KR20020031862A - A METHOD FOR MANUFACTURING Mn ADDED ULTRA LOW CARBON STEEL - Google Patents

Abstract

The present invention relates to a method for producing Mn-added ultra low carbon steel mainly used as a material for fancy goods, battery cases, paint cans, aerosol domes, etc. Thus, to provide a method for producing Mn-added ultra-low carbon steel that can improve the cleanliness of the steel, the purpose is.

The present invention for achieving the above object,

In the manufacturing method of ultra-low carbon steel of C: 0.0050% or less and Mn: 0.20 to 0.30% by weight,

Adding 2.5-3.0 kg / melt-ton of quicklime and 0.5-1.0 kg / melt-ton of slag deoxidizer when tapping the converter or electric furnace;

In a vacuum degassing apparatus (RH) having a vacuum degree of 5 torr or less, decarburizing the molten steel until the carbon concentration reaches 40 ppm or less, and blowing gaseous oxygen into the molten steel during the decarburization reaction;

Deoxidizing molten steel by adding Al after completion of the RH decarburization reaction; And

After the molten steel deoxidation in the RH step of adding a metal Mn of 2 ~ 3kg / molten-ton; Mn-added ultra-low carbon steel manufacturing method characterized in that consisting of the technical gist.

Description

Method of manufacturing Mn-added ultra low carbon steel {A METHOD FOR MANUFACTURING Mn ADDED ULTRA LOW CARBON STEEL}

The present invention relates to a manufacturing method of Mn-added ultra low carbon steel (hereinafter referred to as 'BP material'), which is mainly used as a material for a fancy article, a battery case, a paint can, an aerosol dome, and the like. Specifically, the present invention relates to a method for producing Mn-added ultra low carbon steel which can improve the cleanliness of steel by adding metal Mn after RH molten steel to obtain a Mn concentration of 0.20 to 0.30% in a BP material.

BP material contains 0.20 ~ 0.30% by weight of Mn and 0.0040% by weight or less, and is mainly used as a material for fancy goods, battery case, paint, tin, aerosol dome, etc. In order to be excellent cleanliness is required. In other words, if the BP material contains a large amount of steelmaking non-metallic inclusions and is not clean, defects due to inclusions occur in the rolling process, resulting in poor plating property in the plating process, which causes the consumer to turn away from the product. It will cause a problem.

The cleanliness of the BP material is evaluated as an index indicating the level of non-metallic inclusions present in the steel, that is, the total oxygen amount (hereinafter referred to as T. [O]), which is based on the amount of T. [O ] Is less than 15ppm is considered to be clean, and generally lower T. [O] is classified as a better material.

On the other hand, the Mn-added ultra low carbon BP material has been manufactured as shown in FIG.

First, primary refining in a converter or an electric furnace is a process of removing a large amount of oxygen to remove impurities in molten iron or scrap metal, and oxygen dissolved in molten steel at the end of refining, that is, dissolved oxygen (free oxygen) component Silver is 600 ~ 1000ppm, and carbon content is 0.03 ~ 0.08% by weight.

Next, the molten steel 1 in the non-deoxidation state after the first refining is transferred to the ladle 2 (hereinafter referred to as 'tapping'), and in order to control slag basicity in the process (CaO) is added 3.6 ~ 4.0kg per ton of molten steel, ferro-manganese (Fe-Mn) is added 3 ~ 4kg per ton of molten steel to add Mn component to steel, and iron oxide (T.Fe) in slag In order to reduce lower oxides such as and manganese oxides (MnO), 2 to 3 kg per tonne of molten steel is added.

After that, the molten steel tapped into the ladle is transferred to an RH vacuum degassing apparatus (hereinafter referred to as RH) and decarburized, thereby reducing the carbon concentration in the molten steel below the content required in the final product, that is, 40 ppm or less (hereinafter, decarburized). Reaction). At this time, since the dissolved oxygen concentration reaches 300 to 600 ppm at the end of the decarburization reaction, molten steel deoxidizer is added immediately after the decarburization reaction is completed to perform molten deoxidation in which the dissolved oxygen concentration is within a range in which continuous casting is possible. For example, in the case of Al deoxidation, in order to perform continuous casting, aluminum is added as a molten deoxidizer immediately after the decarburization reaction is completed in RH, and the dissolved oxygen concentration must be reduced to 30 ppm or less.

Finally, the molten steel having finished RH refining is transferred to a continuous casting process, and continuous casting is performed to produce Mn-added ultra low carbon BP material.

However, in the conventional method as described above, since Fe-Mn is added while the molten steel is pulled out in the non-deoxidation state, the Mn component reacts with the dissolved oxygen to generate a large amount of (MnO) and greatly reduce the dissolved oxygen. there was. That is, the large amount of (MnO) is to move to the slag to increase the concentration of (T.Fe + MnO) in the slag. For example, in the case of 300 ton converter, adding 3 to 4 kg of Fe-Mn per ton of molten steel during tapping increases the concentration of (MnO) in slag by 5 to 8% and decreases dissolved oxygen by 150 to 200 ppm. In RH, the oxygen needed for the decarburization of molten steel became insufficient. Therefore, RH had to inject gaseous oxygen by using an oxygen blowing device. At this time, molten steel was oxidized to increase (T.Fe) in the slag, and the decarburization reaction time also increased due to the large amount of oxygen blowing. .

In addition, after molten iron deoxidation in RH, due to the increased (T.Fe) and (MnO), the chemical reactions of the following reactions (1) and (2) at the interface between molten steel and slag (hereinafter referred to as reoxidation reaction) are promoted. There was also a problem that greatly deteriorated the cleanliness of the steel. In the following reaction formulas (1) and (2), [Al] means Al remaining after being dissolved in molten steel after molten steel deoxidation.

3 (T.Fe) + 2 [Al] = Al ₂ O ₃ (s) + 3Fe (l)

3 (MnO) + 2 [Al] = Al ₂ O ₃ (s) + 3Mn (l)

Therefore, the inventors of the present invention have completed the present invention by studying and examining a method for producing BP material which can greatly improve the cleanliness of steel while preventing reoxidation of molten steel and an increase in decarburization reaction time. In order to obtain a Mn content of 0.20 to 0.30% in the BP material, by adding a metal Mn after RH molten steel deoxidized by Al, to provide a method for producing Mn-added ultra-low carbon steel that can improve the cleanliness of the steel, the purpose There is this.

1 is a schematic view showing a manganese addition ultra low carbon steel manufacturing process

2 is a graph showing the (T.Fe + MnO) concentration change of the slag according to the oxygen injection amount in RH

The present invention for achieving the above object,

In the manufacturing method of ultra-low carbon steel of C: 0.0050% or less and Mn: 0.20 to 0.30% by weight,

Adding 2.5-3.0 kg / melt-ton of quicklime and 0.5-1.0 kg / melt-ton of slag deoxidizer when tapping the converter or electric furnace;

In a vacuum degassing apparatus (RH) having a vacuum degree of 5 torr or less, decarburizing the molten steel until the carbon concentration reaches 40 ppm or less, and blowing gaseous oxygen into the molten steel during the decarburization reaction;

Deoxidizing molten steel by adding Al after completion of the RH decarburization reaction; And

Regarding the manufacturing method of Mn-added ultra-low carbon steel, characterized in that consisting of; adding the metal Mn of 2 ~ 3kg / molten-ton after the molten steel deoxidation in the RH.

Hereinafter, the present invention will be described in detail.

In order to produce molten steel in a converter or electric furnace, first, refining molten iron or scrap iron having a C component of 4.3% by weight and blowing a large amount of oxygen to remove impurities such as C, Si, Mn, and P from molten steel Is carried out. When the composition of the impurities is reduced below a certain level, refining is terminated. At the time of completion of the primary refining in the converter or the electric furnace, the C component in the molten steel is 0.03 to 0.08% by weight, Mn is 0.01% by weight, dissolved oxygen is 600 to 1000 ppm, and (T.Fe), (MnO) in the slag. The lower oxide content is 20 to 30% by weight, the slag basicity (CaO / SiO ₂ ) is 3.0 to 4.0, and the phosphate is (P ₂ O ₅ ) to 1 to 3% by weight. When tapping such molten steel by ladle, slag is mixed into the molten steel by about 5 to 10 kg per ton of molten steel, and in the slag immediately after the tapping, P ₂ O ₅ decomposition reaction occurs as shown in the following reaction formula (3). Therefore, phosphorus (P) component increases in molten steel.

(P ₂ O ₅ ) = 2 [P] + 5 [O]

Thus, the inventors of the present invention added 2.5 ~ 3.0kg / molten-ton of quicklime whose main component is CaO in order to suppress the reaction of the reaction formula (3). The reason for this is that when the amount of quicklime added is less than 2.5 kg / melt-ton, the chemical reaction of the following reaction formula (4) does not occur effectively, and when it exceeds 3.0 kg / melt-ton, the reaction of the following reaction formula (4) This effectively prevents the increase in the concentration of phosphorus in the molten steel, but greatly increases the basicity of the slag, namely the CaO / SiO ₂ ratio and the CaO / Al ₂ O ₃ ratio, reducing the ability of the slag to absorb non-metallic inclusions. Because it is.

4CaO + (P ₂ O ₅ ) = 4CaOP ₂ O ₅

In the present invention, it is preferable to add 0.5 ~ 1.0kg / molten-tonne slag deoxidizer during tapping, and to use a solid slag deoxidizer containing 40 to 60% by weight of metal Al as slag deoxidizer. desirable. As described above, the reason why the slag deoxidizer is added during the tapping is to reduce the concentration of lower oxides such as (T.Fe) and (MnO) in the slag that are unnecessarily incorporated into the ladle during the tapping of the converter or the electric furnace. If the slag deoxidizer is not added, due to the lower oxide in the slag, the reactions of the reaction formulas (1) and (2) proceed actively after the molten steel deoxidation, and the non-metallic inclusions in the steel greatly increase and the cleanliness deteriorates.

On the other hand, if the content of the slag deoxidizer is less than 0.5kg / molten-ton, it is difficult to obtain the desired lower oxide reduction effect, when the addition of more than 1.0kg / molten-ton can lower the lower oxide, but slag deoxidizer The reaction with dissolved oxygen greatly reduces the dissolved oxygen, which is not preferable because the refining efficiency is reduced.

After tapping as described above, the ladle containing the molten steel is transferred to RH, and decarburization is performed until the carbon concentration reaches 40 ppm or less while refluxing the molten steel in a vacuum degassing apparatus (RH) having a vacuum of 5 torr or less. . The decarburization reaction proceeds as in the following Reaction Formula (5), the higher the degree of vacuum, the decarburization reaction is promoted. The reason for this is that when the vacuum degree is lower than 5 torr, the decarburization reaction becomes slow and the decarburization reaction time increases.

[C] + [O] = CO (g)

On the other hand, during the decarburization reaction, oxygen is blown as gaseous oxygen to further promote the decarburization reaction, and the blowing amount is preferably limited to 0.35 Nm ³ / molten-ton or less. The reason is that the decarburization reaction of molten steel can be promoted by injecting oxygen during the RH decarburization reaction, but as shown in Fig. 2, when the oxygen injection amount exceeds 0.35Nm ³ / molten-ton, This is because the MnO) concentration is rapidly increased, and the reoxidation reactions of the reaction formulas (1) and (2) are promoted from the end of the RH refining to the end of the continuous casting, thereby deteriorating the cleanliness of the steel. In addition, in order to proceed the decarburization reaction more efficiently, it is preferable to set the start time of blowing the oxygen gas at 3 to 5 minutes after the start of the decarburization reaction.

After the decarburization reaction is completed in RH, the dissolved oxygen deoxidizer Al is added to lower the dissolved oxygen concentration of the molten steel to the extent that continuous casting is possible. For example, in order to continuously cast Al deoxidized steel, it is preferable to lower the dissolved oxygen to 30 ppm or less, because if the concentration of the dissolved oxygen exceeds 30 ppm, break-out of the cast during continuous casting is performed. This is often because continuous casting is difficult.

Next, in the present invention, it is preferable to adjust the Mn concentration in the molten steel to 0.20 to 0.30% by weight by adding 2 to 3 kg / molten-ton of metal Mn immediately after the molten steel deoxidation. As a result, when the content of the metal Mn is less than 2kg / molten-ton or more than 3kg / molten-ton, it was found that it is difficult to obtain the desired Mn concentration of 0.20 ~ 0.30% by weight. In addition, when the Mn component is increased by adding ferro-manganese (Fe-Mn), which is not a metal Mn, the carbon component of molten steel exceeds 40 ppm due to the carbon (C) contained in the ferro-manganese. It was very difficult to obtain the composition of carbon.

On the other hand, in contrast to the addition of ferro-manganese, there is no way to further reduce the carbon concentration of the molten steel during the decarburization reaction, in this case it was found to be economically disadvantageous, such as increased decarburization time of the molten steel decreases RH productivity .

In addition, it is preferable that addition of the said metal Mn in RH is performed in 3 to 5 minutes after adding Al in RH. The reason is that when the metal Mn is added within 3 minutes after the Al is added, the metal Mn reacts with some dissolved oxygen, resulting in a low manganese recovery and a slight increase in the concentration of (MnO) in the slag. This is because, in the case where the metal Mn is added for more than 5 minutes after Al is added, the refining time of the entire RH is increased to uniformly distribute the Mn component in the molten steel.

When the RH refining is finished by the method of the present invention, the ladle is transferred to a continuous casting process to perform continuous casting of steel, thereby producing Mn-added ultra low carbon steel having excellent cleanliness.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example)

After refining the molten steel at 300 ton converter, the steel was discharged after confirming that the C component of the molten steel was 0.05% by weight and dissolved oxygen was 730ppm. As shown in Table 1 below, quicklime and slag deoxidizer were added to molten steel during tapping, and ferromangan was added during tapping in the conventional method. After the tapping was completed, the molten steel was transferred to RH, and oxygen was measured, and slag was collected and analyzed. Then, decarburization was performed while maintaining a vacuum degree of 5 torr or less. During the decarburization reaction, predetermined oxygen was blown if necessary, and after the decarburization reaction was completed, molten steel deoxidation was performed by adding aluminum. When Mn was not added during tapping, the metal Mn was added to control the Mn composition within the target range. At this time, the slag deoxidizer used the slag deoxidizer containing 47.6 weight% of metal aluminum commercially available.

After the RH refining was completed, continuous casting of molten steel completed the production of the Mn-added ultra low carbon steel, and the cleanliness of the slab thus obtained, that is, the total oxygen amount, is shown in Table 1 below.

division Converter pullout (kg / t-s) RH refining result quicklime Slagtal acid Fe-Mn Arrival oxygen (ppm) Arrival (T.Fe + MnO) (wt%) Oxygen uptake (Nm ³ / ts) Decarburization Time (min) Metal Mn (kg / t-s) T. [O] (ppm) Conventional Materials 1 3.8 2.5 3.5 375 13.5 0.65 19.5 - 17.1 Conventional material 2 3.6 2.3 3.5 393 14.3 0.50 18.6 - 16.5 Comparative Material 1 3.0 1.5 - 425 11.1 0.40 17.5 2.5 14.7 Comparative Material 2 3.0 1.0 3.5 435 14.6 0.45 17.9 - 16.6 Invention 1 3.0 1.0 - 475 13.5 0.35 16.8 2.0 12.5 Invention 2 2.5 1.0 - 481 13.9 0.25 16.6 2.5 11.0 Invention 3 2.5 0.5 - 515 14.1 0 16.1 3.0 9.8 Comparative Material 3 2.5 0.4 - 525 15.1 0 16.0 2.5 14.8 Comparative Material 4 2.5 0 - 585 16.9 0 15.5 2.5 17.3

As shown in Table 1, in the conventional method by adding 2.5 ~ 2.3kg / mol-ton, Fe-Mn (ferro-manganese) 3.5kg / mol-ton by adding slag deoxidizer during tapping, prior art (1), (2 ) Is less than 400ppm RH arrival oxygen, and despite the addition of the slag deoxidizer, the slag oxidation degree, that is (T.Fe + MnO) is relatively high (13.5 ~ 14.3% by weight).

On the other hand, in order to determine the content of the MnO component in the slag which is an index indicating the reoxidation of molten steel by slag, the slag composition was analyzed using XRF (fluorescence emission analyzer). As a result, it was confirmed that the composition (MnO) in the slag is significantly high, 5 to 10% by weight. This increased (MnO) is thought to be produced by reaction of dissolved oxygen with a portion of Mn added during tapping.

In addition, the material in the prior art (1), (2) 0.50 ~ 0.65Nm 3 / the amount of molten steel in the oxygen blowing to the RH arrival oxygen to promote decarburization reaction, so less than 400ppm - had to the tones, thereby decarburization time were 18.6 The relative increase was 19.5 minutes. In addition, as a result of collecting and analyzing slabs after continuous casting, the oxygen levels were high as 17.1 and 16.5 ppm, respectively. This result, as shown in Figure 2, by increasing the (T.Fe + MnO) at the time of oxygen injection in RH, by (T.Fe + MnO) increased until the continuous casting from the end of RH refining It is considered to be because property has been promoted.

In the case of the comparative material (1), since the amount of slag deoxidizer was reduced in quicklime at the time of tapping, the RH arriving oxygen increased to 425 ppm. In addition, even though (T.Fe + MnO) was reduced to 11.1% by weight, it was difficult to obtain excellent steel cleanliness with an oxygen content of 14.7 ppm due to the oxygen injection amount of 0.40 Nm ³ / mol-ton in RH. .

In the case of the comparative material (2), due to Fe-Mn added during tapping, the RH arrival (T.Fe + MnO) was relatively high as 14.6 wt%, and the oxygen blowing amount reached 0.45 Nm ³ / molten steel-ton. The total oxygen content was 14.7 ppm, which made it difficult to obtain excellent cleanliness.

In the case of the comparative material (3) and the comparative material (4), the slag deoxidizer was greatly reduced and no manganese was added during tapping, so that the dissolved oxygen at the time of RH arrival was high, and (T.Fe + MnO) was the present invention. It can be seen that more than 1% by weight than the invention materials (1) to (3). In this case, it is not necessary to blow oxygen during the decarburization reaction in RH, and despite the relatively short decarburization time, it is difficult to obtain excellent cleanliness in the slab. This is because (T.Fe + MnO) content in slag is excessively high from the beginning, and reoxidation was promoted by (T.Fe + MnO) from the end of RH refining to the end of continuous casting.

On the other hand, in the case of the invention materials (1)-(3), when the slag deoxidizer is added at the time of tapping, 0.5-1.0 kg / molten-ton is added, and Fe-Mn is not added at all, so that the dissolved oxygen of RH arrives at 475-515 ppm, ( T.Fe + MnO) 13.5-14.1 weight% was obtained. In addition, in the case of RH refining, the amount of oxygen in the slab is significantly lower than that of the conventional materials and the comparative materials by controlling the amount of injection to 0.35 Nm ³ / mol-ton or less even when oxygen is not blown at all or when oxygen is blown. ˜12.5 ppm level. The decarburization reaction time was also good at 17 minutes or less.

According to the present invention as described above, in the Mn-added ultra-low carbon steel manufacturing method, by limiting the amount of oxygen intake in RH to a certain amount or less, by reducing the amount of additives such as quicklime, slag deoxidizer, reducing the production cost of steel, It reduces the amount of slag generated in the process and improves the cleanliness of steel.

Claims (5)

In the manufacturing method of ultra-low carbon steel of C: 0.0050% or less and Mn: 0.20 to 0.30% by weight, Adding 2.5-3.0 kg / melt-ton of quicklime and 0.5-1.0 kg / melt-ton of slag deoxidizer when tapping the converter or electric furnace; In a vacuum degassing apparatus (RH) having a vacuum degree of 5 torr or less, decarburizing the molten steel until the carbon concentration reaches 40 ppm or less, and blowing gaseous oxygen into the molten steel during the decarburization reaction; Deoxidizing molten steel by adding Al after completion of the RH decarburization reaction; And After the molten steel deoxidation in the RH step of adding a metal Mn of 2 ~ 3kg / molten-ton; Mn-added ultra-low carbon steel manufacturing method comprising The method of manufacturing Mn-added ultra low carbon steel according to claim 1, wherein the start time of injecting gaseous oxygen into the molten steel during the decarburization reaction is 3 to 5 minutes after the start of the decarburization reaction. The method for producing Mn-added ultra low carbon steel according to claim 1 or 2, wherein the oxygen blowing amount is 0.35 Nm ³ / molten ton or less during the decarburization reaction in the RH. The method for producing Mn-added ultra low carbon steel according to claim 1 or 2, wherein the addition of the metal Mn is performed at a time point of 3 to 5 minutes after adding Al in RH. The method of manufacturing Mn-added ultra low carbon steel according to claim 3, wherein the addition of the metal Mn is performed at a time point of 3 to 5 minutes after adding Al in RH.