JPH01252753A - Method for refining of stainless steel mother molten metal, arrangement of tuyere at bottom of reactor for refining and bottom tuyere - Google Patents

Abstract

PURPOSE:To obtain the title stainless mother molten metal having excellent purity in high yield by charging molten iron and scrap into a reactor, melting the scrap, successively adding Cr and C thereto, melting and reducing it and thereafter subjecting the same to final reducing by oxygen blowing. CONSTITUTION:Molten iron and scrap are charged into a reactor in which slag is present, and the scrap is melted while C-contg. material and O-contg. material are supplied. The molten metal is heated and is subjected to melting and reducing by adding Cr-contg. material and C-contg. material thereto while supplying an O-contg. gas to reduce the Cr content into the objective value. The material is then subjected to final reducing by the blowing of an O-contg. gas and is poured as the molten metal while suitable amt. of slag is left. At the time of scrap melting, the amt. of the slag is preferably regulated to at least about >=50kg/t, to >=100mm thickness on the surface of the molten iron bath, and a stirring gas of about >=1.0Nm<3>/min/t is preferably blown from the bottom of the reactor. As for the bottom blowing tuyeres of the reactor, the structure in which each one is arranged in rows at intervals at the furnace bottom is suitable.

Description

[Detailed Description of the Invention] (Industrial Application Field) A chromium-containing stainless steel high-carbon molten metal (hereinafter referred to as "stainless steel mother molten metal") for producing stainless steel in order to melt stainless steel highly efficiently and inexpensively. related to the improvement of the manufacturing process.

(Conventional technology) Scrap, FeCr,
The process of melting FeNi and other ferroalloys as the main raw material in an electric furnace, followed by decarburization and reduction refining using AOD or VOD to produce stainless steel.
) process is the most common. However, this process using an electric furnace has problems as an inexpensive method for producing stainless steel because it requires the use of expensive electrical energy and there are restrictions on the selection of raw materials.

On the other hand, hot metal is charged into a top-bottom blowing converter without using an electric furnace, and scrap and ferroalloys (FeCr and FeN1) are added during or before decarburization blowing to become the components of stainless steel. For example, a process is described in the literature (Tetsu to Hagane (1985
), Vol. 71. S180) D is written. However, even with this method, the amount of scrap and ferroalloy that can be input into the hot metal is limited due to heat balance. In addition, in the method of adding carbonaceous material as a heat source to remove this restriction, the blowing time is extended and the amount of dust generated increases, causing problems in terms of yield and in terms of matching with continuous casting. Furthermore, it cannot be said that efficient stainless steel melting using inexpensive materials is sufficient.

In recent years, chromium ore or partially reduced chromium ore pellets (hereinafter referred to as "pre-reduced pellets") have been melted and reduced to produce stainless steel instead of ferrochrome as part of the stainless steel melting process. The technology has been developed, for example, in the literature Tetsu and M (1987),
VoA, 73+ S 875t' is a top-bottom blowing converter in which dephosphorized hot metal is charged and heated by adding backing material, then chromium ore or pre-reduced pellets and carbon material are charged and melted and reduced, and then blowing acid and A technique has been disclosed in which a chromium-containing molten metal is melted by continuing to supply carbonaceous material, and after removing slag and slag, decarburization is subsequently performed. On the other hand, special public service Sho 62-50545
This publication also discloses an improvement in the technology of melting and reducing ore in the same furnace, melting a chromium-containing molten metal, removing only the slag, and subsequently decarburizing the slag. In these methods, smelting reduction and oxidation refining are performed in the same furnace.
Even if slag is removed during the process, it is not always sufficient to remove it, and there is a problem that a large amount of sulfur, an impurity, remains even after decarburization and smelting, and there is also the disadvantage that the refractories in the furnace are severely eroded. there were. In addition, Japanese Patent Publication No. 62-50545 cites a technique for using scrap in decarburizing chromium-containing molten metal, and it is possible to appropriately input stainless steel scrap and use the scrap as a raw material when decarburizing molten stainless steel. This is also a conventionally known technique.

However, even when stainless steel scrap is used as a composite material when decarburizing molten stainless steel, the amount used must of course be limited, and from that point of view, it is still insufficient as a process that can use inexpensive raw materials. It leaves a mark.

Particularly in stainless steel melting, a process that can use large amounts of inexpensive chromium- and nickel-containing scrap is necessary, and in this respect, with conventional technology, an electric furnace that can use large amounts of scrap was absolutely necessary.

(Problem to be solved by the invention) It is an object to provide a fundamental solution to the conventional technology as described above, and to provide an efficient process for stainless steel melting that guarantees high quality. The process uses hot metal, Cr ore, large amounts of scrap and ferroalloy, and has a wide range of choices in terms of the use of inexpensive raw materials. Moreover, impurity components such as phosphorus and sulfur can be sufficiently controlled, and The first object of the present invention is to provide a method for melting a stainless steel mother metal, which causes less erosion of refractories in the furnace, has excellent cleanliness, and has a significantly low concentration of gas components as impurities.

In particular, instead of melting scrap in an electric furnace, which requires expensive electrical energy, a top-bottom blowing converter alone can use the energy of cheap carbonaceous materials, making it possible to use a large amount of scrap.Moreover, instead of ferrochrome, it is possible to use inexpensive rom ore. This provides a process that can use semi-reduced pellets.

It is a further object to provide a reaction vessel bottom tuyere arrangement and bottom lining that can be advantageously utilized in carrying out this process.

(Means for solving problems) The above purpose is achieved by the following configuration.

When melting a stainless steel mother metal from hot metal together with chromium-containing substances and carbon-containing substances, the scrap is charged together with the hot metal into a reaction vessel containing slag, and the carbon-containing substances and oxygen-containing gas are supplied. Following the melting process of melting the scrap, the temperature is raised, and further, a chromium-containing substance and a carbon-containing substance are added to the hot metal while supplying an oxygen-containing gas, and a melting reduction process is performed until the chromium content reaches the target value.
A method for producing a stainless steel mother molten metal, which is characterized in that a finishing reduction process is then performed by blowing oxygen-containing gas, and the molten metal is tapped leaving an appropriate amount of slag. (First invention).

This method requires that the amount of slag present in the reaction vessel in the scrap melting process is at least 50 kg or more and has a thickness of 100 mm or more on the surface of the hot metal bath; ONm! /mi
It is more desirable to suck in stirring gas of n/t or more.

Next, the bottom blowing tuyere arrangement of the reaction vessel exclusively used in the method of the first invention is such that the bottom blowing tuyeres are arranged in rows at intervals from each other at the bottom of the furnace, and the number of the arrangement is four or more, and The ratio d/D between the distance d between the two tuyeres closest to the center and the diameter of the bottom of the reactor vessel is 0.1 to 0.5, and the sum of the distances to the tuyere group is minimum. The distance between the straight line and the diameter parallel to this straight line! The ratio between that and the diameter of the bottom of the hearth! ! , /D is 0.1 or less. (Second invention).

The bottom tuyere of the reaction vessel used exclusively in the method of the first invention is a concentric double tube consisting of an outer tube and an inner tube inserted into the outer tube, and at least at the tip of the inner tube, a plurality of oxygen gases are A bottom blown surface of a reaction vessel for melting a stainless steel mother melt, which has a structure in which jets are ejected in a spiral manner. (3rd
invention).

In the method of the first invention, first, the hot metal is deSted and dephosphorized in a torpedo car, and the Si and P:a degrees after treatment are set to 0.02% by weight or less and 0.015% by weight or less, respectively. A top-bottom blowing converter is charged at a temperature of 1180-1270''C.

At that time, before or after that, the scrap is charged into the reaction vessel, oxygen is supplied from the top blowing lance and the bottom blowing tuyere, and a carbon material such as coke is added to melt the scrap ( After the first stage), the hot metal is heated to 1550°C or higher and 1620°C while continuously maintaining the carbon concentration in the hot metal in the reaction vessel at least 4% by supplying carbonaceous materials and oxygen.
A period (period ■) is provided in which the temperature is raised to the following conditions.

Subsequently, chromium ore or prereduced pellets, carbonaceous material, and oxygen are supplied to melt and reduce the chromium ore. In the melt reduction, (%CaO) / (
Keep %5i(h) between 1.5 and 3.5, and ((
MgO) + (Aj!z03) ) / ((CaO)
+ (SiO□) + (MgO) + (81203
)) is maintained at 45% or more and 55% or less (this period is referred to as period Ⅰ).

After the introduction of chromium ore to achieve a predetermined chromium concentration, a period is set in which oxygen gas is supplied from the top blowing lance and the bottom blowing tuyere (this period is called the second period).

At the end of the third period, the supply of oxygen from the top blowing lance and the bottom blowing tuyere is stopped, and first, the slag and chromium-containing molten iron are discharged from the first top and bottom blowing converter.

At this time, when the first top-bottom blowing converter is repeatedly operated, at least 10% or more of the slag amount of the previous charge remains.

Furthermore, the bottom blowing gas flow rate range Q in the first stage operation was set to 1.
．． 0 (Nm'/min/l) or more. However, Q
O2: Bottom-blown oxygen flow! (Nm'/win) QI: Bottom-blown active gas flow rate (Nm3/m1n) Q, 1: Bottom-blown propane flow fl (Nm'/win) The process procedure of the first invention described above is shown in FIG. That's right.

(Function) When efficiently melting stainless steel mother metal, according to the first invention, first, desiliconization is performed using a torpedo car.
After dephosphorization, the hot metal is charged into a smelting reduction furnace.

At this time, the amount of hot metal charged is set to be 65% or less of the amount of steel tapped in the RH degasser so that a predetermined stainless steel mother metal can be obtained by using Crjff, stones, alloys, and scraps in the next process and subsequent steps. Here, the amount of inexpensive scrap used can be significantly increased compared to the conventional method, and the amount of scrap used is commensurate with the need.

Therefore, the weight of hot metal used in the smelting reduction furnace may be the weight obtained by subtracting the amount of scrap used in the smelting reduction furnace from 65% of the output at of the RH degasser. In addition, P after dephosphorization treatment
The concentration is set to 0.015% by weight or less in order to cope with the increase in phosphorus from input raw materials in the next process.

In addition, in order to maintain high dephosphorization efficiency, the hot metal after treatment is
Control the temperature between 0 and 1270°C.

Hot metal is charged into the smelting reduction furnace with the above considerations in mind, but scrap can be charged in advance or after charging the hot metal, taking into consideration economical costs.
It is efficient to use 25 tons of scrap.

However, it is of course also applicable to cases where a larger amount of scrap is used.

The first stage is required to supply only the above-mentioned scrap material and oxygen gas. This is because if chromium oxide is added immediately, the melting of the scrap will be delayed, and the rise in steel bath temperature will also be delayed, which will worsen the reduction of the chromium oxide and extend the blowing time due to unmelted scrap. .

Furthermore, at that time, it is also necessary to always maintain the carbon concentration in the steel bath at 4% or higher. This is because a quick means of melting scrap is not only by simply supplying heat, but also by carburizing it with carbon in a steel bath. In addition, when melting scrap containing chromium, it is necessary to increase the carbon concentration during the scrap melting stage, suppress chromium oxidation during the scrap melting stage, and make the next smelting reduction stage advantageous.

Furthermore, the inventors have tried various improvements when melting scrap and have found that there is a suitable condition for the bottom-blowing flow rate in order to quickly melt the scrap.

That is, the relationship between the amount of oxygen supplied and the scrap melting rate in the first stage of melting scrap is shown in FIG. 2. Furthermore, if sampling is performed after the amount of oxygen supplied is 10,100 N/nl1n, the bottom blowing tuyere flow rate Q is 1. 0) Lm3/m
In/t or more, it was found that the scrap melting rate (the percentage of scrap input that has been completely melted) is approximately 100%.

This is because when melting scrap, it is important to increase the bottom blowing stirring force to increase the chances of contact between the scrap surface and the molten steel surface.

Next, as shown in Table 1, we conducted experiments with various tuyere arrangements, and found that the number of tuyeres is 4 or more, preferably 6 to 8, as shown in Figure 3, in order to quickly melt scrap. The ratio of the distance d between the innermost tuyeres and the diameter of the hearth bottom d/
D is set to 0.1 to 0.5, more preferably 0.2 to 0.4, and furthermore, the straight line that minimizes the sum of the distances to the tuyere group and the diameter parallel to this straight line. It has been found that it is necessary to set the ratio 1/D of distance 2 and D to 0.1 or less, preferably 0.006 or less.

Table 1 Oxygen supply 100 Nm'/lon (hot metal + scrap) Scrap melting conditions after elapse of time This is because the amount of oxygen supplied is 100 N.
m'/11 in/lon (molten pig iron + scrap) When the inside of the furnace was observed, it was observed that only some scrap was melted.

In addition, the rest of the scrap melt often exists mainly in the center, and even if the number of tuyeres is 4 or more, if the distance d between the tuyere in the center exceeds 0.5 with respect to D, Remaining scrap melting was observed between the tuyeres. Also, d/D is 0.
When the value was less than 1, there was no scrap remaining, but the tuyere melting loss increased as shown in Figure 4. This is thought to be because as the distance between the tuyeres became smaller, the interference between the tuyeres increased the erosion loss. Also, the tuyere is eccentric, and 2/
If D is larger than 0.1, some scrap will remain after being melted, and setting f/D to a large value is also not suitable for rapid melting of scrap. Regarding the arrangement of the tuyeres, we took into account the large slag volume that is a characteristic of smelting reduction, and also arranged the tuyeres in a straight line or in a neutral position to minimize damage to the refractories on the furnace wall caused by vibration of the furnace body. It is desirable to have a horizontal arrangement, and also an arrangement that is slightly offset from the center so that the slag does not cover the slag when the furnace body is tilted.

In addition, when we examined the yield during the scrap melting stage, we found that it was necessary to suppress the generation of dust (particularly fume caused by the top-blown lance). In other words, 1.5 to 2.5 ()cg/w in the scrap melting stage (first stage)
(in/lon hot metal + scrap) dust is generated, which has a large negative impact on yield. Therefore, the inventors made various improvements, and as a result, the thickness of the slag was always maintained at 100 mm or more during the scrap melting period, and the generation of fume from the hot spot formed by the top blowing lance was prevented by covering the slag. We have found that it is effective to suppress it.

In the melting and reduction of chromium ore in the post-sarasha process, strengthening the stirring power with the bottom-blowing tuyere can improve the reduction rate of chromium ore, so securing a bottom-blowing gas flow rate is essential. In reduction, fine metal particles that are directly reduced from chromium ore by the carbonaceous material in the slag are suspended in the slag.

If the stirring is strengthened using a bottom-blown stirring gas, the number of metal particles will increase at the end of melting and reduction. As a result, if the entire amount of slag after melting and reduction is directly removed, metal particles will be discharged and the yield will decrease.

Therefore, instead of discharging the entire amount of slag, an attempt was made to discharge only a portion of the slag. The results are shown in Table 2.

Table 2 Amount of dust generated during operation with slag left behind and chromium loss due to granulated iron in slag If the slag thickness in the first stage is kept at 100 am or more and the amount of slag left is 50 kg/t or more, the amount of dust generated during scrap melting can be reduced. It can be seen that it is possible to suppress chromium loss to the slag due to metal particles in the slag during slag discharge. Furthermore, if the amount of bottom-blown gas is reduced, the loss of chromium to the slag due to metal particles in the slag can be reduced, but as mentioned above, it is more advantageous to increase the amount of bottom-blown gas and perform strong agitation for scrap melting. The most effective method is to discharge the entire amount of slag, leaving the slag from the previous charge at 50 kg/lon or more, and keeping the slag thickness at the next scrap melting at 100 kg or more.

After the scrap melting is completed according to Fig. 1 in the process procedure of the first invention, the temperature of the molten steel is raised to 1550"C or higher until the start of smelting reduction. When this temperature rise is completed, chromium ore is produced. and carbonaceous materials are supplied together with oxygen gas, and the process moves on to the second stage in which chromite is melted and reduced.At this time, lime and lightly calcined dolomite are added to suppress MgO elution, which causes refractory erosion, and to reduce the melting and reducing stage. It is important to form the proper slag composition.

Normal (CaO) / (Si(h) 1.5 or more 3.5
and ((MgO) + (Aj2zOs ”)
) / ((CaO) + (SiO□) + (Mg
O) + (Alx(h)) from 0.45 to 0.5
It is effective to keep the slag composition below 5.

Because ((MgO) + (AfzOs) ]
/((CaO) + (Sift) + (MgO
) + (AjLO3)) Although the melting point of the slag is lowered, the melting loss of the refractory increases. On the other hand, ((MgO) + (AfzOs) ) /
((CaO) + (Sing) + (MgO)+
(AfzOs) ) increases the melting point of the slag, which is extremely disadvantageous for melting and reducing chromium ore.

As previously shown in Tetsu to Hagane 69 (1984), S 117, (MgO) + (Af, 03) is 45%
It was known that a temperature higher than this would be disadvantageous for melting and reducing chromium ore, but it is possible to further increase the basicity (CaO).
Increasing /(Sing) to 1.5 or more was conventionally considered to be disadvantageous for melt reduction (MgO) + (8zzo:
+) Melting reduction can be carried out without any problem even once, and it is advantageous in terms of protecting refractories.

Furthermore, increasing the basicity is advantageous in terms of desulfurization.

Furthermore, the inventors also attempted to improve the tuyere in order to improve the melting reduction of the chromium concentration and increase the yield, and as shown in Figure 5, the oxygen gas jets are ejected in a spiral pattern so as to interfere with multiple pressure chambers. We have found that the reduction rate of chromium ore can be improved and the chromium yield can be increased by using a tuyere.

This is because the smelting reduction of chromium ore is thought to proceed through a slag-metal reaction in which the charged chromium ore is once dissolved in slag and the slag reacts with molten steel or coke, or through a coke-slag reaction. For acceleration, using a tuyere in which the oxygen gas jets eject in a spiral manner and interfere with each other, rather than a conventional tuyere, makes it possible to form a large number of fine bubbles and promote the entrainment of slag into molten steel. It is believed that the slag-metal reaction rate increases and as a result, the smelting reduction of chromium ore is improved. As such a tuyere, a tuyere made by twisting a plurality of double tone tuyeres together (Fig. 5(a)) or a tuyere capable of spouting a plurality of spiral jets in an inner pipe (Fig. 5Q)) are suitable.

After melting and reducing the chromium ore until a predetermined chromium concentration is reached in this manner, the supply of carbonaceous material and chromium ore is stopped in the second stage, and oxygen is supplied. At this time, it is better to supply carbonaceous material in excess of the amount consumed by oxygen by the first stage, and not to add carbonaceous material at this stage. This is because in stage II, a large amount of metal grains produced by direct reduction of chromium ore are present in the slag. Therefore, if carbonaceous material is added at this time, metal particles will adhere to the surface of the added carbonaceous material, and as a result, precipitation of the metal particles into the molten metal will be inhibited, leading to a deterioration of the chromium yield. In addition, the carbonaceous material remaining in the slag will be discharged during slag removal, which is disadvantageous in terms of energy, so it is most desirable to consume the carbonaceous material that has been put in until stage II in stage II. .

In the second stage, oxygen is supplied to reduce the chromium oxide, and the temperature of the molten metal begins to rise and the process continues.

After the molten metal temperature is in the range of 1,570 to 1,620°C and the period (2) is completed, tapping and slag is carried out.

At that time, an appropriate amount of slag is left in the slag to maintain a valence of 50 (kg/l) or more and a thickness of slag of 100 or more during the next scrap melting.

Thereafter, the stainless steel mother metal obtained as described above is charged into a decarburization furnace, and the amount of tapped steel is 30 to 40%, which is the optimum amount to balance the heat supply amount and promote the reduction rate of chromium oxide.
The equivalent amount is added to the furnace sequentially as alloy iron or scrap. In the decarburization furnace, a mixed gas of 0□ and inert gas is blown from the top blowing lance and the bottom blowing double pipe tuyeres, and at the same time, hydrocarbon gas is blown from the bottom blowing tuyeres at a ratio of 3 to 7 to bottom blowing oxygen. %
At the same time as flowing, the slag is decarburized to a predetermined carbon concentration, and in some cases, a ferroalloy containing Si is introduced into the furnace to reduce chromium oxide in the slag and desulfurize at the same time.

The tapped molten metal is immediately transferred to an RH degassing device and treated at a vacuum level of 10 torr or less for 20 to 30 minutes. The reason why R1+ treatment is performed under these conditions is that since multiple processes have gone through before the previous process, the nitrogen concentration in the steel increases due to nitrogen absorption during tapping, and the cleanliness of the steel is improved by reducing hydrogen and oxygen in the steel. This is from the perspective of improvement.

Thereafter, the RH degassed molten stainless steel is cast using a conventional continuous casting machine.

(Example) Hot metal desiliconization and dephosphorization process A desiliconizing agent and a dephosphorizing agent are injected into hot metal in a torpedo car 1 using a powder suction lance 2 to treat the hot metal.

Hot metal processing amount: 200 before treatment Hot metal component C: 4.5% by weight St: 0.12% by weight Mn: 0.14% by weight P: 0.14% by weight S: 0.025% by weight Temperature before treatment: 1370 °C Desiliconizing agent: Dust generated in sintering furnace unit: 25kg/t Dephosphorizing agent: Dust generated in sintering furnace (75% by weight)C
aO (22% by weight) CaPz (3% by weight) Basic unit 60kg/t Powder blowing speed: 500 kg/win Components after treatment C: 4.2% by weight Si: 0.01% by weight or less Mn: 0.10 Weight % P: 0.015 weight % S: 0.024 weight % Temperature after treatment: 1240°C 23.0 tons of stainless steel scrap was charged into an 85 ton top-bottom blowing converter using a scrap chute.

Thereafter, 42.2 tons of the dephosphorized pig iron was charged, and then the furnace was shaped into a furnace and blowing was performed. At that time, add 3 slugs from the previous charge.
Leave a ton of scrap and melt it! (1st period), the slag thickness was 210 wn.

Scrap melting was carried out while supplying carbonaceous agent and oxygen, and then heating blowing was carried out. The average rate of dust generation during the scrap melting period was 22 kg/min.

When the oxygen supply amount was 600 ONm' after the start of blowing, temperature measurement and sampling were performed, and the temperature measurement was 1560°C, and melting reduction was performed. Also, it was confirmed from the analytical values of the sampling at this time that the scrap had completely dissolved at this point. It was also [%C) -4.9%. Top blowing acid rate is 220 Nm'/min, bottom blowing acid rate is 60 Nm'
/min propane flow rate was 5.0 Nm'/min. In addition, six tuyeres capable of spouting oxygen in a spiral shape as shown in Figure 5(a) were used as tuyeres, and in this experiment, d/D
= 0.25, Il/D = 0.06.

As a result, the amount Q of bottom-blown gas generated during the scrap melting period was . Subsequently, chromium ore was melted and reduced using an oxygen supply amount of 6200 Nm'. In addition, during the scrap melting and heating periods, carbonaceous agent was supplied at a rate of 1.8 kg/Nm'Oz.

Now, in the Cr oxide reduction period, half-reduced Cr pellets and carbonaceous agent were added to maintain the iron bath temperature constant for the sake of heat balance.

The components of the semi-reduced Cr pellets are shown in Table 3 below.

Table 3 0 after completion of semi-reduced pellet input! Total 1830ON
At point m', the final reduction period (stirring) started. In other words, reduce the top blowing acid rate and top blow 0□: 6O for 10 minutes.
Nm'/mfn, bottom blow (h: 6ONffi'/w
It was done indoors and the hot water was taken out.

The amount of hot water tapped was 71.3 tons, and the refining time (from the start of blowing to the end of blowing) was 71 minutes.

When the sublance was introduced before entering the final reduction period, the bath temperature was 1570''C, and it was confirmed that the iron bath temperature was kept almost constant during the Cr oxide reduction period.

The bath temperature and components at the time of tapping were as shown in Table 4 below.

Table 4 (%) The slag composition at the time of tapping was as shown in Table 5 below.

Furthermore, Table 6 shows the Cr pellets and coke used.

Table 6 In the above experiment, Cr yield: 98.7%,
Production yield: 95.7%, Ni yield: 8100
%, which was extremely good.

(Comparative Example) Exactly the same operation was carried out using a top-bottom blowing converter equipped with six conventional double front tuyeres under conditions that no slag was left behind. The amount of scrap is 22.5 tons, and the amount of hot metal charged is 41.5 tons.
It was on. The other operating conditions were almost the same.

After finishing reduction (■ period), an investigation revealed that the Cr yield was 83% and the production yield was 86.2%. This means that the dust generation rate during the scrap melting period is 130 to 140 km.
g/win, and the discharged slag contained a large amount of granulated iron with a high chromium concentration, so it is thought that the yield was reduced by the granulated iron in the dust and slag.

(Effect of the invention) The first study regarding the melting of chromium-containing iron as a stainless steel mother molten metal.
The present invention enables the use of a large amount of inexpensive scrap raw material compared to the conventional method, suppresses dust generation during scrap melting, and improves yield.
The tuyere structure of the invention was useful in the practice of the first invention.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the process flow of the first invention, Figure 2 is the flow rate of bottom blown gas during the scrap melting period and oxygen supply 10
A graph showing the relationship between the scrap melting rate after the passage of 0 Nm'/t, Figure 3 is an arrangement diagram showing the positional relationship of the bottom tuyeres, and Figure 4 is a
FIG. 5 is a graph showing the relationship between /D and tuyere melting loss, and FIG. 5 is an explanatory diagram of the tuyere. d... Tuyere spacing D... Furnace bottom diameter! ... Deviation from the furnace bottom diameter 1 ... Outer cylinder 2 ... Inner cylinder
3...Narrow gap 4...Spiral hole 7...
Outer tube 8...Inner tube

Claims (1)

[Scope of Claims] 1. In melting a stainless steel mother metal from hot metal together with a chromium-containing substance and a carbon-containing substance, the scrap is charged together with the hot metal into a reaction vessel in which molten slag is present, and the carbon-containing substance and Following the melting process in which the scrap is melted while supplying oxygen-containing gas, the temperature is raised, and then chromium-containing substances and carbon-containing substances are added to the hot metal while supplying oxygen-containing gas until the chromium content reaches the target value. A method for producing molten stainless steel mother metal, which is characterized by performing a melting reduction process, followed by a finishing reduction process by blowing with oxygen-containing gas, and tapping the metal with an appropriate amount of slag remaining. 2. The method according to claim 1, wherein the amount of slag present in the reaction vessel in the scrap melting step is at least 50 kg/t or more and has a thickness of 100 mm or more on the surface of the hot metal bath. 3. In the scrap melting process, 1.
The method according to claim 1 or 2, wherein the stirring gas is blown at a rate of 0 Nm^3/min/t or more. 4. A bottom tuyere arrangement of a reaction vessel exclusively used in the method according to claim 1, in which the bottom blowing tuyeres are arranged in rows at intervals from each other at the bottom of the furnace, and the number of the arrangement is 4 or more; and the ratio d/D of the distance d between the two tuyeres closest to the center and the diameter D of the bottom of the reactor vessel is 0.1 to 0.5, and the sum of the distances to the tuyere group is 0.1 to 0.5. A tuyere arrangement at the bottom of a reaction vessel for melting a stainless steel mother melt, where the ratio l/D of the distance l between the minimum straight line and the diameter parallel to this straight line and the diameter D of the furnace bottom part is 0.1 or less. . 5. The bottom tuyere of the reaction vessel exclusively used in the method according to claim 1 is a concentric double tube consisting of an outer tube and an inner tube inserted into the outer tube, and at least at the tip of the inner tube there is a plurality of concentric tuyeres. A bottom blowing tuyere of a reaction vessel for melting a stainless steel mother melt, which has a structure in which an oxygen gas jet is ejected in a spiral manner.