JPH01294815A - Refining method by electric furnace - Google Patents

Abstract

PURPOSE:To enable melting and reduction at high efficiency without any remaining solid chromium ore by melting metallic ore raw material with arc heat, reducing with added reducing agent, blowing inert gas into the molten metal to stir the molten metal. CONSTITUTION:The powdery chromium ore, etc., is supplied in forming range of arc 4 between electrodes 3 and the molten metal 5 in an electric furnace 1. As this arc 4 is under extremely high temp. condition, the chromium ore, etc., having high m.p. and difficult-to-reducing property is easily melted and reduced with the reducing agent separately added in the electric furnace 1. The reducing agent added in the electric furnace 1 is melted in the slag 6 by a part thereof and also in the molten metal 5. Further, as the gas is blown into the molten metal 5 to stir the molten metal 5, the molten metal 5, slag 6, reducing agent and chromium ore are brought into contact with each other and reacted, and chromium ore, etc., are reduced with carbonaceous reducing agent for a short time and the chromium concn. in the molten metal 5 is raised.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is an electric furnace that uses arc heat to melt and reduce scrap, ferroalloy, etc. This article relates to a bottom-blowing electric furnace refining method that efficiently melts and reduces carbon dioxide with high efficiency and high recovery rate.

[Prior Art] Here, examples of chromium-containing steels such as stainless steel and high alloy A using chromium ore and the like will be explained as examples of high melting point, hard-to-reducible oxides.

Chromium-containing steels such as stainless steel and high-alloy steel are manufactured by melting raw materials in an electric furnace and then using the next process of argon oxygen decarburization refining equipment (hereinafter referred to as AOD) or vacuum oxygen decarburization equipment (hereinafter referred to as VO).
D) to decarburize to a predetermined carbon concentration. In this case C
Conventionally, r is added by charging ferrochrome, which is an alloy of 20 to 60% by weight of Cr and iron, into the molten metal. This method of producing ferrochrome involves charging chromium ore and limestone, which are hard-to-reducible and hard-to-dissolve oxides, into an electric furnace, and then adding a reducing agent to the primary slag melted by electricity to reduce the chromium ore. , melted and manufactured.

[Problems to be Solved by the Invention] However, when producing chromium-containing steel using ferrochrome, a large amount of electrical energy is required to produce the ferrochrome, and it is difficult to convert the ferrochrome into a molten metal. After charging, the molten metal is stirred using a stirrer, which poses a problem in that the stirring is weak and refining takes time, making the manufacturing cost of chromium-containing steel extremely high.

This invention was made in view of such circumstances, and
An object of the present invention is to provide an electric furnace refining method that can quickly produce chromium-containing steel at low cost by using inexpensive chromium ore as a chromium source.

[Means for Solving the Problems] The present invention provides an electric furnace for refining molten metal by forming an arc between an electrode and the molten metal, in which a powdered metal raw material ore is placed in a region where the arc is formed or in the vicinity thereof. The metal raw material ore is melted by the arc heat generated between the electrode and the molten metal, and is reduced by a reducing agent added separately into the electric furnace. It is characterized by the arrangement of a blowing nozzle to blow gas into the molten metal in the electric furnace.

Furthermore, the powdered metal raw material ore and the reducing agent are passed through the hollow electrode by forming a passageway opening at the lower end of the electrode along the central axis of the electrode. It can also be supplied to the arc region or a high temperature region near it.

[Operation] In this invention, powdered chromium ore or the like is supplied to the arc forming region between the electrode and the molten metal in the electric furnace. Since this arc is at an extremely high temperature of 3000° C., it has a high melting point, and even chromium ore, which is difficult to reduce, is easily melted and reduced by a reducing agent added separately into the electric furnace. The reducing agent is preferably in powder or granular form in order to quickly reduce chromium ore and the like. This powder and granular reducing agent (for example, coke, coal, etc.) added to the electric furnace partially dissolves into the slag and molten metal. Furthermore, as gas is blown into the molten metal and the molten metal is stirred, the molten metal, slag, reducing agent, and chromium ore come into contact and react, and the chromium ore etc. are reduced by the carbon-based reducing agent in a short time, reducing the chromium in the molten metal. concentration increases.

[Example] Hereinafter, an example in which a VOD is used as a decarburization refining furnace for molten metal discharged from an electric furnace will be described. The molten metal discharged from this electric furnace is further decarburized by VOD to produce a specified low carbon steel. In this case, if the carbon concentration of the molten metal supplied from the electric furnace to the VOD is high, it will take time to refine the VOD.

D's efficiency decreases. Therefore, the final carbon concentration in a typical electric furnace is 1% or less.

In such a molten metal with a low carbon concentration, even if chromium ore is simply introduced into the molten metal, the chromium ore, which has a high melting point and is difficult to dissolve, is not easily reduced.

The reason for this is that chromium ore is mainly composed of chromite (Mg, Fe) O. (Cr, Af, Fe) 203 with a spinel structure, and the characteristics of the spinel structure are: ■ strong bonding force, ■ high melting point. ■It is thermally and mechanically stable, etc., so it has traditionally been considered difficult to industrially reduce chromium ore in electric furnaces, and chromium ore is used to manufacture chromium-containing steel in electric furnaces. It had not been done.

Against this background, the present invention was developed by injecting chromium ore powder into the arc formation region where the arc between the electrode of the electric furnace and the molten metal has an extremely high temperature of 3000°C. The chromite structure dissolves into oxidized bodies (MgO, FeO, AJ?
203. Cr20. ) and then reduced with a reducing agent such as carbon, silicon, or aluminum using a slag containing CaO as a medium. At this time, in the conventional one-type stirrer stirring of the molten metal, (Cr203) + 3C → 2Cr + 3CO2 (Cr203)
)+38i-+4Cr+3Si022<Cr203)
+ 2 A 4 → 4 Cr±2 A Since the reaction of 4203 etc. is slow and the steelmaking time is extended, and the reduction rate of chromium is small, the molten metal is stirred strongly by blowing gas into the molten metal, and the molten metal is stirred for a short time. It was based on the idea that molten metal and chromium ore would react. Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing a first embodiment of the present invention. In the electric furnace 1, three electrodes 3 are inserted perpendicularly to the longitudinal direction of the furnace M2.

First, scraps, ferro-alloys such as ferrosilicon, flux, etc. are charged into the furnace, and a three-phase AC voltage is supplied to the electrodes 3 from a power source. Then, an arc 4 is formed between the @ pole 3 and the scrap, etc., and the scrap is melted by the arc heat, and a molten metal 5 and slag 6 on the molten metal are obtained. A vibrator 7 is inserted into the electric furnace 1, and a nozzle 8 at the tip of the vibrator 7 connects the electrode 3 and the slag 6.
We are now approaching arc 4 between the two. The base end side of the pipe 7 is connected to a tank 9, and the vibe 7 is further connected to an inert gas supply source (not shown) via a pipe 10. Powdered chromium ore is stored in the tank 9. And electric furnace 1 corresponding to three electrodes 3
Three gas blowing nozzles 12 for blowing the gas in the molten metal 5 into the bricks 11 at the bottom of the furnace are installed. At the bottom of each gas blowing nozzle 12, an inert gas (Ar,
An inert gas supply pipe 13 for supplying N2) is connected, and inert gas is supplied from an inert gas supply device (not shown).

Note that the gas flow rate for each gas blowing nozzle 12 can be independently controlled. The material of the gas blowing nozzle 12 is Mg0-C, and MHP (multiple-hole
e-plB (trade name) was used.

The arrangement of the gas blowing nozzle 12 is 300 to 800 III 11 from the pitch circle of each electrode 3 to the furnace wall side of the electric furnace 1.
This is the position of The thin tubes in the gas blowing nozzle 12 were stainless steel pipes arranged in a number of 23 tubes per 1 mm.

The gas blowing nozzle 12 has a truncated conical shape, and the overall dimensions are 80 mmΦ on the head side and 130 mm on the bottom side.
IIIΦ, and the total length of the gas blowing nozzle 12 is 690 mm.

When manufacturing the chromium-containing steel according to the present invention using the apparatus configured as described above, first, raw materials such as scrap are charged into the electric furnace 1, and fluxes such as lime and silica sand are also charged. Then, a three-phase AC voltage is supplied to the electrode 3,
An arc is formed between the electrode 3 and the scrap to melt raw materials and the like. At the same time, inert gas is blown in from the blowing nozzle 12 located at the bottom of the electric furnace 1. After the raw materials, etc. are completely melted, burned lime, FSi, etc. are introduced into the electric furnace 1 through the charging door 14. Furthermore, reducing agents such as chromium ore and coke are cut out from the tank 9 at a predetermined speed and blown into the arc 4 from the nozzle 8 together with the carrier gas. The reducing agent may be added separately from the chromium ore without being mixed with the chromium ore. In this case, the reducing agent may be blown into the arc, or
It may also be blown into the slag. During this chromium ore injection period, an inert gas is blown from a gas injection nozzle 12 arranged at the bottom of the electric furnace 1.

The chromium ore injected into the slag 6 floating on the surface of the molten metal has a spinel structure called chromite.
Cab is a slag component.

In the case where it is in a mixed state with 5in2 etc. or due to high temperature arc heat, this spinel structure decomposes and becomes MgO, A, Rz O3°Fed, Fe2 which constitutes chromium ore.
It is presumed that the strong chemical bond with Cr2O3 such as 03 is broken and the slag 6 is in a mixed molten state with CaO, 5i02, etc., which are the constituent components of the slag 6. In any case, chromium exists in the slag 6 immediately after being blown into the slag 6 in an unreduced state of Cr2O3. In order to efficiently reduce the chromium content of Cr2O3 in the slag 6 into the molten metal, in the embodiment of the present invention, a powder called a slag conditioner is added into or on the slag 6 during the injection of chromium ore. Immediately after completing the injection of chromium ore, 350 kg of ferrosilicon was injected.
g was added. Also during this reduction period, the reduction reaction was promoted by stirring the slag and molten metal using bottom-blown gas.

Furthermore, in order to compensate for the lack of reduction reaction in the furnace, when tapping,
By putting a small amount of ferrosilicon (100 kg) into the ladle, the chromium reduction rate can be further increased with high efficiency by stirring the argon gas from the porous plug blown from the bottom of the ladle.

As in this invention, by supplying chromium ore to the arc forming region, Cr2O3 in the added chromium ore is melted into the slag by the arc heat between the electrode and the molten metal, and the added coke is dissolved. Carbon or slag conditioner as shown in Table 1 (shape + 3mmΦ or less) medium or smaller, A!
2. It is thought that SiC causes a direct reduction reaction of Cr2O3.

The role of this slag conditioner is that the Af contained in this conditioner,
It is thought that part of the direct reduction reaction of Cr2O3 by SiC,C is occurring. Furthermore, the purpose of this slag conditioner is to: (1) form by carbon content (C+O→CO
20g of Cr due to foaming of slag due to gas generation)
Activation of the entire slag including (2) metals A, Q, SiC
The entire slag heats up due to the exothermic reduction reaction caused by the Si inside, 〈＼) and A! 2209.5i02. The reduction reaction is promoted by improving the fluidity of the slag by adding R20 (alkali) and Na2AρF6.

Table 1 (Sheep rank: weight %) Next, the results of reducing chromium ore by the method of the present invention will be explained. Tables 2 and 3 show the composition (% by weight), particle size, etc. of the chromium ore used.

Table 2 (wt%) Table 3, Figure 2 shows the changes in Cr concentration [Cr], carbon concentration [C], and molten metal temperature in the molten metal when chromium ore is reduced, and the changes in Cr oxide in the slag. FIG. 2 is a graph diagram showing changes in concentration (CrzOl), basicity, and elapsed time after the start of addition of chromium ore.

After melting the scrap, we started blowing in chromium ore, but
As a preliminary step, 300 kg of ferrosilicon was added in order to prevent chromium oxidation in the molten metal during scrap melting.

This chromium ore is stored in tank 9 and weighs 4.5 kg/c.
o! using an inert gas at a pressure of 125 as a carrier gas.
It was blown into the vicinity of the arc 4 for 16 minutes at a supply rate of kg/mis. This blowing amount is 40 kg per molten metal T. On the other hand, the reducing agent slag conditioner was blown into the furnace slag for 16 minutes from a separate tank at a feeding rate of 22 kg/mil during the chromium ore injection period. It weighs 7 kg. During the injection period of chrome ore, molten heirgon gas is injected from the bottom of the furnace. The amount of argon blown into the molten metal during chromium ore injection was 70ρ/ffl111×3. After the supply of chromium ore, reducing agent coke, and slag conditioner was completed, 300 kg of ferrosilicon was placed in an electric furnace in order to reduce (Cr2 o3) remaining unreduced in the slag into the molten metal.

Next, the molten metal 5 is tapped into a ladle, and Fe is added into the ladle during tapping.
While charging Si, Ar gas was blown into the molten metal in the ladle to stir the molten metal, thereby compensating for the insufficient reduction of Cr in the electric furnace 1. After the injection of the chromium ore and the injection of the slag conditioner are started, [C] and [Crl in the molten metal gradually rise, and (Cr20i) in the slag also gradually rises. After the chrome ore injection is completed,
After 33 minutes, (Cr2 ol ) in the slag rapidly decreases, while [Cr 2 ] in the molten metal increases significantly. This is because (Cr203) in the slag was reduced by the added ferrosilicon and [Crl in the molten metal increased. In this manner, in the production of chromium-containing steel, chromium ore can be reduced with high efficiency without any molten chromium ore remaining in the electric furnace 1. In addition, the molten metal and slag are stirred by blowing inert gas into the molten metal from the gas blowing nozzle installed at the bottom of the electric furnace 1, so that the added chromium ore, ferrosilicon, and slag conditioner are absorbed into the electric furnace. evenly distributed.

FIG. 3 is a melting and refining process diagram showing a second embodiment, in which a carbon reduction method is used in place of ferrosilicon as an inexpensive reducing agent using bottom-blown stirring.

The difference from the first example is that the carbon reduction method has a weaker reducing power than the ferrosilicon reduction method, so the reduction time is 2.
In addition, 10 kg/ton of carbon was blown into the slag during the chromium ore injection stage.

FIG. 4 is a graph showing the progress of chromium reduction in Example 1. In this figure, the vertical axis indicates the pure amount of chromium brought in from the chromium ore injected into the furnace, and is represented by bar graph A with an index of 100. The horizontal axis shows each work process, bar graph B is at the end of chromium ore injection, bar graph C is before ladle tapping,
Bar graph D is before VOD processing. The shaded area indicates the proportion of pure chromium reduced from the slag. This pure chromium was determined from the changes in [Crl and (Cr303) in FIG. 2. As is clear from FIG. 4, stirring of the molten metal is promoted by blowing chromium ore into the arc region, adding a slag conditioner and ferrosilicon, and simultaneously blowing argon into the molten metal from the bottom of the electric furnace.
Chromium ore is reduced in each step. It can also be seen that the pure chromium content in the molten metal increases.

Here, the pure chromium content it (kg) is: Chromium ore injection amount (kg) x chromium oxide in chromium ore (Cr 20 s>wt% x 104/152
x 1/100 FIG. 5 is a diagram showing a comparison of the reduction rate of the pure chromium content in the charged chromium ore between Examples 1 and 2 and the conventional method.

Here, the vertical axis is the reduction rate of pure chromium introduced into the electric furnace, and the horizontal axis is the conventional method (stirrer agitation, carbon reduction),
Examples (bottom-blown stirring, carbon reduction) and examples (bottom-blown stirring, silicon reduction) are shown. For comparison, the reduction time is the reduction rate in the electric furnace after 33 minutes (constant).

The reduction rate (%) of the pure chromium content is calculated as the reduced pure chromium content (kg)/the pure chromium content (kg) of the input chromium ore x 10'O1.

As is clear from this figure, the reduction rate of the pure chromium input in the method of this example is improved by about 2 to 3 times as compared to the conventional method.

FIG. 6 is a diagram showing a comparison of the reduction time in the electric furnace between Example 1, Example 2, and the conventional method.

Here, the vertical axis is the reduction time in the electric furnace, and the horizontal axis is the conventional method (stirrer stirring, carbon reduction), Example 2 (bottom blowing stirring, carbon reduction), Example 1 (bottom blowing stirring, silicon reduction). ), and for comparison, the reduction time required to obtain the same reduction rate (72%) as silicon reduction was used. As is clear from this figure, the reduction time is 1
/3 to 2/3, and the reduction rate is 2 to 3 times higher.

Next, a third embodiment of the present invention will be described with reference to FIG.

In FIG. 7, the same parts as those in FIG. 1 described above are given the same reference numerals, and explanations thereof will be omitted. The three electrodes 14 have a cylindrical shape, and a passage (not shown) for powdered chromium ore extending in the longitudinal direction is formed in the center thereof. Each passageway is connected to a distribution vibrator 15, and the distribution pipe 15 is connected to a supply vibrator 16. This supply pipe 16 is connected to a suitable inert gas supply source (not shown), and a hopper 9 is disposed in the supply pipe 16.

And the bricks 1 at the bottom of the electric furnace 1 corresponding to the three electrodes 3
Three gas blowing nozzles 12 for blowing gas inside the molten metal into the molten metal are installed. An inert gas supply pipe 13 for supplying an inert gas (Ar, N2) is connected to the bottom of each gas blowing nozzle 12, and the inert gas is supplied from an inert gas supply device (not shown). There is.

Note that the gas flow rate for each gas blowing nozzle 12 can be independently controlled. The material of the gas blowing nozzle 12 is Mg0-C, and MHP (multiple-hole
e-plug (trade name) was used.

The gas blowing nozzle 12 is arranged at a position of 300 to 800 inches from the pitch circle of each electrode 3 toward the furnace wall side of the electric furnace 1. The thin tube inside the gas blowing nozzle 12 is 1 m long.
There are 23 of them in m.

The blower 5/zure 12 has a truncated conical shape,
The overall dimensions are 80nu++Φ on the head side and 13nu on the bottom side.
0mmΦ, the overall length of the gas blowing nozzle 12 is 6
It is 90 mm.

The chromium ore and reducing agent in this hopper 9 are
The high-pressure carrier gas is blown onto the arc 4 from the discharge I at the lower end of the electrode through the flow path of the electrode 3. The operating conditions are the same as in the first and second embodiments described above. Also in this third example, like the first example and the second example, chromium ore could be reduced with high efficiency in the electric furnace.

[Effects of the Invention] According to the present invention, powdered chromium ore, etc., which has a high melting point and is hardly soluble, and a reducing agent are mixed in an electric furnace in an arc region between an electrode and molten metal, or in a high temperature region in the vicinity thereof. Inert gas is blown into the molten metal from the gas injection nozzle at the bottom of the furnace, and the molten metal is stirred, so there is no residual chromium ore and the melt angle can be reduced with high efficiency.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the first embodiment of the present invention, and Figure 2 is the Cr concentration [Cr] in the molten metal when chromium ore is reduced.
, changes in carbon concentration [C] and molten metal temperature, and Cr in slag
A graph showing changes in the concentration of vitreous (Cr20s), basicity, and elapsed time after the start of addition of chromium ore; FIG. 3 is a melting and refining process diagram showing the second embodiment of the present invention; The figure is a graph showing the transition of chromium reduction in Example 1, and FIG. 5 is a graph showing the transition of chromium reduction in Example 1. FIG. 6 is a diagram showing a comparison of the reduction rate of pure chromium in the charged chromium ore between Example 2 and the conventional method. FIG. 7 is a diagram showing a comparison of the reduction time in the electric furnace between Example 2 and the conventional method, and is a schematic diagram showing the second example of the present invention. 1... Electric furnace, 3... Furnace lid, 3... Electrode, 4...
・Arc, 5... Molten metal, 6... Slag, 7, 10.
... Pipe, 8... Nozzle, 9... Tank, 11.
...Bricks at the bottom of the hearth, 12...Blow nozzle, 13...
・Inert gas supply pipe.

Claims (2)

[Claims] (1) In an electric furnace that refines the molten metal by forming an arc between the electrode and the molten metal, powdered metal raw material ore is supplied to the arc formation area or a high temperature area in the vicinity, and the electrode and the molten metal are The metal raw material ore is melted by the arc heat generated between the two and reduced by a reducing agent added separately into the electric furnace. An electric furnace refining method characterized by blowing gas into molten metal. (2) the powdered metal raw material ore and the reducing agent form a flow path in the electrode that opens at the lower end of the electrode along its central axis;
2. The electric furnace refining method according to claim 1, wherein the metal raw material ore is melted by supplying the material from the lower end of the electrode to an arc region or a high temperature region in the vicinity thereof through the flow path.