KR100328052B1 - A method for manufacturing high-clean steel - Google Patents

Abstract

PURPOSE: To manufacture high clarity steel by floating inclusions entrained in molten steel by refluxing. CONSTITUTION: The method includes the steps of transferring a ladle(1) into which molten steel(2) tapped from converter is introduced for powder injection; dipping a top lance from upper side of the ladle into the molten steel; injecting a hydrogen gas through the top lance at an injection rate of 30 to 70 kg·powder/min accompanied with inert gas injection at a pressure of 5.0 to 10.0 kg/cm¬2 and in a flow rate of 0.5 to 1.0 Nm¬3/min, wherein the hydrogen gas includes powdery Ca(OH)2 in an amount of 0.4 to 1.2 kg/ton·molten steel or powdery TiH4 in an amount of 0.14 to 0.42 kg/ton·molten steel; transferring the ladle into RH degassing facility; blowing argon gas at a blow rate of 0.32 to 0.80 Nm¬3/hr and at a pressure of 5.0 to 10.0 kg/cm¬2 for reflux, thereby stripping dissolved hydrogen gas entrapped in the molten steel in the form of hydrogen bubbles(11).

Description

A method for manufacturing high-clean steel

The present invention relates to a method for manufacturing high-clean steel in the steelmaking process, more specifically, by injecting a molten steel (flux) containing molten gas components in the molten steel tapping in the converter forcibly dissolved, non-metallic inclusions in the molten steel in the decompression step (Hereinafter referred to as "inclusion") relates to a method for producing a high-purity steel by trapping, removing, and separating by generating gas bubbles.

The basic composition of steelmaking industry is mainly composed of converter → secondary refining → continuous casting process. In the converter operation, oxygen is injected to molten iron during the Songsan blasting process, and carbon (C), manganese (Mn), silicon (SI) and phosphorus (P) Hundreds of ppm of free oxygen is contained in the molten steel after removing impurity elements such as back and refining the converter. In order to remove such dissolved oxygen, aluminum, silicon, manganese, and the like are added to the converter steel. As a result, the deoxidation product is suspended and dispersed in the molten steel. Since the deoxidation product remains until the final product causes surface defects, it must be separated and removed from molten steel before the continuous casting is carried out, and a number of high-purity steel production methods for easily removing them have been proposed.

Conventionally, high-purity steel is manufactured by adding slag modifiers during and after the converter's tapping and / or tapping to change slag properties or prevent reoxidation. (Korean Patent Registration No. 3736,393299) No. 118956, 110322, Patent Application Nos. 95-45965, 95-56445, and 96-67584. Although this method contributes to the production of high clean steel, the slag modifier or slag oxidizer is added to 1 to 10kg per ton of molten steel, has the disadvantage of further increasing the slag generation. The slag generated is classified as a kind of waste and is also a source of environmental pollution. Therefore, an increase in the amount of slag generated means an increase in the amount of waste generated, which is disadvantageous in terms of the environment. In addition, the slag has to be reprocessed with a harmless material, which requires a huge cost.

On the other hand, one of the methods of manufacturing high-purity steel, the length of the immersion pipe consisting of two reflux pipes, such as the rising pipe and the down pipe to reflux the molten steel in the RH vacuum degassing apparatus (hereinafter referred to simply as "RH") Forming differently to improve the molten steel stirring force to promote coarsening of inclusions (Korean Patent Registration No. 95381) has been proposed. However, this method has the disadvantage that the refractory erosion of the long length of the immersion pipe is extremely difficult, the maintenance of the immersion pipe is very difficult, the maintenance cost is increased, and a separate manpower for maintenance is required.

Accordingly, the present inventors have repeatedly conducted research and experiments to solve the above problems and propose the present invention based on the results, and the present invention provides a compound powder containing soluble gas in molten steel withdrawn from the converter. Blowing by immersion in molten steel, forced employment of the soluble gas component in the molten steel, and then under reduced pressure refining in RH, the molten steel is applied to the fact that the inclusions in the molten steel becomes the place where these bubbles are generated when the soluble gas is generated as bubbles. By reflux, it is to provide a high-purity steel manufacturing method to easily remove the inclusions in the molten steel, the object is.

1 is a schematic diagram of a powder blowing device (PI process)

2 is a schematic diagram of an RH refining apparatus;

Figure 3 is a schematic diagram for explaining the separation mechanism of the inclusion when refining in accordance with the present invention

Explanation of symbols on the main parts of the drawings

1: ladle 2: molten steel

3: slag 4: inclusions

5: hydrogen compound powder 6: phase lance

7: vacuum chamber 8a: riser

8b: down pipe 9: reflux gas supply device

10: molten steel 11: hydrogen bubble

12: hydrogen bubbles combined with inclusions

In order to achieve the above object, the present invention provides a method for manufacturing high-clean steel, comprising: transferring a ladle (ladle) containing molten steel outgoing from the converter into a process capable of powder injection; Lowering the upper lance from the upper ladle and depositing the molten steel in the molten steel, and simultaneously blowing the compound powder Ca (OH) ₂ or TiH ₄ containing hydrogen gas together with the transport gas through the lance; And transferring the ladle to RH to reflux the molten steel so that hydrogen dissolved in the molten steel is generated as hydrogen bubbles in the molten steel to remove inclusions.

Hereinafter, the present invention will be described in detail by dividing step by step.

In the present invention, the ladle (ladle) containing the molten steel outgoing from the converter is subjected to the process of transferring the powder blowing.

The ladle containing the molten steel from the converter is transferred to a process capable of blowing powder. At this time, the powder injection process is a process having a device that can blow the powder to the upper ladle, for example, ladle (LF, Ladle Furnace), BAF (BAP, Bubbling, Al-wire feeding & Powder injection), Powder Injection (PI).

In the present invention, while lowering the upper lance from the top of the ladle and deposited in the molten steel, the compound powder Ca (OH) ₂ or TiH ₄ containing hydrogen gas is blown through the lance.

Among the apparatuses capable of blowing the powder onto the ladle, a powder processing apparatus (PI process) will be described as an example. 1 is a schematic diagram schematically showing a powder blowing device (PI process).

The lance 6 is lowered from the top to be deposited in the molten steel 2, and the powder 5 containing Ca (OH) ₂ or TiH ₄ containing hydrogen components is simultaneously blown with the carrier gas. will be. At this time, the particle size of the powder is preferably 1mm or less in diameter. When it exceeds 1 mm, penetrating flow is generated when blowing the powder, which is disadvantageous because only the transport gas is blown and the powder does not tend to be blown.

As the transport gas, a gas having an inert property such as argon, nitrogen, and neon may be used. However, nitrogen is dissolved in molten steel to increase the nitrogen content of the molten steel unnecessarily, and neon gas is expensive and economically disadvantageous. Therefore, argon gas is most preferably used.

In addition, the transport gas is preferably controlled to a pressure of 5.0 to 10.0kg / cm ² , flow rate 0.5 to 1.0 Nm ³ / min range. If the pressure is less than 5.0, clogging of the lance occurs, it is difficult to blow the powder, and at 10.0 or more, it is impossible to operate because molten steel may be scattered out of the ladle. When the flow rate of the transport gas is 0.5 or less, clogging of the lance occurs and is disadvantageous. In 1.0, molten steel is scattered and through flow is generated, which may adversely affect the metallurgical effect.

The powder is molten steel, and blowing so that the amount of hydrogen dissolved 10-30ppm, for example, if blowing the Ca (OH) _2, the molten steel per ton 0.4~1.2kg, TiH ₄ is hydrogen when blown per ton of the molten steel 0.14~0.42kg A content of 10-30 ppm can be obtained. If the hydrogen content is less than 10ppm, it is difficult to obtain the desired inclusions removal effect, and if it is 30ppm or more, the powder blowing amount is increased, but it is disadvantageous in economics and workability because the powder removing amount is not obtained.

The powder blowing rate is preferably set to 30 to 70 kg per minute. If it is less than 30kg, it takes a long time to blow the desired amount of powder, and if it is more than 70kg, it is disadvantageous because the error rate compared to the powder injection amount may be lowered to dissolve the hydrogen component in molten steel.

When the powder is blown by the above method, in the case of Ca (OH) ₂ , TiH ₄ is dissolved in molten steel by the reaction of the following formula (1) and (2) to increase the hydrogen content in the molten steel. do.

Ca (OH) SUB {2} ~ = ~ CaO (s) ~ + ~ H SUB {2} O

H SUB {2} O ~ = ~ 2 [H] ~ + ~ [O]

TiH SUB {4} ~ = ~ [Ti] ~ + ~ 4 [H]

In the present invention, by transferring the ladle to RH to reflux the molten steel, hydrogen dissolved in a large amount of molten steel is generated as hydrogen bubbles in the molten steel to remove the inclusions.

2 is a schematic view schematically showing an example of a process for performing molten steel reflux using the RH refining apparatus. The molten steel 2 into which the hydrogen compound powder 5 is blown is transferred to RH composed of a vacuum chamber 7, a rising pipe 8a, a falling pipe 8b, a reflux gas supply device 9, and the like. Is carried out. The internal pressure of the vacuum chamber (7) is lowered to 0.01 atm while the rising reflux pipe (8a) and the down reflux pipe (8b) are deposited on the molten steel (2) in the ladle (1), and the molten steel is blown while blowing argon gas into the rising pipe. Forced reflux.

In order to facilitate the reflux of the molten steel, the molten steel reflux gas is preferably controlled in a flow rate of 0.32 to 0.80 Nm ³ / hr per ton of molten steel and a pressure of 5.0 to 10.0 kg / cm ² . If the reflux gas flow rate is less than 0.32, it is difficult to reflux molten steel effectively due to the lack of floating capacity necessary for reflux of molten steel.In the case of 0.80 or more, it is easy to reflux molten steel, but a large amount of current is attached inside the vacuum chamber and the loss of nozzle part is severe. Can be a barrier to city. When the pressure is 5.0 or less, reflux of the reflux gas is difficult, and when the reflux gas is more than 10.0, the reflux gas is injected more than the wood flow rate, so that a large amount of current is attached to the inside of the vacuum chamber or the refractory loss of the nozzle portion may be severe.

By refluxing molten steel at RH as described above, in the molten steel 2 in the ladle 1, the hydrogen partial pressure P (H ₂ ) in the molten steel exceeds the sum of the iron static pressure P (m) and the stirring power (ε). In the micro-bubbles 11 of the hydrogen gas is generated. The reaction formula for hydrogen evolution is the following equation (4), its chemical equilibrium constant K, H ₂ partial pressure, the relationship between the hydrogen concentration and molten steel temperature in the molten steel is the following formula (5), the iron static pressure is the following formula (6), the stirring power of the molten steel Can be respectively represented by following formula (7). In Equation (5), K is the equilibrium constant for the chemical reaction of Equation (4), P (H ₂ ) is the partial pressure of hydrogen in the molten steel (atm), and [% H ₂ ] is the amount of dissolved hydrogen in the molten steel (wt%). , T denotes the absolute temperature (K) of the molten steel, in the formula (6), P is the molten steel density (g / cm ³ ), g is the acceleration of gravity (m / sec ² ), h is the molten steel height (m) do. In the following formula (7), M represents the amount of molten steel in the ladle (ton), Q is the molten steel reflux speed (ton / sec), U represents the molten steel outflow linear velocity (m / sec) in the downcomer.

[H] ~ = ~ ½H SUB {2} (g)

P (m) ~ = ~ p * g * h

ε ~ = ~ ρ ~ / ~ (2000 * M) * Q * U SUP {2}

Meanwhile, floating separation of inclusions 4 in molten steel 2 can be explained by separation of molten steel and inclusions, that is, the Stokes equation by the following equation (8), where V is the floating speed of nonmetallic inclusions, g is gravitational acceleration (= 9.8 m / sec ² ), r is inclusion radius (m), ρ _Fa and ρ _inclu are molten steel and inclusion density (ton / m ³ ), and η is the viscosity coefficient of molten steel (= 0.005kg, respectively). / m-sec). It can be seen from Equation (8) that the larger the particles of the inclusions are, the faster the flotation speed is, the smaller the density of the inclusions is.

V ~ = ~ (2/9) ~ * [g * r2 * (ρ SUB {Fe} -ρ SUB {inclu})] ~ / ~ η

Figure 3 is a schematic diagram for explaining the floating separation mechanism of inclusions when refining according to the present invention. As shown in FIG. 3, the hydrogen bubbles 11 generated inside the molten steel 2 in the ladle collide with each other by interposing the inclusions 4. At this time, the floating speed combined with the hydrogen bubble has a value similar to the floating speed of the hydrogen bubble (11). That is, since the volume of the inclusions 12 combined with the hydrogen bubbles is greatly increased and the density is greatly reduced, the floating speed of the inclusions is greatly increased according to Equation (8). The present invention is to increase the floating speed of the inclusions in the molten steel by the above method, it is possible to effectively produce high clean steel.

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

Example 1

For molten iron of 0.01 ~ 0.90wt% of carbon, 0.10wt% of silicon, 0.10 ~ 1.00wt% of manganese, and 0.02 ~ 0.08wt% of aluminum, finish the Songsan refining in 100 ton converter and add aluminum to molten steel during tapping Was deoxidized, and iron alloy was added to adjust the molten steel component. The ladle 1 to hold the molten steel 2 was transferred to a PI refining apparatus, and the lance 6 was lowered from the top to be deposited on the molten steel and Ca (OH) ₂ was blown. The powder blowing amount was 0 to 1.4 kg per ton of molten steel, respectively, as shown in Table 1 below, and the powder blowing rate was controlled to 50 kg per minute. At this time, argon was used as the transport gas, and the transport gas pressure was 8.0 kg / cm ² and the flow rate was 0.75. Adjusted to Nm ³ / min. As a result of collecting and analyzing the molten steel sample after powder injection, the total oxygen amount representing the hydrogen content and the inclusion content of the molten steel was as shown in Table 1 below.

division Comparative Example 1 Comparative Example 2 Inventive Example 1 Inventive Example 2 Inventive Example 3 Comparative Example 3 Powder blowing amount (kg / t-s) 0 0.3 0.4 0.8 1.2 1.4 Hydrogen content (ppm) ≤2 8 11 21 29 31 Oxygen amount (ppm) 117 108 116 113 121 119

As shown in Table 1, in Comparative Example (1) without powder injection, it can be seen that the hydrogen content is very low, 2ppm or less.

The ladle containing the molten steel was transferred to an RH vacuum degassing apparatus, and molten steel was refluxed. When the molten steel was refluxed, the argon gas was controlled to 0.40 Nm ³ / min per ton of flow rate molten steel at a pressure of 8.0 kg / cm ² while lowering the internal pressure of the vacuum chamber to 0.01 atm or less. After the molten steel was refluxed for 12 minutes at RH, the molten steel sample was collected and analyzed. The results are shown in Table 2 below.

division Comparative Example 1 Comparative Example 2 Inventive Example 1 Inventive Example 2 Inventive Example 3 Comparative Example 3 Hydrogen content (ppm) ≤2 2 3 2 2 3 Oxygen amount (ppm) 26 24 10 9 8 13

As can be seen from Table 2, even when Ca (OH) ₂ powder is blown, the hydrogen content after RH reflux is lowered to 2-3 ppm, which is similar to that of Comparative Example (1) when the hydrogen-containing powder is not blown. It was confirmed to represent. On the other hand, the total oxygen amount after RH reflux was 8-10 ppm of Inventive Examples (1)-(3), which was significantly lower than that of Comparative Example (1) without powder injection and Comparative Example (2) with relatively low powder injection amount. Able to know. This is the result obtained because hydrogen bubbles are generated in molten steel during the reflux of molten steel at RH, collide with the inclusions, trap the inclusions, and float. On the other hand, Comparative Example (3) in which the powder was blown at 1.4 kg per ton of molten steel showed similar results to the invention example in terms of reducing the total oxygen, but it was found that the powder blowing amount did not show an increased effect. In this way, when excessively blown the powder, hydrogen gas in the molten steel does not dissolve more than a certain value at the steelmaking temperature, and thus the blown powder is not dissolved in the molten steel.

Example 2

For the same molten iron as in Example 1, the termination of the Songsan blow in a 100 ton converter and aluminum was added to the molten steel during tapping to deoxidize the molten steel. The ladle containing the molten steel was transferred to a PI refining apparatus, from which the lance was deposited in the molten steel and TiH ₄ was blown. The powder blowing amount was 0 to 0.5kg per ton of molten steel, respectively, as shown in Table 3 below, and the powder blowing rate was controlled to 40kg per minute. At this time, the pressure and flow rate of the transport gas were the same as in Example 1. After powder injection and after 12 minutes of refluxing molten steel at RH, the molten steel sample was collected and analyzed. The molten steel reflux condition in RH was maintained the same as in Example 1.

division Comparative Example 1 Comparative Example 4 Inventive Example 4 Inventive Example 5 Inventive Example 6 Comparative Example 5 Powder blowing amount (kg / t-s) 0 0.07 0.14 0.28 0.42 0.50 After powder blowing Hydrogen content (ppm) 2 6 11 20 31 30 Oxygen amount (ppm) 117 104 116 128 112 120 After RH reflux Hydrogen content (ppm) ≤2 2-3 ≤2 ≤2 ≤2 2-3 Oxygen amount (ppm) 25-30 25-30 5-10 5-10 5-10 10-15

As can be seen from Table 3, even when the TiH ₄ powder is blown, the hydrogen content after RH reflux was found to be lowered to 2-3ppm, and the total oxygen content after RH reflux is inventive examples (4)-(6) It can be seen that it is significantly lower than Comparative Example (1) in which powder is not blown at 5-10 ppm and Comparative Example (5) in which the powder blowing amount is relatively small. This result is obtained because hydrogen bubbles are generated in molten steel during the reflux of RH and collide with inclusions to trap inclusions and float. In Comparative Example (5) in which 0.50 kg of powder was blown per ton of molten steel, the effect of reducing total oxygen was similar to that of the present invention, but the powder blowing amount was not shown to be increased.

As described above, the present invention is similar to the conventional hydrogen concentration after the treatment by injecting the hydrogen-containing compound powder in molten steel, but the effect of reducing the total oxygen amount is 5-10ppm at the conventional 20-25ppm level, thereby significantly including The taper effect can be realized.

Claims (1)

In the method of manufacturing high clean steel, Transferring the ladle 1 containing the molten steel 2 pulled out of the converter to a process capable of powder blowing; The upper lance 6 is lowered from the upper part of the ladle 1 and deposited in molten steel, and the compound powder of less than 1 mm containing hydrogen gas (5) Ca (OH) ₂ : 0.4 to 1 ton of molten steel through the lance 6. 1.2 kg or TiH ₄ : 0.14 to 0.42 kg per ton of molten steel, blown at a speed of 30 to 70 kg per minute simultaneously with inert transport gas with a pressure of 5.0 to 10.0 kg / cm ² and a flow rate of 0.5 to 1.0 Nm ³ / min step; And The ladle 1 is transferred to RH, and argon gas is melted in molten steel by refluxing the molten steel by blowing a flow rate in the range of 0.32 to 0.80 Nm ³ / hr per ton of molten steel and a pressure in the range of 5.0 to 10.0 kg / cm ^2. Method for producing a high clean steel comprising the step of removing the inclusions by causing the generated hydrogen to be hydrogen bubbles in the molten steel inside the ladle

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