The newly designed cryogenic high-Mn steel plates (Fe-23Mn-1.5Al-0.45C) were joined by metal inert gas (MIG) multi-pass welding process. To evaluate the inhomogeneity of microstructure and cryogenic toughness in heat-affected zone (HAZ) of welded joint, the impact samples were prepared by zonal sampling method. The microstructure features and embrittlement mechanism in HAZ of welded joint were systematically investigated. The results reveal that grains obviously grew in the coarse-grain HAZ (CGHAZ). C element segregated and nano-sized lamellar and granular (Cr, Mn)₇C₃ carbides precipitated at the grain boundary in HAZ, and the size of precipitate carbides in CGHAZ and fine-grain HAZ (FGHAZ) was about 100 nm and 40 nm, respectively. The interface between (Cr, Mn)₇C₃ and γ-austenite matrix in CGHAZ was incoherent with the lattice misfit of 45.13%. Higher fraction of low angle grain boundaries (LAGBs) appeared in CGHAZ (25.89%) and FGHAZ (11.99%), compared with the base metal (4.33%). Such microstructural differences can degrade the impact toughness in CGHAZ. From cryogenic Charpy impact tests, the impact toughness in different zones of the joint at each test temperature follows this sequence: base metal > fine-grain HAZ > coarse-grain HAZ > fusion line. These results can provide a fundamental understanding and guidance on the brittle failure of cryogenic high-Mn steel welded joint during service.

新设计的低温高锰钢板（Fe-23Mn-1.5Al-0.45C）通过金属惰性气体（MIG）多道焊工艺连接。为评价焊接接头热影响区（HAZ）组织和低温韧性的不均匀性，采用带状取样法制备冲击试样。系统研究了焊接接头热影响区的显微组织特征和脆化机制。结果表明，晶粒在粗粒热影响区（CGHAZ）内明显生长。C元素偏析的纳米级层状和粒状(Cr, Mn) ₇ C ₃碳化物在HAZ晶界析出，CGHAZ和细晶HAZ(FGHAZ)中析出碳化物的尺寸约为100 nm和40 nm ， 分别。(Cr, Mn) ₇之间的界面CGHAZ中的C ₃和γ-奥氏体基体不相干，晶格错配为45.13%。与贱金属 (4.33%) 相比，CGHAZ (25.89%) 和 FGHAZ (11.99%) 中出现了更高比例的低角度晶界 (LAGB)。这种微观结构差异会降低 CGHAZ 的冲击韧性。从低温夏比冲击试验来看，每个试验温度下接头不同区域的冲击韧性遵循以下顺序：母材>细晶HAZ>粗晶HAZ>熔合线。这些结果可为深冷高锰钢焊接接头服役过程中的脆性破坏提供基本的认识和指导。