JPS5852449A - Melting and refining method for metallic chromium - Google Patents

Abstract

PURPOSE:To obtain high purity metallic Cr by sintering and molding metallic Cr into an electrode having a through hole and by melting lump Cr in a furnace with arc while introducing an inert gas from the hole to efficiently melt the Cr. CONSTITUTION:A sintered molded body having a through hole in the direction of the major axial line is manufactured using powdered metallic Cr. This molded body is used as an electrode, a terminal connected to a power source is attached to the electrode, and arc is generated between lump Cr and the tip of the electrode to melt and refine the Cr. At this time, the arc melting is carried out while introducing an inert gas or a gaseous mixture of the inert gas with a reducing gas from the hole of the electrode. By this method the high m.p. metallic Cr can be melted efficiently, and a high purity metallic Cr ingot usable as a superior starting material for an alloy is obtd.

Description

[Detailed description of the invention] The present invention provides a method for melting and refining metallic chromium.

More specifically, the present invention relates to a method for refining metal chromium by arc melting using a consumable hollow electrode.

As machines and equipment are required to be more precise and have higher performance, the materials that make up these devices are also required to be of high purity.

High-purity products of metallic chromium have traditionally been produced by electrolysis of chromium solutions, but in recent years, with the development of industry, high-purity products have become increasingly desirable and are being used not only as raw materials for alloy addition, but also as metallic chromium itself. has become possible to think about.

Metallic chromium is a substance with an extremely high melting point (1890°C ± 10°C), so naturally high temperatures are required to melt it.
Furthermore, since metallic chromium is active at high temperatures, it tends to corrode the furnace material during melting, and contamination of impurities from the furnace material is unavoidable. In addition, in order to prevent the above-mentioned disadvantages caused by high temperatures, melting is performed under reduced pressure in a vacuum furnace, etc., resulting in a high vapor pressure (1
928℃/20 ig) Metallic chromium has a significantly high evaporation loss.

Therefore, it is difficult to apply a scouring method that involves a melting process like the usual smelting of metals to the smelting of metallic chromium.

Traditionally, metal melting and refining methods use a consumable electrode for the metal to be refined. Arc heat gradually melts the metal from the tip of the electrode, solidifies the melt in a water-cooled mold, and produces a high-purity ingot. ) has been proposed.

This method usually involves melting and solidifying the metal to be melted into an electrode shape, and then remelting it using arc heat.

However, as described above, metal chromium is extremely difficult to melt, making it difficult to form electrodes by the conventional melting method.

The present inventors have discovered a method of obtaining high-purity metallic chromium by using a specially shaped electrode obtained by sintering metallic chromium in metal refining by arc melting of a consumable electrode formed of metallic chromium. The invention has been completed.

That is, in the present invention, metallic chromium is formed into an electrode having a hollow hole penetrating in the long axis direction by a sintering method, the raw material chromium is pre-purified in the process of forming this electrode, and the molded body is further refined. The present invention provides a method for refining chromium by using a consumable electrode as a consumable electrode, and melting the gas by arc melting while introducing an inert gas or a mixed gas of this and a reducing gas through the hollow hole.

Next, the present invention will be explained in more detail.

The metallic chromium used in the present invention is mainly powdered (hereinafter referred to as metallic chromium powder), and any material that can be obtained by electrolysis or other smelting methods may be used, but in terms of purity, it is preferable to use electrolytic chromium. It is preferable to obtain a good result.

The metallic chromium powder is mixed and kneaded with a binder, for example, an organic polymer material such as starch or polyvinyl alcohol, and carbon if necessary, and then formed into a shape having hollow holes penetrating in the long sleeve direction, which characterizes the present invention. do.

The molding can be performed by a conventional molding method such as a rubber press method. Further, the shape of the molded body is not particularly limited except that it has a hollow hole penetrating in the longitudinal direction, but its appearance is preferably in the shape of a general electrode, such as a rod shape such as a cylinder or a prismatic cylinder.

The size of the hollow hole penetrating the molded body in the long axis direction may be large enough to allow gas to flow smoothly and stabilize the arc during the implementation of the present invention, and the size is determined by the electrode used.

Pre-drying the raw material for the molded body before the ceramic molding to remove most of the moisture contained in the raw material gives good results in improving the moldability during subsequent molding.

The molded body is sintered under an inert atmosphere, preferably under reduced pressure, e.g.
It is carried out for 1 to 5 hours at a temperature of .

In the present invention, the metal chromium molded body described above is arc melted as a consumable electrode, but a mixture of metal chromium, chromium oxide, and carbon can be molded and sintered to be used as the electrode. Use of such an electrode is advantageous because chromium can be efficiently smelted and purified.

At this time, the amount of chromium oxide to be mixed with metallic chromium can be 50% by weight as pure chromium.

Cr2O3-1-5C→20r+5c.

In the present invention, carbon is used in a stoichiometric amount based on the above chemical formula and in an amount sufficient to remove oxygen contained in the metal chromium powder, similar to when only the metal chromium powder is used.

Metallic chromium powder, chromium oxide.

The carbonaceous mixture is shaped and sintered in the same manner as described above.

When sintering is performed under these conditions, the chromium oxide used is reduced to metallic chromium, and when used as a consumable electrode, the strength and conductivity are almost the same as electrodes made of metallic chromium powder. It is.

The present invention is characterized in that during arc melting, an inert gas or a mixed gas of an inert gas and a reducing gas is introduced into the melting part through a hollow hole penetrating in the direction of the long axis of the consumable electrode. The inventor previously filed a patent application for a method of arc melting metal consumable electrodes by introducing inert gas through a hollow hole in one electrode to stabilize the arc and melt the metal consumable electrodes (patent application dated September 6, 1980). Application) The invention related to the above patent application is
This relates to a method for remelting and refining consumable electrodes with hollow holes made of carbon steel, stainless steel, and many other heavy metals or light metals using an arc while introducing an inert gas, etc. through the hollow holes. .

The present inventors applied this method to the melting and refining of metal chromium, which has a particularly high melting point and is difficult to melt, as described above, and incidentally, chromium obtained by a special method as described above. The inventors discovered that consumable electrodes could be used and completed the present invention.

The arc melting furnace used in the present invention comprises a lifting device that supports the consumable electrode vertically and moves it up and down, a seal portion that blocks the molten metal from the outside air, and a power source for generating an arc.

DC power is usually used as the power source for arc generation, and DC positive polarity (
Either of DC reverse polarity (electrode: positive, metal: negative) (electrode: negative, metal: positive) may be used. The arc can also be an alternating current.

When melting the consumable electrode, an inert gas such as argon gas or a mixed gas of an inert gas and a reducing gas such as hydrogen gas is introduced from the upper part of the hollow hole penetrating the consumable electrode.

Supplying such a gas during melting stabilizes the electrode arc, reduces electrical flicker, and improves the power factor, making operation extremely efficient and easy.

Further, the use of the mixed gas has the effect of reducing residual carbon in the obtained ingot.

The gas supply speed varies depending on the size of the electrode used, but a suitable speed is required for the arc to become stable, and if the speed is higher than necessary, the arc will become unstable, which is not preferable.

Melting is performed by momentarily bringing an electrode into contact with the metal mass to be melted placed at the bottom of the mold to generate a starting arc and begin melting. As melting progresses, the electrode tip is lowered to maintain a constant distance from the melting surface to continue melting. It is preferable to add flux during melting for the purpose of maintaining a good casting surface of the ingot obtained by melting and for refining (desulfurization).

The flux to be removed is a multi-component 7-lux consisting mainly of CaF and other heptafides, oxides, chlorides, etc., such as OaF, -NaF, CaF2-
fiJ40g, CaF2 Cab, 0aF2
Am03-Cab, CaF2-Ba.

C! aF, -BaC! 4 is preferred.

Further, in the present invention, metallic chromium powder or grains can be added to the melting part during melting of the electrode, and these can be melted at the same time. The amount of metallic chromium that can be added at this time can range from 10 to 50% by weight of the weight of the consumable electrode.
Alternatively, add it to the dissolution section using a separate system.

This method makes it possible to efficiently melt chromium metal, which has a high melting point.

The metal chromium ingot obtained by the present invention has high purity and has undergone a melting operation, so it can be easily melted as an alloy raw material.
It can also be processed and used as a single metal chromium material.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Metallic chromium powder obtained by electrolytic method, -60 mesh product 2
(11J+y), -525 mesh product 1 part (aS & 9
) to the mixture of artificial graphite powder (-525 mesh) 92.
49 was added and mixed thoroughly, and then 500 d of a 16 wt% polyvinyl alcohol aqueous solution was added and thoroughly kneaded.

Analysis values and particle size distribution of electrolytic metal chromium.

0-60 mesh product Cα021chi Sα022-Nα
0271G 0(L5411i 40upα2% 6ON100515%100-15
02FL6% 150~200'1&6% 200"
ud2t1% 6-525 mesh product Cα025chi 8α024-
N1029% 0α56chi 200 up Q, 4% 20G-525'FL
8*525 ud9A8% This mixture was pre-dried for about 1 hour in a hot air dryer at 120°C, filled into a rubber mold having a core, and pressurized to 5tβ using a hydrostatic press to mold. The molded product was thick, had an outer diameter of 19%φ, a hollow hole inner diameter of 6×φ, a total length of 310%, and weighed about 410 g. This molded body was dried in a hot air dryer at 120° C. for about 6 hours.

Next, this dried molded body was placed in a resistance heating type vacuum furnace equipped with a carbon heater and heated at 1400°C9 (L1~5
Sintering was performed under Torr conditions for 2 hours. The oxygen tFi in the obtained sintered body was α01chi (oxygen ass' in the raw material chromium). A power connection terminal made of iron is attached to this sintered body, and the inner diameter is 54%φ to 56%φ.

A chromium ingot (20% φ x 20%) was charged into the bottom of a reversely tapered copper water-cooled mold with a depth of 140%, and the tip of the consumable electrode was brought into instantaneous contact to generate an arc.

Then, argon gas was supplied from the electrode hollow hole at 1217+ and to the gas seal section at Fia & min, and then a total of 10
9 of CaF were added sequentially. The conditions for dissolution are as follows.

Voltage: 16-52V, Current: 50G-800A.

Required time = 155 seconds, Dissolution amount: 275F, Dissolution amount [:1
22 seconds, polarity: DC positive polarity The analysis value of the obtained metal chromium ingot is: Oxygen: α0
5%, Carbon: (102%, Nitrogen: (LOO4CH, Sulfur:
[LO15 was.

Example 2 Electrolytic metal chromium 160 mesh powder 10kl, same 32
5 mesh powder 5J9 and chromium oxide for pigments 7.5j9.
Artificial graphite powder (-525 mesh) 1.7852 and 16
Thoroughly mix 600 d of vt% polyvinyl alcohol aqueous solution with a kneader type mixer.

The mixture was kneaded, pre-dried and molded in the same manner as in Example 1, and then sintered in the same vacuum furnace (1400°C 11-8 Torr).
r+' hours) The molded body after sintering is exposed to oxygen (LO49G.

It was carbon a5chi.

Next, a power supply connection terminal was attached in the same manner as in Example 1, and a mixed gas of argon and hydrogen (hydrogen 1 oz.
vots) from the hollow hole to the gas seal part,
Argon gas was supplied at 844, and CaaF, 80
A total of 409 lacs of 7 lux having a composition of 0.2% and 0.2% Caa were added and dissolved. The melting conditions are voltage: 19-54
V, current = 500 to 80oA, time required = 156 seconds,
Dissolution amount: 240F, dissolution rate: 9297%, polarity: DC positive polarity.

The obtained metal black ingot was homogeneous and had an oxygen content of 104
%, carbon: α05ti, nitrogen: l1oosl.

Sulfur: Contained nooB%.

Example 5 Electrolytic metal chromium powder 1019 (80-150 mesh = 4
54%, 150-200 Messi: 29.3%, 200
~250 mesh unia, 21,250 mesh: 2α1
h) and -525 mesh powder 5J19 artificial graphite powder (-5
25 me, sh) 97 f! , 16wt Tivoli vinyl alcohol aqueous solution 450- was treated in the same manner as in Example 1 to obtain a chromium consumable electrode.

Use this material to fill the hollow hole of the electrode with argon gas.
L15+ was supplied to the sealing part for 10 minutes, and then 100 g of metal chromium powder ([L1 to 5'X) and flux (CaF, 240%, j403 [0%) were supplied from around the electrode.

CaO: 50% composition and particle size (Ll ~2%) 459 were added and dissolved so that they were all charged during melting.

The melting conditions are voltage: 17-62v, current = 500-80v.
0 A, Required time: 175 seconds. Dissolution amount: 580 g, dissolution rate + 150 g Counterfeit, polarity: DC positive polarity All the chromium powder added from around the electrode was dissolved, and the obtained chromium ingot was homogeneous, containing oxygen α06-1 carbon α0
It was made of 100% nitrogen, α007% nitrogen, and 015% sulfur, and had a Vickers hardness (20 pass load) of 120 to 140, making it easy to machine.

Patent applicant: Toyo Soda Kogyo Co., Ltd. Patent applicant: Takashi Kusakawa

Claims (1)

[Scope of Claims] (1) Metallic chromium is sintered and formed into a shape having a hollow hole penetrating in the long sleeve direction, and the molded body is used as a consumable electrode to reduce inert gas or inert gas from the hollow hole. A method for melting and refining metallic chromium, which is characterized by arc melting the mixed gas while introducing it. (2) The method according to claim (1), wherein argon is used as the inert gas and hydrogen is used as the reducing gas. (6) The method according to claim 1 or 2, in which a molded body obtained by sintering and forming metal chromium, chromium oxide, and carbon is used as a consumable electrode. (4) Electrode hollow hole that consumes metal chromium grains! or added to the melting part from a separate system and dissolved together with the consumable electrode, claim 1, 2 or 5.