某钢厂在开工初期持续出现Q235B钢板断后伸长率不合格的现象，通过化学成分分析、力学性能试验、断口形貌分析、金相检验等方法对不合格原因进行了分析。结果表明：钢板中残留的氢元素、轧制后产生的严重带状组织、中心偏析以及非金属夹杂物等，使得钢板成分不均匀且金属基体的连续性遭到破坏，最终导致该Q235B钢板断后伸长率不合格。

The phenomenon of unqualified elongation after fracture of Q235B steel plates constantly appeared in a steel plant at the initial stage, the causes of unqualified elongation after fracture were analyzed by means of chemical composition analysis, mechanical property test, fracture surface analysis, metallographic examination and so on. The results show that the residual hydrogen elements in the steel plates, serious banded structure produced after rolling, center segregation and non-metallic inclusions resulted in the uneven composition of the steel plates and damaged the continuity of the metal matrix, which eventually led to the unqualified elongation after fracture of the Q235B steel plates.