KR101400042B1 - Method for producing high quality slab - Google Patents

Abstract

The present invention relates to a method for manufacturing a high-quality cast steel, comprising the steps of: periodically measuring and collecting a level of a hot-dip tread in a mold; counting a number of abnormalities exceeding a set reference range, Calculating a hot-walled hit ratio using the total number of times of measurement, calculating a mold slag incorporation rate using the hot-wall surface hit ratio, comparing the mold slag incorporation rate with a reference admixture index tolerance, and comparing the mold- If it is within the exponential permissible rate, it provides a step of putting into the post-processing after the surface grinding treatment.

Description

[0001] METHOD FOR PRODUCING HIGH QUALITY SLAB [0002]

The present invention relates to a method for manufacturing a high-quality cast steel, and more particularly, to a method for manufacturing a cast steel such as a high-quality cast steel such as a slab, which comprises predicting the quality of a plate using a mold slag incorporation ratio, And a manufacturing method thereof.

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 casting mold for forming a tundish and a molten steel that is guided in the tundish first to form a cast slab having a predetermined shape, and a casting member connected to the mold, A plurality of pinch rolls.

In other words, molten steel introduced from the ladle and the tundish is formed into a cast slab having a predetermined width, thickness and shape in the mold and is transported through the pinch roll, and the slab transferred through the pinch roll is cut by a cutter A slab having a predetermined shape or a cast such as a bloom or a billet.

Related prior art is Korean Patent Publication No. 2010-0074482 (published on Mar. 07, 2010, titled: Improvement of surface quality of cast steel).

The present invention relates to a method for producing a cast slab by calculating the hot-dip angle hit ratio through the variation of the hot-dip level of the mold, calculating the mixed slag inclusion ratio using the calculated hot-dip angle hit ratio, and then adjusting the degree of the slab inclusion inclusions in the cast And to provide a method for manufacturing a high-quality cast steel.

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

In order to achieve the above object, the present invention provides a method for manufacturing a high-quality cast steel, comprising the steps of: periodically measuring and collecting a level of a mold- Calculating a tangential plane hit rate using the number of abnormal times and the total number of measurement times that the tangent level value collected during the unit period exceeds the set reference range when the set unit period has elapsed; Calculating a mold slag incorporation rate using the hot water surface hit ratio; Comparing the mold slag incorporation rate with a reference admixture index allowance; And adding the mold slag addition rate to the post-process if the incorporation rate of the mold slag exceeds the reference admixture index tolerance, followed by further removing the defective portion after surface grinding treatment.

If the mold slag mixing rate is within the allowable standard admixture index, it may be added to the post-surface finishing process.

Further, the hot water tank hit rate can be calculated by the following relational expression.

In this case, the total number of times of measuring the level of the bath surface level is the number of times the bath surface level is measured during the unit period, and the number of times of exceeding the reference value is the number of times that the bath surface level value collected during the unit period is out of the reference range.

Further, the mold slag incorporation rate can be calculated by the following relational expression.

Relation

The unit cycle may be set based on any one of a casting time, a length of a casting casting, and a molten steel discharge amount.

As described above, according to the present invention, by calculating the mixing rate of the mold slag using the fluctuation amount of the melt level in the mold, it is possible to determine the degree of milling of the plate to be produced, thereby further processing the cast steel having the mixed- Can be improved.

1 is a conceptual view showing a continuous casting machine according to an embodiment of the present invention, focusing on the flow of molten steel.
2 is a view showing a high-quality cast steel production apparatus according to an embodiment of the present invention.
3 is a view showing defects on the slab surface due to the inflow of mold slag.
Figure 4 is a diagram showing product surface defects due to mold slag inflow.
5 is a flowchart illustrating a method for manufacturing a high-quality cast steel according to an embodiment of the present invention.
6 is a view showing a result of measurement of the mold bath surface level.
FIG. 7 is a graph showing the relationship between the hot water surface hit ratio and the inclusion of the slag with respect to the variation of the hot water level of the mold.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols whenever 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 view showing a continuous casting machine according to an embodiment of the present invention, focusing on the flow of molten steel.

Continuous casting is a casting process in which a molten metal is continuously cast into a bottomless mold while continuously drawing a steel ingot or steel ingot. 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, secondary cooling bands 60 and 65, and a pinch roll 70.

A tundish 20 is a container for receiving molten metal from a ladle 10 and supplying molten metal to a 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.

Mold 30 is typically made of water-cooled copper and allows the molten steel taken to be first 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, mainly the walls, of the mold 30 may be rotated to be 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 is formed such that a solidified shell or a solidified shell 81 is formed so as to maintain the shape of the casting pluck pulled out from the mold 30 and to prevent the molten metal from being hardly outflowed from flowing out. . 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. 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. The powder is added to the molten metal in the mold 30 to become slag and the lubricant of the mold 30 and the solidification shell 81 as well as the prevention and oxidation of the molten metal in the mold 30, It also functions to absorb the emerging nonmetallic inclusions. 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 bands 60 and 65 further cool the molten steel that has been 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. Most of the solidification of the cast steel is accomplished by the secondary cooling.

The pulling device employs a multi-drive type or the like in which a plurality of pinch rolls (70) are used so as to pull out the casting slides without slipping. The pinch roll 70 pulls the solidified leading end portion 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.

In the continuous casting machine constructed as described above, the molten steel M contained in the ladle 10 flows 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 solidifying shell 81 in the casting direction as the pinch roll 70 (Fig. 1) pulls the tip end portion 83 of the fully-solidified cast slab 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 steel 80 reaches one point 85, the cast steel 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 view showing a high-quality cast steel making apparatus according to an embodiment of the present invention. The cast steel making apparatus 100 includes a hot-dip level sensor 120, a storage unit 130, an input unit 140, a display unit 150, And a processing unit (160).

The bath surface level sensor 120 is fixed on the upper side of the mold 30 and periodically measures the bath surface level according to the bath surface flow of the molten steel in the mold 30. Here, the bath surface level sensor 120 may be an eddy current type sensor for measuring the bath surface level by analyzing the induced voltage caused by the eddy current of the molten steel due to the magnetization of the high frequency current.

The storage unit 130 may store the unit cycle for measuring the level of the hot water level, the reference range for determining abnormality of the hot water level, the hot water level value and the hot water level hit rate, which are measured periodically, under the control of the central processing unit 160.

The input unit 140 is configured to receive various operation commands and setting reference values from the outside, and to transmit the operation command and the setting reference values to the central processing unit 160.

The display unit 150 may display the bath surface level collected through the bath surface level sensor 120, the bath surface hit rate per hour, and the predicted quality of the billet quality, in a character or graph, under the control of the central processing unit 160.

The central processing unit 160 collects the tare surface level value measured by the tare surface level sensor 120 and then calculates the tare surface hit rate using the number of abnormal times and the total number of times the tare surface level value collected during the set unit period deviates from the set reference range The calculated rate of inclusion of the mold slag is used to calculate the inclusion rate of the mold slag, and the quality of the slab is estimated using the calculated mold slag incorporation rate, and the progress of the subsequent process of the casting is controlled.

3mm 이내의 범위로 설정될 수 있다. Here, the reference range is set based on the molten steel level (mold level) in the mold 30

And can be set within a range of 3 mm or less.

The unit cycle can be set based on the casting time (for example, 10 minutes), the length of the cast steel 80 (for example, 20 m), or the molten steel discharge amount. In the case where the unit cycle is a molten steel discharge amount, the central processing unit 160 can calculate the molten steel discharge amount using the width, thickness, density, and peripheral speed of the preformed casting spindle. If the unit cycle is time, When the period is the length of the casting slab 80, the casting length of the cast slab 80 can be obtained using the peripheral speed. The circumferential speed is calculated using the rotational speed of the pinch roll 70, which is a known matter, and thus a detailed description thereof will be omitted.

As described above, in the central processing unit 160 of the present invention, the waffle surface level value collected during the set unit period after collecting the measured waffle surface level value as shown in FIG. 3 in the waffle surface level sensor 120 is divided into units And the amount of mold slag inclusion is calculated by using the calculated total inclusion ratio of the tongue, and the degree of quality of the plate is predicted by comparing the incorporation rate of the mold slag and the calculated inclusion rate of the reference mold slag And control the progress of the next process of the casting.

Generally, in the case of automobile exterior panels, it is possible to produce solidified alloying elements, particularly carbon with extremely few extremely low carbon steel of not more than 70 ppm in order to achieve high-quality formation. However, due to the mold level fluctuation caused by the molten steel flow in the mold 30 during casting, the mold powder is brought into contact with the molten steel and the mold slag is mixed in the molten steel, There arises a problem that defects are formed.

The sheet material on which the large scale defects are formed on the surface of the slab in this manner causes a problem that a part of the product tears during the final product molding as shown in Fig.

In the present invention, by predicting the incorporation rate of the mold slag using the fluctuation amount of the melt level in the mold, and predicting the quality of the plate to be produced through the predicted mixing ratio of the mold slag, the unnecessary subsequent process of the slab within the mold slag inclusion reference value In order to prevent a reduction in productivity and unnecessary cost wasted in advance.

In an embodiment of the present invention, it is preferable to use an automotive exterior plate material which is required to have a beautiful surface condition as a material used for parts exposed to the outside of the vehicle, among the cast slabs.

FIG. 5 is a flow chart illustrating a method for manufacturing a high-quality cast steel according to an embodiment of the present invention. First, the casting mold level sensor 120 periodically measures the mold casting mold level value. At this time, the bath surface level value according to the flow of the molten steel in the mold 30 is periodically collected from the bath surface level sensor 120, and the collected bath surface level value as shown in FIG. 6 is sequentially . Of course, the bath surface level sensor 120 periodically measures the bath surface level according to the flow of the molten steel in the mold, for example, in units of one second, and transfers the measured level to the central processing unit 160. At this time, although the bath surface level sensor 120 may periodically measure the bath surface level, the central processing unit 160 may calculate the corresponding bath surface level value measured in the set period among the measured bath surface level values measured in real time by the bath surface level sensor 120 It can also be collected periodically.

Then, the central processing unit 160 calculates a waxing hit ratio using the counted number of times that the counted total measurement count and the waxing plane level value are out of the reference range (S20).

3mm 이내의 범위로 설정될 수 있다. 예컨대, 용강레벨이 800mm일 경우 기준범위는 797~803mm 이내의 범위로 설정될 수 있다. In the above, the reference range of the bath surface is determined based on the molten steel level in the mold 30

And can be set within a range of 3 mm or less. For example, when the molten steel level is 800 mm, the reference range may be set within a range of 797 to 803 mm.

At this time, in the embodiment of the present invention, as shown in Fig. 6, a portion exceeding 3 mm, which is the reference range, is detected.

Here, the method for obtaining the hot water surface hit rate is expressed by the following relational expression 1.

Relationship 1

At this time, the total number of times of measuring the level of the bath surface level is the number of times the bath surface level is measured during the unit period, and the number of times of exceeding the reference value is the number of times the bath surface level value collected during the unit period is out of the reference range. Here, it is preferable that the total number of times of measuring the level of the bath surface level means the number of times of measurement per one piece of the steel strip.

For example, when the unit cycle is 10 m (length of the casting drum), the number of times of the bath surface level of 100 times (the total number of times of measurement) is measured during the unit period and the number of times the measured bath surface level value is out of the reference range is five , The hit rate will be '95'.

The thus obtained bath surface hit rate is stored in the storage unit 130 together with the time information.

Subsequently, the central processing unit 160 obtains the rate of hot water surface area per unit cycle, and calculates the mold slag incorporation rate using the hot water surface hit ratio (S30). Here, the method of determining the incorporation rate of the mold slag is as shown in the following relational formula 2.

Relation 2

Subsequently, the mold slag incorporation rate is compared with the reference admixture index allowance (S40). At this time, the reference incorporation rate is preferably within 3 to 5%.

Table 1 below shows the hot water surface hit ratio and the mold slaad incorporation rate, and the correlation formula between the hot water surface hit ratio and the mold slag incorporation rate is as shown in the relationship (2). In FIG. 7, the dot is actual data between the hot-face hit ratio and the mold slag incorporation rate, and the solid line is a predictive model fitted with the actual data in advance, and the actual and predicted models are somewhat matched (R ² => about 89%) appear.

Table 1

Subsequently, when the mold slag incorporation rate is within the allowable standard inclusion index, surface grinding is performed (S50). At this time, if the mold slag incorporation rate exceeds the reference admixture index allowance, the surface rubbing process S50 is performed first, and then the process of secondly removing the joint portion is performed (S60).

As shown in Table 1, when the incorporation rate of the mold slag is compared with the reference incorporation rate, only the automatic surface-finishing treatment corresponding to the primary treatment is carried out if the mold slag inclusion ratio is less than 5%, and when the molding slag inclusion ratio exceeds 5% It is preferable to proceed with the defect addition and removal in addition to the automatic surface finishing as the treatment.

Then, when the surface grinding process is completed, the process is put into a post-process (S70).

Therefore, unnecessary secondary treatment is not performed on the cast slab having a low content of the mold slag, so that the productivity can be improved, the defect of the cast slab can be predicted, and defects can be further removed to produce a high quality cast slab.

The above-described high-quality cast steel making method is not limited to the construction and operation of the above-described embodiments. The embodiments may be configured so that all or some of the embodiments may be selectively combined so that various modifications may be made.

10: Ladle 15: Shroud nozzle
20: tundish 25: immersion nozzle
30: mold 31: left short side
35: right short side 40: mold oscillator
50: Powder feeder 51: Powder layer
52: liquid fluidized bed 53: lubricating layer
60: Support roll 65: Spray
70: pinch roll 80: performance cast
81: Solidification shell 82: Non-solidified molten steel
91: Cutting point 120: Wet surface level sensor
130: storage unit 140: input unit
150: display unit 160: central processing unit

Claims (5)

Periodically measuring and collecting the melt level of the mold in the mold;
Calculating a tangential plane hit rate using the number of abnormal times and the total number of measurement times that the tangent level value collected during the unit period exceeds the set reference range when the set unit period has elapsed;
Calculating a mold slag incorporation rate using the hot water surface hit ratio;
Comparing the mold slag incorporation rate with a reference admixture index allowance; And
And adding the removed portion to the post-process after the surface-finishing process if the mold slag mixing rate exceeds the reference admixture index allowance,
Wherein the hot-dipper hit ratio is calculated by the following equation (1), and the mixing ratio of the mold slag is calculated by the following equation (2).
Relationship 1

In this case, the total number of times of measuring the level of the bath surface level is the number of times the bath surface level is measured during the unit period, and the number of times of exceeding the reference value is the number of times that the bath surface level value collected during the unit period is out of the reference range.
Relation 2

The method according to claim 1,
And adding the molded slag to a post-finishing step after the surface grinding treatment if the incorporation rate of the mold slag is within a permissible reference admixture index.
delete delete The method according to claim 1,
Wherein the unit cycle is set based on any one of a casting time, a length of a casting casting and a molten steel discharge amount.

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