KR100783082B1 - Method for continuous casting - Google Patents

Abstract

A continuous casting method is provided to improve stability of a process and productivity by preventing break-out caused by thin solidified cell on corners. A continuous casting method includes the steps of: obtaining process data; calculating an estimated thermal conductivity flow speed at a target casting speed; determining if the calculated thermal conductivity flow speed is below a standard value or not; starting casting by using a predetermined mold flux if the calculated thermal conductivity flow speed is below the standard value; exchanging the mold flux if the calculated thermal conductivity flow speed exceeds the standard value; checking the calculated thermal conductivity flow speed of the exchanged mold flux to be below the standard value; continuously calculating the thermal conductivity flow speed after starting the process; reducing a casting speed if the calculated thermal conductivity flow speed exceeds the standard value; increasing the casting speed to the target casting speed if the calculated thermal conductivity flow speed is below the standard value; and completing the process with keeping the thermal conductivity flow speed below the standard value.

Description

Continuous casting method {Method for continuous casting}

1 is a schematic view showing a typical continuous casting machine.

2 and 3 are a cut perspective view and a plan view showing the mold installation and the solidification cell formation.

4 is a plan view showing a drift example of molten steel flow;

5 is a graph showing the thickness distribution of the coagulation cell.

6A and 6B are graphs showing the heat transfer flow rate at different casting speeds for two types of mold fluxes.

7 is a process flow chart showing the operation progress of the continuous casting method according to the present invention.

8 is a graph showing the heat transfer flow rate and casting speed of the embodiment according to the present invention.

Figure 9 is a graph showing the heat transfer flow rate and casting speed of the comparative example according to the prior art.

<Explanation of symbols for the main parts of the drawings>

1: ladle 2: tundish

3: tundish nozzle 4: mold

5: solidification cell 15: tundish nozzle

20, 30: Cast copper plate 40: Cooling water slit

50: water jacket

The present invention relates to a continuous casting method, and more particularly, to a continuous casting method for preventing break-out.

Generally, the steelmaking process proceeds in the order of the molten iron pretreatment, converter refining, secondary refining, and continuous casting. 1 shows a typical continuous casting machine.

Referring to FIG. 1, a continuous casting machine is provided with a tundish 2 at a lower part of a ladle 1 for transporting molten steel, and a tundish nozzle for flowing out molten steel at the bottom of the tundish 2. 3) is installed. In addition, a mold 4 for producing molten steel as a slab having a predetermined thickness and width is provided below the tundish nozzle 3, and a plurality of pinch rolls for guiding the slab at the lower end of the mold 4. (5) is installed. This continuous casting machine is a method in which molten steel injected from above solidifies into a cross-sectional shape of the mold 4 as it flows down through the mold 4 and continuously produces.

The mold 4 forms the molten steel injected from the tundish 2 into an appropriate size, and forms a solidified layer of the cast through cooling so as not to be ruptured by the pulling force and the molten steel positive pressure when drawn to the lower portion of the mold 4. . The cooling is performed by circulating cooling water in the mold 4 copper plate, and removes heat from the molten steel inside the solidification layer of the cast steel to form a sound solidification layer. That is, the molten steel is formed by the coagulation cell is formed in the contact with the mold (4), the coagulation cell is pulled down to the mold (4) to move continuously.

In general, the thickness of the coagulation cell when exiting the mold 4 is usually about 15 to 30 mm, and then passes between the rolls 5 supporting the coagulation cell, and the inside of the coagulation cell by the cooling water sprayed therein. The molten steel is completely solidified. Here, in the case where the solidification cell exiting the mold 4 is defective, a break-out occurs in which the internally solidified molten steel flows out, which is no longer possible to proceed with continuous casting. There is a problem that hinders stability and causes damage to the continuous casting equipment.

2 and 3 show a cut perspective view and a plan view showing the mold installation and the solidification cell formation.

Referring to the drawings, the mold installation includes a coolant slit 40 to allow the coolant to flow through the mold copper plates 20 and 30 in contact with the molten steel A. In addition, a backup plate or a water jacket 50 formed outside the mold copper plates 20 and 30 to prevent deformation of the mold copper plates 20 and 30 due to heat and to supply cooling water to the mold copper plates 20 and 30. , water jacket).

The coolant flows into the coolant slit 40 in the lower part of the mold and then flows upward through the slit 40. While the cooling water flows through the slit 40, the mold copper plates 20 and 30 heated by the molten steel A are cooled by the cooling water, and the molten steel A in contact with the mold copper plates 20 and 30 is solidified. The solidification cell B is formed.

If the average thickness is too thin when the coagulation cell exits the mold, breakout occurs because the coagulation cell cannot support the increasing force of iron registration afterwards moving downward. In addition, even if the average thickness is sufficiently thick, if the thickness distribution is uneven in the circumferential direction, cracks are likely to occur in the mold due to the concentration of thermal stress applied to the solidification cell of the thin portion, and the thin film is released by the action of the iron positive pressure. If the part's coagulation cell swells outwards and becomes excessive, eventually the coagulation cell may rupture and breakout may occur. In addition, even if the average thickness is uniform and the thickness distribution is uniform, if the thickness of the solidification cell in the corner portion is particularly thin, breakout may occur because the thinner solidification cell in the corner portion does not overcome the iron static pressure after exiting the mold. have.

Therefore, in order to prevent breakout, the average thickness of the coagulation cells growing in the mold must be kept within a predetermined range. In addition, the thickness of the coagulation cell should show a distribution that gradually thickens as it moves downward in the mold, and should have a uniform distribution in the circumferential direction at the same height. In addition, sufficient thickness of the solidification cell should be ensured at the corners.

First, in order to grow a solidification cell of sufficient average thickness, the cooling water flowing through the cooling water slit of the mold is adjusted to 10 m / sec or more so that the boiling water boiling does not occur at all positions of the mold. It is known to grow normally. Alternatively, the thickness of the mold from the cooling water slit to the place in contact with the molten steel is maintained within the range of 10 to 30 mm to facilitate heat transfer from the molten steel to the cooling water.

In addition, for uniform thickness distribution in the circumferential direction of the coagulation cell, a method of preventing local uneven growth of the coagulation cell is known by controlling the mold level to be stably maintained at a constant position at all times and performing initial solidification relatively slowly. have.

Moreover, in order to grow the coagulation cell of a corner part to sufficient thickness, the method of appropriately giving a taper to a short side mold is known. As the coagulation cell initially formed in the upper part of the mold moves downward, the coagulation cell contracts in the width direction, and the width of the lower part is generally kept smaller than the width of the upper part to compensate for the contracted amount. In the case of medium carbon steel with a large amount of solidification shrinkage, the slope of the short side mold is generally given at about 1.1 to 1.3%, and in the case of low carbon steel or very low carbon steel, it is given at about 1.0 to 1.2%.

In other words, in order to maintain an appropriate average thickness of the solidification cell, to have a uniform thickness distribution, and to sufficiently secure the thickness of the solidification cell at the corners to prevent breakout, the initial solidification speed is slowly performed, but thereafter, It gives cooling conditions to grow the coagulation cell at a speed, and adjusts the slope of the short side mold so that there is no gap between the mold and the coagulation cell.

As a method of determining the thickness of the coagulation cell, it can be known through the change in calories of cooling water flowing through the mold. As can be seen with reference to the mold installation shown in Figures 2 and 3, the cooling water flows from the bottom of the mold to the top and the temperature rises due to the heat exiting from the molten steel (A). In general, the amount of heat escaped from the molten steel through the mold, that is, the heat flux (HF) is calculated as follows using the amount of cooling water, the temperature rise and the effective area of the copper plate. The heat transfer flow rate is a concept of an average of the entire area of the copper plate and is expressed in terms of unit area and amount of heat escaping per second.

HF (MW / m ² ) = 7 × 10 ^-5 × QW × (T _out -T _in ) × 1 / A _eff

In the above formula, QW (l / min) represents the amount of cooling water per unit time flowing through the mold copper plate, T _out represents the temperature of the cooling water exiting the mold, and T _in represents the temperature of the cooling water entering the mold. The constant 7x10 ^-5 contains the specific heat of water and the unit conversion coefficient. In addition, A _eff (m ² ) represents the effective cross-sectional area of the copper plate, in which the solidification cell is in contact with the mold in the mold.

In general, it is possible to determine the heat transfer flow rate by the above formula to determine the thickness of the solidification cell in the mold, it is preferable to satisfy the value of the appropriate heat transfer flow rate for each casting speed for stable operation of the continuous casting. In order to control the value of the heat transfer flow rate, the amount of cooling water or the components of the mold flux are mostly adjusted.

As a method of determining the thickness distribution of the coagulation cells growing uniformly in the circumferential direction, a plurality of thermocouples may be provided in the mold to observe whether the temperature at each position is kept uniform. It is possible to determine the possibility of cracking by estimating the coagulation cell thickness according to the temperature change at a specific position and comparing it for each position. Alternatively, there is a method of determining the thickness and thickness distribution of the solidification cell through the increase in the cooling water temperature of each cooling water slit formed in the vertical direction for cooling the mold.

That is, when the temperature increase is smaller than the normal level, heat transfer is not easy due to the gap between the coagulation cell and the mold at that portion, and it can be estimated that the growth of the coagulation cell is slowed and the thickness becomes thin. By using a plurality of thermocouples in this way or by calculating the increase in the cooling water temperature for each cooling water slit, the thickness distribution can be grasped whether the solidification cell grows uniformly in the circumferential direction. Usually, in order to raise the uniformity of a coagulation cell, the method of adjusting the component of a mold flux is used in order to reduce a heat transfer flow rate, and to advance a coagulation | solidification slowly.

Moreover, as a method of giving a slope to the mold short side so that the solidification cell thickness of a corner part does not become thin, the slope is normally given based on the heat transfer flow velocity of a long side and a short side. For example, if it is determined that the ratio between the heat transfer flow rate of the short side and the heat transfer flow rate of the long side is within 0.8 to 1.0 to prevent the gap between the solidification cell of the corner portion and the mold, the slope of the short side mold is adjusted to adjust the ratio of the heat transfer flow rate. Is kept at 0.9. In the case of low carbon steel, the slope of the short side mold can be set to 1.1%, and in the case of medium carbon steel, it can be set to 1.2%, which is set in consideration of various characteristics such as the structure of the continuous casting machine, the chemical composition of the molten steel, and the thickness of the mold.

In the conventional method described above to prevent breakout as described above, the breakout that occurs as the solidification cell thickness of the edge portion becomes thinner is not easily solved at the source. During the continuous casting operation, the ratio of the heat transfer flow rates in the short side and the long side mold may be out of a desired range, and there are many difficulties in dynamically changing the slope of the short side mold each time.

Alternatively, if the ratio of the heat transfer flow rate of the short side to the heat transfer flow rate of the long side is less than the reference, the slope of the short side should be increased to improve the adhesion between the coagulation cell and the mold of the short side, but the coagulation cell is excessive to the short side mold because accurate control is difficult. Can be closely adhered to. As a result, the wear life of the mold may be increased, and the life of the mold may be decreased. Also, if the slope of the short side is kept higher than necessary, the solidification cell of the long side may overlap, causing a different type of buckling due to buckling. There is a problem that causes breakout.

An object of the present invention is to solve the above problems, by controlling the heat transfer flow rate and by controlling the casting speed in accordance with the change in the heat transfer flow rate, in particular to ensure a sufficient thickness of the solidification cell of the corner portion continuous to prevent breakout It is an object to provide a casting method.

According to the technical idea of the present invention for achieving the above object, in the continuous casting method, the heat transfer flow rate (HF), which is the amount of heat exiting from the molten steel through the mold, is controlled as in the following formula (1),

HF ≤ A + B × Vc ----- Equation (1)

The HF is the heat transfer flow rate (MW / m ² ), the Vc is the casting speed (m / min), the A and B are achieved by the continuous casting method characterized in that the constant set according to the respective operating conditions do.

And preferably calculating the expected heat transfer flow rate prior to casting to select a mold flux such that the calculated expected heat transfer flow rate (HF) satisfies Equation (1).

And in the case of two-steel continuous casting, calculating each of the estimated heat transfer flow rates before casting, to respectively select mold fluxes for which the calculated estimated heat transfer flow rate (HF) satisfies Equation (1). It is desirable to replace the mold flux when converting to steel grade during casting to use each mold flux.

In addition, while calculating the heat transfer flow rate continuously according to the following formula (2),

HF (MW / m ² ) = 7 × 10 ^-5 × QW × (T _out -T _in ) × 1 / A _eff ----- Equation (2)

The QW (l / min) is the amount of cooling water per unit time flowing in the mold copper plate, the T _out is the temperature of the cooling water exiting the mold, T _in is the temperature of the cooling water entering the mold, the A _eff (m ² ) is If the cross-sectional area of the copper plate is effective, and the calculated heat transfer flow rate (HF) does not satisfy the above formula (1), it is preferable to replace the mold flux with a relatively low heat transfer flow rate.

And while casting, continuously calculate the heat transfer flow rate according to the following formula (2),

HF (MW / m ² ) = 7 × 10 ^-5 × QW × (T _out -T _in ) × 1 / A _eff ----- Equation (2)

The QW (l / min) is the amount of cooling water per unit time flowing through the mold copper plate, the T _out is the temperature of the cooling water exiting the mold, T _in is the temperature of the cooling water entering the mold, the A _eff (m ² ) is It is preferable to include the step of reducing the casting speed when the cross-section is an effective cross section of the copper plate and the calculated heat transfer flow rate HF does not satisfy the above formula (1).

In addition, the casting speed is preferably reduced to 1.2 m / min.

Hereinafter, with reference to the accompanying drawings will be described in detail for the continuous casting method according to the present invention.

In the case where breakout occurs due to the thinner solidification cell at the corner portion, the solidification cell thickness distribution in the circumferential direction is precisely analyzed several times, and the process data are simultaneously obtained to accurately examine the operation characteristics. In particular, the root cause of the thinning of the solidification cell of the edge portion compared to the solidification cell of the long side or the central side of the short side is identified. To prevent it.

To this end, the slabs were collected when the breakout occurred due to the thinner solidification cell at the edge, and the average coagulation cell at the long side except the range within 30 mm of the edge for the solidification cell at the position just out of the mold. The thickness and the thinnest solidification cell thickness of the short side edge were measured. In addition, as the metal structure of the coagulation cell was examined, traces of redissolution by the convective heat of the molten steel were found. Based on this, the flow direction of molten steel ejected from the immersion nozzle was estimated.

4 is a plan view showing a drift example of the molten steel flow, Figure 5 is a graph showing the thickness distribution of the coagulation cell. Referring to FIG. 4, the main flow of molten steel discharged from the immersion nozzle does not flow in a direction perpendicular to the cross section and drift occurs, and a small amount of molten steel is supplied in the corner (a) direction, and in the corner (b) direction. It can be seen that a large amount of molten steel is supplied. As mentioned above, this can be estimated by examining the metal structure of the coagulation cell, and the solidification cell at the corner (b) portion to which a large amount of molten steel is supplied remains in the metal structure again by the sensible heat of the molten steel. there was.

Referring to FIG. 5, it can be seen that the thickness of the solidification cell of the edge portion is relatively thin compared to the thickness of the solidification cell of the long side. This phenomenon is common to the edges (a) and (b), and as the thickness of the long side coagulation cell increases, the thickness of the coagulation cell of the short side edge portion decreases further. In addition, as shown in Figure 4, when the molten steel sprayed from the immersion nozzle is not symmetrical and drift, the solidification cell of the corner (b) portion is re-dissolved by the sensible heat of the molten steel due to the inflow of a large amount of molten steel The thickness becomes thinner than the solidification cell of the corner (a) part.

As a result of comparative analysis of the heat transfer flow rate at the long side obtained by using the operation data and the experimentally obtained coagulation cell thickness, the reason is that the thicker the coagulation cell thickness at the long side, the thinner the coagulation cell thickness at the short edge side becomes. It was. When the long side coagulation cell thickness is thick, the heat transfer flow rate, which is the amount of heat exiting the long side, is relatively large, and when the long side coagulation cell thickness is thin, the heat transfer flow rate, which is the amount of heat exiting the long side, is relatively small. If a large amount of heat escapes from the molten steel through the mold during the initial formation of the coagulation cell, the coagulation cell will experience a large temperature drop from the initial coagulation temperature, thus shrinking much. On the other hand, if less calories are drawn through the mold, the degree of shrinkage of the coagulation cell will be relatively small.

In other words, when the value of the heat transfer flow rate at the long side is large, the shrinkage in the width direction of the coagulation cell increases, and at the corner of the short side, an air gap is formed between the coagulation cell and the mold, resulting in a gap. Falls out. If the contactability between the coagulation cell and the mold is poor, the heat transfer is not sufficiently achieved, so that the growth rate of the coagulation cell is greatly slowed, and thus the thickness of the coagulation cell is reduced. Accordingly, as shown in FIG. 5, the larger the value of the heat transfer flow rate at the long side, the thicker the solidification cell thickness of the long side, and the thinner the solidification cell thickness of the short side edge portion.

Figure 6 shows the measurement of the heat transfer flow rate by casting speed for the two types of mold flux used for the ultra low carbon steel in the actual operation. In the case of mold flux A, there is a relation of "heat transfer flow rate = 0.1 + 0.9 × casting speed", and in the case of mold flux B, there is a relation of "heat transfer flow rate = 0.3 + 1.0 × casting speed." In the case of using the mold flux A, since the heat flux is relatively smaller than that of the mold flux B, the shrinkage amount of the long side coagulation cell is small. As a result, the coagulation cell of the short side edge portion also grows normally, and thus the overall uniform distribution thickness is obtained. A coagulation cell was obtained.

On the other hand, in the case of using the mold flux B, the solidification cell thickness of the short side edge portion is about 50% of the thickness of the normally grown solidification side of the long side, and breakout occurs frequently due to the thinner solidification cell of the edge portion. . This is because the shrinkage in the width direction of the coagulation cell increases due to the relatively high heat transfer flow rate, and as the gap between the mold and the coagulation cell of the short side edge is widened, heat transfer is not sufficiently achieved, so that the coagulation cell thickness of the edge part is increased. It seems to be particularly thin.

Therefore, the present invention is to control the heat transfer flow rate to improve the adhesion between the mold and the solidification cell of the corner portion, and to control the casting speed in consideration of the change in the heat transfer flow rate, to secure the thickness of the solidification cell of the corner portion.

The present invention is characterized in that the value of the heat transfer flow rate (HF) during the continuous casting is controlled to below the reference value as shown in the following equation.

HF  ≤ A + B × Vc

Where HF is the heat transfer flow rate (MW / m ² ) and Vc is the casting speed (m / min). A and B are constants, and are set for each machine such as components of molten steel, mold thickness and material, and amount of cooling water flowing into the mold. In other words, it is possible to calculate from the trend data of the heat transfer flow rate and the casting speed obtained from a plurality of casting records accumulated at the factory in consideration of whether breakout has occurred according to each condition.

In order to maintain the value of heat transfer flow velocity below the said reference value, a mold flux can be used. That is, by adjusting the components of the mold flux to change the basicity, crystalline ratio and the like to change the heat transfer flow rate to be maintained below the reference value. For example, the mold flux may be selected to control the value of the heat transfer flow rate before the start of operation below the reference value. In addition, when the value of the heat transfer flow rate continuously measured during continuous casting exceeds the reference value, the value of the heat transfer flow rate may be controlled to be less than or equal to the reference value by replacing it with a mold flux that may reduce the heat transfer flow rate. In addition, even when the estimated heat transfer flow rate exceeds the reference value when the molten steel is switched to another component system during continuous casting, the value of the heat transfer flow rate can be controlled to be equal to or lower than the reference value by replacing it with a mold flux that can reduce the heat transfer flow rate. have.

In addition, the present invention can continuously reduce the casting speed when the value of the heat transfer flow rate is higher than the reference value by continuously measuring the heat transfer flow rate during the continuous casting. Increasing the heat transfer flow rate means that the amount of shrinkage in the width direction of the coagulation cell is increased. Accordingly, the contact between the mold and the coagulation cell at the short edge side is not made properly, resulting in a thinner cell thickness at the edge. As a result, breakouts can result. In order to prevent this, when the value of the heat transfer flow rate is higher than the reference value, the casting speed is decreased, so that the amount of molten steel discharged from the immersion nozzle is reduced and the flow rate of the molten steel in the mold is slowed to redissolve the solidification cell at the corner portion. Can be reduced.

In addition, the solidification cell in the corner portion can further grow by the solidification cell stays in the mold for a long time. Accordingly, the solidification cell thickness of the corner portion can be sufficiently secured, and the solidification cell of the corner portion has a sufficient thickness when exiting the mold, so that breakout can be prevented despite the action of the iron positive pressure.

At this time, the reduced casting speed can be set based on the data obtained from a number of casting experiences. Typically, no breakout occurs due to the thinner solidification cells at the corners at casting speeds of 1.2 m / min or less. Therefore, when the value of the heat transfer flow rate during continuous casting becomes higher than the said reference value, it is preferable to reduce casting speed to 1.2 m / min or less.

As described above, the present invention improves the adhesion between the mold and the solidification cell of the corner portion by controlling the heat transfer flow rate, and also controls the casting speed in consideration of the change in the heat transfer flow rate, thereby securing the thickness of the solidification cell of the edge portion to secure the edge portion. Breakout due to the thin thickness of the can be prevented.

7 is a process flowchart showing the operation of the continuous casting method according to the present invention. First, before starting the operation, the operation data such as steel grade, target casting speed, slope setting of the short side mold, and planned mold flux type are obtained. This is used to calculate the value of the expected heat transfer flow rate at the target casting speed. This can be calculated from trend data obtained from a number of casting records accumulated at the factory.

It is determined whether the calculated value of the estimated heat transfer flow rate is equal to or less than the reference value of the following formula (1).

HF ≤ A + B × Vc ----- Equation (1)

In the formula (1), HF is the heat transfer flow rate (MW / m ² ), and Vc is the casting speed (m / min). A and B are constants, and are set for each machine such as components of molten steel, mold thickness and material, and amount of cooling water flowing into the mold.

When the value of the estimated heat transfer flow rate is below the reference value, the operation is started by using the planned mold flux.

If the value of the estimated heat flux exceeds the above threshold, replace the mold flux. Also for the replaced mold flux, the mold flux which satisfies the conditions by which the value of the estimated heat transfer flow rate computed by repeating the above process is below the said reference value is prepared.

When the operation is started, the heat transfer flow rate is continuously calculated according to the following equation (2).

HF (MW / m ² ) = 7 × 10 ^-5 × QW × (T _out -T _in ) × 1 / A _eff ----- Equation (2)

In the formula (2), QW (l / min) represents the amount of cooling water per unit time flowing through the mold copper plate, T _out represents the temperature of the cooling water exiting the mold, and T _in represents the temperature of the cooling water entering the mold. The constant 7x10 ^-5 contains the specific heat of water and the unit conversion coefficient. In addition, A _eff (m ² ) represents the effective cross-sectional area of the copper plate and the area where the coagulation cell is in contact with the mold in the mold.

When the measured value of the heat transfer flow rate exceeds the above standard value, the shrinkage amount in the width direction of the coagulation cell increases, and an air gap is formed in the corner portion of the mold, so that the solidification cell growth of the edge portion is slowed or thinned. Loss is believed to occur. Thus, the casting speed is reduced. At this time, the casting speed is preferably reduced to 1.2 m / min or less.

Thereafter, similarly, the heat transfer flow rate is continuously calculated according to Equation (2). If the value of the heat transfer flow rate is kept below the reference value again, the casting speed is increased to the initial target casting speed to allow the casting operation to proceed normally.

Thus, the value of heat transfer flow rate is controlled to below the said reference value, and it completes by operating.

In the above, when the value of the heat transfer flow rate exceeds the above reference value, the casting speed is adjusted, but the present invention is not limited thereto, and the mold flux may be replaced. That is, when the value of the heat transfer flow rate during continuous casting exceeds the said reference value, the mold flux which reduces a heat transfer flow rate may be input and controlled.

In addition, in the case of continuously casting the molten steel of the new ladle after casting all the molten steel of the old ladle, the heat transfer flow rate can be controlled through the same process as described above. That is, by continuously measuring the heat transfer flow rate, the casting speed is decreased when the value of the heat transfer flow rate exceeds the reference value, and then the casting speed is increased to the target casting speed when the value of the heat transfer flow rate is controlled again below the reference value. Allow this to proceed normally. Alternatively, instead of adjusting the casting speed, the mold flux may be replaced and added.

In addition, in the case of two-steel continuous casting in which molten steel of different component systems are continuously cast, each mold flux meeting the condition of the above formula (1) is prepared in advance by calculating the expected heat transfer flow rate before starting the operation. Accordingly, when molten steel is converted to another component system during continuous casting, the mold flux may be immediately replaced to control the value of the heat transfer flow rate to be equal to or less than the reference value. Alternatively, as described above, the heat transfer flow rate may be continuously measured and the casting operation may be performed accordingly.

As described above, the present invention can sufficiently secure the thickness of the solidification cell at the corner portion by controlling the value of the heat transfer flow rate to be equal to or less than the reference value or by controlling the casting speed according to the change of the heat transfer flow rate. Accordingly, it is possible to prevent an operation accident in which breakout occurs due to the action of the iron positive pressure after exiting the mold due to the thinner solidified cell at the corner portion.

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

EXAMPLE

In the casting of ultra low carbon steel, the slope of the short-side mold was maintained at 1.1%, and the seven-row casting was performed using a mold flux having a heat transfer flow rate of about 1.6 MV / m ² under the condition of a target casting speed of 1.5 m / min.

Historical operation data in the continuous casting plant to which the method according to the present invention was applied was analyzed precisely, so that constant A in Equation (1) was set to 0.30 and constant B was set to 1.1. That is, the embodiment is to control the value of the heat transfer flow rate (HF) to 1.95MW / m ² or less, which is a reference value (0.30 + 1.1 × casting speed).

8 is a graph showing the heat transfer flow rate and the casting speed of the embodiment according to the present invention. After continuously casting the four ladle molten steels for about 2.5 hours, when the fifth ladle was maintained, the casting speed was 1.5 m / min, and the heat transfer flow rate rapidly increased to exceed the reference value of 1.95 MW / m ² . It was. Accordingly, the casting speed was reduced to 1.2 m / min, and the casting operation was performed. After replacing the sixth ladle, the heat transfer flow rate gradually decreased. When the value of the heat flux decreased below the reference value, the casting speed was increased back to the target casting speed of 1.5 m / min, so that the casting work of the sixth and seventh ladle molten steels could be normally performed. As described above, by controlling the heat transfer flow rate and controlling the casting speed according to the present invention, it is possible to sufficiently secure the thickness of the solidification cell of the corner portion and prevent breakout in advance.

[Comparative Example]

In the casting of ultra low carbon steel, the slope of the short-side mold was maintained at 1.1%, and the seven-row casting was performed using a mold flux having a heat transfer flow rate of about 1.6 MV / m ² under the condition of a target casting speed of 1.5 m / min.

In the comparative example, the casting operation was performed without changing the casting speed according to the change of the heat transfer flow rate.

9 is a graph showing the heat transfer flow rate and the casting speed of the comparative example according to the prior art. When about 3 hours and 15 minutes after the start of casting, the heat transfer flow rate rapidly increased at the casting speed of 1.47 m / min, and the casting operation was performed as it was even though the reference value according to Equation (2) was exceeded. Here, due to the sharply increased heat transfer flow rate, the amount of shrinkage in the width direction of the coagulation cell increases, and thus an air gap is generated between the coagulation cell and the mold of the short side edge part, and thus, the thickness of the coagulation cell of the edge part becomes thin. have. When the heat transfer flow rate increased about 100 seconds, the thinned coagulation cell at the edge portion exited the mold and moved to about 1m below, where the coagulation cell did not overcome the iron static pressure and breakout occurred.

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

The present invention improves the adhesion between the mold of the corner portion and the solidification cell by controlling the heat transfer flow rate, and also controls the casting speed according to the change of the heat transfer flow rate, thereby sufficiently securing the thickness of the solidification cell at the edge portion. Accordingly, the occurrence of breakout due to the thinner solidified cell at the edge portion can be prevented, and the process stability can be improved and the productivity can be improved.

Claims (6)

In the continuous casting method, The heat transfer flow rate (HF), which is the amount of heat exiting the mold from the molten steel, is controlled as in Equation (1) below. HF ≤ A + B × Vc ----- Equation (1) The HF is the heat transfer flow rate (MW / m ² ), the Vc is the casting speed (m / min), the A and B is a continuous casting method characterized in that the constant set according to the respective operating conditions. The method according to claim 1, Calculating an expected heat transfer flow rate prior to casting, and selecting a mold flux such that the calculated expected heat transfer flow rate (HF) satisfies Equation (1). The method according to claim 1, For two steel continuous casting, Calculating each expected heat transfer flow rate prior to casting, selecting each of the mold fluxes for which the calculated expected heat transfer flow rate (HF) satisfies Equation (1), Continuous casting method characterized in that the mold flux is replaced by the input when switching to the second steel type during casting to use each of the selected mold flux. The method according to any one of claims 1 to 3, While casting, the heat flux is continuously calculated according to the following formula (2), HF (MW / m ² ) = 7 × 10 ^-5 × QW × (T _out -T _in ) × 1 / A _eff ----- Equation (2) The QW (l / min) is the amount of cooling water per unit time flowing in the mold copper plate, the T _out is the temperature of the cooling water exiting the mold, T _in is the temperature of the cooling water entering the mold, the A _eff (m ² ) is Effective cross section of copper plate, If the calculated heat transfer flow rate (HF) does not satisfy the formula (1), the method comprising the step of replacing the mold flux with a relatively low heat transfer flow rate comprising the step of inputting. The method according to any one of claims 1 to 3, During casting, the heat transfer flow rate was continuously calculated according to the following formula (2), HF (MW / m ² ) = 7 × 10 ^-5 × QW × (T _out -T _in ) × 1 / A _eff ----- Equation (2) The QW (l / min) is the amount of cooling water per unit time flowing in the mold copper plate, the T _out is the temperature of the cooling water exiting the mold, T _in is the temperature of the cooling water entering the mold, the A _eff (m ² ) is Effective cross section of copper plate, And reducing the casting speed when the calculated heat transfer flow rate (HF) does not satisfy the above formula (1). The method according to claim 5, Continuous casting method characterized in that the casting speed is reduced to 1.2m / min.

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