advances in cryogenic engineering, increasingly stringent performance requirements are imposed on cryogenic structural alloys. Conventional heat treatments are often inadequate to satisfy the demanding performance requirements of 18Ni maraging steel used in aerospace and other high-end applications, creating a need for alternative heat-treatment strategies. Although deep cryogenic treatment has been reported to enhance the properties of various steels, its effects on maraging steels remain insufficiently understood. Accordingly, this study investigates the influence of cryogenic treatment temperature and duration on the microstructure and mechanical properties of 18Ni(200) maraging steel. The material was subjected to a combined process comprising solution treatment, cryogenic treatment, and aging. After solution treatment at 800 °C for 1 h, cryogenic treatments were performed at −78 °C for 4, 8, and 12 h, and at −196°C for 12 h, followed by aging at 550 °C for 4 h. Mechanical properties were evaluated using tensile testing and hardness measurements, while microstructural evolution was characterized by XRD, EBSD, and TEM. The results indicate that deep cryogenic treatment not only promotes the transformation of reversed austenite into martensite and refines martensitic laths, but also induces lattice distortion in martensite. This distortion is manifested by high stress concentrations and a high dislocation density, which increase the internal energy of the material. During subsequent aging, the release of this stored energy enhances the diffusion driving force of alloying elements, thereby promoting the formation of fine precipitates with a high number density. Among the investigated conditions, the specimen cryogenically treated at −78 °C for 12 h exhibited the best overall performance, achieving a yield strength of 1778.9 MPa, a hardness of 484.9 HV, and an elongation of 7.2%. In comparison, specimens treated at −196 °C showed a lower content of reversed austenite after aging. The lower cryogenic temperature induced greater lattice strain in the martensite, leading to the accumulation of a large amount of internal (potential) energy within the material. During subsequent aging, this stored energy was rapidly released, leading to strain recovery, a reduction in dislocation density, and a decrease in both the size and number density of precipitates. These effects ultimately resulted in lower strength and ductility compared with specimens treated at −78 °C. At −78 °C, increasing the cryogenic treatment duration progressively reduced the content of reversed austenite and refined its morphology. Concurrently, the fraction of low-angle grain boundaries and the precipitate size decreased. These microstructural evolutions enhanced grain-refinement and dispersion strengthening, resulting in significant increases in the strength and hardness of the steel. Overall, deep cryogenic treatment effectively optimizes the microstructure and mechanical properties of 18Ni(200) maraging steel by promoting martensite refinement and a favorable precipitate distribution. However, excessively low cryogenic temperatures may accelerate strain recovery during aging and diminish strengthening effects. This study provides practical guidance for designing cryogenic treatment protocols for high-performance maraging steels intended for cryogenic applications.