KR101529287B1

KR101529287B1 - Continuous casting methods

Info

Publication number: KR101529287B1
Application number: KR1020140010186A
Authority: KR
Inventors: 하태준; 권효중; 문홍길
Original assignee: 현대제철 주식회사
Priority date: 2014-01-28
Filing date: 2014-01-28
Publication date: 2015-06-16

Abstract

Disclosed is a continuous casting method. According to one aspect of the present invention, the continuous casting method comprises: a tapping step of tapping molten steel with a continuous casting mold; a calculating step of calculating index of bulging occurrence possibility defined as a function of a carbon equivalent of the molten steel, the super heat degree deviation of the molten steel, a heat rejection rate in the continuous casting mold, and the slab thickness of a slab manufactured from the molten steel; and a deciding step of predicting kinetic bulging occurrence possibility in a strand which is discharged from the continuous casting mold and passes through a strand cooling device by comparing the index of bulging occurrence possibility and the predetermined value.

Description

Continuous Casting Methods {CONTINUOUS CASTING METHODS}

The present invention relates to a continuous casting method.

Iron ore is manufactured by hot-wire processing. The ironmaking process is carried out by adding iron ore to the blast furnace together with coke and limestone. The sintering process includes a sintering process in a broad sense. The molten iron is manufactured as molten steel through the steelmaking process. The steelmaking process includes pre-treatment of molten iron, steelmaking, secondary refining and the like. Molten steel is formed into semi-finished steel products such as slabs, blooms, billets and the like through a continuous casting process. The steel semi-finished product is rolled and finally formed into a finished product such as a rolling coil. In a continuous casting process, molten steel flows from a ladle into a continuous casting mold via a tundish. The molten steel is first cooled in the performance mold. That is, the molten steel forms a solidified shell as solidification proceeds from the molten steel surface adjacent to the playing mold into the molten steel. A strand of molten steel and a solidified shell exits the performance mold and is secondarily cooled while passing through the strand cooling device. The strands are completely cooled while passing through the strand cooling device, and then cut into pieces by a cutter to produce a cast.

The background art of the present invention is disclosed in Korean Patent Laid-Open Publication No. 10-2011-0109200 (October 10, 2011, continuous casting method).

Embodiments of the present invention aim to provide a continuous casting method capable of predicting the possibility of dynamic bulging in the course of a strand discharged from a performance mold through a strand cooling device.

According to an aspect of the present invention, there is provided a method of making a casting machine, A calculating step of calculating a bulging probability index defined as a function of a carbon equivalent of the molten steel, an overheating degree deviation of the molten steel, a total heat amount in the performance mold, and a billet thickness produced from the molten steel; And a judging step of comparing the bulging probability index with a predetermined value to predict the possibility of occurrence of dynamic bulging in the strand discharged from the performance mold and passing through the strand cooling device .

The bulging probability index can be calculated from the following equation (1).

(1)

Y = A + B x X1 + C x X2 + D x X3 + E x X4

(A), (B), (C), and (C), respectively. D: constant)

The carbon equivalent can be defined to satisfy the following equation (2).

(2)

X1 = [C] - 0.1 x [Si] + 0.04 x [Mn] - 0.04 x [Cr] + 0.1 x [Ni] - 0.1 x [Mo]

(X1: carbon equivalent (parts by weight), [C]: component content (parts by weight) of C based on 100 parts by weight of the total amount of molten steel, [Si] (Parts by weight), [Mn]: component content (parts by weight) of Mn based on 100 parts by weight of the total amount of molten steel, Component content (parts by weight) of Ni in a total amount of 100 parts by weight, [Mo]: component content (parts by weight) of Mo based on 100 parts by weight of the total molten steel)

B = 51.5, C = 0.269, D = -13.8 and E = 0.308 in the above constants, when the molten steel has a carbon equivalent of 0.09 parts by weight to 0.13 parts by weight based on 100 parts by weight of the total.

The preset value may be ten.

In the determining step, it can be predicted that if the bulging probability index is greater than or equal to the predetermined value, dynamic bulging may occur in the strand that is discharged from the performance mold and passes through the strand cooling device.

And a control step of decreasing the casting speed of the molten steel until the bulging probability index becomes less than the predetermined value if the bulging probability index is greater than or equal to the predetermined value.

According to embodiments of the present invention, by predicting the likelihood that dynamic bulging may occur during the course of the strand being discharged from the performance mold through the strand cooling device, it is possible to predict the fluctuation of the melt surface of the molten steel in the performance mold, It is possible to predict the possibility of the incorporation of the mold powder caused by the fluctuation of the melt surface of the molten steel and the possibility of the occurrence of the billet crack due to this. As a result, high quality cast steel can be produced by controlling the operating conditions so that dynamic stranding does not occur in the strand.

1 is a view illustrating a continuous casting method according to an embodiment of the present invention.
2 is a view showing a continuous casting apparatus.
Fig. 3 is a graph showing the correlation between the carbon equivalent of the molten steel and the degree of stabilization of the bath surface level, and the degree of stabilization of the bath surface level in the performance mold.
4 is a graph showing the correlation between the degree of superheat of the molten steel and the degree of stabilization of the level of the bath surface.
5 is a graph showing the correlation between the thickness of the cast steel produced from the molten steel and the degree of stabilization of the level of the casting surface.
6 is a graph showing the correlation between the bulging probability index and the batting level hit rate.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Hereinafter, preferred embodiments of the continuous casting method according to the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or corresponding elements, The description will be omitted.

1 is a view illustrating a continuous casting method according to an embodiment of the present invention.

Referring to FIG. 1, a continuous casting method according to an embodiment of the present invention includes a ladle step S100, a calculating step S110, a determining step S120, and a controlling step S130.

First, molten steel is introduced into the performance mold (S100).

2 is a view showing a continuous casting apparatus.

Referring to FIG. 2, the molten steel 10 is introduced into the performance mold 120 through a submerged entry nozzle 110 through a tundish 100 in a ladle.

The molten steel 10 is first cooled in the performance mold 120.

That is, the molten steel 10 forms a solidified shell 11 as solidification progresses from the molten steel surface contacting the performance mold 120 into the molten steel. To this end, the performance mold 120 may be supplied with a cooling fluid, for example, cooling water.

The strand 12 exiting the playing mold 120 is secondarily cooled in the strand cooling apparatus. The strand 12 includes molten steel 10 and a solidifying shell 11 and means an intermediate product which is formed during the process of forming the molten steel 10 into the cast steel 13 through the continuous casting apparatus.

The strand cooling apparatus may include a plurality of guide rollers 130 that guide strand 12 in contact with both sides of strand 12 and a plurality of cooling nozzles 140 that inject cooling fluid to strand 12 . The cooling fluid supplied through the cooling nozzle 140 may be different or the same as the cooling fluid supplied to the performance mold 120, and may include, for example, cooling water.

The strands 12 can undergo bulging due to ferro-static pressure in the region A between the two guide rollers 130 disposed spaced apart along the conveying direction of the strands 12 . That is, a phenomenon that the solidifying shell 11 is swollen due to the static pressure of the molten steel 10 among the strands 12 may occur. The strands 12 can also be pressed by two guide rollers 130 which are in contact with both sides of the strands 12 in the area in contact with the guide rollers 130 and arranged so as to face each other. As a result, the strands 12 are repeatedly expanded and contracted by the iron static pressure of the molten steel 10 and the plurality of guide rollers 130 while passing through the strand cooling device. This phenomenon is called dynamic bulging. The dynamic bulging may result in fluctuation of the melt surface level of the molten steel bath surface 14 in the playing mold 120. [ The variation in the level of the melt surface of the molten steel bath surface 14 due to the dynamic bulging can occur up to about 10 mm to 20 mm at the maximum. As a result, there is a high possibility that a mold powder is mixed into the molten steel 10 or a crack is generated in the cast steel 13. Therefore, in order to produce the high-quality cast steel 13, it is necessary to predict the possibility of dynamic boring occurring in the strand 12, and to control the operating conditions so that dynamic boring does not occur in the strand 12 according to the prediction result It is important. On the other hand, the dynamic bulging shows a tendency to deepen when the initial solidification of the molten steel is unevenly performed in the performance mold 120. The unevenness of the solidifying shell 11 due to the shrinkage reaction due to the phase transformation at the initial solidification, Dynamic bulging can be particularly severe in high peritectic steels compared to steel.

The strands 12 are completely cooled while passing through the strand cooling device and then cut by a cutter 150 to produce a slab 13 such as a slab, bloom, billet or the like.

Next, a bulging probability index, which is defined as a function of the carbon equivalent of the molten steel, the deviation of the superheating degree of the molten steel, the total amount of heat in the performance mold, and the thickness of the cast steel produced from the molten steel, is calculated (S110).

Fig. 3 is a graph showing the correlation between the carbon equivalent of the molten steel and the degree of stabilization of the bath surface level, and the degree of stabilization of the bath surface level in the performance mold.

Referring to the bar graph in FIG. 3, it can be confirmed that there is a correlation between the carbon equivalent of the molten steel and the degree of stabilization of the bath surface level when the molten steel is composed of a capillarity having a carbon equivalent of 0.09 weight part to 0.13 weight part. That is, as the carbon equivalent of the molten steel increases, the degree of stabilization of the bath surface level decreases. If the carbon equivalent of the molten steel is changed, the unevenness of the solidification shell due to the entrapment reaction is changed, and the degree of stabilization of the tank surface level is changed.

The carbon equivalent of molten steel refers to a value obtained by converting the constituent components of molten steel into the content of carbon (C), and a weight portion may be used as a unit.

The degree of stabilization of the level of the hot water level means the degree of stabilization of the hot water level of the molten steel in the performance mold without fluctuating up and down. That is, when the fluctuation amount of the melt surface level of molten steel is large in the performance mold, the stability level of the melt surface level is low.

The degree of stabilization of the bath surface level may be, for example, a bath surface level hit rate. The bath surface level hit rate is calculated as a ratio of the number of times that the bath surface level is within the predetermined allowable range with respect to the total number of measurement times of the bath surface level by measuring the bath surface level at a predetermined time interval. When the hot water level hit rate is high, the degree of stabilization of the hot water level can be considered to be high, so that the hot water level level hit rate and the hot water level stabilization degree can be used with the same meaning. However, the degree of stabilization of the hot-dip level does not necessarily have to be a hot-dip level hit rate, and other types of measured values other than the hot-dip level hit rate may be used as long as the degree of stabilization of the hot-dip level can be expressed. Meanwhile, the time interval for measuring the level of the bath surface level to calculate the bath surface level hit rate can be set to a sufficiently small size such that the maximum value and the minimum value of the bath surface level can be confirmed for each oscillation period of the bath surface level. In addition, the allowable range of the bath surface level used for calculating the bath surface level hit rate can be set to 3 mm respectively up and down with reference to the standard bath surface level. The standard bake level can be set according to the operation management standard at an arbitrary position between the lower end and the upper end of the performance mold.

As described above, since the dynamic bulging may cause a change in the level of the melt surface of the molten steel bath surface in the performance mold, the possibility that the dynamic bulging has occurred may be increased because the degree of stabilization of the melt surface level is reduced. Therefore, the carbon equivalent of molten steel, which is correlated with the degree of stabilization of the hot water level, is a major factor affecting the possibility of dynamic bulging in the forming steel.

Referring to the bar graph and the line graph in FIG. 3, it can be seen that there is a correlation between the amount of heat transferred from the performance mold and the degree of stabilization of the tumbling level. That is, when the total heat of the performance mold is relatively low, for example, when the carbon equivalent of the molten steel is in the range of 0.12 to 0.13 parts by weight, It is confirmed that the carbon equivalent of the molten steel is reduced compared to the stabilization level of the bath surface level in the case of 0.09 weight part to 0.10 weight part. As the amount of heat in the casting mold is relatively low, the thickness of the solidification shell becomes relatively thin and the possibility of bulging is relatively increased.

The total heat amount in the performance mold means the heat energy per unit time discharged from the molten steel to the performance mold through the unit area where the molten steel and the performance mold come into contact with each other, and MW / m2 can be used as a unit.

The degree of stabilization of the level of the hot-dip level means the degree of stabilization of the hot-dip level of the molten steel in the performance mold without fluctuating up and down, for example, it may be a hot-dip level hit rate.

As described above, since the dynamic bulging may cause a change in the level of the melt surface of the molten steel bath surface in the performance mold, the possibility that the dynamic bulging has occurred may be increased because the degree of stabilization of the melt surface level is reduced. Therefore, the amount of heat in the performance mold, which is correlated with the level of stabilization of the hot water level, is a major factor affecting the possibility of dynamic bulging in the canopy.

4 is a graph showing the correlation between the degree of superheat of the molten steel and the degree of stabilization of the level of the bath surface.

Referring to FIG. 4, there is a correlation between the degree of superheat of the molten steel and the degree of stabilization of the bath surface level. That is, when the deviation of the superheating degree of the molten steel is too low or high, it can be confirmed that the degree of stabilization of the melt surface level is reduced. If the superheating degree of the molten steel is too low, the solidification rapidly proceeds in the performance mold, and the possibility of occurrence of an uneven solidification shell increases. If the superheating degree deviation is too large, the thickness of the solidification shell becomes thin, .

The deviation of the superheat degree of molten steel means the absolute value of the difference between the solidification temperature and the actual temperature of molten steel, and can be used in ° C. Here, the solidification temperature of molten steel means the theoretical solidification temperature of molten steel plus a predetermined value to the actual solidification temperature of molten steel. For example, the theoretical solidification temperature of molten steel is set to be 20 to 30 ° C higher than the actual solidification temperature for stable casting, and 22 ° C for porosity steel. In FIG. 4, the deviation of superheat of molten steel is expressed by a value obtained by subtracting the theoretical solidification temperature which is 22 ° C higher than the actual solidification temperature at the actual temperature of the molten steel, not the absolute value.

As described above, since the dynamic bulging may cause a change in the level of the melt surface of the molten steel bath surface in the performance mold, the possibility that the dynamic bulging has occurred may be increased because the degree of stabilization of the melt surface level is reduced. Therefore, the deviation of the superheat of molten steel, which is correlated with the degree of stabilization of the bath surface level, is a major factor affecting the possibility of dynamic bulging in the forming steel.

5 is a graph showing the correlation between the thickness of the cast steel produced from the molten steel and the degree of stabilization of the level of the casting surface.

Referring to FIG. 5, it can be seen that there is a correlation between the thickness of the billet and the degree of stabilization of the brewing surface level. That is, for example, when the carbon equivalent of the molten steel is 0.09 parts by weight to 0.10 parts by weight, it can be seen that the degree of stabilization of the bath surface level at a slab thickness of 250 mm is smaller than the stabilization level of the slab surface at a slab thickness of 225 mm. At this time, the slab width is regarded as constant. As the thickness of the cast steel increases, the thickness of the solidified shell in the cast steel becomes almost the same, but the amount of molten steel that is not solidified in the cast steel increases. As a result, the steel static pressure and the size of the bulge increase, It also increases in size.

Mm may be used as a unit of the thickness of the billet.

As described above, since the dynamic bulging may cause a change in the level of the melt surface of the molten steel bath surface in the performance mold, the possibility that the dynamic bulging has occurred may be increased because the degree of stabilization of the melt surface level is reduced. Therefore, the thickness of the billet having a correlation with the degree of stabilization of the bath surface level is a major factor affecting the possibility of dynamic bulging in the canopy.

As described above, since the carbon equivalent, the superheat deviation, the heat quantity and the thickness of the billet are the main factors affecting the possibility of dynamic bulging, it is possible to calculate the bulging probability index defined by these functions, So that the possibility of dynamic bulging in the strand passing through the strand cooling device can be predicted.

(1)

Y = A + B x X1 + C x X2 + D x X3 + E x X4

X1 is the carbon equivalent (parts by weight), X2 is the superheat degree deviation (占 폚), X3 is the total heat amount (MW / m2), X4 is the slab thickness (mm) B, C, and D are constants. The above equations (1) and constants A, B, C and D included therein are regression analysis based on experimental data observing the presence or absence of dynamic bulging while changing the carbon equivalent X1, the superheat degree deviation X2, the total heat amount X3, Lt; / RTI > Here, the presence or absence of dynamic bulging can be determined indirectly based on the degree of stabilization of the hot-dip level or the hot-dip level hit rate.

The carbon equivalent X1 is a value obtained by converting the constituent components of molten steel into the content of carbon (C), and various conversion equations may be used depending on the purpose of use. In this embodiment, however, it can be defined to satisfy the following expression (2).

(2)

X1 = [C] - 0.1 x [Si] + 0.04 x [Mn] - 0.04 x [Cr] + 0.1 x [Ni] - 0.1 x [Mo]

In the above formula (2), X1 represents carbon equivalent, [C] represents the content of carbon (C) contained in molten steel, [Si] represents the content of silicon (Si) contained in molten steel, and [Mn] [Ni] is the content of nickel (Ni) contained in the molten steel, and [Mo] is the content of molybdenum (Mn) contained in the molten steel. (Mo) contained in the molybdenum (Mo). The content of each component is expressed in parts by weight on the basis of 100 parts by weight of the total amount of molten steel. As a result, carbon equivalent X1 May also be expressed in parts by weight. The carbon equivalent X1 can be calculated by substituting the data of each component contained in the molten steel into the formula (2).

The superheat degree deviation X2 is an absolute value of the difference between the solidification temperature of the molten steel and the actual temperature, and can be calculated by measuring the ladle temperature at which the molten steel is introduced into the performance mold, and setting the actual temperature as the actual temperature.

The total heat amount X3 is the thermal energy per unit time discharged from the molten steel to the performance mold through a unit area where the molten steel and the performance mold come into contact with each other. The cooling fluid supplied to the performance mold, for example, The temperature of the outlet where the cooling water is discharged from the performance mold, the supply amount per unit time when the cooling water is supplied to the performance mold, and the contact area between the molten steel and the performance mold. The contact area between the molten steel and the playing mold can be calculated based on the standard bath surface level.

The casting thickness X4 can be obtained by measuring the width of the short side of the playing mold.

On the other hand, when the molten steel is composed of a capillary having a carbon equivalent of 0.09 part by weight to 0.13 part by weight based on 100 parts by weight as a whole according to the formula (2), A = -50 and B = 51.5 , C = 0.269, D = -13.8 and E = 0.308. That is, when the molten steel is composed of a capillary having a carbon equivalent of 0.09 part by weight to 0.13 part by weight based on 100 parts by weight as a whole, the bulging probability index can be calculated from the following equation (3).

(3)

Y = -50 + 51.5 x X1 + 0.269 x X2 - 13.8 x X3 + 0.308 x X4

Equation (3) has an R square value of 50.3%.

Next, the probability of occurrence of dynamic bulging in the strand discharged from the performance mold and passing through the strand cooling device is determined (S120) by comparing the bulging probability index with a predetermined value.

6 is a graph showing the correlation between the bulging probability index and the batting level hit rate.

Referring to FIG. 6, when the molten steel is composed of a cast steel having a carbon equivalent of 0.09 part by weight to 0.13 part by weight based on 100 parts by weight based on the formula 2, the carbon equivalent X1, the superheat degree deviation X2, When the dynamic bulgeability index is calculated from the above equation (3) while varying the billet thickness X4 and the average value of the dynamic bulge probability indexes in the range of the specific bale level hit rate is displayed, the correlation between the bullet occurrence probability index and the bale level hit rate Is present. That is, if the bulging probability index decreases, it is confirmed that the batting level hit rate increases. As described above, since the dynamic bulging may cause fluctuation of the melt surface level of the molten steel melt surface in the performance mold, the increase in the melt level of the melt surface may lower the possibility that dynamic bulging has occurred.

In addition, if the bulging probability index is 10 or more, it can be confirmed that the batting surface level hit ratio is not in the range of 90% to 100%. Therefore, the predetermined value of the bulging probability index, which is a criterion for determining whether dynamic bulging has occurred, may be 10. That is, if the bulging probability index is 10 or more, it is predicted that dynamic bulging can occur, whereas if the bulging probability index is less than 10, it can be predicted that dynamic bulging does not occur.

Next, if the bulging probability index is equal to or greater than the predetermined value, the casting speed of the molten steel is decreased until the bulging probability index becomes less than a predetermined value (S130).

Dynamic bulging may occur if the bulging probability index is set to a predetermined value, for example, 10 or more, so that it is necessary to control the operating conditions so that dynamic bulging does not occur in order to produce a high quality cast product.

The carbon equivalent and the thickness of the cast steel in the operating conditions are determined by the specification of the molten steel or the performance mold, so that it is almost impossible to control. The total heat amount is varied in accordance with the mold powder and the cooling conditions. Therefore, by lowering the casting speed, the bulging probability index can be controlled to be less than the predetermined value. For example, when the casting speed is reduced by 0.1 m / min, the bulging probability index, which is calculated by modifying the result, is compared with a pre-set value. If the bulging probability index is above a predetermined value, Minute, and if the bulging probability index is less than the pre-set value, the casting speed is kept constant, so that the dynamic bulging can be controlled not to occur.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the invention as set forth in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

10: molten steel
11: Solidification shell
12: Strand
13: Casting
14: Tang surface
100: Tundish
110: immersion nozzle
120: playing mold
130: guide roller
140: Cooling nozzle
150: Cutter

Claims

Feeding the molten steel to the playing mold;
A calculating step of calculating a bulging probability index defined as a function of a carbon equivalent of the molten steel, an overheating degree deviation of the molten steel, a total heat amount in the performance mold, and a billet thickness produced from the molten steel; And
Comparing the bulging probability index with a preset value to predict the probability of occurrence of dynamic bulging in the strand discharged from the performance mold and passing through the strand cooling device,
The bulging probability index is calculated from the following equation (1)
Wherein the carbon equivalent is defined to satisfy the following formula (2).
(1)
Y = A + B x X1 + C x X2 + D x X3 + E x X4
(A), (B), (C), and (C), respectively. D: constant)
(2)
X1 = [C] - 0.1 x [Si] + 0.04 x [Mn] - 0.04 x [Cr] + 0.1 x [Ni] - 0.1 x [Mo]
(X1: carbon equivalent (parts by weight), [C]: component content (parts by weight) of C based on 100 parts by weight of the total amount of molten steel, [Si] (Parts by weight), [Mn]: component content (parts by weight) of Mn based on 100 parts by weight of the total amount of molten steel, Component content (parts by weight) of Ni in a total amount of 100 parts by weight, [Mo]: component content (parts by weight) of Mo based on 100 parts by weight of the total molten steel)

delete

The method according to claim 1,
B = 51.5, C = 0.269, D = -13.8 and E = 0.308 in the constants, when the molten steel has a carbon equivalent of 0.09 to 0.13 parts by weight based on 100 parts by weight of the total Lt; / RTI >

5. The method of claim 4,
Wherein the predetermined value is 10.

The method according to claim 1,
In the determination step,
And predicts that if the bulging probability index is greater than or equal to the predetermined value, dynamic bulging may occur in the strand that is discharged from the performance mold and passes through the strand cooling device.

The method according to claim 6,
Further comprising a control step of decreasing the casting speed of the molten steel until the bulging probability index becomes less than the predetermined value if the bulging probability index is equal to or greater than the predetermined value.