JPH0673426A - Method for decarburizing molten chromium-containing iron - Google Patents

Abstract

PURPOSE:To restrain the oxidations of chromium and iron and to improve the service life of refractory in a refining furnace. CONSTITUTION:At the time of producing a stainless steel by supplying oxidizing gas and inert gas into a molten chromium-containing iron from both of a top and a bottom blowings, water or steam from the top blowing lance is introduced into the furnace, and also, while adjusting the supplying speed in the range of <=2l/min/t, the molten steel temp. is cooled. Further, according to the supplying quantity of the water or the steam from the top blowing lance, the top blowing flow rates of the oxidizing gas and the inert gas are reduced by the gaseous oxygen and hydrogen quantities being the decomposed producing material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cooling and controlling the temperature of a steel bath to decarburize molten chromium-containing iron to produce stainless steel, and to adjust the amount of water or steam supplied from an upper blowing lance. ,
By reducing the flow rates of the top-blown oxidizing gas and the top-blown inert gas, it is possible to suppress the oxidation of chromium and iron and improve the refractory furnace refractory life. It relates to a decarburization method.

[0002]

2. Description of the Related Art Conventionally, in order to control the temperature of a steel bath to be cooled, a method of charging iron ore, manganese ore, ore ore raw material such as chromium ore, or scrap into a converter is generally used. The use of these raw materials is carried out in order to achieve the purpose of reducing and recovering valuable elements and improving the iron yield, but there are the following problems from the viewpoint of accurately controlling the temperature of the steel bath.

That is, it is not suitable for fine adjustment of the temperature of the steel bath because it is difficult to add a small amount because of the introduction system.

Further, although scrap and ore raw materials have large cooling capacity, the cooling effect depends on the melting rate of scrap and the reduction rate of ore, and these rates depend on operating conditions such as steel bath temperature and components. Since it is greatly affected, it is difficult to stably control the cooling of the steel bath. In particular, regarding the ore raw material, the cooling of the steel bath is performed by the reductive endotherm of the ore, but the reduction rate and the like depend on the operating conditions, the steel bath temperature, and the components.

Further, when these cold materials are charged, the temperature of the steel bath which comes into contact with the surface of the cooled material drastically decreases, so that easily oxidizable elements such as iron, silicon, manganese, and chromium are oxidized. As a result, the heat of reaction (heat generation) reduces the cooling effect of the cold material, making stable cooling control of the steel bath difficult.

Further, it has been attempted to use a slag forming agent such as calcium oxide or calcium carbonate as a steel bath cooling agent, but the cooling capacity per unit amount is smaller than that of an ore raw material, and a large amount of it needs to be added. In addition, the addition of slag increases the weight of slag and adversely affects the decarburization reaction, which impedes economic efficiency and productivity.

On the other hand, as a method for controlling the temperature of the steel bath with high accuracy, a method using water or steam is disclosed in Japanese Patent Laid-Open No. 52-95.
No. 502. In this method, atomized water is carried by a water-active gas or an oxidizing gas and blown into or sprayed on a molten metal bath to control the temperature of the bath. According to this method, compared with the use of a solid coolant such as scrap, the flow rate of the injected water can be controlled more easily, so that the bath water can be controlled more accurately.

Regarding the addition of water, a method of blowing water from the tuyere of the furnace bottom by using carrier gas to blow water from the bottom tuyeres improves the efficiency of cooling by decomposition of water and the stirring power of the metal bath. It is said to be suitable as compared with the method of spraying from the bath surface.

Further, as a method of introducing water into the tuyere in a mist form, a technique of press-fitting water into the bottom-blown gas pipe is disclosed. This is because the ratio of the flow rate of water to the flow rate of carrier gas is 4
It is supposed to be over 000.

According to this method using water or steam,
Although it is possible to avoid the above-mentioned problems in the method of inputting ore raw materials, scraps, etc., there are the following problems.

That is, before the mist-like water reaches the bottom blowing tuyere, the water may aggregate in the pipe and remain in the pipe, and there is a possibility that a desired water injection flow rate cannot be obtained. . Furthermore, when the distance from the position where water is introduced into the pipe to the tuyere is long, the timing at which mist-like water flows out from the tuyere can be significantly delayed compared to the timing of supplying water to the pipe. There is also a nature. As a result, it becomes difficult to accurately control the bath temperature.

In addition, in this method of supplying water from the tuyere immersed in the molten metal bath, that is, the bottom blowing tuyere, in order to prevent the molten metal from entering the tuyere, the bottom blowing is performed at a predetermined flow rate or less. The gas flow cannot be throttled. Therefore, as compared with the method of supplying water into the bath without being immersed in the bath, such as the top blowing lance, it is required to press the water into the gas pipe at a high pressure, so that the equipment must have a high pressure. It becomes necessary to do so, and the equipment cost becomes high.

As a method for solving the above-mentioned problems in the supply of water, a method of introducing water into the furnace from a top-blowing lance is disclosed in JP-A-58-193309 and JP-A-62-1.
46209 and JP-A-63-103018.

In these techniques, a coolant such as water is supplied to the hot spot formed on the collision surface between the upwardly blown oxidizing gas and the molten metal bath to lower the hot spot temperature.
It is intended to suppress dust generation due to evaporation.

That is, water or steam and an oxidizing gas or a mixed gas of an oxidizing gas and an inert gas are mixed in the upper blowing lance or in the vicinity of the outlet of the oxygen blowing nozzle of the upper blowing lance and introduced into the furnace. These techniques can advantageously solve the above problems.

Further, in these methods, since the top-blown lance can be arranged at a position where it is not immersed in the molten iron, there is no fear of leakage of the molten iron, and in addition, mixing of the top-blown gas with water or water vapor and oxidizing gas is also possible. Since it is carried out in the lance which is a vertical pipe or near the lance nozzle outlet, there is no risk of water remaining in the pipe even if it is cooled and condensed by mixing with an oxidizing gas, and all the supplied water and steam are stored in the furnace. Supplied.

Further, as compared with the bottom-blown gas pipe, the top-blown gas pressure can be made low in the top-blown lance or in the vicinity of the oxygen-blown nozzle outlet of the top-blown lance, so it is necessary to introduce water into the pipe at high pressure. Since there is no need to increase the equipment pressure, the equipment cost is low.

As described above, the problem in supplying water into the furnace can be solved by supplying water using the upper blowing lance.

[0019]

However, in the above-mentioned prior art, how to control the cooling of the steel bath temperature or the flow rate of the gas blown from the top and bottom when water or steam is supplied. There was no mention of how to adjust.

The present invention has been made to solve the above-mentioned conventional problems, and is an economical decarburization of molten iron containing chromium, which suppresses oxidation of chromium and iron and can improve refractory life of refining furnace. The purpose is to provide a method.

[0021]

The present invention is a refining converter having a top-bottom blowing function, in which the chromium-containing hot metal charged into the furnace is supplied with an oxidizing gas or an oxidizing gas from both top-bottom blowing. When a molten iron containing chromium is decarburized and stainless steel is smelted by supplying an air-fuel mixture of a gas and an inert gas, water or steam is supplied from the top blowing lance to the inside of the furnace depending on the carbon concentration in the molten iron and the bath temperature. In addition, the feed rate of water or steam is
The above object was achieved by controlling the cooling of the steel bath temperature while adjusting the amount in the range of 2 l / min. / T or less in terms of water.

Further, when water or steam is supplied from the top-blowing lance, the top-blowing oxidation is performed by the amount of oxygen and hydrogen gas, which are decomposition products thereof, depending on the amount of water or steam supplied. It is designed to reduce the flow rates of the inert gas or the oxidizing gas and the inert gas.

Further, the supply amount ΔQH _{2 of} water or steam
Depending on O, the injection flow rate Qi of the top-blown oxygen QO ₂ and the top-blown inert gas can be calculated by the following equation: QO ₂ (N m ^{3 /} min.) After the flow rate adjustment = Q before the flow rate adjustment
O ₂ (N m ³ /min.)-ΔQH ₂ O (l / min.) × 0.
622 Qi after flow rate adjustment (N m ³ /min.)=Qi before flow rate adjustment
(N m ³ /min.)-ΔQH ₂ O (l /min.)×1.24
It is adjusted according to 4.

[0024]

According to the research conducted by the inventors, when the coolant such as water or steam is supplied into the furnace from the top blowing lance to decarburize the molten iron containing chromium, the controllability of the temperature of the steel bath is improved. Therefore, it became clear that it is essential to suppress the oxidation of iron and chromium.

That is, when a cooling agent such as water or steam is simply added, in addition to the effect of promoting the cooling of the steel bath, oxygen produced by the decomposition of water or steam acts as an oxidizing gas, so that the rate of oxygen transfer is increased. Also has the effect of increasing. For this reason, the oxidation of iron and chromium is promoted, and the heat generated by the oxidation of iron and chromium causes the apparent cooling effect of the addition of water or water vapor to decrease.

Therefore, when a coolant such as water or steam is used, the conventional decarburization of stainless steel in which the flow rates of the oxidizing gas and the inert gas blown from the top and bottom are adjusted according to the carbon concentration in the molten iron and the temperature of the steel bath. In addition to the method, oxygen gas and hydrogen gas that are decomposed and produced by the supply of water or steam are also considered as oxidizing gas and inert gas, respectively. It is desirable to reduce the flow rate of the inert gas from the viewpoints of suppressing the oxidation of iron and chromium, effectively controlling the cooling of the steel bath, and suppressing the amount of refractory melt loss.

In decarburizing and refining chromium-containing hot metal,
The use of a converter for refining with a top-bottom blowing function not only enables a large amount of oxygen from both top-bottom blows to enable high-speed decarburization, but its strong bottom-blown agitation also oxidizes chromium. It is effective in the sense that the loss can be suppressed and the decarburization can be effectively performed.

The technique, which is the essence of the present invention, limits the supply rate of water according to the carbon concentration in the molten iron and the temperature of the steel bath when supplying a coolant such as water or steam from the top blowing lance into the furnace. In addition, it reduces the flow rate of the oxidizing gas and the inert gas blown in both the upper and lower parts according to the water supply rate, suppresses the oxidation of iron and chromium, and controls the cooling of the steel bath temperature. The life of the refining furnace refractory can be improved.

In order to suppress the oxidation of iron and chromium and effectively progress the decarburization reaction, the blowing flow rates of the oxidizing gas and the inert gas blown from the top and bottom should be adjusted to the carbon concentration in the molten iron and the steel bath temperature. It is important to adjust accordingly. In addition, when adding a coolant such as water or steam from the top blowing lance, from the viewpoint of enhancing the apparent cooling effect of the coolant,
Suppressing the oxidation of iron and chromium is important because it suppresses reactions that generate large amounts of heat.

Further, when water or steam is added to the furnace from the viewpoint of merely cooling the temperature of the steel bath, the oxygen transfer rate is increased by oxygen produced by the decomposition of water or steam, and the oxidation of iron or chromium is increased. Promotes.

Therefore, it is necessary to optimize the injection timing and supply rate of water or water vapor.

In this respect, according to the researches of the inventors, adjustment of the water injection timing and the supply rate is performed according to the magnitude of the surplus heat energy determined by the carbon concentration in the molten iron and the molten iron temperature.
It has been found that it is important from the viewpoint of suppressing the oxidation of iron and chromium, and in particular, when determining the water supply rate, it is desirable to limit it to 2 l / min. / T or less. Therefore, the blowing timing of water or steam, that is, the blowing section is determined from the surplus heat energy and the supply rate of water or steam.

In addition, the most important matter is that when water or steam is added from the top blowing lance, oxygen gas and hydrogen gas, which are decomposition products thereof, are also top blowing oxidizing gas and inert gas. Considering it as a gas, it is necessary to reduce the flow rate of the upward blowing oxidizing gas or inert gas and to blow it. In this case, we also examined a method of reducing the flow rate of oxidizing gas or inert gas in the bottom blow according to the addition amount of water or steam, but the stirring force of the steel bath decreases due to the decrease in the bottom blow flow rate. In addition, it became clear that the oxidation of iron and chromium increased due to the increase in the rate of acid feeding in the top blowing, which was not desirable.

Using the upper blowing lance 10 shown in FIG. 1 and FIG. 2, the upper blowing oxygen and water are mixed at the outlet of the oxygen blowing nozzle 12, atomized and sprayed onto the molten chromium-containing iron below. Depending on the amount of water supplied, if the flow rates of oxygen and argon gas for the top blowing are reduced by the amounts of oxygen and hydrogen gas that are the decomposition products of water (marked with ● in Fig. 3), FIG. 3 shows an example of the relationship between the temperature change in the steel bath and the carbon concentration in molten iron that affects the chromium oxidation amount with respect to the decarburization amount, when the acid transfer is carried out regardless of the amount (marked with ◯ in FIG. 3). Depending on the amount of water supplied, the flow rate of top-blown oxygen and argon is reduced by the amount of oxygen and hydrogen gas, which are decomposition products of water. It is as shown in Table 2.
Table 4 below shows the conditions of acid feeding for blowing from the top and bottom when acid feeding is carried out regardless of the amount of water supplied.

From FIG. 3, even under the same water supply amount and bottom blowing flow rate conditions, the amount of oxygen and hydrogen gas, which are decomposition products of water, corresponding to the amount of water supplied, is different from that of top blowing oxygen. It is understood that the temperature rise of the steel bath and the oxidation amount of chromium can be reduced by decreasing the flow rate of argon. In the low coal area, it is better to decrease the flow rates of top-blown oxygen and argon by the amount of oxygen and hydrogen gas, which are decomposition products of water, depending on the amount of water supplied. It can be seen that the temperature can be controlled accurately.

As described above, by controlling the condition of the acid to be blown upward depending on the supply of water, it is possible to simultaneously suppress the oxidation of chromium and improve the cooling effect of water.

[0037]

Embodiments of the present invention will now be described in detail with reference to the drawings.

This embodiment was carried out by using the upper-bottom blow converter 20 having a furnace capacity of 5 tons shown in FIG. In FIG. 4, 22
Is a bottom-blowing tuyere of a double pipe structure, 24 is molten iron containing chromium, 2
6 is a flux tank.

As the bottom blowing tuyere 22, the inner tube inner diameter 1
It uses four 0 mmφ double tube tuyere, supplies a mixture of oxygen or argon gas from the inner tube, and a mixture of propane (Pr) or argon gas from the gap between the inner and outer tubes. Are blown in for tuyere cooling.

As shown in FIGS. 1 and 2, the upper blowing lance 10 has three holes and each nozzle has a throat diameter of 9.5 mm. From the nozzle, oxygen or argon is used. The air-fuel mixture, and further water, is mixed with the top-blown gas and sprayed.

In the operation, chromium ore, coke, etc. are put into the hot metal dephosphorized in the same 5 ton top-bottom blowing converter in advance,
Melt reduction was performed to obtain crude molten iron containing chromium.

Next, the molten iron was separated from the slag, tapped, and then charged again. Table 1 shows the temperature and components of the chromium-containing crude molten iron at this time.

[0043]

[Table 1]

Mixing and spraying of water and the top-blown gas in the top-blown lance 10 is performed as shown in FIGS.
A water blowing nozzle 14 was arranged at the outlet of each oxygen blowing nozzle 12, and the upper blowing gas and water were mixed and atomized at the outlet of the oxygen blowing nozzle. In this case, the relative angle θ between the water blowing nozzle 14 and the oxygen blowing nozzle 12 was 15 °, and the inner diameter of the water blowing nozzle 14 was 1.5 mm.

As the conditions for blowing the upper and lower gas and water, considering the generation of hydrogen gas, which is a decomposition reaction product of water, and the oxygen in the water, the ratio of oxygen to diluting gas is the first in the oxidative refining process. Oxygen and argon supplied from the upper blowing lance 10 so that 1/0 in the 0th period, 4/1 in the 1st period, 2/1 in the 2nd period, and 1/2 in the 3rd and 4th periods. The gas flow rate was adjusted. Table 2 shows an example of operating conditions at the time of oxidation refining and reduction refining.

[0046]

[Table 2]

In the second and third stages of the oxidation refining process,
The temperature of the steel bath is adjusted to 1680 by measuring the temperature with a sublance
In order to control the temperature to ± 2 ° C, the flow rate of top-blown water was adjusted within a range of ± 10% based on the operating conditions shown in Table 2, and the flow rates of top-blown oxygen and argon gas were changed correspondingly.

In this case, in each step, as described above, oxygen and hydrogen gas, which are decomposition products of water, are also considered as substitutes for oxygen and argon gas, respectively, and the upper blowing oxygen gas and argon gas are correspondingly supplied. The flow rate was decreased so that the total oxygen transfer rate of the top and bottom blows and the ratio of oxygen gas to dilution gas were constant.

In addition, as is apparent from Table 2, the flow rate of water blown during the blowing was limited to 2 l / min. / T or less for the operation.

During the operation, the auxiliary raw material was added by injecting quicklime powder from the bottom blowing tuyere 22 at the initial stage of oxidation refining so that the slag basicity at the time of reduction refining storage was 1.9. Further, in the initial stage of reduction refining, 15 kg / t Fe 2 Si alloy was charged from above the furnace.

In this embodiment, 36 minutes were required for oxidation refining and 5 minutes for reduction refining, for a total of 41 minutes. However, during the oxidation refining, particularly during the second and third periods, the steel bath temperature was 1680 ± 2 ° C. It was possible to control accurately in the range of. Further, the chromium oxide transferred to the slag could be sufficiently recovered in the metal.
Table 3 shows the results of the operation.

[0052]

[Table 3]

After the completion of the blowing, the melting loss of the refractory material was measured and found to be 3 mm as the average value of the furnace bottom and the furnace side.

Next, a comparative example will be described.

According to the same equipment and operating method as in the above-mentioned example, the addition of water from the top-blowing lance 10 and the conditions of the top-bottom blowing acid were as shown in Table 4, with oxygen being a decomposition product of water. Without considering hydrogen gas, the ratio of the total oxygen blown to the bottom and the dilution gas was 1/0 in the 0th period of the oxidation refining process, 4/1 in the 1st period, 2/1 in the 2nd period, and 3rd. 1 / in the 4th period
A comparative example in which the value was set to 2 was also performed.

[0056]

[Table 4]

In this comparative example, the addition of water from the upper blowing lance 10 adjusted the spraying flow rate only from the viewpoint of cooling control of the steel bath temperature.

At the temperature of the steel bath during the operation, particularly in the second and third stages of the oxidation blowing process, 168 as in the above embodiment.
Although the flow rate of water was adjusted to control within the range of 0 ± 2 ℃, even if the maximum flow rate of water was 10l / min., It could not be controlled within the range of 1680 ± 2 ℃, and at the end of the 3rd term. The steel bath temperature has risen to 1730 ° C.

Table 5 shows the operation results of the comparative example.

[0060]

[Table 5]

Further, as can be seen by comparing Tables 2 and 4, the reduction amount of the chromium concentration at the time of spraying with respect to the chromium concentration of the crude molten iron is 1.2 in the comparative example with respect to the examples of the present invention. % Increased. As a result, in the comparative example, in order to make the component composition at the time of reduction refining equal to that of the example of the present invention, the Fe Si basic unit is 22 kg / t and 7 kg compared with 15 kg / t of the example of the present invention. / T I had no choice but to put in an extra. Also, the refining time is 40 in the oxidation refining process.
Min, 7 minutes in the reduction and refining process, for a total of 47 minutes, and an extra 6 minutes for the blowing time in comparison with the examples of the present invention.

Further, in the comparative example, the melting loss amount of the refractory became 7 mm due to the rise of the molten iron temperature during the oxidation period,
This resulted in a 4 mm increase over the examples of the present invention.

From the above results, in the comparative example, for the purpose of controlling the molten iron temperature in the oxidation period, the method of adjusting the water supply amount independently of the upper and lower blown gas was the method of local supercooling of the steel bath. , Oxygen gas generated by the decomposition of water causes an increase in the rate of oxygen transfer in the upward blowing, resulting in an increase in the oxidation amount of chromium during the oxidation period and a consequent decrease in the cooling effect of water. It is clear that it is difficult to operate economically because it causes an increase in the Fe 2 Si basic unit in the reduction period, further increases in the temperature of the steel bath and an increase in the amount of refractory erosion due to the extended blowing time.

On the other hand, in the embodiment of the present invention,
Considering oxygen and hydrogen gas, which are decomposition products of water supplied from the top blowing lance, as oxidizing gas and diluting gas,
By reducing the flow rates of the oxygen gas and argon gas for the upper blowing by this amount, the oxidation of iron and chromium can be suppressed, and as a result, the apparent cooling effect of water is improved,
The controllability of the steel bath temperature was improved. As a result, it became possible to shorten the blowing time, reduce the Fe Si basic unit, and reduce the amount of refractory erosion.

[0065]

As described above, according to the present invention, it is possible to suppress oxidation of chromium and iron, improve the refractory life of refining furnace, and realize economical decarburization of molten chromium-containing iron. It has an excellent effect that it can be done.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a top blowing lance for blowing water, which is used for implementing the present invention.

[Figure 2] Similarly, bottom view

FIG. 3 is a characteristic diagram showing the relationship between the steel bath temperature, the ratio of decarburization amount to chromium oxidation amount, and the carbon concentration in molten iron when water is supplied to the molten iron containing chromium.

FIG. 4 is a cross-sectional view schematically showing a 5-ton scale converter equipment used for carrying out the present invention.

[Explanation of symbols]

 10 ... Top blowing lance 12 ... Oxygen blowing nose 14 ... Water blowing nozzle 20 ... Top bottom blowing converter 22 ... Bottom blowing tuyere 24 ... Chromium molten iron

Claims (3)

[Claims] 1. A smelting converter having a top-bottom blowing function, wherein chrome-containing hot metal charged in the furnace is supplied with an oxidizing gas or a mixture of an oxidizing gas and an inert gas from both top-bottom blowing. When supplying and decarburizing the chromium-containing molten iron and melting stainless steel, water or steam is introduced into the furnace from the top blowing lance according to the carbon concentration in the molten iron and the bath temperature, and Alternatively, the water vapor supply rate is 2 l / water equivalent.
A decarburizing method for molten chromium-containing iron, which comprises cooling and controlling the steel bath temperature while adjusting the temperature within the range of min./t or less. 2. The supply of water or steam from the upper blowing lance according to claim 1, depending on the supply amount of the water or steam, only the amount of oxygen and hydrogen gas which are decomposition products thereof. A method for decarburizing molten chromium-containing iron, which comprises reducing the flow rate of the top-blown oxidizing gas or the blowing of the oxidizing gas and the inert gas. 3. The injection flow rate Qi of the top-blown oxygen QO ₂ and the top-blown inert gas according to the supply amount ΔQH ₂ O of the water or steam according to the following equation, respectively. ₂ (N m ^{3 /} min.) = Q before flow rate adjustment
O ₂ (N m ³ /min.)-ΔQH ₂ O (l / min.) × 0.
622 Qi after flow rate adjustment (N m ³ /min.)=Qi before flow rate adjustment
(N m ³ /min.)-ΔQH ₂ O (l /min.)×1.24
4. A method for decarburizing molten chromium-containing iron, which is characterized in that