JPH1136007A - Method of discharging slag generated during stainless steel production and method of recycling slag - Google Patents

Abstract

(57) [Summary] The present invention provides a method of discharging slag generated during the production of stainless steel, which facilitates the discharge of waste from a decarburization furnace or a transport container, and a method of recycling slag discharged by the method. It is intended to provide usage. SOLUTION: A chromium raw material and calcined lime are charged into hot metal in a converter type smelting reduction furnace, and a separately charged carbon material is burned with an oxidizing gas to generate heat, thereby melting and reducing the chromium raw material, Next, the produced chromium-containing crude molten steel is transferred to another converter type decarburizing furnace to perform decarburization refining to produce stainless steel, and the slag generated in the decarburizing furnace is supplied with a coolant /
A coolant for the slag is charged so that the volume ratio of the slag is 0.2 or more, and the slag after mixing, cooling, and solidifying is discharged to a transport container while suppressing aggregation of the slag.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for discharging slag generated during the production of stainless steel and a method for recycling slag.

[0002]

2. Description of the Related Art Recently, expensive ferrochrome alloys conventionally used to reduce the manufacturing cost of stainless steel,
Alternatively, inexpensive chromium ore has been used directly instead of reduced pellets. That is, as disclosed in Japanese Patent Publication No. 4-38806, "using two converters having different functions, powdered chromium ore is charged into hot metal in the first converter, and the ore is made of carbonaceous material. A method of producing a stainless steel by melt-reducing and blowing a molten metal for producing stainless steel, and subjecting the molten metal to decarburization and refining as usual in a second converter. At that time, slag containing chromium oxide is generated even in the second decarburization furnace, and it is necessary to recover expensive chromium from this slag. At present, a method is adopted in which slag is discharged from the decarburization furnace into a transfer vessel (ladle), returned to the first smelting reduction furnace via the vessel, and then recovered again in the molten metal for stainless steel by smelting reduction. doing.

[0003] However, chromium oxide is cooled and solidified in the transfer container that receives the slag from the first decarburization furnace, and the slag becomes a large solid. For this reason, even if the slag is discharged from the decarburizing furnace to the transfer container, or the slag is returned from the container to the first smelting reduction furnace, the agglomerated slag is caught on the furnace wall or the container wall or sticks to the furnace wall. Not all emissions. In addition, this poor discharge not only reduces the amount of expensive chromium recovered, but also causes a troublesome problem of treating slag remaining in the transport container.

[0004] In recent years, high quality has been demanded for all types of stainless steel, and various refining methods have been developed and put to practical use in the steelmaking process accordingly. However, these refining methods use a larger amount of slag-making material than before,
The treatment of slag, a by-product of smelting, is a major problem. For this reason, technical development on the reduction of the amount of slag-making material used and the method of reusing slag has been actively carried out.

For example, Japanese Patent Publication No. 58-31362 proposes a "steel making method in which molten slag of a previous charge is left in a furnace and reused as a part of a slag material of a next charge." Also, Japanese Patent Publication No. Sho 62-50543,
"A method for reducing and recovering chromium by melting and reducing slag containing chromium oxide generated during the production of stainless steel using an inexpensive carbon material in a top-bottom blower-type reactor"
Is disclosed.

However, in the technique described in Japanese Patent Publication No. 58-31362, the molten slag of the previous charge is left in the furnace and reused as a part of the slag material of the next charge. Will increase the amount of slag. Chromium in molten steel is oxidized and transferred to slag with blowing, but this technique has a problem that a large amount of expensive Fe-Si is used to reduce and recover the chromium oxide. doing.

Further, the technique described in Japanese Patent Publication No. Sho 62-50543 was tried, but the slag did not melt unless oxygen was blown at a higher temperature (for example, 1650 ° C. or higher) than ordinary smelting reduction. In other words, it seems that this technique has a problem of promoting the wear of the refractory lining of the smelting reduction furnace and shortening the furnace life.

[0008]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention provides a method of discharging slag generated during the production of stainless steel, which facilitates the discharge of waste from a decarburization furnace or a transport container, and a method of discharging slag generated by the method. The purpose of the present invention is to provide a method for reusing recycled slag.

[0009]

Means for Solving the Problems In order to achieve the above object, the inventor conducted research to find a state of slag easily discharged from a decarburizing furnace or a transport container, and cooled and solidified without coagulating the slag. Then, it was concluded that it would be good if it could be made into a powdery and granular state, so-called smooth state. Means for making the slag after the completion of the refining in the decarburization furnace intensely studied, and completed the present invention.

That is, the present invention provides a chromium raw material in which a chromium raw material and calcined lime are charged into hot metal in a converter type smelting reduction furnace, and a separately charged carbon material is burned with an oxidizing gas to generate heat. Then, the resulting chromium-containing crude molten steel is transferred to another converter type decarburization furnace to perform decarburization refining to produce stainless steel, and slag generated in the decarburization furnace is produced. The slag coolant is supplied so that the volume ratio of the coolant / slag becomes 0.2 or more, and the slag after mixing, cooling, and solidifying while suppressing aggregation of the slag is discharged to a transport container. This is a method of discharging slag generated during the production of stainless steel.

[0011] The present invention is also a method for discharging slag generated during the production of stainless steel, wherein the coolant is carbonaceous material or calcined lime. Further, according to the present invention, the basicity (CaO / SiO ₂ ) of the slag generated in the decarburization furnace is set to 1.8 to 3.
This is a method for discharging slag generated during the production of stainless steel, characterized by being set to 0.

[0012] In addition, the present invention provides a method of smelting and reducing the chromium raw material again by charging the slag generated during the production of stainless steel discharged by any of the above methods into the hot metal of the converter type smelting reduction furnace. Or the melt temperature at that time is 1550
It is also a method of reusing waste slag characterized by being at most １６1650 ° C. or lower. According to the present invention, since the slag in the decarburization furnace is in a granular state and in a smooth state, the waste from the decarburization furnace and the transport container is smooth. As a result, all of the expensive chromium in the slag generated in the decarburization furnace is recovered, and a reduction in the production cost of stainless steel can be achieved. In the present invention, since the slag coolant is a carbon material or calcined lime used as an auxiliary material even in smelting reduction, they are effectively used in the waste slag recycling method and are not wasted. Further, the wear of the refractory lining of the smelting reduction furnace is suppressed, and the furnace life can be extended. As the cold material, particularly, a carbon material, which is indispensable for the operation of the smelting reduction furnace and represented by coke, which has substantially no restriction on the increase, is most suitable. On the other hand, lime can be used, but given that it has a higher specific gravity than carbon and must be used in a larger amount than carbon, and that lime solidified at the same time as slag delays slagging, Is limited. Therefore, in the present invention, it is preferable to appropriately mix and use the carbonaceous material and the lime.

In the present invention, the input amount of the coolant is determined by the volume ratio of the coolant / slag, and the volume of the slag is set to a bulk specific gravity of 2.5 t / m ³ and the volume of the coolant is Calculated using the specific gravity of the bulk material of charcoal and calcined lime. For example,
Small coke (grain size 10 to 25 mm) and calcined lime (grain size 5
２０20 mm) were used in the practice of the invention, their bulk specific gravities were 0.5 t / m ³ and 1.0 t / m ³ , respectively.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below, taking into account the circumstances leading to the invention. First, the inventor studied various ways to cool and solidify the slag generated in the second decarburization furnace into a granular and smooth state. Among them, the result shown in FIG. 1 was the most preferable. That is, Fig. 1 shows that the material to be charged into the decarburization furnace as the slag coolant is carbon material (specifically, coke).
The amount of slag that can be variously changed by determining the amount of addition based on the volume ratio with the generated slag and returned to the first smelting reduction furnace (slag recovery rate = (weight of returned slag / weight of generated slag) × 100) (Represented by).

As is clear from FIG. 1, regardless of the presence or absence of chromium oxide contained in the slag, the effect of the added coolant differs at a coolant / slag volume ratio of 0.2. I have. That is, the volume ratio of the coolant / slag is 0.1.
When it is less than 2, slag aggregation is promoted after cooling and solidifying,
The slag was caught or stuck in the slag transport container, and the slag generated in the decarburization furnace could not be returned to the smelting reduction furnace in its entirety.

The inventor made various changes in the types of coolants that can be used, and made the same study as described above. as a result,
In addition to charcoal, calcined lime, MgO clinker, gravel, brick debris,
Even industrial waste such as dust and blast furnace slag, and waste generated from steelworks,
Almost the same results as in FIG. 1 were obtained. Therefore, the inventor
These findings were embodied as the present invention.
If the volume ratio of the coolant / slag is 0.2 or more,
Since the above effects can be obtained, there is no upper limit on the volume ratio. However, if it exceeds 0.2 or more, the effect is saturated, so that the amount of the coolant to be used in actual operation may be determined from the viewpoint of economy. It is also important that the coolant does not prevent the slag from being returned to the smelting reduction furnace and reused.

Further, the inventor investigated the basicity (= CaO / SiO ₂ ) of the slag generated in the decarburization furnace. The reason is that slag is recycled between the decarburizing furnace and the smelting reduction furnace, so that the increase in Cr oxidation loss in the decarburizing furnace caused by the increase in slag volume and the size of the slag discharge container It is to suppress. As a result, it was concluded that it was appropriate to limit the slag basicity to 3.0 or less in the decarburization furnace. On the other hand, by the reduction of chromium oxide by Fe-Si performed after the decarburization refining in the decarburization furnace,
In order to expect desulfurization from molten steel, the basicity of the slag must be 1.8 or more. Therefore, in the present invention, the basicity of the slag generated in the decarburization furnace is set to 1.8 to 3.0. It is preferable to be within the range.

Next, the inventor studied an optimal method of reusing the slag obtained by the above-described waste disposal method according to the present invention in a smelting reduction furnace. The reason is that in the prior art described in Japanese Patent Publication No. Sho 62-50543, the slag did not melt unless oxygen was blown at a higher temperature (for example, 1650 ° C. or higher) than ordinary smelting reduction. That is, when the slag is reused, there is a problem that the wear of the refractory lining of the smelting reduction furnace is promoted and the furnace life is shortened.

First, the inventor returns the molten slag generated in the decarburization furnace to the smelting reduction furnace by employing the above-described waste method according to the present invention, and performs smelting reduction of chromium ore again. The relationship between the molten metal temperature and the total Cr concentration in the slag at the end of the smelting reduction (hereinafter referred to as T.Cr) was investigated. As is clear from FIG. 2, even if the slag from the decarburizing furnace contains 10 wt% of chromium, if the temperature of the molten metal is set to about 1650 ° C., the T . It has been found that Cr can be reduced to 0.5 wt% or less, which is the same level as ordinary smelting reduction slag. This is considered to be because the carbon material and the slag-making agent charged as the coolant were effectively used in the above-described slag discharge method according to the present invention, and the smelting reduction of chromium ore was smoothly performed.

Further, during these recycling operations, the refractory erosion of the smelting reduction furnace was investigated, and the results are shown in FIG. As is clear from FIG. 3, when the temperature of the molten metal during the smelting reduction exceeds 1650 ° C., the refractory wear of the smelting reduction furnace (indicated by an index with the refractory wear rate at 1550 ° C. being 1) becomes severe. It turns out that it becomes. If the temperature is lower than 1550 ° C., the T.G. If there is a large amount of Cr, T.C. This is because Cr is increased and smelting reduction is insufficient.

Therefore, the inventor set the temperature of the molten metal in the range of 1550 to 1650 ° C. when reusing the slag obtained by the waste disposal method according to the present invention in the smelting reduction furnace. In addition, T.C. in slag generated in the decarburization furnace was used. Cr should be 7wt% if possible
% Seems to be preferable.

[0022]

EXAMPLE Stainless steel was manufactured using two converter type reaction vessels, and the waste disposal method and the waste slag recycling method according to the present invention were employed for the operation. (Embodiment 1) A second decarburization furnace is provided with an upper-bottom blowing function.
A 0t converter (K-BOP) was set therein, and 120 ton of chromium-containing crude molten steel melted in the first smelting reduction furnace was charged therein, and crude decarburization was performed. At that time, calcined lime or Fe-Cr alloy iron was charged, and 13.1 per ton was added to the molten stainless steel after the rough decarburization.
kg / t of Fe-Si was charged to reduce oxides in the slag generated during the decarburization and desulfurize the molten steel.

The breakdown of the slag produced by the decarburization refining is Ca
O = 10.4 ton, SiO ₂ = 5.2 ton, Al ₂
O ₃ = 1.0 ton, MgO = 1.6 ton, and the total slag weight is 18.2 ton. This total weight was divided by a bulk specific gravity of 2.5 t / m ³ to reduce the volume of the produced slag to 7.2.
8 Nm ³ . Then, in order to employ the waste disposal method according to the present invention, 2.0 tons of coke having a bulk specific gravity of 0.5 t / m ³ was used as a coolant. That is, the volume ratio of the coolant / slag was 0.55.

After the decarburization was completed, coke powder was charged into the produced slag in accordance with this volume ratio, and the furnace was shaken to sufficiently mix with the slag, and was cooled and solidified. As a result, the slag was in an appropriate size and smooth.
Then, when the slag was discharged into a discharge container (a ladle), almost all of the generated slag could be recovered smoothly. next,
The waste slag was charged into a first smelting reduction furnace, and smelting reduction was performed together with separately charged hot metal, chrome ore, calcined lime, and carbonaceous material. At that time, when the temperature of the molten metal was adjusted to 1550 ° C., the operation was completed in a blowing time of 90 minutes. (Embodiment 2) A second decarburization furnace is provided with a top-bottom blowing function.
A 0t converter (K-BOP) was used, and 123t of chromium-containing crude molten steel melted in the first smelting reduction furnace was charged therein, and crude decarburization was performed. At that time, calcined lime and Fe-Cr alloy iron were charged, and 10.3 / ton was added to the molten stainless steel after rough decarburization.
kg / t of Fe-Si was charged to reduce oxides in the slag generated during the decarburization and desulfurize the molten steel.

The slag produced by the decarburization refining is composed of Ca
O = 9.2 ton, SiO ₂ = 4.6 ton, Al ₂ O
₃ = 0.7 ton, MgO = 1.4 ton, and the total slag weight is 15.9 ton. This total weight was divided by a bulk specific gravity of 2.5 t / m ³ to reduce the volume of the produced slag to 6.36.
Nm ³ . Then, in order to adopt the waste disposal method according to the present invention, 4.0 ton of calcined lime having a bulk specific gravity of 1.0 t / m ³ was used as a coolant. That is, the volume ratio of the coolant / slag was 0.63.

After the decarburization was completed, calcined lime powder was charged into the produced slag in accordance with this volume ratio, and the furnace was shaken to sufficiently mix with the slag, and was cooled and solidified. As a result, the slag was in an appropriate size and smooth.
Then, when the slag was discharged into a discharge container (a ladle), almost all of the generated slag could be recovered smoothly. next,
The waste slag was charged into a first smelting reduction furnace, and smelting reduction was performed together with separately charged hot metal, chrome ore, calcined lime, and carbonaceous material. At that time, the temperature of the molten metal was adjusted to 1600 ° C., and the operation was completed in a blowing time of 85 minutes. (Comparative Example 1) A second decarburization furnace was equipped with a top-bottom blowing function.
A 0t converter (K-BOP) was set therein, and 125t of chromium-containing crude molten steel melted in the first smelting reduction furnace was charged therein, and crude decarburization was performed. At that time, calcined lime and Fe-Cr alloy iron were charged, and 14.3 per ton was added to the molten stainless steel after the rough decarburization.
kg / t of Fe-Si was charged to reduce oxides in the slag generated during the decarburization and desulfurize the molten steel.

The slag produced by the decarburization refining is composed of Ca
O = 12.6 ton, SiO ₂ = 6.3 ton, Al ₂
O ₃ = 1.2 ton, MgO = 1.9 ton, and the total slag weight is 22.0 ton. The total weight was divided by the bulk specific gravity of 2.5 t / m ³ to reduce the volume of the produced slag to 8.8.
Nm ³ . And the bulk specific gravity 0.5t /
0.5 tons of m ³ coke was used. That is, the coolant / slag volume ratio is 0.11.

After the decarburization was completed, calcined lime powder was charged into the produced slag in accordance with this volume ratio, and the furnace was shaken to sufficiently mix with the slag, and was cooled and solidified. However, slag is
Coagulation and solidification resulted in a large size, or stuck to a refractory, preventing smooth discharge. Therefore, when the slag was discharged into a discharge vessel (a ladle), most of the generated slag could not be collected and remained in the furnace.

Next, the waste slag was charged into a first smelting reduction furnace, and was subjected to smelting reduction together with separately charged hot metal, chrome ore, calcined lime, and carbonaceous material. At that time, when the temperature of the molten metal was adjusted to 1550 ° C., the blowing time was as long as 102 minutes. The results of these two examples of the present invention and comparative examples are shown in Tables 1 to 4. Tables 1 and 2
Is the composition of the molten metal component and slag from the decarburizing furnace, respectively. Table 3 shows a comparison of the amount of recycled slag when returned to the smelting reduction furnace. This is the composition of the slag obtained by performing smelting reduction again.

As is clear from Table 3, in Comparative Example 1, only 80% of the slag produced in the decarburization furnace was recovered.
Further, the slag generated in the smelting reduction furnace after reuse in Example 1 is T. slag. Cr is 0.4%, which is about the same as slag obtained by operation of a conventional smelting reduction furnace that does not reuse slag. This suggests that the smelting reduction was performed smoothly by reuse. Further, the slag generated in the decarburization furnace of Example 2 Although the Cr content is as high as 5.3%, the T.C. in the slag produced in the smelting reduction furnace is set by setting the temperature of the molten metal to 1600 ° C., which is slightly higher than before, when reusing it. Cr is set to 0.
The slag could be reduced to 3%, and the same reduction as the slag generated in the conventional smelting reduction furnace without slag reuse was achieved.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

As described above, according to the present invention, stainless steel is produced by direct smelting reduction of inexpensive chromium ore and decarburization of the melt obtained by the smelting reduction using two converter type reaction vessels. During the production of slag, the slag generated in the decarburization furnace was smoothly discharged, and could be reused in the smelting reduction furnace. In addition, at the time of its disposal, the carbon material used in the smelting reduction furnace, calcined lime, etc. were effectively used as the coolant for the slag,
It was not necessary to increase the operating temperature when recycling the slag in the smelting reduction furnace.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram for explaining an amount of coolant to be supplied to slag produced in a decarburization furnace, and shows a relationship between a volume ratio of coolant / slag and a recycling rate of the slag in a smelting reduction furnace.

FIG. 2 shows the temperature of molten metal during smelting reduction using slag produced in a decarburization furnace and the T.C. It is a figure showing the relation with Cr.

FIG. 3 is a diagram showing a relationship between a molten metal temperature during smelting reduction and a wear state of a furnace refractory.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyasu Morioka 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Chiba Works, Ltd. (72) Inventor Yasuo Kishimoto 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki (72) Inventor Yoshihisa Kitano 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Chiba Works Chiba Works

Claims (6)

[Claims] 1. A chromium raw material and calcined lime are charged into hot metal in a converter-type smelting reduction furnace, and the carbon material separately charged is burned with an oxidizing gas to generate heat, thereby melting and reducing the chromium raw material. Then, the chromium-containing crude molten steel thus produced is transferred to another converter type decarburizing furnace to perform decarburization refining to produce stainless steel. In the slag generated in the decarburizing furnace, coolant / A slag coolant is supplied so that the volume ratio of the slag is 0.2 or more, and the slag after mixing, cooling, and solidifying while suppressing aggregation of the slag is discharged to a transport container. Of slag generated during the production of stainless steel. 2. The method of claim 1, wherein the coolant is a carbonaceous material. 3. The method of claim 1, wherein the coolant is calcined lime. 4. The basicity (CaO / SiO ₂ ) of slag generated in a decarburization furnace before charging the coolant is 1.8 to 3.
4. The method of claim 1, wherein the slag generated during the production of stainless steel is set to zero. 5. The slag generated during the production of stainless steel discharged by the method according to any one of claims 1 to 4, is charged into the hot metal of the converter-type smelting reduction furnace, and the chromium raw material is melt-reduced again. A method of recycling waste slag characterized by the following. 6. The molten metal temperature in the smelting reduction furnace is set to 1550.
The method for recycling waste slag according to claim 5, wherein the temperature is set to 1650C or lower.