KR20090068992A - Method for cooling control of hot-rolled steel sheet - Google Patents

Abstract

A cooling control method of a hot rolled steel sheet is provided to produce uniform steel coils by preventing the outermost part of a hot rolled steel sheet coil from supercooling in comparison with the inner part. A cooling control method of a hot rolled steel sheet, for controlling the quantity of cooling water sprayed to a hot rolled steel sheet to make a hot rolled coil to have uniform mechanical properties in the longitudinal direction, comprises the steps of tracking and detecting the progress of a hot rolled steel sheet passing through a finishing mill(1) in a hot rolling process using a detection sensor(11), judging whether to reach the starting location of start using a control unit receiving the signals detected by the detection sensor, in case of the starting location of control, bring under cooling control to raise the temperature by 50~70°C higher than the target CT, and brining the hot rolled steel sheet under cooling control by the preset target CT on a run-out table(3) until reaching the starting location of control.

Description

Method for cooling control of hot rolled steel sheet {Method for cooling control of hot-rolled steel sheet}

The present invention relates to a cooling control method of a hot rolled steel sheet, and more particularly, to a cooling control method of a hot rolled steel sheet to produce a hot rolled steel sheet of a uniform material by controlling the amount of cooling in consideration of the cooling rate of the wound hot rolled steel coil. will be.

Generally, hot rolled steel sheet (hereinafter referred to as 'hot rolled steel sheet') is injected through a slab manufactured by continuous casting into a heating furnace and reheated to a high temperature to undergo a process of rough rolling, intermediate rolling, finishing rolling, and the like. Corresponds to the final steel rolled to thickness and width.

The hot rolled steel sheet forms the same shape as the final product during finishing rolling in a continuous working process, and after passing through the finishing rolling, by the cooling water sprayed from a cooling facility installed above and below a run out table. Is cooled. And the hot rolled steel sheet is wound in a coil shape by a predetermined length in the winding machine for convenient movement.

In this case, since the mechanical properties of the hot rolled steel sheet passed through the finishing mill are determined according to the cooling temperature, the amount of cooling water sprayed on the hot rolled steel sheet is important to secure desired mechanical properties.

A conventional method for controlling cooling of hot rolled steel is disclosed in Korean Patent No. 1998-053190. In the above-described special 1998-053190, a method of cooling and controlling the steel so that the hot-rolled steel has a predetermined target material constant in the longitudinal direction. In other words, by setting the target value for the coil (CT, Coiling Temperature) when the hot rolled steel sheet passing through the finishing mill is coiled, the hot rolled steel sheet in the winding machine is controlled by cooling control in the run out table (ROT). When winding the coil to maintain a uniform CT for the entire coil to ensure the material of the steel sheet.

The coiling temperature (CT) is managed as a very important factor in ensuring a constant material in the longitudinal direction in the hot rolled products. However, in the case of hot rolled products, a 100% hit of coiling temperature (CT) does not necessarily guarantee a uniform material force.

In order to solve this problem, by using a mathematical model to learn, by controlling the coiling temperature (CT) it can be a constant material in the longitudinal direction of the hot-rolled steel sheet. However, in such a system, when the coiling temperature CT is uniformly maintained with respect to the entire rolled steel sheet, as shown in FIGS. 1 and 2, the coiled hot rolled steel sheet has a rapid cooling at the outermost part of the coil, so that the rear end of the coil is fast. The material of the part has higher strength and lower elongation than the material of the middle part. This material change is more severe when the transformation is active at the end of cooling. (For reference, in FIG. 2, the rear end of the hot rolled steel sheet is the direction from the coil position toward the origin.)

In order to evaluate the material of a general coil, samples are taken at a predetermined interval from the rear end portion of the coil, and the tensile strength, yield strength, and elongation of the representative portion are measured. However, when the cooling of the hot rolled steel sheet is controlled by the above method, the outermost portion of the coil is supercooled than the inner portion of the coil so that an accurate data value cannot be obtained, and the hot rolled steel sheet is determined to be a material defect, thereby ensuring reliability of the product. Of course, there is a problem that the error rate of the product is also lowered.

In particular, the steel sheet having a strength of about 35kg or less has a wide range of material acceptance level, but the steel sheet having a strength of about 40 ~ 45kg has a narrow range of material coalescence level, so that the uniform and proper material level is maintained throughout the coil. It is important to have skills to maintain.

The present invention is to solve the conventional problems as described above, an object of the present invention is to prevent the outermost coiled portion of the coil is supercooled compared to the inner winding portion to produce a hot coiled steel sheet of a uniform material It is to provide a cooling control method of.

The present invention is to solve the conventional problems as described above, the present invention is a method for controlling the amount of cooling water sprayed on the hot-rolled steel sheet so that the coil is hot-rolled coil has a uniform mechanical property in the longitudinal direction In addition, the rear end portion of the hot rolled steel coil wound on the outermost portion of the coil is characterized in that the cooling control to place a temperature deviation with the other parts of the hot rolled steel sheet before winding.

The rear end of the hot rolled steel sheet controls the amount of cooling water sprayed so that the cooling control temperature is cooled to a temperature higher by about 50 to 70 ° C. than other portions of the hot rolled steel sheet.

The cooling control is applied at the rear end of the hot rolled steel sheet, that is, 15 m or less at the rear end of the hot rolled steel coil.

The cooling control is applied when the end of the hot rolled steel sheet passes through the finishing mill.

In the method of controlling the amount of cooling water sprayed on the hot rolled steel sheet so that the coils wound by hot rolling have uniform mechanical properties in the longitudinal direction, the sensing sensor tracks the progress of the hot rolled steel sheet passing through the finishing mill during the hot rolling process. And a second step of determining whether or not the control unit has reached a control start position by receiving a signal detected by the detection sensor; If the control unit determines that the control start position is configured to include three steps to perform the cooling control to rise 50 ~ 70 ℃ than the target CT, the hot rolled steel sheet is a target set in the run-out table until the control start position is reached Cooling control by CT.

According to the present invention, before the outermost part of the wound hot rolled steel coil is wound with a coil so as to prevent overcooling than the inner winding part, cooling control is performed such that the rear end of the hot rolled steel sheet rises 50 to 70 ° C. above the target CT. Therefore, in the present invention, since the hot rolled steel sheet is wound with a coil and the outermost portion is cooled faster than the inner portion, a hot rolled steel sheet of uniform material can be obtained. Therefore, the error rate of the product is increased as compared to the conventional target CT. It works.

Hereinafter, a preferred embodiment of a method for controlling cooling of a hot rolled steel sheet according to the present invention will be described in detail with reference to the accompanying drawings.

3 shows a schematic diagram of a cooling system for producing a hot rolled steel sheet according to the present invention, and FIG. 4 shows a graph showing a relationship between a coil position and a coiling temperature CT in which a preferred embodiment of the present invention is employed. FIG. 5 is a graph showing the mechanical properties of the coil and the coil position when the coil wound by FIG. 4 is released.

Hot rolling process is to produce slabs heated in the furnace into strip-shaped hot rolled steel sheets having the desired thickness and width through rough rolling, intermediate rolling and finishing rolling. It is a key process to secure

As shown in FIG. 3, the hot rolled steel sheet S is finished rolled in a finishing mill (finishing rolling mill) 1 and then passed through a run out table 3 to a coil form in the winder 5. It is wound up. During this process, a cooling process is performed to ensure the required material.

The cooling is performed by the cooling water sprayed from the cooling device 7 provided above and below the run out table 3. The material of the hot rolled steel sheet (S) is determined according to the cooling temperature at this time. However, the final material of the hot-rolled steel sheet (S) may also be determined by the difference in cooling rate due to the wound position during air-cooling made after being wound into the coil.

Therefore, the present invention proposes a method for controlling the amount of cooling water sprayed on the hot rolled steel sheet (S) so that the coil is hot-rolled and has a uniform mechanical property in the longitudinal direction.

The control method takes into account that the outermost part of the hot rolled steel coil wound in the coil form is supercooled compared to the inner winding part, so that the rear end of the hot rolled steel sheet, which is the outermost part of the coil, rises approximately 50 to 70 ° C from the target CT. It is to control the amount of coolant.

At this time, the rear end of the hot-rolled steel sheet (S) in which the amount of cooling water injected from the cooling device is controlled is about 15m from the end of the coil of the hot-rolled steel sheet assuming that the diameter of the wound coil is about 6 ~ 7m Becomes

The following equation is used to obtain the rear end point of the hot rolled steel sheet to which the amount of cooling water should be controlled using the thickness and width of the hot rolled steel sheet and the target thickness.

(One)

△ H = H _cal (i-1) -H _cal (i)

Where Ld _cal (i) is the coil prediction length, Rd _cal (i) is the rolling roll radius, and H _cal (i) is the calculated target thickness.

The exit side of the run-out table 3 is provided with a cooling exit temperature sensor 9. The cooling exit temperature sensor 9 is installed above the winding machine 5 to measure CT (Coiling Temperature), which is a temperature when the hot rolled steel sheet S is cooled by winding with cooling water. The coiling temperature CT detected by the cooling exit temperature sensor 9 is transmitted to the controller.

The method using the CT (cooling exit temperature) is a method of setting a target value for the CT and controlling the amount of cooling water in the run-out table 3 when the hot-rolled steel sheet S is wound from the winder 5 to a coil. Ensure uniform temperature over the entire coil.

A detection sensor 11 is further provided on the exit side of the run out table 3. The sensor 11 detects whether the rear end of the hot rolled steel sheet S wound by the coil corresponds to a set point. At this time, the detection sensor 11 predicts the total length of the coil to be wound to detect whether the unrolled hot rolled steel sheet (S) is set, that is, corresponds to the 15m point of the rear end of the hot rolled steel sheet (S). The data detected by the sensor 11 is transmitted to the controller.

The control unit controls the injection amount of the cooling water according to the signals of the cooling exit temperature sensor 9 and the detection sensor 11. In this case, the detection result of the detection sensor 11 is preceded by the detection result of the cooling exit temperature sensor 9.

More specifically, by predicting the coil length by the equation (1) and tracking the progress of the hot-rolled steel sheet (S) in the sensor 11, the calculated coil length value is input to transfer the data value to the controller, The controller determines whether the hot-rolled steel sheet has reached a predetermined control start position and performs cooling control by the input program. At this time, the target temperature during cooling control of the hot-rolled steel sheet is set by feeding back the temperature of the portion immediately before the cooling control.

Such a control method is a run-out table 3 in which an existing method, that is, a target CT set in advance according to the thickness of steel grade, is detected until the set rear end point of the hot-rolled steel sheet S is detected by the sensor 11. The hot rolled steel sheet is cooled by cooling control at. After the set rear end point of the hot rolled steel sheet S is detected by the detection sensor 11, the amount of cooling water sprayed is increased by 50 to 70 ° C. above the target CT with respect to the rear end of the hot rolled steel sheet S under the control of the controller. To control.

In other words, by controlling the amount of cooling water sprayed to 50 ~ 70 ℃ higher than the target CT with respect to the rear end of the hot rolled steel sheet is wound around the coil to prevent the outermost portion of the coil is supercooled compared to the inner winding portion.

Hereinafter, a cooling control method of a hot rolled steel sheet according to a preferred embodiment of the present invention will be described in detail.

First, in order to produce a hot rolled steel sheet (S) of a uniform material, a process of reheating the continuously cast slab must be preceded, and therefore, a description will be made first in the order of a heating furnace process, a hot rolling process, and a winding process.

First, a heating furnace process is performed to reheat the continuously cast slab.

In the furnace process, in order to re-use segregated components during slab casting, reheating to 1200 ± 50 ° C. and homogenizing is performed. At this time, when the reheating temperature is lower than 1200 ± 50 ℃, the segregated components are not reusable, and if excessively high, the austenite grain size is increased and the ferrite grains are coarsened to decrease the strength, so the temperature of 1200 ± 50 ℃ Reheating is preferred.

Next, a hot rolling process is performed.

The slab subjected to homogenization in the heating furnace process is hot rolled at 850 ℃ ~ 900 ℃ directly above Ar3. In this case, when the finish hot rolling temperature is 850 ° C. or less, residual stress after rolling is present to coarsen grains during cooling or winding, so the finish hot rolling is preferably performed at 850 ° C. to 900 ° C. directly above Ar3.

Next, the winding process of winding up the hot rolled steel sheet hot-rolled and rolled is performed.

Winding temperature finishes with coiling temperature (CT) of 590 degreeC-620 degreeC. This is because the crystal grains and carbides are coarsened when winding above 620 ℃, and the tensile strength decreases and the elongation increases throughout the coil.When winding below 590 ℃, the tensile strength increases due to the supercooling of the hot rolled sheet and the elongation decreases. to be.

Cooling control by the coiling temperature CT is controlled by setting the target CT and target thickness of the hot rolled steel sheet. For example, the target CT and target thickness of the hot-rolled steel sheet are matched in the cooling system arranged in the order of finishing mill, run out table and winding machine. Of course, different values may be provided depending on the steel sheet.

Cooling water as much as a target CT is injected into the hot-rolled steel sheet S by the cooling control by the coiling temperature CT. At this time, the cooling exit temperature sensor 9 measures the temperature of the hot-rolled steel sheet (S) wound by the coil after cooling in the run-out table (3) to maintain a uniform CT (cooling exit temperature).

As described above, in the process of winding the hot rolled steel sheet S in the form of a coil, cooling amount control considering the cooling speed difference between the inner winding portion of the coil and the outermost portion is applied to the rear end portion of the hot rolled steel sheet S wound around the outermost portion of the coil. Is applied.

That is, in the winding process of the coil, if the sensor 11 detects the 15m point (the value calculated by Equation (1)) at the rear end of the hot rolled steel sheet S and transmits it to the controller, the controller resets the cooling pattern. When the rear end of the hot-rolled steel sheet S passes through the cooling device 7 on the run-out table 3, the coolant is sprayed to be 50 to 70 ° C higher than the target CT. In this case, the hot rolled steel sheet S may be wound with a coil to obtain a hot rolled steel sheet having a uniform material even when the outermost portion is cooled faster than the inner winding portion.

Hereinafter, the cooling control method of the hot rolled steel sheet according to the present invention will be described in detail in comparison with the conventional method through an embodiment.

EXAMPLE

The steel grade is carried out with SAPH440, and the cooling amount is set to be 50 ~ 70 ℃ higher than the target CT at 15m of the rear end of the hot rolled steel sheet. The results are shown in FIG. As a result shown in FIG. 4, cooling control was performed on the rear end portion of the hot rolled steel sheet S, and a tensile test was performed at a predetermined interval from the outermost portion of the hot rolled steel sheet S, and the results are shown in FIG. 5. .

4 and 5 it can be seen that the cooling control method of the hot-rolled steel sheet according to the present invention shows a uniform tensile strength, yield strength and elongation than conventional.

Next, another embodiment of the cooling control method of the hot rolled steel sheet according to the present invention will be described in detail.

Cooling control method of the hot rolled steel sheet according to another embodiment of the present invention is to control the amount of cooling water so that the hot rolled steel sheet rises 50 ~ 70 ℃ than the target CT by detecting the time point passing the finishing mill.

That is, in the coil winding process, the temperature of the finishing mill is lowered after the end of the hot-rolled steel sheet S passes through the finishing mill 1, rather than detecting a 15m point at the rear end portion of the hot-rolled steel sheet by Equation (1). Using this, the sensor 11 detects whether the end of the hot rolled steel sheet S has passed through the finishing mill. At this time, the result detected by the detection sensor 11 is transmitted to the control unit, the control unit performs the cooling control by the input program in the same manner as the above-described process. Therefore, the hot rolled steel sheet (S) is wound with a coil, even if the outermost portion is cooled faster it is possible to obtain a hot rolled steel sheet (S) of a uniform material.

For reference, the present invention is applicable to a steel sheet of 40 ~ 45kg strength, and for other types of steel, when the coiling temperature (CT) is higher than the transformation temperature by varying the cooling conditions according to the strength and elongation and process conditions Can be applied.

Within the scope of the basic technical idea of the present invention, many other modifications are possible to those skilled in the art, and the scope of the present invention should be interpreted based on the appended claims. will be.

1 is a graph showing the relationship between the coil position and the coiling temperature (CT) according to the prior art.

Figure 2 is a graph showing the mechanical properties according to the coil position and coil position when the coil wound by Figure 1 is released.

Figure 3 is a schematic diagram of a cooling facility for the production of hot rolled steel sheet according to the present invention.

Figure 4 is a graph showing the relationship between the coil position and the coiling temperature (CT) employing a preferred embodiment of the present invention.

5 is a graph showing the mechanical properties according to the coil position and the coil position when the coil wound up by FIG.

Explanation of symbols on the main parts of the drawings

1: Thought mill 3: Run out table

5: Winder 7: Cooling device

9: Cooling temperature sensor 11: Detection sensor

S: hot rolled steel sheet

Claims (5)

In the method of controlling the amount of cooling water sprayed on the hot-rolled steel sheet so that the hot-rolled coil has a uniform mechanical property in the longitudinal direction, Cooling control method of the hot rolled steel sheet characterized in that the cooling control to place a temperature deviation with the other part of the hot rolled steel sheet before winding to the rear end of the hot rolled steel sheet wound on the outermost part of the coil. The method of claim 1, The rear end of the hot-rolled steel sheet cooling control method of the hot-rolled steel sheet, characterized in that for controlling the cooling water injection amount is cooled to a temperature 50 ~ 70 ℃ higher than the other parts of the hot-rolled steel sheet. The method of claim 2, The cooling control is a cooling control method for a hot rolled steel sheet, characterized in that applied to the rear end of the hot rolled steel sheet, that is, 15m or less of the rear end of the hot rolled steel coil. The method according to claim 1 or 2, The cooling control is a cooling control method of the hot rolled steel sheet, characterized in that applied to the end of the hot rolled steel sheet passing through the finishing mill. In the method of controlling the amount of cooling water sprayed on the hot-rolled steel sheet so that the hot-rolled coil has a uniform mechanical property in the longitudinal direction, A first step of detecting and detecting a progress state of the hot rolled steel sheet passing through the finishing mill during the hot rolling process; A second step of determining, by the controller, whether the control start position is reached by receiving the signal detected by the detection sensor; If the control unit determines that the control start position is configured to include three steps to perform the cooling control to rise 50 ~ 70 ℃ than the target CT, The hot rolled steel sheet cooling control method of the hot rolled steel sheet, characterized in that the cooling control by the target CT preset in the run-out table until reaching the control start position.

Images