夹杂物对厚规格X80热轧钢带DWTT性能的影响

Effect of inclusions on DWTT properties of thick gauge X80 hot rolled steel strip

采用22 mm厚X80热轧钢带替代传统宽厚板平板的生产工艺,在实现提高成材率、降低工程制造成本及提高管线外径可调节性方面具有显著的优势.本文针对开发试制过程中出现产品低温抗落锤撕裂性能(DWTT)不合格问题,通过扫描电镜(SEM)对不同比例脆性断口形貌以及铸坯厚度方向成分偏析程度进行系统分析,得出断口处硫化物与Ca O·Al2O3钙铝酸盐复合夹杂物分布较多,尺寸过大对X80管线钢抗落锤撕裂性能造成了影响,进而分析了钢水氮含量高对应抗落锤撕裂性能下降的关系,同时钢材中长条状硫化锰偏聚破坏组织连续性,易成为韧脆性断口裂纹的根源.通过优化精炼Ca线喂入工艺、连铸过程保护浇铸,及改善铸坯中心偏析程度,减小了钢中夹杂物数量,有效提高了产品抗落锤撕裂性能,实现了稳定开发生产22 mm厚X80管线钢热轧钢带.

The 22mm thick X80 hot-rolled coil production process replaces the traditional wide and thick plate production process, which has remarkable advantages in improving the yield,reducing the cost of manufacturing,and improving the outer diameter adjustment of pipeline. Aiming at the unqualified problem of low temperature drop weight tear resistance ( DWTT) of products during development and trial production,the morphology of brittle fracture and the segregation degree of composition in slab thickness direction at different proportions were systematically analyzed by scanning electron microscopy ( SEM) . It is concluded that the distribution of sulphide and CaO·Al2O3 calcium aluminate composite inclusions at the fracture site is more than that of CaO·Al2O3 calcium aluminate composite inclusions,and the large size effects the drop weight tear resistance performance of X80 pipeline. Also the relationship between high nitrogen content in molten steel and the decrease of drop weight tear resistance performance was analyzed. Moreover,the steel strip manganese sulfide segregation destruction of tissue continuity,easy to become a source of ductile brittle fracture crack. Through the optimization of refining Ca wire feeding technology and the protective casting technology in continuous casting process,improving the centerline segregation degree,decreasing the number of inclusions in steel,can effectively improve the performance of drop weight tear resistance,to achieve a stable development and production of 22-mm thick X80 pipeline steel hot rolled steel strip.