某Q550D钢拉伸试样在拉伸试验后出现拉伸断口分层现象。通过宏观观察、金相检验、硬度测试、能谱分析等方法，对拉伸断口的分层原因进行了分析。结果表明：Q550D钢板坯在连铸过程中采用了不适宜的连铸工艺，造成连铸钢坯在上、下1/4处出现成分正偏析，在连铸钢坯的1/2处存在负偏析、夹杂物，后续经轧制后在板材的1/4厚度处存在较严重的贝氏体偏析带，在心部区域有大量的B类夹杂物，最终导致拉伸试样断口出现分层现象。

The tensile fracture delamination of a Q550D steel tensile sample occurred after tensile test. The causes of tensile fracture delamination were analyzed by means of macro observation, metallographic examination, hardness test and energy spectrum analysis. The results show that the unsuitable continuous casting process was adopted in the continuous casting process of Q550D steel slab, resulted in positive segregation at the upper and lower 1/4 of the continuous casting billet, negative segregation and inclusions at 1/2 of the continuous casting billet. After the subsequent rolling, there was a serious bainite segregation band at 1/4 of the thickness of the plate, and there were a large number of class B inclusions in the core area, which finally led to delamination in the fracture of the tensile samples.