Study on the cause and mechanism of black spot defect on the surface of hot rolled pickled plate
Aiming at the problem that the black spot defect on the surface of hot rolled pickled plate produced in a domestic steel mill seriously affects the subsequent pickling quality,the microscopic morphology,element distribution and phase composition of the black spot defect were analyzed by field emission scanning electron microscopy,electron probe,X-ray diffractometer and di-mensional hardness tester,and the residual oxide scale pressing-in rule under different rolling processes was studied.The results show that the oxide scales at black spot defect position and no defect position are both two-layer structure,but the oxide scale at black spot defect position are thicker,and there is a"C"shape thickness gradient trend at the junction.Si elements of the oxide layer inside black spot is enriched in the form of Fe2SiO4,which has a pinning effect on the oxide scale,resulting in difficulty in descaling and the formation of oxide scale pressing defects,and the outer thicker Fe3O4 layer resulting that the defect surface ap-pears black.In the experiments simulating residual oxide scale pressing-in,residual oxide scale pressed into the matrix at both roughing and finishing rolling temperatures will lead to black spot on the surface of the hot rolled plate,and with the increase of the reduction rate,the black spot will be more closely combined with the matrix.The surface microscopic morphology of the black spot defect shows the form of oxide scale pressing-in,and the surface hardness is close to the black spot formed by residual oxide scale pressing-in,both much greater than the matrix hardness.The fundamental reason of the black spot defect is the oxide scale pressing-in caused by Fe2SiO4,and the incidence of black spot defect can be reduced by improving the descaling process and controlling the formation of Fe2SiO4.
hot rolled pickled plateblack spot defectresidual oxide scaleFe2SiO4Fe3O4reduction rate
万方数据
维普
