Abstract
The variation of total oxygen (T.O) content, characterization of inclusions, slag composition, and off-gas behavior during the smelting process of silicon-deoxidization bearing steel were investigated with industrial experiments. The change of content of combined oxygen during RH (Ruhrstahl–Hereaeus vacuum degassing furnace) process was calculated and compared with T.O content change. It is found that the decrease of oxygen content is mainly caused by the removal of dissolved oxygen rather than the removal of oxides during RH process. Carbon was found to be a strong deoxidizer (stronger than aluminum) in high vacuum degree. Top slag is an oxygen source of the deoxidization process, leading to the re-oxidization of liquid steel, even though the FeO content is low in top slag. During the RH process, the change of oxygen mainly exists in three processes: 1) Deoxidization reaction in vacuum chamber, 2) oxygen mass transfer process between liquid steel out from a vacuum chamber and in ladle, and 3) oxygen mass transfer between ladle slag and liquid steel. It depends mainly on the mass transfer of the oxygen in the liquid steel.
Highlights
Bearing steel is often used for roller and ball bearings in engineering structures as bearing, for example, metallurgy, wind power, mining machinery, and aerospace [1]
In order to ensure the quality of bearing, there are two kinds of control conception: One controls the cleanliness of bearing steel, meaning very low total oxygen (T.O) content in the steel, and the other controls the type and morphology of inclusions by reducing inclusions unfavorable to fatigue life, such as TiN and large-sized calcium aluminate (Ca–Al–O) [5]
The first control conception is widely applied in the production of bearing steel and the T.O content can be controlled below 5 ppm, even 3–4 ppm, due to the development of production technology
Summary
Bearing steel is often used for roller and ball bearings in engineering structures as bearing, for example, metallurgy, wind power, mining machinery, and aerospace [1]. The life of bearing is significant for security in engineering. Non-metal inclusion as a kind of defect is one of the most important causes of life reduction of bearing [2,3,4]. The first control conception is widely applied in the production of bearing steel and the T.O content can be controlled below 5 ppm, even 3–4 ppm, due to the development of production technology. The production process for bearing steel is usually EAF (electric arc furnace)/BOF (basic oxygen furnace) → LF (ladle furnace) → VD (vacuum degasser) → CC (continuous casting) [6], where Al is used for deoxidization as a kind of strong deoxidizer and the oxygen content can be reduced to 3–4 ppm
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