KR20130088293A - Continuous casting method for hot-rolled coil - Google Patents

Abstract

PURPOSE: A continuous casting method for hot-rolling coils is provided to reduce the edge defects of the hot-rolling coils by controlling casting thickness and casting speed while casting B-containing steel in a continuous casting process for thin slabs. CONSTITUTION: A continuous casting method for hot-rolling coils is as follows. When a continuous casting process is implemented by low carbon steel containing carbon, silicon, manganese, phosphorus, sulfur, boron, and nitrogen as essential components, casting speed is controlled. The low carbon steel is composed of 0-0.04 wt.% of the carbon and 15-35 ppm of the boron. [Reference numerals] (AA) Start; (BB,DD) No; (CC,EE) Yes; (FF) Finish; (S11) Supply molten steel manufactured by an electric furnace and LF secondary refining process to a continuous casting process; (S12) Continuous casting(Thin slab); (S13) Analyze the contents of the components of the molten steel which is in the middle of the casting process; (S14) Saving the analyzed contents of the components; (S15) The molten steel is low carbon and boron added steel?; (S16) Calculating casting factors by using the casting speed and the casting thickness; (S17) The calculated value is smaller than a reference value?; (S18) Increasing the casting speed

Description

Technical Field [0001] The present invention relates to a continuous casting method for hot-

The present invention relates to a continuous casting method, and more particularly, to a continuous casting method for hot-rolled coils capable of reducing the degree of occurrence of edge defects such as saw-mark defects in final rolled products.

Furnaces for steelmaking include blast furnaces and electric furnaces. A blast furnace is a furnace that is used to make pig iron from stones. In the electric furnace, steel scrap and coal are charged into the furnace, and oxygen of high purity is blown from one side to oxidize and burn carbon, manganese, silicon, phosphorus and sulfur contained in the molten steel. At this time, the oxide is slagged and removed by lime, and deoxidation and deoxidation are performed in parallel, so that a steel having a low content of phosphorus and oxygen is produced.

The electric arc furnishes a high current to the electrode rod to generate high-temperature arc heat, thereby dissolving the charged scrap. The molten steel thus dissolved is fed to a continuous casting machine through a refining process.

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 and the like. The 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. The slab transported through the pinch roll is cut by a cutter to have a predetermined shape Slabs, blooms, billets, and the like. The slabs, such as slabs, are rolled and then produced as hot rolled coils.

As related prior art, Korean Patent Laid-Open Publication No. 2011-414 (published on Jan. 1, 2011, entitled "Method of Predicting Surface Quality of Thin Slab Hot-Rolled Coil and Method of Manufacturing Thin Slab Hot-Rolled Coil Using the Same").

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to predetermine the degree of occurrence of edge defects such as a saw defect of a hot-rolled coil produced through an electric furnace and LF secondary refining, performance and rolling processes in advance through a casting factor, To provide a continuous casting method for a hot-rolled coil.

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

The continuous casting method for hot-rolled coils according to the present invention for realizing the above object is characterized in that when continuous casting is carried out by using low carbon steel containing carbon, silicon, manganese, phosphorus, sulfur, boron and nitrogen as essential components, The casting speed can be controlled.

Equation

는 기준값으로, 0.085 내지 0.089 사이의 값이다.here,

Is a reference value and is a value between 0.085 and 0.089.

In the above, the carbon may be more than 0 to less than 0.04 wt%, the boron may be 15 to 35 ppm, and the continuous casting may be a thin slab casting process.

The casting speed during the continuous casting can be adjusted in the range of 4.3 to 5.5 m / min.

The hot-rolled coils can be manufactured by a CSP (Compact Strip Production) process in which electric furnace steelmaking, ladle furnace (LF) secondary refining, thin slab continuous casting and rolling are continuously performed in batch.

As described above, according to the present invention, it is possible to reduce the edge defects of the hot-rolled coil by controlling the casting speed according to the casting thickness and the casting width in casting the B-added steel in the thin slab casting process, There is an advantage that the saw blade defects for the hot-rolled coils of grade 3 or higher can be remarkably reduced.

1 is a conceptual diagram showing a continuous casting machine according to an embodiment of the present invention mainly on the flow of molten steel.
2 is a view showing a continuous casting apparatus for a hot-rolled coil according to an embodiment of the present invention.
Fig. 3 is a view showing an edge defect (defect of the sawtooth) of the hot-rolled coil. Fig.
4 is a flowchart illustrating a continuous casting process according to an embodiment of the present invention.
FIG. 5 is a graph showing an edge defect occurrence rate according to the casting factor according to the embodiment.

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

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

Continuous casting is a casting 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 make long products of simple cross-section, such as square, rectangular or round, and mainly slabs, blooms or billets, which are materials for rolling.

The continuous casting machine may include the ladle 10 and the tundish 20, the mold 30, the secondary cooling bands 60 and 65, and the pinch roll 70, as shown.

The ladle (10) contains molten steel whose content of the steel component is improved through the refining process.

The tundish 20 is a container for receiving molten metal from the ladle 10 and supplying the molten metal to a mold 30. Ladle 10 is provided in a pair, alternately receives molten steel to supply to the tundish 20. In the tundish 20, the supply rate of the molten metal flowing into the mold 30 is controlled, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the nonmetallic inclusions are separated.

The mold 30 is typically made of water-cooled copper and allows the molten steel to be primary cooled. The mold 30 has a pair of structurally opposed faces open to form a hollow portion for receiving molten steel. In the case of manufacturing the slab, the mold 30 includes a pair of barriers and a pair of end walls connecting the barriers. Here, the end wall has a smaller area than the barrier. The walls of the mold 30, mainly short walls, may be rotated away from or close to each other to have a certain level of taper.

The mold 30 serves to form a strong solidification angle or solidified shell 81 so that the cast steel drawn from the mold maintains a certain shape and a molten metal which is still less solidified does not flow out. Do it. 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 to prevent the molten steel from adhering to the wall of the mold, and powder to prevent burning and to reduce friction between the mold 30 and the solidification shell 81 during oscillation. Lubricants such as Powder are used. The powder is added to the molten metal in the mold to become slag, and functions not only to lubricate the mold 30 and the solidified shell, but also to prevent oxidation / nitrification of the molten metal in the mold and to maintain the temperature and absorption of nonmetallic inclusions floating on the surface of the molten metal do.

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

The drawing device adopts a multidrive method using a pair of pinch rolls 70 and the like so as to pull out the cast pieces without slipping. The pinch roll 70 pulls the solidified tip of the molten steel in the casting direction, thereby allowing the molten steel passing through the mold 30 to continuously move in the casting direction.

Continuously produced cast pieces are cut to a certain size by a predetermined cutter (not shown).

That is, the molten steel M flows to the tundish 20 in the state accommodated in the ladle 10. For this flow, the ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends so as to be submerged in the molten steel in the tundish 20 so that the molten steel M is not exposed to the air to be oxidized / nitrided.

The molten steel M in the tundish 20 flows into the mold by a submerged entry nozzle 25 extending into the mold. 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, discharge speed, and stop of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 installed in the tundish 20 in response to the immersion nozzle 25. Specifically, the stopper 21 may be vertically moved along the same line as the immersion nozzle 25 to open and close the inlet of the immersion nozzle 25.

The molten steel M in the mold starts to solidify from the part 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.

As the pinch roll 70 pulls the front end portion 83 of the completely cast solid cast steel 80, the unsolidified molten steel 82 moves together with the solidified shell 81 in the casting direction. 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 a point 85, the cast steel 80 is filled with the solidification shell 81 of the entire thickness. 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.

The thin slabs produced through the continuous casting machine are rolled and then produced as hot rolled coils or plates. The thickness of the thin slabs produced through the casting process may be about 40 to 100 mm, and the thickness of the hot-rolled coil produced through the rolling process may be about 1 to 20 mm.

2 is a view showing a continuous casting apparatus for a hot-rolled coil according to an embodiment of the present invention. The casting apparatus 100 includes a sampler 110, a component analyzer 120, a storage unit 140, an input unit 130, A processing unit 170, and a display unit 150. In the present invention, an edge defect means a saw defect.

The sampler 110 is immersed in the molten steel of the ladle 10 or the tundish 20 in the refining process or the performance process to collect a portion of the molten steel.

The component analyzer 120 analyzes the component content of the molten steel sampled through the sampler 110. The content of the components in the molten steel is a predetermined value in the refining process at the time of operation. If the component content in the molten steel is not analyzed in the refining process, the content of the molten steel can be easily obtained by sampling and analyzing the sample in the molten steel accommodated in the ladle 10 or the tundish 20 in the performance process. The component content thus analyzed can be transmitted to the central processing unit 170 for predicting edge defects of the hot-rolled coil.

The input unit 130 is configured to receive various operation parameters and setting reference values from the outside. Here, the input unit 130 may be an input means such as a keyboard or an input means connected to an external PLC (Programmable Logic Controller) to receive predetermined operation information. The operating information may be a casting parameter such as the content of the cast steel, the casting width of the casting casting, the casting thickness, and the casting speed.

The storage unit 140 stores the content of the molten steel in the casting, the width, the thickness, and the casting speed of the casting machine through the continuous casting machine under the control of the central processing unit 170. The component content may be transmitted from the component analyzer 120, or may be input through the input unit 130.

The display unit 150 can display the casting speed and the degree of occurrence of edge defects in characters or graphs under the control of the central processing unit 170. [

The main speed control unit 160 controls the rotation speed of the pinch roll 70 to control the casting speed.

The central processing unit 170 may perform a continuous casting process of thin slabs in which the content of the component C stored in the storage part 140 is less than 0.04 wt% and boron added is 15 to 35 ppm when the boron- In the case of the steel, the casting speed is controlled through the main speed control unit 160 so as to satisfy the following equation (1). Of course, the central processing unit 170 can adjust the casting speed so as to satisfy the following expression 1 after confirming the current casting speed through the pinch roll 70. [

Equation 1

는 미리 설정된 기준값으로, 0.085 내지 0.089 사이의 값이 될 수 있다. 기준값(

)은 에지결함 여부와 주조속도를 고려하여 0.085 내지 0.089 사이에서 설정되는 것이 바람직하다.here,

Is a predetermined reference value, and may be a value between 0.085 and 0.089. Reference value (

) Is preferably set between 0.085 and 0.089 in consideration of the presence of edge defects and the casting speed.

In the present invention, the low carbon steel to which boron is added contains carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), boron (B) Where C is greater than 0 and less than 0.04 wt%, B is between 15 and 35 ppm, Si is greater than 0 and less than 0.03 wt%, Mn is greater than 0 and less than 0.40 wt%, P is greater than 0 and less than 0.02 wt% wt%, S is more than 0 and less than 0.01 wt%, and N may be more than 0 and 100 ppm.

The reason why the value of the casting thickness multiplied by the casting width in Equation 1 is divided by 1000 is because the unit of casting thickness and width is mm and the unit of casting speed is m / min. Therefore, In order to exponentiate in units. It goes without saying that, conversely, the casting speed can be multiplied by " 1000 " and indexed in the same unit as the casting thickness and width.

That is, when the steel being cast is a low carbon steel with boron added, the central processing unit 170 calculates the thickness, width, and casting speed of the current casting cast steel according to Equation 1 and then determines whether or not it exceeds the reference value. The speed control section 160 is controlled to increase the casting speed so as to control the formula 1 to exceed the reference value. Here, the casting thickness and the casting width are not factors that can be varied as needed, so that the casting speed is controlled.

In general, the scrap that is input to the electric furnace contains a trace element. The trace element is a trace element that adversely affects the quality of the steel product. It is also removed in the ladle furnace (LF) secondary refining process Uneasy. The most common types of harmful elements are alloying elements (Cr, Ni, Mo, Nb, Ti, V), impurity elements (P, S, O, N) , Ni, Mo, Co, Pb, Sn, Sb, As, Cu, P).

As shown in FIG. 3, when scrap containing a large amount of copper (Cu) and tin (Sn) is used, and when the content of nitrogen in the steel is large (boron precipitates are generated in grain boundaries) A saw mark defect is generated on the surface of the edge of the substrate. The reason for adding boron (B) in the steel is to control the strength of the hot-rolled coil after rolling, and B is vacant with the nitrogen present in the steel due to its chemical nature. Such a defective material (BN) is precipitated in crystal grain boundaries in the tissue during solidification, thereby lowering the high temperature ductility of the material. The amount of BN precipitates increases with the cooling rate, and the high temperature brittle zone is rapidly widened by the increased BN. In particular, since supercooling concentrates on the corner portion of the cast steel during casting, BN precipitates increase at the coil edge during rolling in the hot rolling process.

That is, since the high temperature brittleness of the corner portion is increased by the increased BN, defects such as saw blades are generated on the edge of the hot-rolled coil in the hot rolling process. Therefore, in order to prevent supercooling of the corner portion of the casting slab 80, Management is very important.

FIG. 4 is a flowchart illustrating a continuous casting process for a hot-rolled coil according to an embodiment of the present invention, and will be described in detail with reference to the accompanying drawings.

First, molten steel produced through a secondary refining process of an electric furnace and a ladle furnace is supplied to a continuous casting machine. In the continuous casting machine as shown in FIG. 1, the supplied molten steel is produced as a thin slab (S11, S12).

On the other hand, a part of molten steel is sampled through the sampler 110 in the ladle 10 or the tundish 20 in the secondary refining process of the ladle furnace or the performance process, (S13). ≪ / RTI > The analyzed content of the molten steel in the casting is transferred or inputted through the component analyzer 120 or the input unit 130 and stored in the storage unit 140 (S14).

Here, molten steel is basically a steel which is produced through steel scrap in an electric furnace and supplied to the casting process through secondary refining with ladle. The molten steel is made of a thin slab having a thickness of about 40 to 100 mm in the casting process, and is produced as a hot-rolled coil having a thickness of 1 to 20 mm through a rolling process. The molten steel is a low carbon steel to which C is added in an amount of more than 0 to less than 0.04 wt% and boron is added in which B (boron) is 15 ppm to 35 ppm. In addition to C and B, the molten steel may have a Mn of more than 0 and less than 0.40 wt%, Si of more than 0 and less than 0.03 wt%, P of more than 0 and less than 0.02 wt%, S of more than 0 and less than 0.01 wt% 100 ppm of N as an essential component.

That is, the edge defect prediction according to the present invention is basically performed by a hot strip coil (CSP) manufactured by a CSP (Compact Strip Production) process in which electric furnace steelmaking, ladle furnace (LF) secondary refining, thin slab continuous casting, Or heavy plates.

When the contents of C, Si, Mn, P, S, B, and N of the steel being currently cast stored in the storage unit 140 satisfy the set range (S15) To calculate the current casting speed. Of course, the casting speed may be preset in the storage unit 140 as the operating variable.

) 이상인지를 판단하게 된다(S17). 여기서, 기준값은 0.085 내지 0.089 사이의 값이 될 수 있다.Then, the central processing unit 170 calculates a casting factor based on the formula 1 using the width and height of the casting casting being stored in the storage unit 140 and the casting speed calculated in the step S16, When the casting factor value is less than the reference value

) (S17). Here, the reference value may be a value between 0.085 and 0.089.

If the calculated value is smaller than the reference value, the central processing unit 170 sets the casting speed in the set range (maximum 5.5 m / min, min (for example, 0.1 m / min) (S18).

After increasing the circumferential speed by a predetermined amount, the central processing unit 170 calculates a value using the increased casting speed, the casting thickness and the casting width based on Equation 1, and compares the calculated value and the reference value again. Of course, such a process is repeatedly carried out until the expression 1 is satisfied while increasing the casting speed by a predetermined amount within a set range (S16 to S18).

The central processing unit 170 predicts the possibility of occurrence of an edge defect in real time through the casting factor as expressed by Equation 1, and displays the predicted result through a display unit 150 as a graph or displays a predicted edge defect with a reference value (for example, 0.085 '), it may output an alarm sound through a predetermined alarm means.

주조폭)/1000"을 구하면, 그 값은 최소 45((50

900)/1000) 내지 최대 78((60

1300)/1000)이 산출된다. 따라서, "(주조두께

주조폭)/1000"의 평균값은 '61.5'가 산출된다. 이를 정리하여 나타내면 하기 표 1과 같다.The casting thickness of the cast steel according to the present invention may be 50 to 60 mm and the casting width may be 900 to 1300 mm. Here, the casting factor "(casting thickness

Quot; 1000 "), the value is at least 45 ((50

900) / 1000) to a maximum of 78 ((60

1300) / 1000) is calculated. Thus, "(casting thickness

The average value of "1000 gauge" / "1000 gauge" is calculated as "61.5".

Speed 4.3 4.4 4.5 ... 5 5.1 5.2 5.3 5.4 5.5 medium 61.5 61.5 61.5 ... 61.5 61.5 61.5 61.5 61.5 61.5 Equation 1  value 0.070 0.072 0.073 ... 0.081 0.083 0.085 0.086 0.088 0.089

주조폭)/1000"의 값들에 대한 평균값이고, 수식 1은 "주조속도/평균값(평균값=(주조두께

주조폭)/1000)"이다. 주조두께와 주조폭의 단위는 mm이다.In Table 1, the main rate is the casting speed (m / min) and the average value is "

Quot; casting speed / average value (average value = (casting thickness / average value) "

1000 mm). "The unit of casting thickness and casting width is mm.

주조폭)/1000)}에 의한 값이 0.085 이상에서 에지결함 발생율이 거의 없는 것으로 나타났다. 주조속도의 증가시 연주주편의 표면온도가 상승되어 코너부의 과냉 방지에 유리하고, 주조두께의 증가시 주조속도가 느려져 연주주편의 코너부의 과냉 방지에 불리하고, 주조폭의 증가시에도 주조속도가 느려져 연주주편의 코너부의 과냉 방지에 불리하다. 따라서, 주조두께 및 주조폭에 따라 주조속도를 조절하여 에지결함 발생율을 저감시키는 것이 중요하다.FIG. 5 is a graph showing the occurrence rate of edge defects according to the value of Equation 1 according to the embodiment, and is expressed by Equation 1 {casting speed / ((thickness of casting

The ratio of edge defects was found to be almost 0.085 or more. When the casting speed is increased, the surface temperature of the casting cast steel is increased to prevent overcooling of the corner portion. When the casting thickness is increased, the casting speed is slowed, which is disadvantageous for preventing overcooling of the corner portion of the casting cast. It is disadvantageous for prevention of supercooling of the corner part of the playing casting. Therefore, it is important to reduce the occurrence rate of edge defects by controlling the casting speed according to the casting thickness and casting width.

As shown in FIG. 5, the third grade is a higher grade in which the defect occurrence level is weaker than the fifth grade, while in the third grade, relatively weak edge defects are continuously generated and in the fifth grade, edge defects occasionally appear. However, as the x-axis casting factor increases, the edge defects decrease. At 0.082 or more, the edge defects of the 5th grade product disappear, but at the third grade, weak edge defects still occur. However, the grade 3 should not be an edge defect because the down grade (grade 1 and grade 2 is normal) through the subsequent process. Therefore, the factor of the x axis should be controlled to 0.085 or more based on the third grade.

Thus, in the present invention, edge defects of the hot-rolled coil can be reduced by controlling the casting speed according to the casting thickness and the casting width during casting of the B-added steel in the thin slab casting process. In particular, The saw blade defects with respect to the hot-rolled coil can be remarkably reduced, and the productivity can be improved.

The continuous casting method for edge defect reduction as described above is not limited to the configuration and operation of the embodiments described above. The above embodiments may be configured such that various modifications may be made by selectively combining all or part of the embodiments.

10: Ladle 20: Tundish
30: mold 51: powder layer
60: support roll 65: spray
70: pinch roll 80: performance cast
81: Solidification shell 82: Non-solidified molten steel
90: Cutter 91: Cutting point
100: prediction device 110: sampler
120: Component analyzer 130: Input unit
140: storage unit 150: display unit
160: Main speed control unit 170: Central processing unit

Claims (6)

Continuous casting method for hot-rolled coil to control the casting speed to satisfy the following formula when continuous casting using low carbon steel containing carbon, silicon, manganese, phosphorus, sulfur, boron and nitrogen as essential components.
Equation

here,

Is a reference value and is a value between 0.085 and 0.089
The method according to claim 1,
The carbon (C) is more than 0 to less than 0.04wt%, boron (B) is 15 to 35ppm continuous casting method for hot rolled coil.
The method according to claim 2,
The silicon (Si) is greater than 0 to less than 0.03wt%, the manganese (Mn) is greater than 0 to less than 0.40wt%, phosphorus (P) is greater than 0 to less than 0.02wt%, sulfur (S) is greater than 0 To less than 0.01wt%, nitrogen (N) is more than 0 to 100ppm continuous casting method for hot rolled coil.
The method according to claim 1,
Wherein the continuous casting is a thin slab casting process.
The method according to claim 1,
Wherein the casting speed is controlled in the range of 4.3 to 5.5 m / min.
The method according to claim 1,
Wherein the hot-rolled coil is manufactured by a CSP (Compact Strip Production) process in which electric furnace steelmaking, ladle furnace (LF) secondary refining, thin slab continuous casting and rolling are continuously performed in a batch.

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