在不同热输入（1.27，1.52，1.90 kJ·cm^-1）下对800 MPa级微合金化碳锰钢板进行了激光对接焊，研究了热输入对焊接接头显微组织、室温拉伸性能和-40℃冲击性能的影响。结果表明：热输入对焊接接头显微组织的影响很小，3种热输入下焊缝区和热影响区粗晶区的显微组织均为板条马氏体，热影响区细晶区的为细晶铁素体及其晶界处的马氏体-奥氏体（M-A）组元，混晶区的为尺寸不等的铁素体和M-A组元；随着热输入的增加，热影响区粗晶区的晶粒尺寸增大，细晶区的变化较小；热输入对焊接接头拉伸性能的影响很小，拉伸断裂位置均位于母材中；随着热输入的增加，焊缝区冲击功先增大后降低，当热输入为1.52 kJ·cm^-1时达到最大，冲击断口都为韧性断口。

Laser butt welding was carried out on 800 MPa microalloyed carbon manganese steel plates under different heat inputs (1.27, 1.52, 1.90 kJ·cm^-1), and then the effects of heat input on microstructure, room temperature tensile property and -40℃ impact property of the welded joints were studied. The results show that the heat input had little effect on microstructure of the welded joint. Under three heat inputs, the microstructures of the weld zone and coarse-grained heat affected zone consisted of lath martensite, that of the fine-grained heat affected zone was composed of fine grain ferrite and martensite-austenite (M-A) constituent at grain boundaries, and that of the mixed grain zone was composed of ferrite and M-A constituent with different size. With increasing heat input, the grain size of coarse-grained heat affected zone increased and that of the fine-grained zone changed little. The heat input had little effect on the tensile properties. All tensile fracture positions were located in base metal. With increasing heat input, the impact energy of the weld zone first increased and then decreased, and reached the maximum value when the heat input was 1.52 kJ·cm^-1. The impact fracture exibited ductile fracture.