Intensification of the secondary cooling by the presence of the oxide layer on the steel slab surface

Intensification of the secondary cooling by the presence of the oxide layer on the steel slab surface

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Oxide layer is formed on the slab surface during steel casting process. This oxide layer primarily influences the surface quality and material losses during steel processing, but it can also intensify the spray and mist cooling due to the increase of the Leidenfrost temperature, which is an important border between film boiling regime (low cooling intensity) and nucleate boiling regime (high cooling intensity). The oxide layer can also act as a thermal barrier during film boiling regime and during dry casting, where no or minimal water is used. The oxide layer influence is not as important as the water impact density and slab surface temperature, but it should be also included in the modelling and regulation of the secondary cooling zone to minimalize formation of surface defects and cracks. The influence of the oxide layer on the Leidenfrost temperature and also on the heat transfer coefficient is investigated in this paper. Laboratory measurement compares the spray cooling of oxide-free steel surface and oxidized steel surface. Results show significant increase of the Leidenfrost temperature for oxidized surface. This can cause intensification of the cooling process. Results also show, that the local breaking up of the oxide layer can influence the spray cooling homogeneity.

Oxide layer is formed on the slab surface during steel casting process. This oxide layer primarily influences the surface quality and material losses during steel processing, but it can also intensify the spray and mist cooling due to the increase of the Leidenfrost temperature, which is an important border between film boiling regime (low cooling intensity) and nucleate boiling regime (high cooling intensity). The oxide layer can also act as a thermal barrier during film boiling regime and during dry casting, where no or minimal water is used. The oxide layer influence is not as important as the water impact density and slab surface temperature, but it should be also included in the modelling and regulation of the secondary cooling zone to minimalize formation of surface defects and cracks. The influence of the oxide layer on the Leidenfrost temperature and also on the heat transfer coefficient is investigated in this paper. Laboratory measurement compares the spray cooling of oxide-free steel surface and oxidized steel surface. Results show significant increase of the Leidenfrost temperature for oxidized surface. This can cause intensification of the cooling process. Results also show, that the local breaking up of the oxide layer can influence the spray cooling homogeneity.