JP2005200762A - Hot metal desulfurization method - Google Patents

Abstract

[PROBLEMS] To produce a low-sulfur steel at a low cost even by adding a cold iron source having a high sulfur content, and to efficiently increase the [C] concentration in dephosphorization so as to produce high-quality [Mn]. Provided is a method capable of producing molten steel with high concentration at low cost.
When dephosphorization is desulfurized using a mechanical stirrer, a deoxidizer (Si source, Al source) is added and desulfurized, followed by decarburization. Further, when dephosphorizing the dephosphorization using a mechanical stirrer, a carbonaceous material is added to increase the [C] concentration, followed by decarburization. If the carbon material is added by blowing carbon material powder into the hot metal from the impeller shaft of the mechanical stirrer, dissolution of the carbon material into the hot metal becomes even easier. In addition, it is effective in promoting desulfurization of dephosphorization by adding a carbonaceous material to increase the [C] concentration and adding a deoxidizer during desulfurization treatment.
[Selection figure] None

Description

  The present invention relates to a hot metal desulfurization method in which hot metal after dephosphorization (dephosphorization) is desulfurized using a mechanical stirring device.

  As a method for melting high-quality steel with low phosphorus and low sulfur, conventionally, a process of desulfurizing hot metal discharged from a blast furnace, dephosphorizing, and then decarburizing has been generally adopted.

  For example, in Patent Document 1, hot metal after desulfurization is poured into a dephosphorization furnace, a refining agent mainly composed of a converter furnace generated in a decarburization furnace in the next step is added, and the hot metal temperature is 1400 ° C. or lower. A steelmaking method is described which includes a step of performing hot metal dephosphorization while maintaining a low temperature, and a step of decarburizing and finishing dephosphorization of the obtained dephosphorized hot metal in a decarburization furnace. In both dephosphorization and decarburization processes, a converter-type furnace is used, and the converter slag generated in the decarburization furnace is used as a refining agent, so that high quality steel can be melted at low cost. it can. However, in this process, there is a problem that scraps and carbon materials having a high sulfur content cannot be added during the dephosphorization process, and that some degree of resulfurization occurs during the dephosphorization process.

  On the other hand, in Patent Document 2, cold iron is added to hot metal in a dephosphorization furnace in order to solve the problems that the desulfurization generated during the dephosphorization process and a large amount of cold iron source (scrap) cannot be added to the dephosphorization furnace. A steel refining method is disclosed in which a source and carbon material are added, dephosphorized, desulfurized in a desulfurization facility (using a KR desulfurization facility that performs mechanical stirring), and then decarburized and refined in a decarburization furnace. .

The characteristics of this process are the following two points.
(A) In order to add a large amount of scrap in the dephosphorization furnace (the hot metal ratio is 90% by mass with respect to the normal 95% by mass), a large amount of carbonaceous material (sulfur content of sulfur content) is used as a heat source. Add high coke and coal). Normally, carbonaceous material is not added, but 14 to 42 kg / pig iron t is added.
(B) After the dephosphorization treatment, the [C] concentration in the dephosphorized soot is almost saturated (4.5% by mass). Since the carbon in the hot metal can be used as a heat source, Mn ore and the like can be added in a decarburizing furnace in an amount corresponding to the heat margin. However, the amount of charcoal added is large.

  However, this method has the following problems. That is, when a carbon material is added to the dephosphorization furnace, the carbon material is trapped in the slag, and it is difficult for the carbon material to dissolve in the molten iron, and the undissolved carbon material is discharged together with the slag after the dephosphorization treatment. The cause is that the specific gravity of the carbon material is close to that of dephosphorized slag and is light, so that it floats in the slag and is difficult to contact the hot metal.

  Also, the sulfur content in the scrap added to the dephosphorization furnace may be unexpectedly high, and if the [S] concentration in the dephosphorization furnace increases from 0.03 to 0.05% by mass, The KR desulfurization method has a problem that it cannot be reduced to a desired [S] concentration (for example, 0.0020% by mass or less).

  As a reason why the [S] concentration in the hot metal after KR desulfurization of dephosphorized iron cannot be reduced to a desired value (for example, 0.0020% by mass or less) by the method described in Patent Document 2, normal hot metal is used. Compared with, dephosphorization has a higher oxygen potential. This is because desulfurization is more likely to proceed as the oxygen potential is lower, but the hot metal after the dephosphorization treatment is not in a condition that facilitates such desulfurization reaction.

  Therefore, it seems that the addition of a deoxidizing agent is effective for desulfurizing dephosphorized soot as efficiently as normal hot metal. For example, Patent Document 3 describes a method of “using hydrogen gas as a deoxidizing agent”. Has been. This method uses hydrogen gas or a gas containing hydrocarbon gas that decomposes to generate hydrogen gas when desulfurization is performed by adding a desulfurizing agent to the hot metal from the surface of the hot metal contained in the hot metal ladle and performing mechanical stirring. Is a method in which hot metal is sprayed on the hot metal surface under predetermined conditions. However, since hydrogen gas or hydrocarbon gas that generates hydrogen gas is handled during operation, there is a concern about safety problems.

Regarding the method of “adding carbonaceous material” when hot metal desulfurization is performed, Non-Patent Document 1 states that “reduction of the atmosphere inside the kneading vehicle increases as the amount of C mixed in the desulfurizing agent increases, so that η _CaO (CaO reaction efficiency) Is improved "(page 3, right column, lines 6 to 7). That is, in the past, C was added during the desulfurization treatment of C saturated hot metal to improve the desulfurization efficiency η _CaO . At that time, the effect of C was “naturally, since C cannot be dissolved in hot metal, it is exclusively reduced. It was only “enhancement of sexual atmosphere”. Therefore, the added C is uneconomical because it is discharged out of the system together with the slag after the desulfurization treatment. The amount of C added in Non-Patent Document 1 is (70-β)% CaO-25% CaCO ₃ -5% CaF ₂ -β% C (β = 5 to 20%).

Japanese Patent Laid-Open No. 62-290815

JP-A-7-138628 JP 2003-166209 A “Kawatetsu Technical Report” vol. 14 (1982), pages 1-9

  As described above, in the “desulfurization → dephosphorization → decarburization” process (conventional process), a large amount of carbon material having a high sulfur content cannot be added in the dephosphorization furnace. Therefore, the [C] concentration in dephosphorization is low, there is little heat margin in the decarburization furnace, and manganese ore or iron ore (high cooling capacity) for improving the yield of Mn and Fe can be added in large quantities. Disappear. In addition, desulphurization occurs in the dephosphorization furnace. Therefore, in order to melt ultra-low sulfur steel, problems such as excessive desulfurization by desulfurization (hereinafter also referred to as “KR desulfurization”) using a mechanical stirrer, or desulfurization by secondary refining, etc. was there.

  This problem is almost solved by adopting the “dephosphorization (mixed with many carbonaceous materials) → KR desulfurization → decarburization” process described in the above-mentioned Patent Document 2. In addition, even if it is somewhat rephosphorized at the time of KR desulfurization, since it can be dephosphorized in the decarburization furnace, the load applied to the entire refining is much smaller than that of desulfurization by secondary refining as a countermeasure for resulfurization in the conventional process.

  However, if the [S] concentration in the dephosphorization is increased too much due to the addition of scrap with a high sulfur content, the usual [KR] desulfurization process will produce the desired [S] concentration (for example, 0.0020% by mass). The following may not be possible: In addition, when the carbon material is added to the dephosphorization furnace, as described above, the carbon material is trapped in the slag and is not easily dissolved in the hot metal, and the undissolved carbon material is discharged together with the slag after the dephosphorization process. .

The present invention has been made in view of such a situation, and its purpose is to desulfurize dephosphorization using a mechanical stirrer and then decarburize the following (i) to (c). An object of the present invention is to provide a hot metal desulfurization method capable of solving the problems.
(B) Even if the [S] concentration in the dephosphorization tank becomes 0.03 to 0.05% by mass by adding a large amount of scrap having a high sulfur content to the dephosphorization furnace, it is desired to be obtained by subsequent KR desulfurization. Desulfurize to [S] concentration.
(B) The dephosphorization flux basic unit and the amount of dephosphorization slag to be generated are set to the same level as the process described in Patent Document 2 described above.
(C) Increase the dissolution rate (yield) of the carbonaceous material in the hot metal as much as possible.

  As a result of repeated studies to solve the above problems, the present inventors have come up with the idea of adding a deoxidizer when KR desulfurization of dephosphorization. Moreover, it came to the idea of adding a carbon material when desulfurizing dephosphorization, and adding a deoxidizer and a carbon material. This has the following advantages (1) to (5). In the following, “%” of each component in hot metal and slag means “mass%”.

  (1) In order to promote desulfurization of dephosphorization, the oxygen potential of the system should be lowered. As the method, it is considered that (i) addition of Si source (ferrosilicon Fe—Si, SiC waste, etc.) and (ii) addition of Al source (Al grains, Al ash, etc.) are effective.

  (2) The [C] concentration in the dephosphorization is about 3.3 to 4.2%, and the carbonaceous material can be dissolved up to the [C] saturation concentration (about 4.5% at 1250 ° C.). Therefore, if the KR desulfurization treatment is performed after the [C] concentration in the dephosphorization is determined, the carbon material can be added by an appropriate amount, and the waste of the carbon material can be reduced.

  (3) Most of the carbon material added in the dephosphorization furnace is trapped in the dephosphorization slag and hardly comes into contact with the hot metal, but the carbon material added during the KR treatment is one in which the slag is caught in the hot metal one after another, Since the carbonaceous material is also involved in the same manner, there are many opportunities to contact the hot metal, and since the carbonaceous material can be efficiently contacted with the hot metal, the carbonaceous material is easily dissolved in the hot metal.

  (4) If carbon powder is blown into the dephosphorizer from the impeller shaft of the mechanical stirrer, dissolution of the carbon is further facilitated.

  (5) The presence of some carbonaceous material on the dephosphorization bath surface reduces the oxygen potential at the reaction interface between the desulfurizing agent and dephosphorization so that the desulfurization rate may be improved.

  The present invention has been made based on such a concept, and the gist thereof is the following desulfurization method.

  That is, one of the present inventions is “a hot metal desulfurization method in which a deoxidizer is added and desulfurized when dephosphorized using a mechanical stirrer”.

  In this method, it is effective to use the Si source (ferrosilicon Fe—Si, SiC waste material, etc.) and the Al source (Al grains, Al ash, etc.) as the deoxidizer.

  Another aspect of the present invention is “a method for desulfurizing molten iron in which carbonaceous material is added to desulfurize dephosphorization using a mechanical stirrer to increase the concentration [C], and then decarburize”. It is.

  In this desulfurization method, if the carbon material is added by blowing the carbon material powder into the hot metal from the impeller shaft of the mechanical stirrer, the dissolution of the carbon material into the hot metal becomes even easier.

  In addition, if the deoxidizer is added during the desulfurization treatment as described above and the carbon material is added to increase the [C] concentration, it is effective not only in promoting desulfurization of dephosphorization. In addition, since it is possible to reduce the amount of expensive metal Mn used by performing smelting reduction of Mn ore in the subsequent decarburization furnace, it is very economical.

  The above-mentioned “desulfurization treatment using a mechanical stirring device” means that a rotating blade (impeller) 3 immersed in hot metal is rotated at a high speed from directly above a container 2 containing hot metal 1 as shown in FIG. This is a so-called KR desulfurization process in which a depression due to a vortex is formed in the vicinity of the impeller shaft 4 and the slag on the surface of the hot metal is successively wound into the hot metal 1 and processed while stirring.

  According to the hot metal desulfurization method of the present invention, inexpensive scrap with a high sulfur content can be added in a dephosphorization furnace, so that the cost of steel melting can be reduced. In addition, the [C] concentration in the dephosphorization can be increased efficiently, and as a result, a large amount of Mn ore can be added in the decarburization furnace. Can be made at low cost.

  As described above, the hot metal desulfurization method of the present invention includes a “desulfurization method of hot metal in which dephosphorization treatment is performed by adding a deoxidizer when dephosphorizing the dephosphorizer using a mechanical stirrer”, and “ This is a hot metal desulfurization method in which a carbonaceous material is added to increase the [C] concentration when dephosphorizing the dephosphorization using a mechanical stirrer, followed by decarburization. The feature is that, for example, even when desulfurization treatment is performed on hot iron of high [S] concentration after dephosphorization treatment to which a cold iron source having a high sulfur content is added, low [S] molten steel can be produced at low cost, and carbon The point is to increase the [C] concentration by adding a material.

  Since dephosphorization usually has a higher oxygen potential than hot metal, the addition of a deoxidizer (metal Si-containing material or metal Al-containing material) accelerates the desulfurization reaction.

  The reason why the [C] concentration in the dephosphorization is increased is that the higher the [C] concentration, the more Mn ore can be added during the decarburization treatment. Thereby, since the [Mn] density | concentration in the molten steel after decarburization becomes high, in order to raise [Mn] density | concentration, the quantity of the expensive metal Mn added at a next process can be reduced.

  The reason why the carbon material is added when the desulfurization treatment is performed is that the yield can be made higher than that when the carbon material is added during the dephosphorization treatment. At the end of the dephosphorization process, the [C] concentration is 3.3 to 4.2%, but during the previous dephosphorization process, the [C] concentration is high (close to the saturation concentration), so the carbonaceous material dissolves. It is hard to do. Therefore, it is easier to dissolve the carbonaceous material when the carbonaceous material is added during the desulfurization process with a lower [C] concentration.

  In addition, if the carbon material is added when the desulfurization treatment is performed, the carbon material is added after the [C] concentration in the dephosphorization is determined, so it is possible to add an appropriate amount. The waste of charcoal can be reduced. The appropriate amount is an amount obtained by adding a small amount to the amount corresponding to increasing the [C] concentration to the saturated concentration, and by floating a small amount of carbonaceous material on the surface of the dephosphorization tank, As described above, the oxygen potential at the reaction interface between the desulfurizing agent and the dephosphorizing agent is lowered, so that the desulfurization rate may be improved.

  The desulfurization process is performed using a mechanical stirring device because the impeller is rotated at a high speed, and slag and carbonaceous materials are entrained one after another into the hot metal and processed while stirring. It is because it can contact efficiently and carbonaceous material is easy to melt into hot metal.

FIG. 3 is a diagram schematically showing a state in the dephosphorization furnace when a carbonaceous material (for example, earth graphite) is added during the dephosphorization process. In this case, oxygen (O ₂ ) is blown from the top blowing lance 7 and nitrogen (N ₂ ) is blown from the bottom blowing tuyere 8, but the hot metal 1 and the dephosphorized slag 9 are layered, and the added carbon material Most of (earth-like graphite 5) is trapped in the dephosphorization slag.

  On the other hand, FIG. 1 is a diagram schematically showing a state in the desulfurization apparatus when carbonaceous material (earthy graphite) is added to a desulfurization apparatus having a mechanical stirring device. In this case, the slag is continuously wound into the hot metal 1 and stirred, and the earth graphite 5 and the desulfurizing agent 6 introduced into the surface of the hot metal 1 are also wound in the same manner, so there are many opportunities to come into contact with the hot metal, The carbonaceous material is easily dissolved in the hot metal.

  In this desulfurization method, the [C] concentration in the dephosphorization is preferably 3.3 to 4.2%. If it exceeds 4.2%, the effect of adding the carbonaceous material is saturated, and it is not very advantageous if the increase in man-hours required for adding the carbonaceous material is taken into consideration. On the other hand, if it is less than 3.3%, the amount of carbon material added during KR desulfurization increases, and there arises a problem that the carbon material cannot be completely dissolved in the hot metal within the desulfurization time. In addition, when dephosphorization blowing is performed such that the [C] concentration after treatment is less than 3.3%, an increase in the amount of carbonaceous material added during the desulfurization treatment and the [C] in the hot metal that has risen thereby Cost increase due to an increase in the amount of oxygen source added to lower the concentration becomes a problem.

  In the desulfurization method of the present invention, if the carbon material is added by blowing the carbon material powder into the hot metal from the impeller shaft of the mechanical stirrer, the dissolution of the carbon material into the hot metal becomes even easier.

  FIG. 2 is a diagram schematically showing the state in the desulfurization apparatus when carbonaceous powder is blown into the hot metal from the impeller shaft of the mechanical stirring apparatus. In this case, the earth-like graphite powder 5a as the carbon material is passed from the impeller shaft, that is, through the internal space of the impeller shaft 4a configured in a tubular shape (indicated by a broken line in the figure), and a carrier gas (nitrogen or the like) from its lower end. At the same time, since it is blown into the hot metal 1, the contact area between the hot metal 1 and the earthy graphite powder 5 a is remarkably increased, and the dissolution rate and dissolution rate of the graphite powder 5 a are greatly improved.

  The particle size of the carbonaceous material (such as earth graphite powder) in this case is not particularly limited. Any particle size that can be blown into the hot metal together with the gas from the impeller shaft of the mechanical stirring device may be used.

  Further, in this desulfurization method, if a carbon material is added and a deoxidizer is added at the time of desulfurization treatment, desulfurization of dephosphorization can be promoted and the [C] concentration can be increased.

  For example, even if a high sulfur content scrap is added to the dephosphorization furnace and the [S] concentration in the dephosphorization tank rises to 0.03 to 0.05%, a deoxidizer is added and the oxygen in the system If the potential is lowered, desulfurization of the dephosphorization is promoted, and the [S] concentration can be reduced to 0.0030% or less by KR desulfurization. It should be noted that the desulfurization behavior is hardly affected even if a carbon material is added during the desulfurization treatment. Therefore, if a deoxidizing agent and a carbon material are added during the desulfurization treatment, it is possible to enjoy the advantages of both the promotion of the desulfurization reaction and the increase in the [C] concentration in the dephosphorization.

  As the deoxidizer, Si source (Fe-Si, SiC waste, etc.) and Al source (Al grains, Al ash, etc.) can be used, and these are added in an appropriate amount depending on the [S] concentration in the dephosphorization machine. It is effective to do. Either one of Si source or Al source may be used, or both may be used.

In particular, Si source addition is effective for the following reasons.
(A) Conventionally, KR desulfurization slag is recycled to the sintering process. When a Si source is used as a deoxidizer, SiO ₂ is mixed in the desulfurized slag, and when an Al source is used, Al ₂ O ₃ is mixed. As the sintered ore used in the blast furnace, the content of Al ₂ O ₃ is restricted, so if possible, KR desulfurization slag having a low Al ₂ O ₃ concentration should be used. From this point, the addition of the Si source is somewhat advantageous.
(B) When soda ash (Na ₂ CO ₃ ) -containing material is used as a desulfurization agent for dephosphorization, most of the soda ash is obtained by the reaction of Na ₂ CO ₃ + 2C = 2Na (g) + 3CO (g). Evaporation loss occurs and the yield is extremely low. However, if there is a SiO ₂ source in the desulfurized slag, soda ash reacts with SiO ₂ to form a Na ₂ O · SiO ₂ -based compound, so that the yield in the desulfurized slag is improved. As a result, the desulfurization rate is increased. It will increase.

  In addition, since Si source is used in order to deoxidize dephosphorization, addition of Si source is restricted to the following time. (Ii) Place the dephosphorized rice cake in the pan in advance, or add the dephosphorized rice cake to the pan when tapping the hot water. (B) Add before or during KR desulfurization treatment.

  In the desulfurization method of the present invention described above, the dephosphorization flux basic unit is the same level as the process described in Patent Document 2 described above. Comparative examples 2 and 3 of the examples described below correspond to the process described in Patent Document 2, but the flux used therein is iron oxide (scale) 2t, quick lime approximately 4.2t, while the examples 1 to 4 use the same amount of the same flux, the hot metal to be treated is 250 t, and the dephosphorization flux basic unit is not changed at all. Although not shown, there is no difference in the amount of dephosphorization slag to be generated.

  The desulfurization method of the present invention and the KR desulfurization treatment in which a deoxidizer is added at the time of KR desulfurization of dephosphorization, while comparing with Comparative Examples 1 to 3 in which no carbonaceous material is added or at the time of dephosphorization treatment. The desulfurization method (Examples 1 to 5) of the present invention in which a carbon material is added will be described. Fe-Si or Al ash was used as the deoxidizer, and earth graphite was used as the carbon material. In addition, in Table 1 shown later, the concentration of specific components such as C and S in each treatment step of dephosphorization, desulfurization, and decarburization, addition amounts of deoxidizer, carbonaceous material, and Mn ore are collectively shown.

(Comparative Example 1)
[Dephosphorization]
Hot metal discharged from the blast furnace [[Si] concentration (hereinafter simply expressed as [Si]; other components are also expressed in the same manner): 0.3%, [Mn]: 0.20%, [P]: 250% of 0.1%, [S]: 0.025%, 1340 ° C.] was charged into a converter (25 tons of scrap was charged before pouring), and dephosphorization was performed. Oxygen was blown into the hot metal for 6 minutes from the top blowing lance at a flow rate of 22000 m ³ / h, and nitrogen was blown into the hot metal from the bottom blowing port at a flow rate of 50 m ³ / min, while iron oxide (scale) 2 t and quick lime approximately 4. 2t (mixed basicity CaO / SiO ₂ : about 2.5) was added.

  After dephosphorization blowing, hot metal having [C] 3.7%, [Mn] 0.15%, [P] 0.020%, [S] 0.018%, and a temperature of 1355 ° C. was obtained.

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurization agent, 1.5t of quick lime and 0.17t of soda ash were added.

After the KR desulfurization treatment, hot metal having [C] 3.7%, [Mn] 0.15%, [P] 0.021%, [S] 0.0029%, and a temperature of 1270 ° C. was obtained. The concentration of desulfurized slag (Na ₂ O) was about 3%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / h, with blown from the bottom吹羽opening the CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore (Mn content 55 %) 0.7 t, quick lime approximately 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : approximately 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.26%, [P] 0.015%, [S] 0.0030%, and a temperature of 1650 ° C. was obtained.

(Comparative Example 2)
[Dephosphorization]
250 t of molten iron discharged from the blast furnace ([Si]: 0.3%, [Mn]: 0.19%, [P]: 0.1%, [S]: 0.024%, 1345 ° C.) The furnace was charged with 25 tons of scrap before pouring and dephosphorized. Oxygen was blown into the hot metal for 6 minutes from the top blowing lance at a flow rate of 22000 m ³ / h, and nitrogen was blown into the hot metal from the bottom blowing port at a flow rate of 50 m ³ / min, while iron oxide (scale) 2 t and quick lime approximately 4. 2t (mixed basicity CaO / SiO ₂ : about 2.5) and earth graphite (C content 85%) 2.4t were further added as a carbonaceous material.

  After dephosphorization blowing, hot metal having [C] 4.1%, [P] 0.020%, [S] 0.019%, and a temperature of 1355 ° C. was obtained. Residual graphite mass was confirmed in the discharged slag (calculation rate of dissolution of graphite in dephosphorization (yield) was about 50%).

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurization agent, 1.5t of quick lime and 0.17t of soda ash were added.

After the KR desulfurization treatment, hot metal having [C] 4.0%, [Mn] 0.15%, [P] 0.021%, [S] 0.0030%, and a temperature of 1268 ° C. was obtained. The concentration of desulfurized slag (Na ₂ O) was about 3%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / h, with blown from the bottom吹羽port CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore 2.2 T, quicklime About 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : about 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.49%, [P] 0.015%, [S] 0.0030%, and a temperature of 1653 ° C. was obtained.

(Comparative Example 3)
[Dephosphorization]
250 t of molten iron discharged from the blast furnace ([Si]: 0.3%, [Mn]: 0.19%, [P]: 0.1%, [S]: 0.024%, 1345 ° C.) The furnace was charged (25t of scrap with a high sulfur content before pouring) and dephosphorized. Oxygen was blown into the hot metal for 6 minutes from the top blowing lance at a flow rate of 22000 m ³ / h, and nitrogen was blown into the hot metal from the bottom blowing port at a flow rate of 50 m ³ / min, while iron oxide (scale) 2 t and quick lime approximately 4. 2t (mixed basicity CaO / SiO ₂ : about 2.5) and earth graphite (C content 85%) 2.4t were added.

  After dephosphorization blowing, hot metal having [C] 4.1%, [P] 0.020%, [S] 0.040%, and a temperature of 1353 ° C. was obtained. Residual graphite lump was confirmed in the discharged slag (calculation rate of dissolution of graphite in dephosphorization (yield) was about 50%).

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurization agent, 2.0 t of quick lime and 0.22 t of soda ash were added.

After the KR desulfurization treatment, hot metal having [C] 4.0%, [Mn] 0.15%, [P] 0.021%, [S] 0.0055%, and a temperature of 1269 ° C. was obtained. The concentration of desulfurized slag (Na ₂ O) was about 3%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / h, with blown from the bottom吹羽port CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore 2.2 T, quicklime About 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : about 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.49%, [P] 0.015%, [S] 0.0056%, and a temperature of 1657 ° C. was obtained.

(Example 1)
[Dephosphorization]
250 t of molten iron discharged from the blast furnace ([Si]: 0.3%, [Mn]: 0.20%, [P]: 0.1%, [S]: 0.025%, 1338 ° C.) The furnace was charged (25t of scrap with a high sulfur content before pouring) and dephosphorized. Oxygen was blown into the hot metal for 6 minutes from the top blowing lance at a flow rate of 22000 m ³ / h, and nitrogen was blown into the hot metal from the bottom blowing port at a flow rate of 50 m ³ / min, while iron oxide (scale) 2 t and quick lime approximately 4. 2t (mixed basicity CaO / SiO ₂ : about 2.5) was added.

  After dephosphorization blowing, hot metal having [C] 3.7%, [P] 0.021%, [S] 0.039%, and a temperature of 1350 ° C. was obtained.

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurizing agent, 1.5 t of quick lime and 0.17 t of soda ash were added, and 400 kg of Fe—Si was further added as a deoxidizing agent.

After the KR desulfurization treatment, hot metal having [C] 3.7%, [Mn] 0.15%, [P] 0.021%, [S] 0.0022%, and a temperature of 1261 ° C. was obtained. The concentration of desulfurized slag (Na ₂ O) was about 5%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / h, with blown from the bottom吹羽port CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore 0.7 t, quicklime About 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : about 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.26%, [P] 0.015%, [S] 0.0023%, and a temperature of 1657 ° C. was obtained.

(Example 2)
[Dephosphorization]
250 t of hot metal discharged from the blast furnace ([Si]: 0.3%, [Mn]: 0.19%, [P]: 0.1%, [S]: 0.024%, 1342 ° C.) The furnace was charged with 25 tons of scrap before pouring and dephosphorized. Oxygen was blown into the hot metal for 6 minutes from the top blowing lance at a flow rate of 22000 m ³ / h, and nitrogen was blown into the hot metal from the bottom blowing port at a flow rate of 50 m ³ / min, while iron oxide (scale) 2 t and quick lime approximately 4. 2t (mixed basicity CaO / SiO ₂ : about 2.5) was added.

  After dephosphorization blowing, hot metal having [C] 3.7%, [P] 0.020%, [S] 0.019%, and a temperature of 1355 ° C. was obtained.

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurizing agent, 1.5 t of quick lime and 0.17 t of soda ash were added, and 2.4 t of earthy graphite (C content 85%) was further added as a carbonaceous material.

After the KR desulfurization treatment, hot metal having 4.3% [C], 0.15% [Mn], 0.021% [P], 0.0026% [S], and a temperature of 1264 ° C. was obtained. In the discharged slag, almost no graphite lump could be confirmed (calculations show that the dissolution rate (yield) of graphite in dephosphorization was about 75%). The concentration of desulfurized slag (Na ₂ O) was about 3%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / h, with blown from the bottom吹羽port CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore 3.7T, quicklime About 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : about 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.72%, [P] 0.015%, [S] 0.0027%, and a temperature of 1653 ° C. was obtained.

(Example 3)
[Dephosphorization]
250 t of hot metal ([Si]: 0.3%, [Mn]: 0.20%, [P]: 0.1%, [S]: 0.024%, 1341 ° C.) from the blast furnace was converted into a converter (Scrap was charged 25t before pouring) and dephosphorization was performed. Oxygen was blown into the hot metal for 6 minutes from the top blowing lance at a flow rate of 22000 m ³ / h, and nitrogen was blown into the hot metal from the bottom blowing port at a flow rate of 50 m ³ / min, while iron oxide (scale) 2 t and quick lime approximately 4. 2t (mixed basicity CaO / SiO ₂ : about 2.5) was added.

  After dephosphorization blowing, hot metal having [C] 3.7%, [P] 0.020%, [S] 0.019%, and a temperature of 1355 ° C. was obtained.

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurization agent, quick lime 1.5t, soda ash 0.17t, and earth graphite (C content 85%) 1.4t are added, and earth graphite powder (C content 85%, particle size: 0). .15 mm or less) 1.0 t was blown into the hot metal from the lower end of the impeller shaft using nitrogen as a carrier gas.

After the KR desulfurization treatment, hot metal having [C] 4.42%, [Mn] 0.15%, [P] 0.021%, [S] 0.0026%, and a temperature of 1260 ° C. was obtained. In the discharged slag, almost no graphite lump could be confirmed (calculations show that the dissolution rate (yield) of graphite in dephosphorization was about 90%). The concentration of desulfurized slag (Na ₂ O) was about 3%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / h, with blown from the bottom吹羽port CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore 4.7 T, quicklime About 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : about 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.87%, [P] 0.015%, [S] 0.0027%, and a temperature of 1651 ° C. was obtained.

Example 4
[Dephosphorization]
250t of hot metal ([Si]: 0.3%, [Mn]: 0.20%, [P]: 0.1%, [S]: 0.025%, 1340 ° C.) from the blast furnace was converted into a converter (Scrap with a high sulfur content was charged in 25 tons before pouring) and dephosphorization was performed. Oxygen was blown into the hot metal for 6 minutes at a flow rate of 22000 m ³ / min from the top blowing lance, nitrogen was blown into the hot metal at a flow rate of 50 m ³ / min from the bottom blowing tuyere, 2 t of iron oxide (scale), and about 4 lime. 2t (mixed basicity CaO / SiO ₂ : about 2.5) was added.

  After dephosphorization blowing, hot metal having [C] 3.7%, [P] 0.020%, [S] 0.041%, and a temperature of 1350 ° C. was obtained.

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurization agent, 1.5 t of quick lime and 0.17 t of soda ash were added, and further, 2.4 t of earth graphite (C content 85%) and 200 kg of Al ash as a deoxidizer were added.

After the KR desulfurization treatment, hot metal having 4.3% of [C], 0.15% of [Mn], 0.021% of [P], 0.0021% of [S], and a temperature of 1264 ° C. was obtained. In the discharged slag, almost no graphite lump could be confirmed (calculations show that the dissolution rate (yield) of graphite in dephosphorization was about 75%). The concentration of desulfurized slag (Na ₂ O) was about 3%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / min, together with the blown from the bottom吹羽port CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore 4.7 T, quicklime About 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : about 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.88%, [P] 0.015%, [S] 0.0022%, and a temperature of 1655 ° C. was obtained.

(Example 5)
[Dephosphorization]
250t of hot metal ([Si]: 0.3%, [Mn]: 0.20%, [P]: 0.1%, [S]: 0.025%, 1340 ° C.) from the blast furnace was converted into a converter (Scrap with a high sulfur content was charged in 25 tons before pouring) and dephosphorization was performed. Oxygen was blown into the hot metal for 6 minutes from the top blowing lance at a flow rate of 22000 m ³ / h, and nitrogen was blown into the hot metal from the bottom blowing port at a flow rate of 50 m ³ / min, while iron oxide (scale) 2 t and quick lime approximately 4. 2t (mixed basicity CaO / SiO ₂ : about 2.5) was added.

  After dephosphorization blowing, hot metal having [C] 3.7%, [P] 0.021%, [S] 0.039%, and a temperature of 1355 ° C. was obtained.

[Desulfurization treatment]
The dephosphorization pad was subjected to KR desulfurization treatment. As a desulfurization agent, 1.5 t of quick lime and 0.17 t of soda ash were added, and 2.4 t of earth graphite (C content 85%) and 400 kg of Fe—Si were further added.

After the KR desulfurization treatment, hot metal having 4.3% [C], 0.15% [Mn], 0.021% [P], [S] 0.0024%, and a temperature of 1264 ° C. was obtained. In the discharged slag, almost no graphite lump could be confirmed (calculations show that the dissolution rate (yield) of graphite in dephosphorization was about 75%). The concentration of desulfurized slag (Na ₂ O) was about 5%.

[Decarburization treatment]
The dephosphorization desulfurization soot was decarburized. Blowing oxygen from the top blown lance flow rate for 15 minutes the hot metal 50000 m ³ / h, with blown from the bottom吹羽port CO ₂ gas into the molten iron at a flow rate of 10~40m ³ / min, Mn ore 4.7 T, quicklime About 1.5 t, silica stone 0.4 t (mixed basicity CaO / SiO ₂ : about 3.7) was added.

  After decarburization blowing, molten steel with [C] 0.1%, [Mn] 0.87%, [P] 0.015%, [S] 0.0025%, and a temperature of 1657 ° C. was obtained.

  Regarding the comparative examples and examples described above, the concentrations of specific components, deoxidizers, carbonaceous materials, addition amounts of Mn ore, and the like are summarized in Table 1.

  From Table 1, in Comparative Example 1 in which no carbonaceous material was added, the amount of Mn ore added was restricted in order to ensure the molten steel temperature, and the [Mn] concentration after decarburization was 0.26. %Met. In Comparative Examples 2 and 3, since the carbonaceous material was added, the amount of Mn ore added could be increased, and the [Mn] concentration after decarburization increased to 0.49%. Since it was added at the time of processing, the dissolution rate (yield) of the carbonaceous material was as low as 50%. In Comparative Example 3, since the scrap with a high sulfur content was charged into the converter before pouring, the [S] concentration was high and remained at 0.0055% even after the KR desulfurization treatment.

On the other hand, in Example 1, since the scrap with a high sulfur content was charged into the converter before pouring, the [S] concentration was high, but Fe-Si was added during the desulfurization treatment, so Since the oxidation potential is reduced and the soda ash yield in the slag (concentration of (Na ₂ O) in the slag) is improved, the [S] concentration after the desulfurization treatment is 0.0022% without adding any carbonaceous material. Declined.

  In Example 2, since the carbon material was added during the desulfurization treatment, the dissolution rate (yield) was as high as 75%, and the amount of Mn ore added could be increased accordingly, and the [Mn] concentration after decarburization was increased. It could be increased to 0.72%.

  In Example 3, since a part of the added amount of the carbon material was blown from the impeller shaft, the dissolution rate increased to 90%, and a large amount of Mn ore could be added. It was as high as 87%.

  In Examples 4 and 5, scraps with a high sulfur content were charged into the converter before pouring, so the [S] concentration was high. However, carbonaceous materials were added during the desulfurization treatment. Since Fe—Si was added in Example 5, the oxidation potential of the system was lowered, and the [S] concentration after desulfurization was lowered to 0.0021% and 0.0024%, respectively.

  According to the hot metal desulfurization method of the present invention, the [S] concentration can be reduced even when inexpensive scrap having a high sulfur content is added during the dephosphorization process, and [C] in the dephosphorization process. The concentration can be increased and a large amount of Mn ore can be added in the decarburization furnace. Therefore, high-quality molten steel having a low [S] concentration and a high [Mn] concentration can be produced at low cost, and is useful for the production of high-quality steel materials used in the fields of civil engineering, construction and the like. It can be suitably used as a method having excellent practicality.

It is a figure which shows typically the state in a desulfurization apparatus when carbonaceous material (earth-like graphite) is added to a desulfurization apparatus provided with a mechanical stirring apparatus. It is a figure which shows typically the state in a desulfurization apparatus when carbonaceous material powder is blown in into hot metal from the impeller shaft of a mechanical stirring apparatus. It is a figure which shows typically the state in the dephosphorization furnace when carbonaceous material (earth-like graphite) is added in the dephosphorization process.

Explanation of symbols

1: Hot metal 2: Container 3: Rotating blade (impeller)
4, 4a: Impeller shaft 5: Soil graphite 5a: Soil graphite powder 6: Desulfurizing agent 7: Top blowing lance 8: Bottom blowing tuyere 9: Dephosphorization slag

Claims (5)

  A desulfurization method for hot metal, wherein a deoxidizing agent is added to desulfurize the dephosphorization cake using a mechanical stirring device.   The hot metal desulfurization method according to claim 1, wherein one or both of a Si source and an Al source is used as the deoxidizer.   A desulfurization method for hot metal, which comprises adding a carbonaceous material when desulfurizing dephosphorization using a mechanical stirrer to increase the [C] concentration and subsequently decarburizing.   4. The hot metal desulfurization method according to claim 3, wherein the carbonaceous material is added by blowing carbonaceous powder into the hot metal from an impeller shaft of a mechanical stirring device. 5. The hot metal desulfurization method according to claim 3, wherein, during the desulfurization treatment, a carbonaceous material is added to increase the [C] concentration and a deoxidizer is added.

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