JPS61253311A - Method for melting and reducing chrome ore - Google Patents

Abstract

PURPOSE:To advantageously melt and reduce chrome ore in the manner of practical operation by charging molten mother pig iron and the chrome ore into a composite blowing converter, melting the chrome ore, slagging it, adding coke to carry out carburization reduction, and subjecting the resulting molten high-C pig iron contg. Cr to decarburization refining. CONSTITUTION:Molten mother pig iron and chrome ore are charged into a composite blowing converter, a flux is added, and the chrome ore is rapidly melted and slagged by blowing an inert gas for agitation from the bottom and oxygen for refining from the top. While the inert gas is blown from the bottom, coke is added to carry out carburization reduction. At this time, the oxygen blowing may be continued. The resulting molten high-C pig iron contg. Cr is separated from slag, charged into a decarburization refining furnace and subjected to decarburization refining.

Description

[Detailed Description of the Invention] The present invention enables solid chromium ore to be charged into a top-bottom blowing composite blowing converter, melted, and reduced to advantageously produce molten stainless steel. Concerning the smelting reduction method of chromium ore.

Conventionally, chromium-containing hot metal and master alloy for producing molten stainless steel and the like have been mainly produced by melting chromium ore together with coke in an electric furnace. This prescription consumes a lot of energy.

In response to this established recipe, in recent years, a method of direct smelting reduction of chromium ore using a combined blowing converter capable of top-bottom blowing has been studied. A composite blowing converter is a converter that has a tuyere at the bottom of the furnace and is equipped with a top blowing lance, and inert gas and, in some cases, oxygen gas can be introduced through the tuyere at the bottom of the furnace. Therefore, it is advantageous in that sufficient agitation can be given to the contents in the furnace and the atmosphere can also be controlled. Although various studies have been conducted to directly melt and reduce chromium ore by taking advantage of this property, the reality is that it has not yet been established as an actual operational technology.

In order to realize smelting reduction of chromium ore using a combined blowing converter, it is necessary to understand the appropriate conditions to promote smelting reduction under conditions that do not cause melting of the furnace refractories, but data from actual operation examples are available. There is a shortage of chromium ore, and in reality, there are many points that are unclear as to how to proceed with the most efficient melting reduction of chromium ore.

In particular, the gangue content accompanying chromium ore (TIgO, 8120
However, it is unclear how this can be done efficiently.

The present invention aims to overcome these problems and provides a method for realizing melting and reduction of chromium ore using a composite blowing converter in an advantageous manner in actual operation.

The present invention is a method for smelting and reducing chromium ore using a composite blowing converter.

Mother hot metal and chromium ore are charged into a composite blowing converter that can blow top and bottom, and flux is added.

A chromium ore melting process in which chromium ore is turned into molten slag by top-blowing with oxygen while bottom-blowing stirring is performed.

Coke is added to this melted slag.

It consists of a carburization and reduction step in which high-C chromium-containing hot metal is produced with or without oxygen blowing, and a decarburization refining step in which the obtained high-C chromium-containing hot metal is decarburized and refined.

The content of the present invention will be explained in detail below.

The top-bottom blown converter used in the present invention is as follows.

This is a composite blowing converter that has a mechanism for blowing an inert gas such as nitrogen gas, argon gas, or other gas into the bottom of the furnace, and is equipped with an oxygen top blowing lance.

The melting process of the chromium ore and the subsequent carburization and reduction process are performed at least in this composite blowing converter. The chromium ore melting process, carburization reduction process, and decarburization refining process can be carried out in one combined blowing converter, but more preferably, at least two combined blowing converters are prepared, and one It is preferable that one unit performs the chromium ore melting process and the carburization/reduction process, and the other unit performs the decarburization refining process. I for each process
This will be explained below with reference to Jll.

[Chrome ore molten slag process]

In this process, mother hot metal, chromium ore, and flux are added to produce a melt. The mother hot metal may be ordinary pig iron that does not contain Cr, but it is advantageous to use chromium-containing hot metal that contains 20% by weight or less of Cr. Chromium-containing hot metal can be produced in an electric furnace according to two conventional methods. The chromium ore is charged at the same time as the mother hot metal.

In other words, the charging of chromium ore into a composite blowing converter.

In order to promote the formation of chromium ore into molten slag, it is desirable to perform this at the time of charging the mother hot metal, i.e. at the beginning (outside the time when the reducing agent is added to the chromium ore).

In this process, in order to quickly turn chromium ore consisting of chromium oxide, iron oxide, and other gangue-based solid oxides into molten slag, it is necessary to add flux and its appropriate adjustment, bottom-blowing stirring, and oxygen blowing. Training is required.

Flux is added to adjust the basicity of the slag to be produced and the melting point of the slag including gangue. The flux to be added is one containing CaO, SiO
Sing) is 0.5 to 1.3. Preferably 066-1
．． It is best to select 2.

In the case of a highly basic slag with a higher slag basicity than this, its melting temperature becomes higher and it becomes difficult to finish melting the chromium ore within a limited time. In addition, in the case of a low basicity slag with a lower slag basicity than this, although the formation of chromium ore into molten slag is promoted, it is undesirable because it promotes the melting loss of the furnace refractories, i.e., the addition of flux. Depending on the basicity of the slag, the basicity is between 0.5 and 1.3.
By controlling the slag composition so that it is preferably in the range of 0.6 to 1.2, the formation of chromium ore into molten slag is promoted and the melting loss of the furnace refractory can be kept relatively small.

In order to completely transform the chromium ore into molten slag by adding flux in this manner, bottom-blowing stirring and oxygen blowing are required. Nitrogen gas or argon gas can be used as the bottom blowing gas.

This bottom-blown stirring mixes the mother hot metal with the solid substances chromium ore and flux, and when oxygen blowing is performed on the stirred mixture, the oxidation reaction of mainly C in the mother hot metal takes place sufficiently. As a result of the generation of heat based on this, the chromium ore and flux can be completely melted into slag.

[Carburization reduction process]

In the present invention, coke is added after the molten slag formation of the chromium ore is substantially completed. The main purpose of this carburization is to reduce CrtOx that has become a slag. However, it is also used as a heat source for reducing oxides other than Crabs, such as FeO, and for the subsequent decarburization and refining process. It has been found that by performing this carburization after the chromium ore has substantially turned into molten slag, oxides such as CrtOx and FeO present in the slag can be reduced advantageously.

This carburization operation can be carried out by adding coke from the top of the furnace while continuing to blow inert gas from the previous step.If the tuyere is capable of blowing pulverized coal, the stirring gas can be used to blow pulverized coal into the furnace. May be implemented. Coke can be dissolved only by bottom-blowing stirring, and CrzOs and FeO in the slag can be reduced by the carburization operation accompanied by bottom-blowing. In this case, oxygen may be supplied simultaneously from one tuyere. When oxygen is supplied, it is preferable to reduce the oxygen feeding rate in order to prevent excessive oxidation of chromium in the hot metal. On the other hand, even when oxygen is fed from a top-blowing lance, it is preferable to reduce the oxygen feeding rate in order to prevent excessive oxidation of chromium in the hot metal. Even without such oxygen supply, CrtOx can be produced by carburization only under bottom-blowing stirring.
It is also possible to reduce FeO. It is also advantageous to carry out carburization in several parts and to carry out acid feeding as needed. In any case, when oxygen is supplied, it is important that carbonization is carried out to a sufficient C concentration so that oxidation of chromium does not occur. That is, sufficiently increasing the degree of CtR by carburization is an important requirement for advantageously carrying out the reduction of CrtOx.

The recommended recipe for this process is to add coke while stirring from the bottom, start acid feeding when a sufficient Ct of 1 degree is reached, and carry out carburization again when the C concentration has decreased due to this acid feeding. However, the prescription is to carry out a light supply of acid, or to stop the supply of acid and perform only bottom-blowing stirring. The number of times of carburization and the number of times of acid feeding can be increased or decreased as necessary, but in the final stage, it is necessary to stop the acid feeding while maintaining a high C concentration, and the Cr is removed by secondary stirring.
The 2O3 concentration can be reduced significantly and the reductive recovery of chromium from the melt can be almost completed. And like this CrtL
In order to further reduce and recover chromium from a state where the concentration has decreased, it is possible to force reduction by adding a metal reducing agent such as Fe-3i. According to this recipe, almost 100% of CrJ3 can be reduced to chromium. becomes.

The feature of this one-step process is the carburization operation.

By stirring the chromium ore and, if necessary, supplying oxygen, the chromium ore is sufficiently turned into molten slag in the previous step to reduce CrtOx and FeO present in the slag. The reduction rate of CrzOs at the end of this step can be 90% or more. Therefore, at the end of this process, a molten product consisting of high C-containing hot metal and slag is present in the combined blowing converter, in which all of the chromium source in the initially charged chromium ore has been reduced. I will do it. The obtained high C chromium-containing hot metal is separated from slag and then subjected to a second decarburization refining process.

[Decarburization refining process]

The slag produced in the previous process consists of the gangue in the chromium ore and the Franks components added.

Occurs in relatively large amounts. The high C chromium-containing hot metal from which this slag is separated is the object of refining in this process. In actual operation, it is advantageous to separate the slag by receiving hot metal into a ladle from the combined blowing converter in which the previous two steps were carried out. Then, the received hot metal is charged into a decarburization refining furnace to perform decarburization refining. As this decarburization refining furnace, the combined blowing converter in which the previous two steps were carried out can be used, but another refining furnace can also be used. As this other refining furnace, a combined blowing converter, a ladle refining furnace, for example a VOO furnace, etc. can be used. In any case, these smelting furnaces are Cr
Any method that can suppress oxidation loss and decarburize to the target C level, that is, a low carbon range, is sufficient. Any decarburization refining furnace used in the production of conventional molten stainless steel and the like can be used, such as refining or decarburizing under reduced pressure.

In the method of the present invention, since a large amount of coke is added in the previous step, S
The concentration increases according to the amount of coke. For this reason, desulfurization treatment is required, but this can be done either by adding a desulfurizing agent and desulfurizing the pig iron in the ladle after the previous process is completed, or by performing normal desulfurization after decarburization and refining. Just carry out the processing.

Crz inevitably generated during the decarburization reaction
When a combined blowing converter is used as a decarburization refining furnace, Os can be reduced and recovered by adding St in this furnace, and when a converter and a ladle refining furnace are used together,
Both the crude molten steel and slag obtained in the converter are transferred to a ladle refining furnace, where Si is added and chromium can be recovered.

Next, typical examples of the method of the present invention will be described.

Example 1 C: 4.0%, Cr: 16 melted in electric furnace
．． 8%.

S: 45 tons of 0.008% hot metal was charged into a composite blowing converter, 3 tons of chromium ore and 290 kg of silica sand, the composition of which is shown in Table 1, were added, and bottom blowing Nz: 85 Nm
! /Hr×1 tuyere, top-blown oxygen: flow rate 520ONm'/
fir, start oxygen blowing at lance height 1400mm,
When the chromium ore was melted by increasing the oxygen supply amount to 1100 ON', the added chromium ore completely turned into molten slag. At this time, C98 degree is 2.1% and Cr is 16
．． 7%, the temperature is 1565°C, the basicity (CaO/Stow) of the slag is 1.2, and the melting temperature is 14
The temperature was 80°C. In this example, silica sand 290
kg was added, but instead of this silica sand, an equivalent amount of Si was added to Fe.
The same result can be obtained even if S* is charged (the above is the chromium ore melt slag process).

Table 1 (Composition of chromium ore, weight %) Next, 2.5 tons of coke was added, and 1 ton of oxygen was added.
As a result of supplying 50ONm”, C: 2.0%, Cr: 17
．． 8%, S: 0.033%, and about 50% of the chromium ore was reduced. Furthermore, 1.5 tons of coke was added and held for 30 minutes without oxygen supply. As a result, the composition of the hot metal was: C: 3.2%, Cr: 1B, 7
%, S: 0.043%, Crz in chromium ore
Approximately 95% of O* was reduced.

After that, Fe-5i was added and some remaining unreduced Cr
was reduced by Si (carburization reduction step).

The obtained high C chromium-containing hot metal is poured into a ladle.

This was transferred to another composite blowing converter, and the bottom blowing Nt: 85Nm
”/Hr x 1 tuyere, oxygen flow rate: 670ONm'/
Decarburization refining was performed at Hr for 15 minutes. As a result, C:0
．． 01%.

Stainless steel molten steel with Cr: 1B, 2%, S: 0.037% was obtained, and further Fe-S 1450k
Cr20z generated during blowing is reduced by adding 500kg of CaO and 150k of CaFz.
Desulfurization treatment was carried out by adding As a result, C:0.
05%, Cr: 18.6%, S: 0.010% stainless steel was obtained (decarburization refining step).

Example 2 Mother hot metal: C: 3.9%, Cr: 8.5%, S:Q,
The same chromium ore slag formation process and carburization reduction process as in Example 1 were repeated except that 0.007% hot metal was used. As a result, C: 3.1%, Cr: 10.5%,
S: 0.045% high C-containing hot metal was obtained.

The obtained high C chromium-containing hot metal is poured into a ladle.

This was transferred to another composite blowing converter, and the bottom blowing Nt: 35N+
s'/) Ir X 4 tuyere, oxygen flow rate: 770ON+
Decarburization was carried out for 13 minutes at w”/Hr. As a result,
c: o, o9%.

Stainless molten steel with Cr: 10.0%, S: o, o4o% was obtained, and further Fe-S 1500 k
As a result of reducing Cr1O generated during blowing by adding g, C: 0.05%, Cr: 10.5%, S: 0.
0.4% stainless molten steel was obtained. This molten steel is first desulfurized in a VOD furnace, which is a finishing refining furnace, and S
decreased to 0.005%.

Comparative example This example is an example in which recarburization was performed at an early stage.

C1.7%, Cr:19.8% melted in an electric furnace.

S: 43 tons of 0.007% hot metal was charged into a composite blowing converter, and at the same time 2.9 tons of chromium ore, the composition of which is shown in Table 1, was charged.
2.4 tons of coke and 1.4 tons of Ca0 were added, and bottom blowing Nz: 5ONm”/Hr
Oxygen blowing was started at the tuyere, top-blown oxygen: flow rate 520ONm"10r, lance height 1600s+s, and the oxygen supply amount was increased to 353ONms.

C: Blowing was performed to 0.71%. The temperature at that time was 1745°C, and the slag had a high basicity with a melting point around 1720°C. And Cr after oxygen blowing
was only 19.7%, indicating that the reduction of CrzQs in the chromium ore hardly progressed. This is probably because the C concentration decreased to 0.71% when the chromium ore was not sufficiently melted.

Claims (7)

[Claims] (1) Charge the mother hot metal and chromium ore into a combined blowing converter capable of top and bottom blowing, add flux, and perform top-blowing with oxygen while bottom-blowing stirring to convert the chromium ore into molten slag. a process for melting chromium ore to produce chromium ore; a carburization and reduction process for producing high-C chromium-containing hot metal by adding coke to the molten slag with or without oxygen blowing; A smelting reduction method for chromium ore, comprising: a decarburization refining process for decarburizing high C chromium-containing hot metal; (2) The method for smelting and reducing chromium ore according to claim 1, wherein the mother hot metal is chromium-containing hot metal containing 20% by weight or less of Cr. (3) The flux has a slag basicity of the melt of 0.
The method for melting and reducing chromium ore according to claim 1 or 2, wherein the chromium ore is added in such a manner that the amount of chromium ore is 5 to 1.3. (4) Melting of chromium ore according to claim 1, 2 or 3, wherein the decarburization refining step is carried out in a smelting furnace separate from the chromium ore melting step and carburization reduction step. reduction method. (5) The method for melting and reducing chromium ore according to claim 4, wherein the decarburization refining step is carried out in a composite blowing converter capable of top and bottom blowing. (6) The decarburization refining process is carried out in a combined blowing converter capable of top and bottom blowing, and after this decarburization refining, Cr_2
A method for melting and reducing chromium ore according to claim 1, 2, 3, or 4, wherein O_3 is subjected to a reduction treatment. (7) The decarburization refining process consists of a rough decarburization process using a combined blowing converter capable of top and bottom blowing, and a final decarburization refining process using another smelting furnace.
A method for melting and reducing chromium ore according to claim 1, 2, 3, 4, or 5, which carries out a reduction treatment of _2O_3.