JPS61279608A - Production of high-chromium alloy by melt reduction - Google Patents

Abstract

PURPOSE:To execute chromium reduction with high efficiency by dividing a refining process to two processes and specifying the content of Cr in slag in the 1st period and the contents of Cr and MgO in the slag and slag temp. in the 2nd period. CONSTITUTION:A metallic bath 2 of molten iron is contained into a furnace body 1 and a Cr raw material, carboneous material and fluxing agent are introduced from a banker 8 into the furnace body in the 1st period of blowing. Oxygen is blown into the furnace body from a top blowing lance 4 and oxygen or the gas enriched with oxygen is blown therein from side blowing tuyeres 6, 6' to form the slag 3 on the metallic bath 2 and to adjust the content of Cr in the slag 3 to 5-20wt%. Only the carboneous material is introduced into the furnace from the banker 8 and the oxygen or the gas enriched with the oxygen or the inert gas is blown hterein from the tuyeres 6, 6' in the 2nd period. A stirring gas such as N2 is blown into the furnace from bottom blowing tuyeresd 9, 9' to adjust the content of Cr in the slag 3 to <=3wt% and the content of MgO to <=3wt%. The temp. of the parts a1, a2 of the slag 3 where the slag does not contact with the blowing oxygen is maintained higher by >=50 deg.C than the average temp. of the bath 2 in the 2nd period.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high chromium alloys by smelting reduction using an oxygen top-blown furnace.

More specifically, the present invention includes a gas blowing tuyere for stirring a metal bath, a tuyere for blowing oxygen or an oxygen-enriched gas, and an inert gas such as N2, CO2, CO, etc. into the slag, outside the oxygen top-blowing lance. The present invention relates to a method for efficiently producing a high chromium alloy by smelting reduction using a refining furnace equipped with the above.

BACKGROUND ART Conventionally, high chromium steel such as stainless steel has been produced by reducing chromium ore with coke in an electric furnace to produce high carbon ferrochrome, and using this as a raw material. In other words, in this method, high temperatures are required for the reduction of ores with high Cr% to proceed, so they are treated with an excessive amount of carbonaceous material (
This is a two-step method in which high chromium steel is produced by melting the obtained ferrochrome together with an iron source and decarburizing it again in an electric furnace in the presence of coke.

However, this method called “indirect manufacturing method” has
When viewed as a consistent flow from chrome ore to stainless steel, there are the following problems.

(1) Expensive electricity is used as the large amount of energy required to reduce chromium oxide.

(2) Since ferrochrome manufacturing plants and steelmaking plants are generally located far apart, high-carbon ferrochrome is produced as a molten product, but it is solidified once and then remelted during the steelmaking process, resulting in large energy losses.

(3) Since a large amount of slag is smelted in contact with femchrome with a high [Cr%], the (Cr%) in the flag is
It is difficult to lower the chromium loss, and the loss of chromium is large.

Therefore, in order to reduce the cost of melting high chromium steel, it is necessary to solve these problems, and the following measures have been considered. In other words, (1) use cheap primary energy rather than electricity as energy for reducing chromium ore; (2) minimize energy loss in the integrated process from chromium ore to stainless steel; (3) ) It is necessary to minimize the amount of slag and create a reaction or reaction environment with a high Cr recovery rate.

Based on this technical idea, for example, Japanese Patent Application Laid-Open No. 54-15
No. 8320 proposes a method for producing chromium steel from chromium ore using a bottom-blown converter.

However, when chromium ore is directly added to hot metal,
It is not easy to reduce poorly soluble chromite such as MgO.Cr2O3, which is the main component of chromium ore. For efficient reduction, add SiO, CaO, etc., and MgO'
It is necessary to promote the dissolution of CrzOa into the slag (
Publicly known literature Koroki et al., Tetsu to Hagane 70 (1984) 3.11
4). 1゜In order to solve such problems, Japanese Patent Application Laid-Open No. 60-9815 discloses that while keeping the molten metal temperature below 1650℃,
The amount of gas injected from the bottom of the furnace is controlled, and the
A method of melting and reducing by limiting the I-lag composition and the amount of free carbon material is disclosed. However, this person
Method 1 requires strong stirring of the slag in order to reduce chromium, but there is a major difficulty in refining operations in that this stirring force is transmitted to the slag via stirring of the metal. That is, since the amount of metal stirring gas is extremely large, non-02 gas tends to cause a drop in metal temperature. 0 to maintain temperature
There is a dilemma when 2 is included, which leads to oxidation of chromium in the metal. Furthermore, when separating the slag and metal after the second stage, it is difficult to reduce the amount of blown gas, resulting in an increase in metal loss as suspended particulate iron in the slag.

Problems to be solved regarding H generation The purpose of the present invention is to solve the above-mentioned problems of the prior art, and more specifically, to reduce chromium in a high yield without causing excessive wear and tear on the refractories in the furnace. The object of the present invention is to provide a method for producing a high chromium alloy by smelting reduction that can be realized at a high rate.

Means for Solving the Problems As a result of various experiments and studies in order to achieve the above-mentioned object of the present invention, the present inventors obtained the following knowledge and completed the present invention.

■ JP-A-54-158320 and JP-A-60-9
Chromium reduction is performed using a top-bottom blowing converter disclosed in Publication No. 815, but when oxygen is blown into the metal bath, which should originally be a reducing atmosphere, the reduced chromium is reoxidized and chromium is reduced. Slow down. In addition, special blowing equipment is required to bottom blow pulverized coal into a metal bath, which increases running costs.

■ On the other hand, in smelting reduction, chromium is reduced in slag, and the metal bath is treated as a medium to recover the chromium that falls due to reduction. Separate management of the slag and metal bath improves reaction efficiency, heat management, and fire resistance in the furnace. It was found that this is extremely preferable from the point of view of improving the basic unit of production.

■ In other words, in order to improve the chromium reduction reaction efficiency and recovery rate, the chemical composition, temperature, and reducing atmosphere of the slag should be optimally adjusted, while the metal bath should be sufficiently stirred to maintain a uniform temperature. be.

■ Based on this technical idea, during periods when a large amount of heat source is required, such as at the chromium ore inlet, oxygen is not top-blown, but oxygen or oxygen-enriched gas is also blown into the slag. Heating and slag stirring will be strengthened. On the other hand, stirring gas is blown from the bottom of the furnace to make the temperature of the metal bath uniform, and the metal bath is heated only by conduction heating through contact with the slag.

In addition, during periods when a heat source is not required, such as after the completion of charging chromium ore, the amount of top-blown oxygen is reduced to maintain a balance between calorific value and heat absorption, and to reduce the oxygen concentration of the gas blown into the slag.

If a sufficient heat balance is achieved, it is more desirable to use an inert gas such as N2, CO2, or CO in order to further strengthen the reducing atmosphere within the slag.

At this time, of course, oxygen is not used to stir the metal, and heating is carried out through conduction from the slag.

The present invention has been completed based on the above knowledge, and according to the present invention, a gas blowing tuyere for accommodating a metal bath inside and stirring the metal bath below the surface of the metal bath, and a A smelting furnace is provided with a tuyere located above the bath surface and below the slag surface for blowing oxygen or oxygen-enriched gas and an inert gas such as N2, CO2, CO into the slag, and an oxygen top blowing lance. This is a method for producing a chromium alloy with a Cr content of 39% or less by smelting reduction. The refining process is divided into two stages: the Cr content in the slag at the end of the first stage is 5 to 20% by weight, the Cr content in the slag at the end of the first stage is less than 3% by weight, and the Cr content in the slag at the end of the first stage is less than 3% by weight.
Maintain the Mg0 content in the slab during the period to less than 30%,
There is provided a method for producing a high chromium alloy by smelting reduction, characterized in that the temperature of the portion of the slag that does not come into contact with the blown oxygen is maintained at 50 t' or more higher than the average temperature of the metal bath.

The present invention will now be described in detail with reference to the accompanying FIGS. 1 and 2. FIG.

FIG. 1 is a schematic cross-sectional view of a reactor suitably used to carry out the method of the present invention, and FIG. 2 is a region where the slag and blown oxygen in the refining furnace shown in FIG. 1 come into contact. FIG.

Although FIG. 1 shows a refining furnace that is a modified top-bottom blowing converter, the refining furnace used to carry out the method of the present invention does not have to be a converter type, and may be, for example, a modified electric furnace. . 1st
In the figure, a furnace body 1 is lined with, for example, magnesia-chromate bricks, and a metal bath 2, for example hot metal or molten steel, is accommodated inside the furnace body 1.

A slag 3 is formed above the metal bath 2 , and a top blowing lance 4 for blowing oxygen into the top surface of the slag 3 is provided hanging down from above the opening 5 of the furnace body 1 . A 6.6° horizontal blowing tuyere for blowing oxygen or oxygen-enriched gas and inert gas such as N2, CO2, CO, etc. is provided in the furnace wall of the furnace body 1.

Further, an exhaust gas recovery hood 7 is removably attached to the opening 5 of the furnace body 1, and a bunker 8 is provided for adding chromium raw materials such as chromium ore and reduced pellets, carbon materials such as coke, and solvents into the furnace. It is provided.

On the other hand, the bottom of the furnace body 1 is provided with tuyeres 9 and 9' through which gas is blown into the metal bath 2 to stir it.

According to the method of the present invention, a chromium raw material, a carbonaceous material, and a solvent material are cut out from a bunker 8, placed on a metal bath 1, and oxygen is blown into the metal bath 1 from a top blowing lance 4 to form a slag 3.

Further, according to the method of the present invention, in the first stage of blowing, the chromium raw material, carbon material, and solvent are charged from the bunker 8, oxygen is blown from the top blowing lance 4, and the side blowing tuyeres 6.6' The slag 3 is placed on the metal bath by blowing oxygen or oxygen-enriched gas from
form.

After the first period is completed, in the second period, the injection of chromium raw material and solvent from the bunker 8 is stopped, only the carbonaceous agent is introduced, and oxygen or oxygen-enriched gas or N2 , CO□, CO, etc. through the bottom blowing tuyere 9
．． From 9° onwards, blow in a stirring gas such as nitrogen.

Figure 1 shows the portion of the slag that comes into contact with oxygen blown from the top blow lance 4 and the side blow tuyere 6.6°. The portion a1 and the contact portion a2 between the slag and the oxygen blown from the side blowing tuyeres 6.6'' occupy a considerable portion of the horizontal cross section of the slag 3. In addition, the blowing direction of the side blowing tuyere 6.6゛ is set apart from the radial direction of the horizontal cross section of the furnace body l, so that the slag is effectively stirred, while the top blowing lance 4 is placed at a height position. It is preferable to adjust the area of the contact portion al of oxygen with the slag to be large by changing the horizontal position.

As mentioned above, in the second stage, only carbonaceous material is injected from bunker 8, and the heat balance is maintained by the amount of top-blown oxygen.
If the oxygen-enriched gas from the side blowing tuyere or the heat balance is sufficient, the slag is strongly stirred with an inert gas such as N2, CO2, or CO to reduce chromium in the slag. on the other hand,
In the second period, stirring gas is blown into the furnace bottom through the 9.9° tuyere, and the metal bath 2 is stirred and at the same time conductively heated by contact with the slag 3. Therefore, the metal bath 2 is kept in a reducing atmosphere without coming into contact with oxygen, receives chromium reduced in the slag, and is heated by the slag as described above, so that fluidity can be maintained.

The reasons for limiting each condition in the method of the present invention will be explained below.

The high chromium alloy to be manufactured by the method of the present invention has a Cr content of 39% or less. In the case of a chromium alloy with a Cr content of more than 39%, the Cr content in the slag increases and the fluidity of the slag significantly decreases, so the efficient implementation of the present invention, which mainly involves the reduction of chromium in the slag, cannot be expected. Because I want to. On the other hand, the method of the present invention is applied to the production of chromium alloys having a Cr content of 5% or more. In the production of chromium alloys with a Cr content of less than 5%, since the amount of chromium ore used is small, conventional methods such as reduction of the chromium content with hot metal are sufficient.

The Cr content in the slag at the end of the first stage is 5 to 20% by weight.
The range shall be . If it is less than 5%, the rate of chromium reduction is slow in the method of the present invention, which mainly reduces chromium in the slag, while if it exceeds 20%, the fluidity of the slag decreases, making it necessary to heat the slag to an even higher temperature. , the corrosion of the refractories in the furnace becomes extremely severe.
(Furthermore, in the method of the present invention, the MgO content in the slag in the
%, preferably in the range of 20 to 30%.

IJgO is a component from chromium ore, and forms MgO・(:r20a) in the reaction process of Cr, and the rate-limiting step for chromium reduction is the dissolution of MgO・Crz03.In order to accelerate the reduction rate of chromium, MgO must be low. However, since refractories usually have MgO as their main component, a certain amount of MgO in the slag is necessary from the standpoint of protection.Therefore, the MgO in the slag in stage Ⅰ should be 20% or more. However, if MgO in the slag exceeds 30%, the chromium reduction reaction rate will drop significantly, so it is set to less than 30%.

Furthermore, in the second stage of the chromium reduction method of the present invention, the temperature difference between the slag and the metal bath is maintained at 50° C. or more. This slag temperature is the temperature of the slag in a portion that is not in contact with oxygen blown in from the top blowing lance or the side blowing tuyere. As mentioned above, in the method of the present invention, the chromium reduction is carried out in the slag and not in the metal bath, so it is only necessary to heat the slag to the temperature necessary for the chromium reduction reaction. 7)?=sm*0), sG old 6)
[6°″′”(7)ut Ll”!!!?m“6
°""11 degrees is defined as 0 temperature in the range of 1,550 to 1,750 t: Below 155 degrees, the chromium reduction reaction will not proceed, while if it exceeds 1,750 degrees Celsius, damage to the refractories in the furnace will be significant. It is.
;Example
] Hereinafter, the present invention will be explained with reference to Examples, but these Examples are merely illustrative of the present invention and do not limit the technical scope of the present invention in any way. Chromium reduction was carried out using the reactor shown in FIG.

The metal bath (hot metal) used, chromium raw material (chromium
Table 1 shows the chemical components and usage amounts of (bellet), solvent (calcined lime, silica), and charcoal (coke).
[[.

[Table 1 Tatami, chrome pellets, calcined lime, and silica were all added during the first period, and 3000 kg of coke was added in the first period and 500 kg in the second period.

The treatment time in the first stage was 50 minutes, in which 140 ONm' of oxygen was blown from the top blowing lance, 50 ONm3 of 02 and 30 ONm3 of N2 were blown from the side blowing tuyere, and 10100 N of N2 was blown from the bottom blowing tuyere.

The slag components obtained at the end of the first stage are shown in Table 2.

Table 2 (wt%) Stage Ⅰ requires 30 minutes, and 40 minutes of oxygen is supplied from the top blowing lance.
ONm', 45ONm3 of N2 was blown from the side blowing tuyere, and 5ONm3 of N2 was blown from the bottom blowing tuyere.

The temperatures of the slag (the part not in contact with oxygen) and the metal bath during the second period were approximately 1,650°C and 1,590°C, respectively.

The chemical compositions of the slag and metal bath at the end of period (III) are shown in Tables 3 and 4, respectively.

Table 3 (wt%) Table 4 (wt%) ↑ As explained above, the present invention breaks the common sense of the conventional chromium reduction method by smelting reduction, and only oxygen or oxygen is added to the slag in the smelting furnace. A horizontal blowing tuyere is provided to blow enriched gas and inert gas such as N2, CO2, GO, etc. to reduce chromium only within the slag. Therefore, the metal bath is not blown with oxygen and is always maintained in a reducing atmosphere, making it possible to achieve highly efficient chromium reduction and reduce the consumption of refractory materials in the furnace, making it possible to produce high chromium alloys by smelting reduction. This will greatly contribute to the industrialization of the world.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a smelting furnace preferably used to carry out the method of the present invention, and FIG. 2 shows the portion of the slag in the smelting furnace shown in FIG. 1 that comes into contact with oxygen. It is a schematic diagram.

Claims (1)

[Claims] (1) A metal bath is housed inside, and a gas blowing tuyere for stirring the metal bath below the metal bath surface, and a gas blowing tuyere located above the metal bath surface and below the slag surface to provide oxygen or oxygen in the slag. A method for producing a chromium alloy with a Cr content of 39% or less by smelting reduction using a smelting furnace equipped with a tuyere for blowing oxygen-enriched gas and an inert gas such as N_2, CO_2, CO, and an oxygen top-blowing lance. Therefore, the refining process is divided into Stage I, in which chromium raw materials, carbonaceous materials, and solvents are input, and Stage II, in which only carbonaceous materials are input and chromium is reduced. 5 to 20% by weight, the Cr content in the slag at the end of stage II is kept below 3% by weight, the MgO content in the slag during stage II is kept below 30% by weight, and the blown oxygen in the slag is A method for producing a high chromium alloy by smelting reduction, characterized in that the temperature of non-contact parts is maintained at 50°C or more higher than the average temperature of a metal bath.