Andrei Chychko and Alexander Chychko:
Some aspects of blowhole formation in low-silicon steels
Low-silicon steel, blowhole formation, steel deoxidation, aluminium yield, oxygen activity
Low-silicon steel grades have many benefits like a larger yield because of smaller shrinkage, or lower cost because of a small ferroalloy addition. Also they have good mechanical properties for pipe production. However, they require a strict control of the oxygen level in a melt. Blowhole formation is one of the most important problems during the rolling of such steels.
The influence of metal chemistry and deoxidation practice on blowhole formation was performed at plant conditions at the Belorussian Steel Works. The maximum blowhole sizes were measured on wires with diameters between 5.5 and 6.5 mm, produced from low-silicon steel of different compositions and deoxidizer amounts. The major steel elements mass contents range between 0.06 and 0,12 % for carbon and 0.08 and 0.21 % for Si. Aluminium was used as an additional deoxidizer to decrease the oxygen activity after electric arc furnace (EAF) tapping. The equilibria between element-deoxidizers such as Mn, C, Al, Si and oxygen during the ladle treatment were studied by comparison of the measured oxygen activity with the calculated values.
It was found that the deviation from optimal values of the aluminium mass, used for deoxidation, is responsible for critical blowhole formation. A linear dependence between oxygen activity and yield of aluminium was discovered. This dependence was used for more precise calculations of the aluminium mass required for steel deoxidation. As a result, a decrease in critical blowhole appearance was achieved.
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