CSP生产Q345热轧板边裂的成因分析与控制

Cause analysis and control of edge crack of Q345 hot rolled plate produced by CSP

CSP生产热轧板的边裂与连铸、加热及轧制等多工序的工艺异常有关,采用扫描电镜、金相显微镜等手段研究了Q345热轧板的边裂特征,分析其主要影响工序及成因,以提高控制措施的有效性。结果表明,典型热轧板缺陷试样边部的表面和窄边均存在轧向裂纹,裂纹开口及周围含有K、Na等保护渣特有元素的氧化物,裂纹两侧存在明显脱碳、晶粒长大等高温氧化特征,推测这些缺陷起源于结晶器卷渣形成的铸坯窄边皮下夹渣,经过高温加热、轧制演变而成;窄边裂纹一侧局部存在纤维状金属流变组织,与热轧过程边部过冷有关。降低结晶器卷渣、优化板坯加热及轧制冷却工艺,有助于降低热轧板的边裂缺陷。

The edge crack of hot rolled plate produced by CSP is related to the abnormal process of continuous casting,heating and rolling.The characteristics of edge crack of Q345 hot rolled plate were studied with SEM and metallographic microscope,and the main influencing factors and causes of the edge crack were analyzed,so as to improve the effectiveness of control measures.The results show that there are rolling cracks on the edge surface and narrow side of defect specimen of typical hot rolled plate.Some special elements of mold flux such as K,Na oxides exist in the crack opening and its surrounding,implying that these defects originated from the subcutaneous slag on the narrow edge of the slab formed by mold flux entrapment,which was developed by high-temperature heating and rolling.There is a local fibrous metal flow structure on one side of the narrow edge crack,which is related to the edge super-cooling of the narrow side of hot rolled plate during hot rolling.Reducing mold flux entrapment,optimizing slab heating and rolling cooling process are helpful to reduce edge crack defects of hot rolled plate.