采用ER50-6焊丝对NM450耐磨钢板进行了CO₂气体保护焊，研究了接头的显微组织、力学性能，以及焊接冷裂纹敏感性。结果表明：焊缝组织为块状铁素体+针状铁素体，热影响区粗晶区和正火区的组织分别为板条马氏体和铁素体+渗碳体；焊缝区、粗晶区、正火区和不完全重结晶区的硬度分别为220，412，234，386 HV，马氏体分解导致正火区和不完全重结晶区硬度降低；接头的抗拉强度为768 MPa，焊缝中心、影响区和母材的-20℃夏比冲击吸收功分别为110，140，88 J；此钢有一定的冷裂纹敏感性，在环境温度32.6℃、不预热焊接时不会产生裂纹，在环境温度-1.4℃、不预热焊接时，接头根部裂纹率和截面裂纹率均为100%，80℃预热焊接则不会产生焊接裂纹。

NM450 wear-resistant steel plates were welded with ER50-6 welding wire by CO₂ gas-shield welding. The microstructure, mechanical properties and welding cold crack sensitivity of the joint were studied. The results show that the microstructure of the weld was composed of massive ferrite and needle-shaped ferrite, and that of the coarse-grained heat-affected zone and of the normalized zone was composed of lath martensite and ferrite+cementite, respectively. The hardness of weld metal, coarse-grained zone, normalized zone and incomplete recrystallization zone was 220, 412, 234, 386 HV, respectively. The decomposition of martensite led to the decrease of hardness in the normalized zone and incomplete recrystallization zone. The tensile strength of welded joint was 768 MPa. The impact energy of weld center, heat-affected zone and base metal at -20℃ was 110, 140, 88 J, respectively. The steel had a certain cold crack sensitivity. No cracks were produced for the welding at 32.6℃ without preheating. Both the root crack percentage and cross-sectional crack percentage were 100% for the welding at -1.4℃ without preheating, while no welding cracks were produced after preheating at 80℃.