采用Ar-CO₂气体保护焊通过最高硬度试验和斜Y型坡口焊接冷裂纹试验，研究了Q690ZM中锰钢的焊接冷裂纹敏感性。结果表明：当焊接热输入由10 kJ·cm^-1增加至20 kJ·cm^-1或预热温度由20 ℃升高至200 ℃时，中锰钢焊接热影响区的显微硬度均略微降低，最高硬度均高于430 HV，焊接冷裂倾向严重；当焊接热输入为15 kJ·cm^-1，预热温度由100 ℃升高至200 ℃时，斜Y型坡口焊接裂纹试验中试验焊缝的表面裂纹和根部裂纹逐渐消失，断面裂纹率降低至9.09%。为防止冷裂纹的产生，中锰钢焊前必须进行150～200 ℃的预热，并进行相应的焊后热处理；粗晶热影响区中粗大的马氏体板条晶体学取向差小，大角度晶界密度低，抵抗解理裂纹扩展的能力弱，因此焊接冷裂纹萌生后沿紧邻熔合线的粗晶热影响区扩展。

The sensitivity of welding cold crack of medium-Mn steel was investigated by a maximum hardness test and Y-groove welding cracking test through Ar-CO₂ gas shielded welding.The results show that when the welding heat input increased from 10 kJ·cm^-1 to 20 kJ·cm^-1 or the preheating temperature increased from 20 ℃ to 200 ℃, the microhardness of the welding heat affected zone of medium-Mn steel decreased slightly, and the maximum hardness was higher than 430 HV, indicating the steel had a severe welding cold cracking tendency.The surface crack and root crack of test weld in Y-groove welding cracking test disappeared and the section crack rate decreased to 9.09%, when the welding heat input was 15 kJ·cm^-1 and the preheating temperature increased from 100 ℃ to 200 ℃.In order to prevent welding cold crack formation, the preheating at 150-200 ℃ before welding medium-Mn steel and post-weld heat treatment should be carried out.The large martensitic lath in coarse-grained heat affected zone had little difference in crystallographic orientation and had a low density of large angle grain boundaries, which had weak resistance to cleavage crack propagation; thus, the welding cold crack extended along the coarse-grained heat affected zone adjacent the fusion line after initiation.