KR101529277B1

KR101529277B1 - Methods for manufacturing coil

Info

Publication number: KR101529277B1
Application number: KR1020130165086A
Authority: KR
Inventors: 박종현; 권효중; 박영민
Original assignee: 현대제철 주식회사
Priority date: 2013-12-27
Filing date: 2013-12-27
Publication date: 2015-06-16

Abstract

Disclosed is a method for manufacturing a coil. According to an embodiment of the present invention, provided is the method for manufacturing a coil comprising: a tapping step of manufacturing a slab by tapping molten steel to a casting mold; a measuring step of measuring a mold level of the molten steel at preset time intervals in the casting mold; a calculating step of calculating a mold level hit rate which is a rate of the measurement number wherein the mold level is located within a preset first range in comparison with the total measurement number of the mold level, and a mold level excess number which is a vibration number of the mold level wherein the difference between the maximum value and the minimum value of the mold level exceeds a preset second range during a vibration period of the mold level, and calculating an interposition property defect index defined as a function of the mold level hit rate and the mold level excess number; and a determining step of determining whether a rate wherein an interposition property surface defect can be generated in a rolling coil manufactured to have thickness which is less than first rolling thickness from the slab is located within a tolerance range by comparing the interposition property defect index with a preset value.

Description

[0001] METHODS FOR MANUFACTURING COIL [0002]

The present invention relates to a coil manufacturing method.

The molten iron produced in the blast furnace is subjected to a steelmaking process. The steelmaking process produces molten steel through pre-treatment of molten iron, conversion steelmaking, and secondary refining. Molten steel that has undergone steelmaking process is formed into a steel semi-finished product through continuous casting process. In the continuous casting process, molten steel continuously injected into the performance mold is cooled in the performance mold, thereby forming a steel semi-finished product such as a slab. The slab is rolled and formed into a final product such as a rolling coil.

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).

It is an object of the present invention to provide a coil manufacturing method capable of calculating an interfacial material defect index based on a bath surface level hit rate and an exceeding number of bath surface level in a slab manufacturing process.

According to an aspect of the present invention, there is provided a method of manufacturing a slab, comprising: guiding a molten steel into a performance mold to produce a slab; A measuring step of measuring the level of the molten steel in the performance mold at a predetermined time interval; Wherein a difference between a maximum value and a minimum value of the bath surface level during the oscillation period of the bath surface level and a bath surface level hit ratio which is a ratio of the number of times of measurement that the bath surface level is within a predetermined first range with respect to the total number of times of measurement of the bath surface level, Calculating an intervening material defect index, which is defined as a function of the bath surface level hit rate and the number of times exceeding the bath surface level, by calculating a number of times exceeding the bath surface level that is the number of times of vibration of the bath surface level exceeding the second range; And a determination step of comparing the intervening material defect index with a preset value to determine whether a ratio at which a intervening physical surface defect can occur in a rolling coil manufactured from the slab to a value less than the first rolling thickness is within an allowable range A method for manufacturing a coil is provided.

Wherein the molten steel contains 0.01 to 0.08 parts by weight of carbon (C), less than 1.5 parts by weight of manganese (Mn), less than 0.05 parts by weight of silicon (Si), less than 0.02 parts by weight of phosphorus (P) ) Of less than 0.02 parts by weight of iron (Fe) and other inevitable impurities, and the performance mold is formed by continuously casting a slab having a width of 900 mm to 1600 mm and a thickness of 225 mm And may be made of a parallel mold.

The intervening material defect index can be calculated from the following equation (1).

(1)

X = - 0.18 x X1 + 0.44 x X2

(X: intervening material defect index, X1: hot water level hit ratio (%) when the first range is 3 mm above and below the predetermined standard hot water level, X2: hot water level when the second range is 10 mm Overtime)

The ratio at which the intervening physical surface defects can occur in the rolling coil manufactured to be less than the first rolling thickness can be calculated from the following equation (2).

(2)

Y = 0.9 x exp (0.2485 x X)

(Y: percentage (%) in which intervening physical surface defects can occur in rolling coils manufactured to be less than the first rolling thickness, and X: interposed physical defect index)

The preset value may be 0.42.

In the determining step, when the intervening material defect index is equal to or larger than the predetermined value, the ratio at which the intervening material surface defects can occur in the rolling coil manufactured from the slab to less than the first rolling thickness may exceed the allowable range.

And rolling the slab to the first rolled thickness or more when the intervening material defect index is equal to or larger than the predetermined value.

According to the embodiments of the present invention, by calculating the inclusion defect index on the basis of the bath surface level hit ratio and the exceeding frequency of the bath surface level in the slab manufacturing process, it is possible to prevent the intervening physical surface defects It is possible to judge whether or not the possible rate is within the permissible range.

1 is a view illustrating a method of manufacturing a coil according to an embodiment of the present invention.
2 is a view showing a coil manufacturing apparatus.
3 is a view showing the result of measuring the melt surface level of molten steel in the performance mold at predetermined time intervals.
Fig. 4 is a graph showing the correlation between the bake surface level hit ratio and the rate at which intervening material surface defects can occur in rolling coils manufactured below the first rolling thickness.
5 is a graph showing the correlation between the number of times exceeding the level of the bath surface level and the rate at which intervening material surface defects can occur in the rolling coil produced below the first rolling thickness.
6 is a graph showing the correlation between the interposed defect index and the rate at which intervening material surface defects can occur in a rolling coil produced below the first rolling thickness.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a coil manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals are used to designate identical or corresponding components, The description will be omitted.

1 is a view illustrating a method of manufacturing a coil according to an embodiment of the present invention.

1, a method of manufacturing a coil according to an embodiment of the present invention includes a lecturing step S100, a measuring step S110, a calculating step S120, a determining step S130, and a rolling step S140 .

First, molten steel is poured into a performance mold to manufacture a slab (S100).

2 is a view showing a coil manufacturing apparatus.

2, the molten steel 10 is introduced into the performance mold 120 through the immersion nozzle 110 in the tundish 100, cooled through the performance mold 120 and the plurality of pitch rolls 130, Thereby producing a slab 20.

The molten steel 10 contains 0.01 to 0.08 parts by weight of carbon (C), less than 1.5 parts by weight of manganese (Mn), less than 0.05 parts by weight of silicon (Si), less than 0.02 parts by weight of phosphorus (P) 0.0 > (S) < / RTI > by weight, and the balance of iron (Fe) and other unavoidable impurities. On the other hand, the components, for example, manganese (Mn), silicon (Si), phosphorus (P), and sulfur (S), which are not described in the lower limit of the composition ratio among components of the molten steel 10, .

The playing mold 120 may be a parallel mold.

The playing mold 120 can continuously cast the slab 20 having a width of 900 mm to 1600 mm and a thickness of 225 mm. In this embodiment, the casting speed of the slab 20 is set at 0.8 m / min to 1.8 m / min.

In the slab 20, inclusions may be introduced into the molten steel 10, thereby causing defects in the interstices. For example, large inclusions may be removed from the tundish 100 or the immersion nozzle 120, or inclusions may be introduced into the molten steel 10 due to flow defects. Such interstitial defects can cause intervening physical surface defects on the surface of the rolling coil when the slab 20 is rolled into a thin rolled coil of 6 mm or less in a subsequent process. The surface defect of the intervening material formed on the surface of the rolling coil increases the failure rate of the rolling coil, thereby causing complaints and cost increase of the buyer. However, since most of these interstitial defects are formed inside the slab 20, it is not easy to detect it before rolling the slab 20 into a rolling coil.

On the other hand, the upper surface of the molten steel 10 in the performance mold 120 is referred to as a hot surface 11, and the hot surface level of the molten steel 10 is set to a height from an arbitrary height of the performance mold 120 to the hot surface 11 it means. In this embodiment, the level of the melt surface of the molten steel 10 is set to the height from the lower end of the performance mold 120 to the melt surface 11.

Next, the melt level of the molten steel in the performance mold is measured at a predetermined time interval (S110).

3 is a view showing the result of measuring the melt surface level of molten steel in the performance mold at predetermined time intervals.

Referring to FIG. 3, it can be seen that the level of the melt surface of the molten steel 10 fluctuates irregularly within the playing mold 120.

That is, the molten steel level of the molten steel 10 is not constantly maintained at the predetermined standard molten metal surface level but may fluctuate up and down around the standard molten metal surface level. In particular, as indicated by A in Fig. 3, it may happen that the bath surface level of the molten steel 10 fluctuates so that the difference between the maximum value and the minimum value during one vibration period exceeds 10 mm.

The standard bath surface level of the molten steel 10 can be set according to the operation management standard. In the present embodiment, the performance mold 120 has a height of 900 mm, and the standard melt surface level of the molten steel 10 is set to a position extending from the lower end of the performance mold 120 to 800 mm.

The time interval for measuring the level of the melt surface of the molten steel 10 may be set to a sufficiently small size such that the maximum value and the minimum value of the melt level of the molten steel 10 can be confirmed by the oscillation period of the melt surface level.

The molten steel 10 melt surface level measurement data can be generated for each slab 20.

That is, the bath surface level of the molten steel 10 is measured at predetermined time intervals during the manufacture of one slab 20, so that a group of bath surface level measurement data can be generated.

Next, the bath surface level hit rate, the exceeding number of times of the bath surface level, and the intervening material defect index are calculated from the bath surface level measurement data of the molten steel (S120).

Fig. 4 shows the correlation between the bath surface level hit ratio and the rate at which intervening material surface defects can occur in rolling coils produced below the first rolling thickness; Fig. 5 shows the relationship between the number of times exceeding the bath surface level and the first rolling thickness And the rate at which intervening physical surface defects can occur in the rolling coil.

Referring to FIGS. 4 and 5, the fact that the bath surface level hit ratio and the exceeding number of the hot-dippered surface level have a correlation with the ratio at which the intervening material surface defects can occur in the rolling coils manufactured below the first rolling thickness, Can be confirmed.

Inclusion Induced Surface Defect Index (FDS) is a function of the number of times of exceeding the bath surface level hit ratio and the number of times exceeding the level of the bath surface and the occurrence of intervening material surface defects in the rolling coil when the rolled coil is manufactured from the slab And the number of times exceeding the level of the tepe level is indexed by one index. In this embodiment, the first rolled thickness is set to 6 mm.

Thus, the interfacial defect index can be defined as a function of the bath surface level hit rate and the number of times exceeding the bath surface level.

The bake level level hit rate is calculated as a ratio of the number of times that the hot water level is located within the predetermined first range in terms of the total number of times of hot water level, and the unit of the hot water level hit rate is%. In the present embodiment, the first range is set to 3 mm above and below the standard hot-dip level, respectively.

For example, when the total number of bath surface level measurement data obtained during the manufacture of one slab 20 from molten steel 10 is 100, and the bath surface level is within the range of 3 mm or less from the standard bath surface level, If the number of measured data is 90, the batting surface level hit rate can be calculated as 90%.

The number of times exceeding the level of the hot surface level is calculated as the number of times of vibration of the hot water level at which the difference between the maximum value and the minimum value of the hot water level during the vibration period of the hot water level, that is, the hot water level during one vibration, exceeds the predetermined second range. In this embodiment, the second range is set to 10 mm.

(1)

X = - 0.18 x X1 + 0.44 x X2

X1 is the bath surface level hit ratio (%) when the first range is 3 mm above and below the standard bath surface level, X2 is the bath surface level when the second range is 10 mm, Quot;

6 is a graph showing the correlation between the interposed defect index and the rate at which intervening material surface defects can occur in a rolling coil produced below the first rolling thickness.

Referring to FIG. 6, it is confirmed through a regression analysis that the interfacial defect index calculated from Equation (1) has a correlation with a ratio at which a surface defect of intervening material can occur in a rolling coil manufactured at a thickness less than the first rolling thickness .

The ratio at which the intervening physical surface defects can occur in the rolling coil can be calculated from the following equation (2).

(2)

Y = 0.9 x exp (0.2485 x X)

In the above formula (2), Y represents a percentage (%) in which intervening physical surface defects can occur in a rolling coil manufactured to be less than the first rolling thickness, and X represents interposed defect index.

Next, the intervening material defect index is compared with a preset value to determine whether the ratio at which the intervening material surface defects can occur in the rolling coil manufactured from the slabs to less than the first rolling thickness is within the allowable range (S130) .

The preset value is set to the minimum value of the intervening material defect index such that the ratio at which the intervening material surface defects can occur in the rolling coil manufactured from the slab 20 to less than the first rolling thickness is out of the allowable range.

The allowable range of the rate at which intervening material surface defects can occur depends on the operating conditions. For example, in the case of a hot-rolled coil for a cold rolled steel sheet for automobiles, irregular surface defects may occur if irregular physical surface defects occur irrespective of the degree of the surface defects, but the ratio of the surface defects to the inter- The allowable range of the rate at which intervening material surface defects can occur should be controlled to be less than 1%.

If the allowable range of the rate at which intervening material surface defects can occur is less than 1%, the default value of intervening material defect index can be calculated by substituting 1 into Y in the above formula (2). As a result, the preset value becomes 0.42.

That is, when the intervening material defect index is 0.42 or more, the rate at which intervening material surface defects can occur in the rolling coil manufactured from the slab 20 to a thickness less than the first rolling thickness is 1% or more. On the other hand, if the interfacial defect index is less than 0.42, the rate at which intervening material surface defects can occur in the rolling coils manufactured from the slab 20 to less than the first rolling thickness is less than 1%, and the conformity is judged.

Next, the rolled thickness of the slab is controlled and rolled (S140) according to whether the rate at which intervening material surface defects can occur in the rolling coils manufactured from the slab to less than the first rolling thickness is within an allowable range.

As described above, whether or not the ratio at which the intervening material surface defects can occur in the rolling coils manufactured from the slab 20 less than the first rolling thickness is within the permissible range can be judged by comparing the intervening material defect index with the predetermined value have.

If the intervening material defect index is less than the preset value, the rate at which the intervening material surface defects can occur in the rolling coil manufactured from the slab 20 to less than the first rolling thickness is within the allowable range, Even if the thickness is less than the thickness, the nonconformity is not judged.

However, when the intervening material defect index is equal to or larger than the predetermined value, the ratio at which the intervening material surface defects can occur in the rolling coil manufactured from the slab 20 to less than the first rolling thickness is out of the allowable range, If it is manufactured at a thickness less than the first rolled thickness, it is judged as not conforming. Accordingly, when the intervening material defect index is equal to or larger than the predetermined value, the rolling thickness of the slab 20 is increased up to the first rolling thickness or more to lower the ratio at which the intervening physical surface defects can occur within the allowable range have.

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: Tang surface
100: Tundish
110: immersion nozzle
120: playing mold
130: pinch roll

Claims

Feeding the molten steel to a casting mold to produce a slab;
A measuring step of measuring the level of the molten steel in the performance mold at a predetermined time interval;
Wherein a difference between a maximum value and a minimum value of the bath surface level during the oscillation period of the bath surface level and a bath surface level hit ratio which is a ratio of the number of times of measurement that the bath surface level is within a predetermined first range with respect to the total number of times of measurement of the bath surface level, Calculating an intervening material defect index, which is defined as a function of the bath surface level hit rate and the number of times exceeding the bath surface level, by calculating a number of times exceeding the bath surface level which is the number of times of vibration of the bath surface level exceeding the second range; And
And comparing the intervening material defect index with a predetermined value to judge whether or not the ratio at which the intervening material surface defects can occur in the rolling coils manufactured to be less than the first rolling thickness from the slab is within an allowable range and,
Wherein the intervening material defect index is calculated from the following equation (1).
(1)
X = - 0.18 x X1 + 0.44 x X2
(X: intervening material defect index, X1: hot water level hit ratio (%) when the first range is 3 mm above and below the predetermined standard hot water level, X2: hot water level when the second range is 10 mm Overtime)

The method according to claim 1,
Wherein the molten steel contains 0.01 to 0.08 parts by weight of carbon (C), less than 1.5 parts by weight of manganese (Mn), less than 0.05 parts by weight of silicon (Si), less than 0.02 parts by weight of phosphorus (P) ) Of less than 0.02 parts by weight of iron (Fe) and other inevitable impurities, and the performance mold is formed by continuously casting a slab having a width of 900 mm to 1600 mm and a thickness of 225 mm Wherein the coil is made of a parallel mold.

delete

3. The method according to claim 1 or 2,
The first rolled thickness is 6 mm,
Wherein a ratio at which an intervening material surface defect can occur in a rolling coil manufactured to be less than the first rolling thickness is calculated from the following equation (2).
(2)
Y = 0.9 x exp (0.2485 x X)
(Y: percentage (%) in which intervening physical surface defects can occur in rolling coils manufactured to be less than the first rolling thickness, and X: interposed physical defect index)

5. The method of claim 4,
Wherein the predetermined value is 0.42.

The method according to claim 1,
In the determination step,
Characterized in that when the intervening material defect index is equal to or greater than the predetermined value, it is judged that the ratio at which the intervening material surface defects can occur in the rolling coil manufactured from the slab to less than the first rolling thickness is out of the allowable range Way.

The method according to claim 6,
Further comprising a rolling step of rolling the slab to the first rolling thickness or more when the intervening material defect index is equal to or larger than the predetermined value.