Q345B钢拉伸分层机理分析

Mechanism of tensile layering of Q345B steel

对Q345B带卷成分、过热度和中心偏析进行统计分析,并采用光学显微镜、扫描电镜和能谱分析对其拉伸后产生分层机理进行研究。结果表明,Q345B钢在连铸过程中产生的中心偏析,特别是Mn元素偏析,会导致中心MnS等夹杂物的聚集,从而在轧制过程中形成带宽较大、带间距较近的带状组织;这种带状组织在带卷拉伸时,因局部力学性能差异过大而出现拉伸分层缺陷;拉伸后,分层带卷带状组织密度ρa为62 700μm/mm2,未分层带卷带状组织密度ρb为650μm/mm2,分层带卷带状密度是未分层带卷带状密度的96倍;如果Q345B钢中心存在带宽较大、带间距较近带状组织时,就会出现拉伸分层现象。

The composition, the relationship between overheating and central segregation of Q345B coil stock were analyzed, and metallographic examination （OM）, scanning electron microscopy （SEM） and energy spectrum （EP） were employed to study the mechanism of tensile layering of Q345B plate. The results show that central segregation is formed in the process of continuous casting, which, especially the element segregation of Mn, will lead to the gathering of such inclusions as MnS and results in the formation of banded structure of wider band and closer distance in hot rolling. When the coil stock is stretched, the huge difference in local mechanical properties produces stratified defects. After the stretching, the banded structure density of the layered coil stock （ρa） is 62 700 μm/mm2 , while that of un-layered coil stock （ρb） is 650μm/mm2. The former is 96 times more than the latter. When banded structure of wider band and closer distance exists in the center of Q345B steel, tensile layering will appear.