Low-carbon steel (0.2 mass%) samples were austenitized and quenched at a cooling rate of 10°C/s under GPa level high pressure. The morphology, lattice constant, and order degree of C atom distribution of high-pressure quenching martensite were characterised and analyzed by TEM, EBSD, XRD, and Mössbauer. Besides, the transformation characteristics and strengthening mechanisms were discussed. The results show that the microstructure of 0.2 mass% C steel is fine hierarchical lath martensite with almost no residual austenite, and its laths mostly follow {112} <111> twin relationship, indicating the self-accommodation effect among martensite variants. Compared to atmospheric pressure, the order degree of carbon atom distribution increases in high-pressure quenched martensite, meanwhile the tetragonality (c/a) of martensite lattice increases from 1.009 at atmospheric pressure to 1.012 at 4 GPa. The significant promotion of hardness in 0.2 mass% C steel subjected to high-pressure treatment can be ascribed to a large number of dislocations in the structure, grain refinement strengthening caused by twin boundary, and solution strengthening caused by large distortion due to the increase of the order degree for C atom distribution and the decrease of lattice constant. These findings provide new insights into the carbon steel martensite transformation mechanism, and a new martensite transformation technique can be developed.

低碳钢（0.2质量%）试样在GPa级高压下以10℃/s的冷却速度进行奥氏体化和淬火。采用TEM、EBSD、XRD和Mössbauer等手段对高压淬火马氏体的形貌、晶格常数和C原子分布有序度进行表征和分析。此外，还讨论了转化特征和强化机制。结果表明，0.2mass%C钢的显微组织为细小层状板条马氏体，几乎没有残余奥氏体，板条多呈{112}<111>孪晶关系，表明马氏体变体之间存在自调节作用。与大气压相比，高压淬火马氏体碳原子分布有序度增加，同时四方性（c/a) 的马氏体晶格从大气压下的 1.009 增加到 4 GPa 下的 1.012。0.2质量%C钢经高压处理后硬度的显着提升可归因于组织中存在大量位错、孪晶界引起的晶粒细化强化以及因变形量增加引起的大变形引起的固溶强化。 C原子分布的有序度和晶格常数的降低。这些发现为碳钢马氏体转变机制提供了新的见解，并且可以开发一种新的马氏体转变技术。