采用光学显微镜、扫描电镜和能谱仪对断后伸长率不合格的Q345R钢板的显微组织、断口形貌以及夹杂物进行观察和分析，分析了导致Q345R钢板断后伸长率不合格的原因。结果表明：引起Q345R钢板断后伸长率不合格的主要原因是严重的带状组织，尤其是较宽的贝氏体硬组织带、魏氏组织等；硫化物夹杂的存在对钢板的断后伸长率有一定的影响，但不是主要原因。

The microstructure, tensile fracture morphology and inclusions were observed and analyzed by optical microscope, scanning electron microscope and energy disperse spectrometer respectively to find out the reasons for the disqualification of percentage elongation after fracture of Q345R steel plates. The results show that the main reason for the unqualified percentage elongation after fracture was the serious banded structure, especially the wide bainite hard microstructure band and the widmanstatten structure. Existing sulfide inclusions had a certain effect on the percentage elongation after fracture of the steel plates, but it was not the main reason.