耐酸车厢用热轧带钢边部开裂缺陷形成机理研究

Research on forming mechanism of edge cracking defect of hot rolled strip for acid resistant carriage

耐酸车厢用钢通过添加Sb元素可提高其耐腐蚀性,但热轧过程中却频繁发生带钢边部开裂问题。为此,借助扫描电镜、电子探针和差热分析仪等设备对边裂缺陷形貌特征、显微组织和Sb元素表层富集规律进行了分析,揭示了其边部开裂形成机理并提出了改进措施。结果表明:耐酸车厢用热轧带钢边部出现的分层开裂缺陷周边无明显的大尺寸氧化圆点,但开裂位置存在明显白色颗粒物残留,白色颗粒物区域含有较高的Sb元素,其中局部位置Sb元素质量分数可高达26%~28%;随着温度升高,Sb元素表层富集层深度和富集含量均明显增加;耐酸车厢用热轧带钢边部开裂缺陷形成的机理为长时间加热条件下钢中Sb元素在表层富集并弱化了晶界,造成热卷下线后边部呈多层网状开裂形貌。为此,提出了热轧过程中低温快烧以及除鳞系统多点开启等优化措施,有效改善了热卷边部质量。

The corrosion resistance of acid resistant carriage steel is improved by adding Sb element,but the strip edge cracking occurs frequently in the process of hot rolling.Therefore,the morphology,microstructure and surface enrichment evolution of Sb element were analyzed by means of scanning electron microscopy,electron probe and differential thermal analyzer.The mechanism of strip edge cracking was revealed and the control measures were proposed.The results show that there are no obvious large oxidized dots around the cracking defects on the edge of the hot rolled strip,but there are obvious residues of white particles in the cracking positions.The white particles contain high Sb element,and the mass fraction of Sb element can be as high as 26%-28% in local locations.With the increase of temperature,the thickness and enrichment content of Sb element on the surface layer of hot rolled strip increase obviously.The main mechanism of the edge cracking defects of hot rolled strip is that Sb element enrichment on the surface layer under long-term heating conditions weakens the grain boundary,resulting in a multi-layer network cracking morphology at the edge after the hot coil is taken off the line.The optimization measures such as low temperature fas reheating and multi-point opening of descaling system in hot rolling process are put forward,which can effectively improve the edge quality of hot coil.