Structure formation during sheet steel production in a unit of continuous casting and deformation

Abstract

The paper considers the main problem of improving quality of steel sheets for welded pipes obtained at plate rolling mills and the main reasons that reduce it. There is a possibility of improving quality of steel sheets using technological capabilities of the unit of combined continuous casting and deformation. Problem of determining stress state of metal in cyclic deformation zone is posed and solved. The results of obtaining 09G2S sheet steel in pilot unit of continuous casting and deformation are presented. Magnitude of stresses in the center of cyclic deformation during production of steel sheets was determined for welded pipes at the unit. The authors present results of experimental study of the process of steel sheets production at pilot unit of continuous casting and deformation. The article considers the results of microstructure analysis, microhardness determination and microanalysis of chemical composition of the studied steel in various zones of the strip cross section. Structural inhomogeneity development in ferritic-pearlitic steel is interpreted along the thickness of sheet under conditions of combined thermomechanical processing of metal solidified in the mold. Predominantly ferritic microstructure is generated in the central light interlayer of the strip compared to base metal, characterized by a sharp decrease in carbon concentration in it. There is a possibility of such structure genesis at the first stages of crystallization during forging of low-carbon steel, when the excess phase of high-temperature ferrite that solidifies first is located mainly in the strip center. The size of pearlite grains in the light interlayer covariates with the grain structure of pearlite in the strip base metal and does not form precipitates of lath morphology, which increase tendency of steel to brittle fracture.