STUDY ON INGOT-MAKING PRACTICE (V)
Shizuya Maekawa, Yoshitaka Nakagawa
Molten steel is always oxidized and nitrided by air during pit process. Oxidation of molten steel has a considerable effect upon corrosion of pit-refractories as mentioned in a previous paper in J. Jap. Inst. Metals, 2 (1954) 57, and oxides themselves also have a danger of becoming inclusions in steel.
Thereby the non-metallic inclusion in steel is greatly influenced with oxidation of molten steel by air during pit process.
The authors studied on the oxidation and non-metallic inclusion with experiments in the laboratory.
The result obtained were as follows:
(1) Silicon, manganese, iron, aluminium and carbon were oxidized by oxygen in air and total oxygen in the molten steel increased with pouring to the mould from the ladle. Consequently they remained in the ingot in the form of SiO2, MnO, Al2O3 and FeO. These oxides had a cause of becoming microscopic non-metallic inclusions, and inclusions were extracted by a modifled Dickenson's method and the total oxygen in the ingot obtained by the vacuum fusion method increased.
(2) Silicon, manganese and iron in the high-carbon molten steel were not oxidized strongly in comparison with the other kind of molten steel.
(3) The oxidation of molten steel by air were influenced with the condition of its stream. The molten steel of turbulent stream were more oxidized heavily than the case of a smooth stream.
It was imaginable that the oxidation were also influenced with the chemical composition of molten steel (for instance carbon and aluminium).