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The paper deals with the stability of centerline inhomogenity of continuously cast slabs and hot rolled products. The centerline segregation is a disadvantageous failure of slabs which can affect the quality properties of the final products. During hot rolling of slabs the centerline segregation pattern will become thin and stretch and it can also be detected in the middle part of heavy plates and coils. It is a common experience that the centerline segregation of heavy plates can not be easily decreased by post heat treatment. The pattern of the centerline segregation was modeled physically by preparing a sandwich structure of steel plates with different levels of carbon and alloying elements. Homogenization experiments were performed and the samples were examined metallographically. Diffusional calculations proved the governing role of carbon activity which is influenced by the distribution of alloying elements.

Industrial data set with 400 CC (continuous casting) steel slabs were analysed by a statistical method for revealing the real connections between the technological parameters, heat transfer model results and the precisely determined centerline segregation index. Because of the poor correlations a new model was developed in which the shrinkage and deformations of the shells of the slabs can also be taken into account. It has been proved that the stopping of liquid movement below about 30 % liquid ratio plays an important role in the centerline segregation formation. The conclusions of the calculations are in good accordance with the results of the metallographical analysis.

Industrial data set with 400 CC steel slabs were analysed by a statistical method for revealing the real connections between the technological parameters, heat transfer model results and the precisely determined centerline segregation index. Because of the poor correlations a new model was developed in which the shrinkage and deformations of the shells of the slabs can also be taken into account. It has been proved that the stopping of liquid movement below about 30 % liquid ratio plays an important role in the centerline segregation formation. The conclusions of the calculations are in good accordance with the results of the metallographical analysis.

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Mathematical model was developed to estimate the flow rate and direction and of the expected porosity level in the centre part of a slab. Calculations show that centreline segregation is basically affected, at a given composition and cooling technology by the setting, deformation and eccentricity of the supporting rolls. Bulging of the strand between the supporting rolls can also play role.

No abstract

The paper deals with the stability of centerline inhomogenity of continuously cast slabs and hot rolled products. The centerline segregation is a disadvantageous failure of slabs which can affect the quality properties of the final products. During hot rolling of the slabs the centerline segregation pattern will become thin and stretched and it can also be detected in the middle part of heavy plates and coils. It is a common experience that the centerline segregation of heavy plates can not be easily decreased by post heat treatment. The pattern of the centerline segregation was modeled physically by preparing a sandwich structure of steel plates with different levels of carbon and alloying elements. Homogenization experiments were performed and the samples were examined metallographically. Diffusional calculations proved the governing role of carbon activity which is influenced by the distribution of alloying elements.