JP2842185B2 - Method for producing molten stainless steel by smelting reduction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a carbonaceous material as a fuel and a reducing agent, and melts and reduces Ni ore, Cr ore, semi-reduced chromium pellets, etc. together with hot metal in a converter type smelting furnace to obtain a molten stainless steel. The present invention relates to a method for producing molten stainless steel by smelting reduction.

[0002]

2. Description of the Related Art Conventionally, stainless steel is melted by scrap, alloyed iron such as FeCr or FeNi, or N 2 by an electrolytic method.
This has been done by re-melting raw materials such as i in an electric furnace or a converter. According to this method, Cr and Ni, which are the main components of stainless steel, are made of ferro-alloy reduced in advance in an electric furnace or the like and use expensive electric energy, so that they are not economical. From such a viewpoint, there has been proposed a method for producing stainless steel more economically by using Cr ore as a Cr source and smelting and reducing it in a converter or other melting furnace.

On the other hand, a method of using inexpensive raw materials as a Ni source is to directly use molten FeNi in an electric furnace for the purpose of reducing FeNi melting cost [Iron and Steel, 69 (1983)
7, p. 59], a method of melting and reducing nickel matte in a converter (Japanese Patent Laid-Open No. 58-104153) or a method of preliminarily reducing a nickel oxide mixed with a carbon material and heating the mixture (JP-A-60-36613). Gazette).
On the other hand, several methods have been proposed in which Cr ore is used as a Cr source and is melt-reduced in a converter or other melting furnace. For example, with oxygen blowing from a lance,
It is known to blow oxygen from the bottom tuyere and nitrogen from the side tuyere, or to blow oxygen from the bottom tuyere, and oxygen and nitrogen from the horizontal tuyere together with oxygen from the lance. I have. For example, JP-A-61-279608 can be cited as an example of the latter.

[0004] However, none of the conventional methods for producing a molten Ni-containing metal melt the Ni ore directly into a smelting furnace for smelting reduction. Since the Ni ore has a low Ni content of 2 to 3% by weight, about 70% of the Ni ore weight becomes slag, so that a large amount of slag is generated in the smelting reduction. Therefore, a large amount of slag is generated when trying to obtain a molten metal having a predetermined Ni concentration. For example, when 8% Ni-containing molten metal is obtained, 2-3 tons of slag are generated per ton of molten metal. Along with this, (1) Slopping (scattering of slag lump including metal particles from the furnace port) is generated by the reactant gas generated by the reducing agent or the oxygen and carbon material charged as a heat source during the smelting reduction process. It is difficult to perform regular operation, and there is a risk that the operation may become unstable. (2) Damage to equipment due to the above-mentioned slopping (3) Reduction of Ni yield due to the above-mentioned slopping is remarkable Become.

[0005] Because of these problems, in the above-mentioned conventional technique, Ni ore as a Ni source is not directly charged into a smelting furnace,
What used the thing which increased the ratio of the contained Ni component by performing some pre-processing is used. For the reasons described above,
Japanese Patent No. 221336 discloses a method for smelting and reducing Ni ore that can stably operate despite the generation of a large amount of slag, and can solve problems such as damage to equipment and equipment caused by slopping and a decrease in Ni yield. providing. In the smelting reduction method of Ni ore by the method, Ni ore is charged into a smelting furnace together with a carbonaceous material and a slag-making agent, and oxygen is blown from a top-blown oxygen lance having nozzles for decarburization and secondary combustion, This is a method in which a stirring gas is blown from a bottom blowing tuyere provided at the furnace bottom of the smelting furnace to melt and reduce Ni ore. The secondary combustion ratio (H ₂ O + CO ₂ ) / (H ₂ + H ₂ O + CO + CO ₂ ) in the smelting furnace is 0.3 or more.

According to this method, [C] in the molten metal is decarbonized as CO gas by oxygen for decarburization, and this CO gas is converted to CO ₂ gas by oxygen for secondary combustion.
The reaction heat of the decarburization and the secondary combustion is the main heat source of the smelting reduction, and the generated heat increases as the degree of oxidation of the exhaust gas from the smelting furnace, which is represented by the above equation, increases. Accordingly, it is possible to reduce the amount of carbon material to be supplied to the smelting furnace, and therefore, CO and CO ₂ gas, which are factors causing the occurrence of the slopping, are reduced, so that the frequency of the occurrence of the slopping is remarkably reduced.

In Japanese Patent Application Laid-Open No. 2-274804,
After obtaining Ni-containing hot metal melted and reduced by the above-described method, the molten Ni-containing molten metal which has been dephosphorized and desulfurized by the process of discharging lime, fluorite, silica stone and carbonaceous material and desulfurizing the molten metal is obtained. After that, the Cr raw material is charged into the smelting furnace together with the carbon material and the slag-making agent into the smelting furnace, and the Cr ore is melted by acid supply from the top blowing oxygen lance and stirring by the stirring gas from the bottom blowing tuyere. A method for producing a Ni / Cr molten metal characterized by reduction is proposed.

[0008]

However, Japanese Patent Application Laid-Open Nos. 2-221336 and 2-2748 describe the above.
In the production of a molten Ni / Cr alloy in Japanese Patent Publication No. 04, there are the following problems. That is, as a furnace body refractory used in a smelting furnace generally used for smelting reduction, for example, magnesia bricks such as mag carbon and magcro brick can be considered, but since Ni smelting reduction is a long-term treatment, In high secondary combustion (high slag temperature), (1) elution of MgO into slag (2) elution (oxidation) due to reaction with FeO in slag (3) magcarbon (reduction) of MgO-C at high temperature Furnace body wear cannot be ignored due to reactions and the like. In addition, if bottom blowing is strengthened to increase thermal efficiency and countermeasures against slopping due to secondary combustion, spitting (dispersion of fine metal particles from the furnace opening) will increase, and as a result, the problem of metal loss will be ignored in actual production become unable.

The present invention has been made in view of the above circumstances, and overcomes the problem of furnace body brick wear, has no problem of spitting caused by bottom blown gas, and has a stable Ni ore without slopping. It is an object of the present invention to provide a method for producing a low-phosphorus and low-sulfur molten stainless steel by smelting reduction.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies on the direct smelting reduction of Ni ore, and have completed the present invention based on the knowledge described below regarding furnace body brick wear and operation stability. is there. That is, a first aspect of the present invention is to provide a converter type smelting furnace provided with a top blowing oxygen lance, a bottom blowing and / or a side blowing tuyere. (1) a. B. A step of injecting oxygen from a top-blown oxygen lance c. A step of blowing and stirring a stirring gas such as N ₂ or Ar, CO from a bottom-blowing and / or side-blowing tuyere. d. A smelting and reducing step of Ni comprising a step of obtaining molten Ni-containing hot metal by discharging the slag, and then (2) a dephosphorizing / desulfurizing hot metal by adding a medium solvent, an oxygen source, and / or a carbon material to the molten Ni-containing hot metal. Dephosphorization to get
Desulfurization step, then (3) a. Step of charging Cr ore, semi-reduced chromium pellets, etc. with medium solvent and carbon material to the dephosphorized / desulfurized hot metal b. Step of injecting oxygen from top-blown oxygen lance c. Bottom Step of blowing and / or stirring a stirring gas such as N ₂ or Ar, CO from a blowing and / or side blowing tuyere. D. Cr comprising a step of obtaining molten Ni-Cr hot metal by discharging slag
(1) to (4) of the decarburization step of decarburizing Ni-Cr-containing hot metal
Melting, wherein the secondary combustion ratio (H ₂ O + CO ₂ ) / (H ₂ + H ₂ O + CO + CO ₂ ) represented by the following formula is maintained at less than 0.3 in the Ni reduction step: This is a method for producing a molten stainless steel by reduction.

The second aspect of the present invention is the first aspect of the present invention.
In the Ni smelting reduction step, after the molten metal is discharged to a ladle to obtain molten iron containing Ni, then the molten iron containing Ni obtained in the ladle or is transferred to another smelting furnace, and the smelting furnace Performs the same dephosphorization and desulfurization step as in the first invention, then returns the dephosphorized and desulfurized hot metal to the smelting furnace in the smelting reduction step of Ni, and performs the same smelting reduction step of Cr as in the first invention to include Ni. A step of obtaining Cr hot metal and then decarburizing, and further maintaining the secondary combustion ratio represented by the above formula in the smelting reduction of Ni at less than 0.3 as in the first invention. This is a method for producing molten stainless steel by smelting reduction. Further, the third aspect of the present invention
After obtaining the first or second Ni-Cr hot metal containing iron of the present invention, the whole amount is taken out of the furnace, completely discharged, and then returned to the first smelting furnace again, where the hot metal containing Ni-Cr hot metal is returned. Is a method for producing a molten stainless steel by smelting reduction, which is characterized by decarburizing, and a fourth aspect of the present invention is to omit the dephosphorization / desulfurization step in the first or second aspect of the present invention. A method for producing a molten stainless steel by smelting reduction, which is characterized in that the slag temperature is adjusted to 1580 ° C. or lower in the Ni smelting reduction step described above. T. in Fe should be kept at 10% by weight or less. (3) The stirring gas flow rate from the bottom and / or side blowing tuyere should be 0.
A method for producing molten stainless steel by smelting reduction, wherein the method is adjusted to 1 to 1.0 Nm ³ /min.ton.

[0012]

According to the present invention, as described above, in a converter type smelting furnace provided with a top blowing oxygen lance, a bottom blowing and / or a side blowing tuyere, first, molten iron is charged, and Ni ore and carbon material are added thereto. In charging the smelting furnace and performing smelting reduction, the secondary combustion ratio (H ₂ O + CO ₂ ) / (H ₂ + H ₂ O + CO + CO ₂ ) represented by the following formula is maintained at less than 0.3, It is an object of the present invention to obtain a molten stainless steel by reducing the degree of oxidation of exhaust gas, thereby reducing the heat of reaction and performing smelting reduction, thereby reducing the wear of the furnace body structure of the smelting furnace.

In the present invention, the reason why the secondary combustion ratio is limited to less than 0.3 is that when the secondary combustion ratio is set to 0.3 or more, as shown in FIG. 2 described later, MgO in the slag is saturated. Even if it is controlled, the slag temperature becomes 1600 ° C. or more, and the furnace body bricks rapidly wear. In addition, in order to increase the secondary combustion ratio to 0.3 or more, it is necessary to use a lance having a complicated structure for the secondary combustion nozzle for increasing the degree of oxidation, which makes maintenance of the lance difficult. In addition, there are problems in operability such as difficulty in maintaining and controlling the high secondary combustion ratio at a constant level, and problems such as instability of the secondary combustion ratio during operation. When the combustion ratio increases, the wear of the furnace body brick may be accelerated. From the above, the secondary combustion ratio was set to 0.
It was less than 3.

When the secondary combustion ratio is increased, the degree of oxidation is increased, so that the calorific value is increased, and high productivity can be ensured, but at the same time, the slag temperature rises because the heat transfer efficiency decreases. In the present invention, the slag temperature is set to 1580 ° C. or less in consideration of the heating efficiency. On the other hand, lowering the secondary combustion ratio increases the exhaust gas flow rate,
Although the frequency of slopping tends to increase, the present inventor has conducted intensive experiments and found a condition under which slopping can be suppressed even at a low secondary combustion ratio.

As shown in FIGS. 3 to 5, which will be described later, if the amount of bottom blown gas is 0.1 Nm ^{3 /} min. Fe can be reduced to 10% by weight or less, and slopping can be suppressed. However, the bottom blowing gas amount is 1 Nm ³ / mi
If it exceeds n.ton, FeO in the slag decreases, but spitting becomes severe and the yield deteriorates.
By adjusting the amount of bottom blown gas to 0.1 to 1.0 Nm ³ /min.ton, even without a secondary combustion ratio of less than 0.3, an operation without any slopping and spitting could be achieved. Furthermore, T. in slag The reason why the concentration of Fe is as low as 10% or less is to exert an advantageous effect also on protection of the MgO-based furnace body.

The obtained Ni-containing hot metal is drained, and then discharged into hot water remaining in the smelting furnace or discharged into a ladle, and then transferred to another smelting furnace. Addition of a solvent, oxygen source, and / or carbon material to smelting furnace water to obtain dephosphorized and desulfurized Ni-containing hot metal, and after sufficient slag removal, Cr ore, semi-reduced chromium pellets, etc. Is charged together with a solvent and a carbon material, and Cr is melt-reduced in the same manner as in the above-mentioned Ni melt-reduction step to obtain Ni-Cr-containing hot metal. In addition, when the hot water is once poured into the ladle and dephosphorized and desulfurized in the ladle or in another smelting furnace, the dephosphorized and desulfurized hot metal is returned to the first smelting furnace, where the Cr ore, semi-reduced A chromium pellet or the like is charged together with a medium solvent and a carbon material, and is subjected to smelting reduction in the same manner as in the smelting reduction step of Ni to obtain molten iron containing Ni / Cr. Further, with respect to the obtained Ni / Cr hot metal, normal decarburization is performed after slag disposal. Further, when the waste is discharged in the same furnace, there are the following problems, particularly in the case of a large amount of slag. (1) The problem of resulfurization arises because the slag is not completely removed. (2) It takes a long time to remove a large amount of slag. The time required to occupy the smelting furnace is long, which hinders productivity. B. Since the contact time between the high temperature slag and the furnace body is long, the furnace body is severely worn. For the above, the entire amount of the obtained Ni-Cr-containing hot metal was poured out of the furnace, completely discharged, and then returned to the original smelting furnace again.
By performing the normal decarburization process of Ni reduction-phosphorus / desulfurization-Cr reduction-full tapping-drainage-decarburization, the time required for waste from the smelting furnace can be shortened. The problem of Cr loss and resulfurization at the time is solved. According to this method, since there is no problem of rephosphorization and resulfurization as described above, it is possible to stably produce a hot metal containing Ni / Cr having a low phosphorus and low sulfur concentration. Next, the present invention will be described by way of examples.

[0017]

【Example】

[Embodiment 1] FIG. 1 is an explanatory view of a converter type smelting furnace which is an embodiment for carrying out the present invention. In FIG. 1, 10
Is a converter type smelting furnace made of magnesia-based brick, 11 is a metal layer, 12 is a slag bath, 21 is an upper oxygen lance, 2
4 is a bottom tuyere, 25 is a hopper for charging the raw material Ni ore, carbonaceous material or slag material into a smelting furnace, 26 is a stirring gas, 27 is a slag temperature sensor, and 28 is a sample for exhaust gas analysis. Mouth. The capacity of the smelting furnace body 10 used in this embodiment was 120 tons, and the amount of acid supplied was 35,000 N on average.
m ³ / Hr.

Using such a smelting furnace body 10, a production test of molten stainless steel was performed in batches. First, the operation procedure will be described. (1) Melt reduction step of Ni First, molten iron (Fe: 95% by weight)
0 ton, and then coke (FC: 8
(7% by weight), and oxygen is blown from the upper blowing oxygen lance 21 to raise the temperature of the molten metal to about 1500 ° C., and thereafter, charging of Ni ore is started. On the other hand, a stirring gas 26 such as N ₂ or Ar or CO is blown from the bottom blowing port 24 so as to prevent the bottom blowing port 24 from being blocked from the time when the hot metal is charged, and the blowing amount is increased as necessary. As a result, a smelting reduction reaction occurs, and as shown in FIG.
And the slag bath 12 is generated, and the slag is discharged about twice in the middle, and after 4 to 5 hours, the molten metal is discharged into a ladle to obtain hot metal containing Ni.

(2) Dephosphorization / desulfurization step Next, a medium solvent such as lime and fluorite and a scale and / or a carbon material as an oxygen source are charged into the Ni-containing hot metal in the ladle, and the upper oxygen lance Dephosphorization and desulfurization are performed by blowing oxygen from 21 to sufficiently remove slag to obtain dephosphorized and desulfurized hot metal. In the case where the dephosphorization / desulfurization step is performed after the discharge of the slag, the dephosphorization / desulfurization step is, of course, performed on the Ni-containing hot metal remaining in the smelting furnace after the slag in the step (1). After the slag is poured, the hot metal containing Ni is transferred to another smelting furnace, and a medium solvent such as lime and fluorite, a scale and / or a carbon material as an oxygen source are charged into the hot metal containing Ni, and oxygen is supplied from an oxygen lance above. To remove dephosphorization and desulfurization outside the furnace to sufficiently remove slag to obtain dephosphorization and desulfurization hot metal. (3) Cr smelting reduction step Next, the dephosphorized and desulfurized hot metal treated in this ladle or dephosphorized and desulfurized hot metal treated in another smelting furnace is converted into smelting furnace body 10.
And return the Cr ore, semi-reduced chromium pellets, etc.
It is charged together with the carbonaceous material and melt-reduced in the same manner as in the above (1) Ni melt-reduction step to obtain molten iron containing Ni / Cr. In addition, you may process continuously with the smelting furnace body 10. (4) Decarburization Step The entire amount of the obtained Ni / Cr hot metal is taken out of the furnace, completely discharged, and returned to the original smelting furnace body 10 again for decarburization. The molten stainless steel is manufactured as described above.

In order to determine the secondary combustion ratio (OD) in the smelting reduction step of Ni, the sample port 28 for exhaust gas analysis is used.
Exhaust gas is sampled, exhaust gas is analyzed, and H
₂ , H ₂ O, CO, and CO ₂ concentrations were determined and substituted into Find D. O. D = (H ₂ O + CO ₂ ) / (H ₂ + H ₂ O + CO +
CO ₂ ) This secondary combustion ratio can be adjusted by manipulating the height of the top blowing oxygen lance 21 and the amount of acid supply. For example, if the height of the upper blowing lance 21 is increased, the CO ₂ concentration is increased, and if the height of the lance is decreased, the CO ₂ concentration is decreased and the secondary combustion ratio is decreased. Similarly, the CO ₂ concentration goes up and down due to the increase and decrease in the amount of acid supply, so that the secondary combustion ratio goes up and down. Further, if the amount of the bottom-blown stirring gas is increased, the secondary combustion ratio will be reduced, and if the amount of the bottom-blown stirring gas is reduced, the secondary combustion ratio will be increased. Further, the slag temperature is adjusted by measuring the temperature with a slag temperature measuring element 27, and if the temperature is high, the ore and the slag-making agent are increased.

As described above, the secondary combustion ratio when the melt temperature was set to 1520 ° C. and the degree of wear of the MgO—C bricks in the smelting furnace body 10 when the smelting reduction of Ni ore was performed were examined. In general, when the secondary combustion ratio is increased, the calorific value increases, and high productivity can be ensured, but at the same time, the slag temperature rises due to a decrease in the heat transfer efficiency. Therefore, the slag temperature was also investigated. FIG. 2 is a graph showing the relationship between the secondary combustion ratio, the slag temperature, and the wear index of the MgO-C brick when the temperature of the molten metal is set to 1520 ° C. during Ni smelting reduction. As can be seen from FIG. 2, when the secondary combustion ratio is 0.3 or more, even if the MgO in the slag is controlled to be saturated, the slag temperature becomes 1600 ° C. or more, and the furnace body rapidly wears out. It turns out that the combustion ratio is preferably less than 0.3. Slag temperature is 1580 ℃
The following shows that it is preferable to hold. High secondary combustion of 0.3 or more is obtained by using an upper-blowing oxygen lance of a complicated structure having a nozzle for secondary combustion,
T. in the slag at this time Fe was 8% by weight or less in all cases.

On the other hand, when the secondary combustion ratio is lowered, the flow rate of exhaust gas increases, and the frequency of slopping tends to increase.
In order to examine the effect of this point, the secondary combustion ratio is set to 0.1 to 0.
As T.3 in slag as A test was conducted to examine the relationship between Fe and the frequency of slopping. FIG.
5 is a graph showing the relationship between Fe (% by weight) and the frequency of slopping (%). As shown in FIG. It can be seen that the frequency of slopping is remarkably reduced by making Fe 10% by weight or less. Next, the effect of bottom-blown gas stirring to achieve this condition was investigated. Fig. 4 shows the amount of bottom blown gas and T.C. It is the graph which showed the relationship with Fe (weight%). As shown in FIG. 4, the amount of bottom blown gas is 0.1 Nm ³ /
T. in slag at min.ton It can be seen that Fe can be controlled to 10% by weight and the amount of bottom blown gas should be more than this. However, at 1 Nm ³ /min.ton or more, FeO in the slag decreases, but spitting becomes severe and the yield deteriorates. Further, the effect of the bottom blowing gas amount on spitting was examined from the results of FIG. FIG. 5 is a graph showing the relationship between the bottom blowing gas amount (Nm ³ /min.ton) and the spitting index. From the above, it was found that an operation without any slopping and spitting can be achieved even when the secondary combustion ratio is less than 0.3 by setting the bottom blown gas amount to 0.1 to 1.0 Nm ³ /min.ton. .

Example 2 Next, using the above-mentioned converter type smelting furnace, the batch was subjected to smelting reduction for 4 to 5 hours in the same operation procedure. As described above, the secondary combustion ratio at the time of Ni smelting reduction is set to a range of less than 0.3 because the furnace body wear becomes severe at a high secondary combustion ratio. On the other hand, if the secondary combustion ratio is less than 0.3, the occurrence of slopping becomes a problem as described above. Fe 5
% By weight or less.

Furnace body wear during Ni smelting reduction can be reduced by controlling the actual slag temperature in addition to the factor of the secondary combustion ratio, and is desirably set to 1550 ° C. Furthermore, the slag composition can be reduced by controlling the slag composition. Fe 5% by weight or less,
The composition of MgO% in the slag is (saturation + 1%) or more. MgO% is added during operation with MgO-C brick debris etc. together with Ni ore and carbonaceous material, and MgO% becomes (saturated + 1%)
Always keep it below. T. in slag Fe5
% By weight or less was obtained with a bottom blown gas amount of 0.5 Nm ³ /min.ton, thereby reducing metal loss in long-term operation.

Under these conditions, the average composition of Ni ore having the following composition was 1200 kg / min.
smelting and reducing Ni ore at min.
Approximately 70 tons of hot metal containing i (Ni: 9.7% by weight)
was gotten. The slag temperature could be maintained at 1550 ° C ± 20 ° C.

[0026]

[Table 1]

Further, lime (CaO: 2.9 tons) was added to the 70 tons of Ni-containing hot metal obtained in the smelting furnace body 10 by discharging the slag.
), Fluorite (CaF: 0.8 ton), silica stone (0.8 ton)
), A scale (1.0 ton) and coke (0.8 ton) are charged and dephosphorized and desulfurized by acid supply from the top-blown oxygen lance 21 to remove dephosphorized and desulfurized Ni-containing.
Hot metal was obtained and slag was sufficiently removed. As a result, [P] in the hot metal containing Ni is reduced from 0.09% to 0.005%, and [S] is increased.
Decreased from 0.15% to 0.01%. Next, Cr ore (500 kg / min) and coke (600 kg / min) having the compositions shown in Table 1 were added to the dephosphorized and desulfurized Ni-containing hot metal.
, And acid is fed from the top blowing oxygen lance 21 (amount: 25).
2,000 Nm ³ / Hr), N ₂ gas from the bottom tuyere is blown and stirred at 2,500 Nm ³ / Hr from five tuyeres, and the Cr source is melt-reduced to reduce Ni-Cr hot metal content to about 95 tons.
I got The Ni concentration was finely adjusted by adding electrolytic Ni. The slag temperature at this time was kept at 1600 ± 20 ° C. Further, the obtained Ni / Cr hot metal was discharged and decarburized. Thus, a molten stainless steel having a composition as shown in the following Table 2 was produced.

[0028]

[Table 2]

In the smelting reduction operation of Ni of this embodiment, dust and fume are not generated without slopping, and the measurement result of the rate of wear of the furnace body brick after melting 10 charges is 0.1 mm / Hr. 1 if not implemented
The wear rate was much lower than 2 mm / Hr. Further, in the present embodiment, the dephosphorization / desulfurization step was performed using a converter type smelting furnace. However, in the Ni smelting reduction step, the slag was drained and discharged to a ladle, and then dephosphorized in a ladle or another smelting furnace.・
Even if the desulfurization step is performed, the same effect as in the present embodiment is obtained. As described above, the entire amount of the obtained Ni-Cr-containing hot metal obtained is discharged from the furnace, completely discharged, and then returned to the first smelting furnace again to perform normal decarburization. Desulfurization
It may be a process of Cr reduction, total tapping, waste, and decarburization.

In the smelting furnace of this embodiment, the stirring gas was blown into the smelting furnace through the bottom tuyere to stir the smelting furnace. Stirring gas may be blown from both the tuyere and the bottom tuyere of the smelting furnace provided with both. If the dephosphorization / desulfurization step is not necessary due to the concentrations of [P] and [S] in the hot metal, this step is omitted and
(1) the smelting reduction step of Ni and (3) the smelting reduction of Cr and
The method for producing molten stainless steel in the decarburization step (4) also falls within the scope of the present invention. Furthermore, the solvent, oxygen source, and / or carbon material used in each step of the present invention are not limited to those of the present embodiment, and various types can be used as long as they are commonly used.

[0031]

According to the present invention, acid is supplied from a top blowing lance to a converter type smelting furnace charged with raw materials such as hot metal, Ni ore, carbonaceous material, and slag-making material, and agitated gas is blown from the furnace bottom. By
The secondary combustion ratio was set to less than 0.3, and the T.C.
By controlling the Fe, controlling the slag temperature, and optimizing the bottom blowing gas, it was possible to reduce the wear of the furnace body bricks, to reduce the sloping and spitting, and to achieve a stable smelting reduction of Ni ore. With regard to the hot metal containing Ni, the hot metal is charged together with a medium solvent, an oxygen source, and / or a carbon material to obtain a hot metal containing Ni that has been dephosphorized and desulfurized by a process of dephosphorization and desulfurization. Next, Cr ore and semi-reduced chromium pellets are charged into the dephosphorized and desulfurized hot metal together with a solvent and a carbon material, and are melt-reduced in the same manner as in the process of smelting and reducing Ni to obtain hot metal containing Ni / Cr.
Next, the slag is removed and decarburized to obtain molten iron containing Ni / Cr, and it is possible to stably produce a molten stainless steel having a low phosphorus and low sulfur concentration.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a converter type smelting furnace used in an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a secondary combustion ratio and a wear index of MgO—C brick in Examples.

FIG. 3 is a graph showing T.V. Fe (% by weight)
6 is a graph showing the relationship between the frequency and the dropping frequency (%).

FIG. 4 shows the amount of bottom blown gas (Nm ³ /min.to
n) and T. in slag. It is the graph which showed the relationship with Fe (weight%).

FIG. 5 shows the amount of bottom blown gas (Nm ³ /min.ton) in the embodiment.
7) is a graph showing the relationship between a spitting index and a spitting index.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Smelting furnace body 11 Metal layer 12 Slag bath 21 Top blowing lance 24 Bottom blowing tuyere 25 Raw material hopper 26 Stirred gas 27 Slag thermometer 28 Sample port for exhaust gas analysis

────────────────────────────────────────────────── ─── Continued on the front page (72) Hideaki Mizukami, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Hideo Nakamura 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-2-221310 (JP, A) JP-A-2-22131 (JP, A) JP-A-2-285017 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) C21C 5/28 C21B 11/00 C21B 13/00 C22C 33/04

Claims (7)

(57) [Claims] In a converter type smelting furnace provided with a top blowing oxygen lance, a bottom blowing and / or a side blowing tuyere, (1) a. Hot metal is charged and Ni ore and carbon material are added to the hot metal. A step of charging oxygen into the smelting furnace b. A step of injecting oxygen from the top-blown oxygen lance c. N ₂ or Ar, C from the bottom-blow and / or side-blow tuyere
A step of blowing and stirring a stirring gas such as O. d. A smelting reduction step of Ni consisting of a step of obtaining molten iron containing iron by discharging, and (2) a medium solvent, an oxygen source, and / or Dephosphorization / desulfurization process to obtain dephosphorized / desulfurized hot metal by adding material, and then (3) a. Charge the above dephosphorized / desulfurized hot metal with Cr ore, semi-reduced chromium pellets, etc. B. Injecting oxygen from the top-blown oxygen lance c. N ₂ or Ar, C from the bottom-blown and / or side-blown tuyere
Step of blowing and stirring a stirring gas such as O. d. Cr comprising a step of obtaining molten Ni-Cr hot metal by discharging slag.
Smelting reduction step, and then (4) the decarburization step of decarburizing the Ni-containing Cr hot metal (1)
And (4) maintaining the secondary combustion ratio (H ₂ O + CO ₂ ) / (H ₂ + H ₂ O + CO + CO ₂ ) represented by the following formula in the Ni smelting reduction step at less than 0.3: A method for producing molten stainless steel by smelting reduction. (1) In a converter type smelting furnace provided with a top blowing oxygen lance, a bottom blowing and / or a side blowing tuyere, a. Hot metal is charged, and Ni ore and carbon material are added to the hot metal. A step of charging oxygen into the smelting furnace b. A step of injecting oxygen from the top-blown oxygen lance c. N ₂ or Ar, C from the bottom-blow and / or side-blow tuyere
A step of blowing and stirring a stirring gas such as O. d. A smelting and reducing step of Ni which comprises a step of obtaining molten Ni-containing hot metal after draining and tapping into a ladle; Transferring to another smelting furnace, a dephosphorization / desulfurization step of obtaining a dephosphorized / desulfurized hot metal by adding a medium solvent, an oxygen source, and / or a carbon material to the smelting furnace,
Then, (3) a. A step of returning the dephosphorized and desulfurized hot metal to the smelting furnace of (1) and charging Cr ore, semi-reduced chromium pellets, etc. together with a solvent and a carbon material; b. C. N ₂ or Ar, C from the bottom and / or side blowing tuyere
Step of blowing and stirring a stirring gas such as O. d. Cr comprising a step of obtaining molten Ni-Cr hot metal by discharging slag.
Smelting reduction step, and then (4) the decarburization step of decarburizing the Ni-containing Cr hot metal (1)
And (4) maintaining the secondary combustion ratio (H ₂ O + CO ₂ ) / (H ₂ + H ₂ O + CO + CO ₂ ) represented by the following formula in the Ni smelting reduction step at less than 0.3: A method for producing molten stainless steel by smelting reduction. 3. After obtaining the Ni-Cr containing hot metal, the whole amount is discharged outside the furnace, and after completely draining, the molten iron is returned to the smelting furnace of (1) above. The method for producing a molten stainless steel by smelting reduction according to claim 1 or 2, wherein decarburization is performed. 4. The method for producing a molten stainless steel by smelting reduction according to claim 1, wherein said dephosphorization / desulfurization step is omitted. 5. The method for producing a molten stainless steel by smelting reduction according to claim 1, wherein the slag temperature is adjusted to 1580 ° C. or lower in the Ni smelting reduction step. 6. The method according to claim 1, wherein in the step of smelting and reducing Ni, T.C. 6. The method for producing molten stainless steel by smelting reduction according to claim 1, wherein Fe is kept at 10% by weight or less. 7. A flow rate of a stirring gas from a bottom-blowing and / or side-blowing tuyere is 0.1 to 1.
The method for producing molten stainless steel by smelting reduction according to claim 1, wherein the molten stainless steel is adjusted to 0 Nm ³ /min.ton.