利用电子束焊接方法焊接了60 mm厚Q345钢板，研究了接头焊缝区的显微组织及显微硬度分布。结果表明：电子束焊接能够一次性焊透60 mm厚Q345钢板，得到成形良好且没有明显气孔、裂纹等缺陷的焊接接头，焊缝深宽比很大，约15：1；焊缝中心顶层由先共析铁素体、侧板条铁素体和针状铁素体组成，沿着焊缝深度方向铁素体数量减少、板条状马氏体和针状铁素体数量增加且针状铁素体间距变小，晶粒尺寸减小；从焊缝顶层到底层，焊缝中心的硬度呈波动性增大趋势，焊缝区的显微硬度高于母材和热影响区的，且沿着深度方向焊缝区硬度的增长速率明显增大。

Q345 steel plates with thickness of 60 mm were joined by electron beam welding and the microstructure and microhardness distribution in the weld zone were studied. The results show that the 60 mm thick Q345 steel plates were welded with full penetration by the single pass electron beam welding. The welded joints in good shapes and without obvious defects such as pores and cracks were obtained. The weld depth-to-width ratio was as high as 15:1. The microstructure at the top of weld zone consisted of proeutectoid ferrite, side-plate ferrite and acicular ferrite. Along the depth of the weld, the amount of ferrite decreased while that of the lath martensite and acicular ferrite increased, the spacing between acicular ferrites became smaller and the grain size was reduced. From top layer to root layer of the weld, the hardness in the weld center showed a fluctuant increasing trend. The microhardness of the weld zone was higher than that of base material and heat affected zone. The increasing rate of the hardness in the weld zone increased obviously along the depth.