某公司生产的HRB400热轧带肋钢筋在冷弯过程中发生断裂，采用宏观断口分析、化学成分分析、金相检验、扫描电镜及能谱分析等方法对断裂的原因进行了分析。结果表明：由于该HRB400热轧带肋钢筋的化学成分偏析严重，导致基体中显微组织不均匀，存在马氏体和贝氏体等异常显微组织，使得钢筋强度高、塑性差；而且在该钢筋中存在大量的非金属夹杂物，破坏了钢筋基体的连续性，使钢筋基体容易产生应力集中及形成空隙或裂纹，这两个因素最终造成了钢筋的冷弯断裂。

The HRB400 hot rolled ribbed steel bars produced by a company fractured during cold bending. The causes of fracture were analyzed by means of macro fracture analysis, chemical composition analysis, metallographic examination, scanning electron microscopy analysis, energy spectrum analysis and so on. The results show that due to the serious chemical composition segregation of the HRB400 hot rolled ribbed steel bars, the microstructure of the matrix was inhomogeneous, and there were abnormal microstructures such as martensite and bainite, which resulted in high strength and poor plasticity of the steel bars. In addition, a large number of nonmetallic inclusions existed in the steel bars, which destroyed the continuity of the steel bars matrix and made the steel bars matrix easily produre stress concentration and form voids or cracks. These two factors eventually caused the cold bending fracture of the steel bars.