Chromium-containing metal and manufacturing method thereof

Abstract

The high-Cr-containing metal according to the present invention is a chromium-containing metal manufactured in an arc melting furnace, and contains at least 85% Cr, up to 0.005% Al, up to 0.1% Si, and up to 0.002% S. The manufacturing method of this high-Cr-containing metal comprises the steps of reducing chromium oxides heated and melted in the arc melting furnace with Si, obtaining a molten metal containing at least 85% Cr, then, discharging slag generated in this Si reduction from the arc melting furnace, adding a basic flux into the arc melting furnace after discharging slag, melting the basic flux by electric arc, refining the molten metal by contacting the slag generated through melting of the basic flux with the molten metal, and then, tapping the molten metal from the arc melting furnace and cast.

Description

TECHNICAL FIELD [0001] The present invention relates to high-purity metal chromium and ferrochromium used in electronic materials and corrosion-resistant and heat-resistant superalloys and so on, and a manufacturing method thereof. BACKGROUND ART [0002] High-purity metal chromium and ferrochromium low in impurities are used for electronic materials and corrosion-resistant and heat-resistant super alloys. In the present invention, these metal chromium and ferrochromium are generically called “chromium-containing metals”. An economically available ore serving as a chromium source of the chromium-containing metal is chromite (FeO.Cr2O3). Because it contains much iron, however, the upper limit of the Cr content in ferrochromium obtained from chromite is about 72 mass %. It is therefore the general practice to use chromium oxide (Cr2O3) available by refining chromite as a raw material for metal chromium. [0003] The known manufacturing methods of metal chromium include the aluminum-thermi...

AI Technical Summary

Benefits of technology

[0010] The present invention was developed in view of these circumstances as described above, and has an object to provide a method for economically and efficiently manufacturing a chromium-containing metal having slight contents of impurities such as aluminum, silicon and sulfur, and to provide a chromium-containing metal having small contents of impurity elements, manufactured by this manufacturing method.

Problems solved by technology

This is however based on a batch process, resulting in a small throughput per batch, a low production efficiency, and the process uses expensive metal aluminum as a reducing agent, thus leading to a high manufacturing cost.

Furthermore, the strong reducing atmosphere causes reduction of refractory constituents used for furnace lining, and the reduced constituents are entangled into the metal chromium, posing problems in purity.

It has however a serious quality problem in that silicon serving as a reducing agent remains in an amount of about 0.7 mass % in the manufactured metal chromium.

In the aluminum-thermit process and the silicon reduction process, if metal chromium is manufactured in a state of insufficient reduction by using a small amount of metal aluminum or metal silicon serving as a reducing agent, the amount of aluminum or silicon remaining in metal chromium decreases.

However, this leads to a deteriorated reduction yield of chromium oxide and an increase in the amount of oxygen in manufactured metal chromium, thus causing another problem in manufacturing cost and in quality.

Necessity of many treatments for refining the chromate solution results in economic problems such as complicated manufacturing steps, a high equipment cost, and a large power consumption.

However, the conventional deironing treatment, including this method, cannot be considered to be high in production efficiency because of complicated treatment process.

Regarding these requirements, the chromium-containing metals manufactured by the conventional methods mentioned above contain much impurity elements, and requires a higher manufacturing cost according as the purity is higher, and cannot be considered to satisfy these requirements.