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

The 22 mm 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 Ca O·Al₂O₃calcium aluminate composite inclusions at the fracture site is more than that of Ca O·Al₂O₃calcium 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.