针对Q235B中厚板在拉伸试验中出现的断后伸长率不合格问题，利用扫描电镜、金相显微镜等分析手段对拉伸试样宏观断口、断口微观形貌及金相组织进行观察与分析。分析结果表明，中厚板中的非金属夹杂物、不均匀的带状组织和内应力是导致钢板断后伸长率不合格的主要原因，并就此提出一系列的工艺改进与优化措施，有效地解决了伸长率不合格的问题。

In view of disqualified elongation of Q235B medium plate in tensile test， the macroscopic fracture， morphology and metallographic structure were observed and analyzed by scanning electron microscope and metallographic microscope. The analysis results showed that the nonmetallic inclusions in medium plate， the inhomogeneous banded structure and internal stress were the main cause for the disqualified elongation of steel plate. Correspondingly， a series of process improvement and optimization measures were proposed to effectively solve the problem of disqualified elongation.