Abstract:  Steel for ultra-low-temperature pressure vessel is steel specifically applied to liquid nitrogen （-196 ℃） and below， and requiring sufficient mechanical strength and toughness under extreme low-temperature conditions. In general， the strength and hardness of steels increase as the temperature decreases， but at the same time this is accompanied by a significant increase in the risk of brittle fracture and a decrease in plastic deformability， creating significant difficulties and challenges in their design and application. Based on the demand for high strength and toughness of ultra-low-temperature pressure vessels at temperature of -196 ℃ and below， and in response to the bottleneck problem that it is difficult to combine high toughness and high strength of steel at ultra-low temperatures， the performance characteristics of steel in ultra-low-temperature environments are introduced from the classification of steel and the current status of the research， respectively. In addition， new methods， processes and research and development progress of steel toughening in ultra-low-temperature environments are summarized， focusing on the analysis of low-temperature toughness mechanisms and strengthening strategies of several typical ultra-low-temperature steels， as well as their tough-brittle transition mechanisms， which mainly include martensitic phase transformation， dislocation motion and twin crystal formation and other micro-mechanisms. The effects of factors such as chemical composition， crystal structure and grain size on the low-temperature toughness of steel are summarized. Finally， based on the existing research results， the preparation and strengthening of steels for ultra-low-temperature pressure vessels are prospected.

Key words: Ultra-low Temperature Pressure Vessel, Low-temperature Steel, Low Temperature Toughness, Toughness-ductility Transition, Low Temperature Phase Transition, Mechanical Property

摘要： 超低温压力容器用钢是指专门应用于液氮（-196 ℃）及以下温度的钢材，需要在极端低温条件下拥有足够的机械强度和韧性。一般来说，随着温度的降低，钢材的强度和硬度会增加，但同时伴随着脆性断裂风险的显著提升以及塑性变形能力的下降，给其在设计和应用上带来极大的困难和挑战。本研究立足于超低温压力容器在-196 ℃及以下温度下高强韧的需求，针对钢材在超低温下的高韧性和高强度难以兼顾的瓶颈问题，从钢材的分类和研究现状出发，分别介绍了在超低温环境下钢材的性能特点。此外，归纳总结了钢在超低温环境下强韧化的新方法、新工艺和研发进展，重点分析了几种典型超低温用钢的低温韧性机理与强化策略，并对其韧-脆转变机理进行总结，其主要包括马氏体相变、位错运动与孪晶形成等微观机制。综述了化学成分、晶体结构和晶粒尺寸等因素对钢材低温韧性的影响。最后，基于现有研究成果，对超低温压力容器用钢的制备和强化进行了展望。

关键词: 超低温压力容器, 低温钢, 低温韧性, 韧-脆转变, 低温相变, 力学性能