KR20130099293A - Device for prediction of carbon increase in molten steel and method thereof - Google Patents

Abstract

PURPOSE: A carbon increment prediction apparatus and a prediction method thereof are provided to easily predict the carbon pickup degree of a slab when ultra-low carbon steel is casted. CONSTITUTION: A carbon increment prediction apparatus comprises a measuring unit (110), an input unit (120), a storage unit (130), a central processing unit (150), and a display unit (170). The measuring unit is dipped into the powder of the upper end of molten steel inside a mold, and measures the component and viscosity of the powder. The input unit receives various operation commands and configuration reference values from the outside, and transmits the operation commands and the configuration reference values to the storage unit. The storage unit stores the input casting speed of the molten steel which is casted, and the input component and viscosity of the powder on the upper end side of the molten steel. The central processing unit calculates a carbon pick-up index (CPI) by dividing the viscosity (P vis.) of the powder. The carbon increment (C pick-up) is predicted by substituting the CPI for a relative formula. [Reference numerals] (120) Input unit; (130) Storage unit; (150) Central processing unit; (170) Display unit

Description

DEVICE FOR PREDICTION OF CARBON INCREASE IN MOLTEN STEEL AND METHOD THEREOF}

The present invention relates to the quality prediction of the cast steel, and more particularly, to an apparatus and method for predicting carbon increase in molten steel for predicting the quality of the cast steel for producing a plate using ultra low carbon steel in advance.

The continuous casting machine is a machine that is produced in the steel making furnace, receives the molten steel transferred to the ladle by the tundish, and supplies it to the mold for the continuous casting machine to produce the cast steel of a certain size.

The continuous casting machine includes a ladle for storing molten steel, a playing mold for cooling the tundish and the molten steel discharged from the tundish for the first time to form a casting cast having a predetermined shape, and the casting cast formed in the mold connected to the mold. It includes a plurality of pinch rolls.

In other words, the molten steel tapping out of the ladle and tundish is formed as a cast piece having a predetermined width, thickness and shape in a mold and is transferred through a pinch roll, and the cast piece transferred through the pinch roll is cut by a cutter. It is made of slabs (Slab), Bloom (Bloom), Billet (Billet) and the like having a predetermined shape.

Related prior art is Korean Patent Publication No. 2005-21961 (published on Mar. 03, 2005, entitled " Method of manufacturing ultra-low carbon steel slab).

The present invention is to provide an apparatus and method for predicting carbon increase in molten steel for predicting the carbon pick-up (carbon increase) of a cast steel in advance through the composition and viscosity of the powder in the mold and the casting speed.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above.

The carbon increase amount prediction apparatus of molten steel of the present invention for realizing the above object is a storage unit which receives and stores the casting speed (V) of the molten steel during casting and the powder component and viscosity (P vis.) Of the upper surface of the molten steel And multiplying the casting speed (V) stored in the storage unit by the content of C free in the powder component and dividing the viscosity (P vis.) Of the powder to calculate a carbon pick-up index (CPI). It may include a central processing unit for predicting the carbon pick-up (C pick-up) by substituting the pickup index (CPI) to the following relationship.

Relation

Here, α may be a value between 1.9 and 2.0, and β may be a value between 1.2 and 1.3.

Specifically, the carbon pick-up index (CPI) may be calculated by the following equation.

Relation

The carbon increase amount prediction method of the molten steel of the present invention for realizing the above object, measuring the casting speed of the molten steel during casting and the composition and viscosity (P vis.) Of the powder of the upper surface of the molten steel, the casting measured Calculating the carbon pickup index (CPI) by multiplying the speed (V) and the content of C free in the powder component and dividing the viscosity (P vis.) Of the powder, and the carbon pickup index (CPI) Estimating the C pick-up by substituting for.

Relation

Here, α and β may be a relation constant between C pick-up and CPI.

Specifically, the molten steel may be C greater than 0 ~ less than 0.06wt%.

Α of the above relation may be a value between 1.9 and 2.0, and β may be a value between 1.2 and 1.3.

The carbon pick-up index (CPI) may be calculated by the following relationship.

Relation

According to the present invention as described above, the cast quality can be ensured by easily predicting and coping with the carbon pick-up (carbon increase) amount of the cast steel when casting the ultra low carbon steel into the cast steel.

1 is a conceptual diagram showing a continuous casting machine according to an embodiment of the present invention mainly on the flow of molten steel.
2 is a view showing an apparatus for predicting carbon increase in molten steel according to an embodiment of the present invention.
3 is a flowchart illustrating a carbon increase prediction process using a carbon pick-up index (CPI) according to an embodiment of the present invention.
4 is a graph showing the relationship between the carbon pick-up index (CPI) and the carbon increase amount of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like elements in the figures are denoted by the same reference numerals wherever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a conceptual diagram showing a continuous casting machine according to an embodiment of the present invention mainly on the flow of molten steel.

Continuous casting is a casting method in which molten metal is continuously cast (P) or steel ingot while solidifying in a mold without mold (Mold) (30). Continuous casting is used to manufacture slabs, blooms and billets, which are mainly rolled materials, and long products of simple cross-section such as square, rectangle, and circle.

The shape of a continuous casting machine is classified into a vertical type and a vertical bending type. In Fig. 1, a vertical bending type is illustrated.

1, a continuous casting machine may include a ladle 10 and a tundish 20, a mold 30, a secondary cooling stand, and a pinch roll 70. [

The tundish 20 is a container that receives the molten metal from the ladle 10 and supplies the molten metal to the mold 30. In the tundish 20, the supply rate of the molten metal flowing into the mold 30 is controlled, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the nonmetallic inclusions are separated.

The mold 30 is typically made of water-cooled copper and allows the molten steel to be primary cooled. The mold 30 has a pair of structurally opposed faces open to form a hollow portion for receiving molten steel. In the case of manufacturing the slab, the mold 30 includes a pair of barriers and a pair of end walls connecting the barriers. Here, the end wall has a smaller area than the barrier. The walls of the mold 30, mainly short walls, may be rotated away from or close to each other to have a certain level of taper. This taper is set to compensate for the shrinkage due to the solidification of the molten steel M in the mold 30. The degree of solidification of the molten steel (M) varies depending on the carbon content according to the steel type, the kind of the powder (strong cold type Vs and cold type), the casting speed and the like.

The mold 30 has a strong solidification angle or solidified shell 81 so as to maintain the shape of the cast steel piece 80 extracted from the mold 30 and prevent molten metal which is still less solidified from flowing out. It serves to form. The water-cooling structure includes a method using a copper tube, a method of water-cooling the copper block, and a method of assembling a copper tube having a water-cooling groove.

The mold 30 is oscillated by the oscillator 40 to prevent the molten steel from sticking to the wall surface of the mold 30. A lubricant is used to reduce the friction between the mold 30 and the solidification shell 81 during oscillation and to prevent burning. As the lubricant, there is oil to be sprayed and powder added to the molten metal surface in the mold 30. A powder feeder 50 is installed to feed the powder into the mold 30. The portion of the powder feeder 50 for discharging the powder is directed to the inlet of the mold 30.

The secondary cooling zone further cools the molten steel primarily cooled in the mold (30). The primary cooled molten steel is directly cooled by the spraying means 65 for spraying water while being maintained by the support roll 60 so that the coagulation angle is not deformed. The solidification of the cast steel 80 is mostly made by the secondary cooling.

The pulling device employs a multi-drive type or the like which uses several pairs of pinch rolls 70 so that the casting piece 80 can be pulled out without slipping. The pinch roll 70 pulls the solidified tip portion 83 of the molten steel in the casting direction so that molten steel passing through the mold 30 can be continuously moved in the casting direction.

The continuous casting machine configured as described above allows the molten steel M accommodated in the ladle 10 to flow into the tundish 20. For this flow, the ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends into the molten steel in the tundish 20 so that the molten steel M is not exposed to the air to be oxidized and nitrided.

The molten steel M in the tundish 20 is caused to flow into the mold 30 by the submerged entry nozzle 25 extending into the mold 30. The immersion nozzle 25 is disposed at the center of the mold 30 so that the flow of the molten steel M discharged from both the discharge ports of the immersion nozzle 25 can be made symmetrical. The start, the discharge speed and the interruption of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 provided on the tundish 20 in correspondence with the immersion nozzle 25. Specifically, the stopper 21 can be vertically moved along the same line as that of the immersion nozzle 25 so as to open and close the inlet of the immersion nozzle 25. The control of the flow of the molten steel M through the immersion nozzle 25 may use a slide gate method different from the stopper method. The slide gate controls the discharge flow rate of the molten steel (M) through the immersion nozzle (25) while the plate material slides horizontally in the tundish (20).

Molten steel (M) in the mold (30) starts to solidify from a portion in contact with the wall surface of the mold (30). This is because the periphery of the molten steel M is liable to lose heat by the water-cooled mold 30. The rear portion along the casting direction of the cast slab 80 is formed into a shape in which the non-solidified molten steel 82 is wrapped in the solidifying shell 81 by the method in which the peripheral portion first coagulates.

The non-solidified molten steel 82 moves together with the solidification shell 81 in the casting direction as the pinch rolls (Figs. 1 and 70) pull the distal end portion 83 of the fully cast solidification casting 80. The non-solidified molten steel (82) is cooled by the spraying means (65) for spraying the cooling water in the up-shifting process. This causes the thickness of the non-solidified molten steel (82) to gradually decrease in the cast steel (80). When the cast slab 80 reaches one point, the cast slab 80 is filled with the solidified shell 81 as a whole. The solidification casting 80 having been solidified is cut to a predetermined size at the cutting point 91 and is divided into a slab P such as a slab or the like.

FIG. 2 is a conceptual diagram illustrating a distribution form of molten steel M in the prediction apparatus 100 of the present invention and the mold 30 and the adjacent portion of FIG. 1. The prediction apparatus 100 includes a measuring unit 110 and an input unit. And a storage unit 130, a storage unit 130, a central processing unit 150, and a display unit 170.

The measuring unit 110 is deposited on the powder and the upper end of the molten steel in the mold 30 to measure the composition and viscosity of the powder. In particular, the powder component includes a free carbon (C free) content in the powder. The free carbon (C free) content of the powder is a value determined while preparing the powder during operation. If the free carbon (C free) content is not measured in the mold 30, the powder component prepared for the operation may be transferred to the storage 130 through the input unit 120.

In addition, as shown in FIG. 2, the distribution form of the molten steel M in the mold 30 and the portion adjacent thereto is typically formed with a pair of discharge holes on the left and right sides of the immersion nozzle 25. . The shapes of the mold 30 and the immersion nozzle 25 are assumed to be symmetrical with respect to the center line C.L, and only the left side is shown in this drawing.

The molten steel M discharged together with argon (Ar) gas at the discharge port draws a trajectory flowing in the upward direction A1 and downward direction A2 as indicated by arrows A1 and A2.

A powder layer 51 is formed on the upper portion of the mold 30 by the powder supplied from the powder feeder 50. The powder layer 51 may include a layer present in a form in which powder is supplied and a layer sintered by heat of molten steel M (sintered layer is formed closer to uncoagulated molten steel). Below the powder layer 51 is a slag layer (liquid fluidized layer) 52 formed by melting powder by molten steel (M). The slag layer 52 maintains the temperature of the molten steel M in the mold 30 and blocks the penetration of foreign matter.

On the other hand, the powder layer 51 is a portion containing the powder supplied to the top of the molten steel in the mold. These powders are added to the molten metal in the mold 30 to become slag, as well as the lubrication of the mold 30 and the solidification shell 81, as well as the oxidation / nitriding prevention and thermal insulation of the molten metal in the mold 30, the surface of the molten metal It also performs the function of absorption of the nonmetallic inclusions which emerged in the.

A portion of the powder layer 51 solidifies at the wall surface of the mold 30 to form the lubrication layer 53. The lubrication layer 53 functions to lubricate the solidified shell 81 so as not to stick to the mold 30. As the powder layer 51 solidifies on the upper side of the lubrication layer 53, the carbon component contained in the powder layer 51 is concentrated and solidified to form a carbon concentration region 55.

The carbon concentration region 55 has a higher concentration of carbon than the peripheral portion, resulting in a concentration gradient. Therefore, free carbon (C free) may be diffused from the carbon concentration region 55 to the powder layer 51, the slag layer 52, and the like by the concentration gradient. In particular, the molten steel refined to ultra low carbon steel whose carbon (C) content is controlled to less than 30 ppm is severely fluctuated (Mold Level Fluctuation), so that some of the level is raised above the slag layer 52. When the hot water surface and the carbon concentration region 55 are adjacent to each other, free carbon flows from the carbon concentration region 55 into the molten steel, thereby acting as a direct cause of increasing the carbon content in the molten steel.

The thickness of the solidification shell 81 becomes thicker as it progresses along the casting direction. The portion of the solidification shell 81 located in the mold 30 is thin, and an oscillation mark 87 may be formed by oscillation of the mold 30. The solidification shell 81 is supported by the support roll 60, the thickness thereof is thickened by the spray means 65 for spraying water.

In addition, the input unit 120 is configured to receive various operation commands or setting reference values from the outside and transmit them to the storage unit 130. In particular, the casting speed (V) of the molten steel can be measured and input directly. The casting speed V is calculated using the rotational speed of the pinch roll 70 (shown in FIG. 1), which is well known and thus detailed description thereof will be omitted.

The storage unit 130 stores the casting speed (V) of the powder and the molten steel transferred through the input unit 120 and transmits the stored portion to the central processing unit 150. In the storage unit 130, a relational expression for predicting the C increase (C pick-up), a calculation value thereof, and the like may be stored under the control of the central processing unit 150.

The central processing unit 150 receives the viscosity of the powder, the free carbon (C free), and the molten steel casting speed (V) from the storage unit 130, and calculates a carbon pick-up index (CPI), using the carbon increase amount ( After predicting the C pick-up, the result is output to the display unit 170.

Here, the carbon pick-up index (CPI) is calculated according to the following relational expression.

Relationship 1

Specifically, the carbon pickup index (CPI) is calculated by multiplying the casting speed (V) by the content of free carbon (C free) in the powder and dividing the viscosity (P vis.) Of the powder.

The carbon pick-up is obtained by substituting the calculated carbon pick-up index (CPI) into the following relational expression.

Relation 2

Here, α and β are calculated as a relation constant between the carbon pick-up index (CPI) and the carbon increase (C pick-up), which will be described later with reference to FIG. 4. Specifically, α may be a value between 1.9 and 2.0, and β may be a value between 1.2 and 1.3.

In addition, the display unit 170 may include the powder component and the casting speed (V) of the molten steel, the carbon pick-up index (CPI), the predicted carbon increase (C pick-up), etc., in the central processing unit 150. Can be displayed in text or graph mode.

Generally, in the case of automobile shell plates, it is possible to produce solidified alloying elements, especially carbon with extremely few extremely low carbon steel of less than 30 ppm in order to achieve high-quality formation. Therefore, carbon is removed through vacuum decarburization during steelmaking, and the carbon content of subsidiary materials such as flux in the tundish 20 and powder of the mold 30 is also 5% or less to prevent the increase of carbon even during continuous casting. The lower product is used. However, as described above, the powder is in contact with the molten steel due to the severe level fluctuation of the mold 30 caused by the molten steel flow in the mold 30 during casting, thereby increasing the carbon content in the molten steel. Will occur.

As the carbon content in the molten steel increases, a sheet (hot rolled coil) having low moldability causes a problem in that a part of the product is damaged during molding of the final product. Subsequent processes, such as increase in unnecessary processing costs and at the same time increase the cost of defective processing.

In the present invention, by easily predicting and coping with the degree of carbon pick-up (carbon increase) of the slab P when casting the ultra low carbon steel into the slab P, due to unnecessary subsequent process of the slab exceeding the carbon tolerance standard, This is to prevent productivity loss and unnecessary waste of money.

3 is a flowchart illustrating a process of predicting carbon pick-up (C pick-up) using a carbon pick-up index (CPI) according to an embodiment of the present invention, which will be described with reference to the accompanying drawings.

First, molten steel produced through a secondary refining process of an electric furnace and a ladle furnace is supplied to a continuous casting machine, and in the continuous casting machine as shown in FIG. 1, the supplied molten steel is manufactured into a slab-like casting piece P.

On the other hand, when the molten steel is injected into the mold 30, the casting speed (V) of the molten steel being cast and the component and viscosity (P vis.) Of the powder of the powder layer 51 (Fig. 2) are measured. The casting speed (V) of the molten steel and the viscosity (P vis.) Of the molten steel and the free carbon (C free) content of the powder components thus measured are transferred directly or through the input unit 120 to control the central processing unit 150. According to the storage unit 130.

Subsequently, the central processing unit 150 multiplies the casting speed (V) stored in the storage unit 130 and the content of the free carbon (C free) of the components of the powder, and then divides the viscosity (P vis.) Of the powder to pick up the carbon. The index (CPI) is calculated. (S20) A method of calculating the carbon pickup index (CPI) is shown in Equation 1 below.

Relationship 1

In detail, the casting speed (V) is increased as the casting speed (V) is increased because the molten surface of the mold 30 becomes a mold level fluctuation state, so that the carbon concentration region 55 and the molten steel may be adjacent to each other. Acts as. In addition, the content of free carbon (C free) in the powder has a greater effect on the molten steel as the carbon content of the carbon concentration zone 55 increases as the amount of carbon (C) contained in order to control the melting rate of the powder increases. It acts as an increasing factor. In addition, the viscosity of the powder (P vis.) Increases the surface tension between the slag and molten steel as the viscosity increases, thereby reducing the fluctuations in the water surface acts as a reducing factor.

For example, if the casting speed (V) is 1.3 m / min, the content of free carbon (C free) is 1.50 wt%, and the viscosity (P vis.) Is 3.14 dPas, the carbon pickup index (CPI) is '0.62'. Will be.

The carbon pick-up index (CPI) calculated as described above is stored in the storage unit 130.

Thereafter, the central processing unit 150 predicts the carbon pick-up amount (C pick-up) using the carbon pick-up index (CPI). (S30) Here, the carbon increase amount (C pick-up) is calculated according to the following Equation 2. Can be.

Relation 2

Where α and β are relational constants calculated by the relationship between the carbon pick-up index (CPI) and the carbon pick-up (C pick-up) of FIG. 4, wherein α is a value between 1.9 and 2.0, and β is 1.2 to 1.3 Is a value between. The relationship between the carbon pick-up index (CPI) and the carbon pick-up amount (C pick-up) is shown in the graph of FIG. 4 according to the values in the following table. As the carbon pick-up index (CPI) increases, the carbon pick-up amount (C pick-up) is increased. It can be seen that) increases.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Casting speed (V)
(m / min) 1.3 1.8 1.4 2.0 1.8 2.0 2.0 c free (wt%) 1.50 2.20 1.60 0.70 1.50 1.00 1.00 Viscosity (dPas) 3.14 2.12 2.62 3.42 4.6 3.5 2.2 CPI 0.62 1.87 0.85 0.41 0.59 0.57 0.91 C pick-up (ppm) 5 5.4 3 3 2 2 3

That is, as shown in FIG. 4, the carbon pick-up index CPI and the carbon pick-up C have approximately a proportional relationship under different operating conditions. The correlation between the carbon pick-up index (CPI) and the carbon pick-up (C pick-up) is the same as the above equation 2. In FIG. 4, the dots are actual data (Examples 1 to 7) according to the carbon pick-up index (CPI) and the carbon pick-up amount (C pick-up), and the solid line is a predictive model that fits the actual data linearly. And the predictive model were found to be somewhat in agreement (R ² = 0.83).

Here, the first constant α according to the correlation between the carbon pick-up index CPI and the C pick-up may be '1.9979', and the second constant β is preferably ' 1.2792 '.

When the C pick-up is calculated, the central processing unit 150 can calculate the final carbon content by adding the calculated C pick-up to the carbon content in the initial molten steel. The initial carbon content in the molten steel is the carbon content of the molten steel at the time when the molten steel is injected into the mold 30, and is mainly a value within the range of the ultra low carbon steel in which the carbon (C) is less than 30 ppm.

Then, the central processing unit 150 compares the calculated final carbon content with the set reference carbon amount, and determines whether the final carbon amount exceeds the reference carbon amount. The reference carbon amount can be cut according to the steel grade or the specification, and the reference carbon amount in the case of the automobile exterior plate can be up to about 24 ppm.

Thus, when the predicted final carbon amount exceeds the set reference carbon amount, the central processing unit 150 outputs the warning message to the display unit 170 and at the same time, the cast steel P is introduced into a subsequent process such as rolling. It stops and waits for reanalysis of the carbon content of the cast (P). This is to prevent unnecessary process waste such as the failure cast P proceeding to a subsequent process. Of course, when the final carbon amount predicted does not exceed the set reference carbon amount, the central processing unit 150 causes the cast P to be put into a subsequent process such as rolling.

In addition, during the reanalysis of the carbon content of the cast steel, by adjusting the casting speed (V) is set or replaced with a powder with a carbon content to form a powder layer 51 of the molten steel flowing into the mold 30 afterwards Quality can be guaranteed.

Alternatively, a low carbon / high viscosity powder capable of adjusting the casting speed V or adjusting the carbon content of the powder layer 51 may be supplied during the casting without pause.

Therefore, in the present invention, the casting quality can be guaranteed by easily predicting and coping with the carbon pick-up (carbon increase) amount of the cast steel when casting the ultra low carbon steel into the cast steel.

The apparatus for predicting the carbon increase in molten steel and the method thereof are not limited to the construction and the manner of operation of the embodiments described above. The above embodiments may be configured such that various modifications may be made by selectively combining all or part of the embodiments.

10: Ladle 15: Shroud nozzle
20: tundish 21: stopper
25: immersion nozzle 30: mold
40: mold oscillator 50: powder feeder
51: powder layer 52: slag layer
53: lubricating layer 55: carbon concentration zone
60: support roll 65: spray means
70: pinch roll 80: performance cast
81: Solidification shell 82: Non-solidified molten steel
83: tip portion 85: solidified point
87: Oscillation mark 91: Cutting point
100: prediction device 110:
120: input unit 130: storage unit
150: central processing unit 170:

Claims (6)

A storage unit receiving and storing a casting speed V of the molten steel being cast and a component and a viscosity P vis. And
The carbon pick-up index (CPI) is calculated by multiplying the casting speed (V) stored in the storage unit by the content of C free in the powder component and dividing the viscosity (P vis.) Of the powder. Central processing unit for predicting the carbon pick-up (CPI) by substituting (CPI) in the following relationship;
Relation

Wherein α is a value between 1.9 and 2.0, and β is a value between 1.2 and 1.3.
The method according to claim 1,
The carbon pickup index (CPI) is a carbon increase amount prediction apparatus of molten steel calculated by the following equation.
Relation

Measuring the casting speed (V) of the molten steel being cast and the composition and viscosity (P vis.) Of the powder on the upper surface of the molten steel;
Calculating a carbon pick-up index (CPI) by multiplying the casting speed (V) and the content of C free in the powder component and dividing the viscosity (P vis.) Of the powder; And
Predicting the carbon pick-up (C pick-up) by substituting the carbon pick-up index (CPI) in the following relationship.
Relation

Where α and β are the relational constants between C pick-up and CPI.
The method according to claim 3,
The molten steel is a method of predicting carbon increase in molten steel, which is a very low carbon steel C is greater than 0 ~ less than 0.06wt%.
The method according to claim 3,
Α of the above relation is a value between 1.9 and 2.0, and β is a value between 1.2 and 1.3.
The method according to claim 3,
The carbon pick-up index (CPI) is a method of predicting carbon increase in molten steel calculated by the following equation.
Relation

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