KR100931204B1 - Method of manufacturing hot-rolled steel sheet - Google Patents

Abstract

The present invention relates to a hot rolled steel sheet capable of effectively improving the flying phenomenon while reducing the supercooling phenomenon of the tip portion by determining the specifications of the nozzle by mathematically calculating the resistance of the steel sheet and the force of the horizontal spray, And a method for producing the same.

The method proposed by the present invention is a method for precisely setting the force required to press the upward steel plate and the spraying conditions of the horizontal spray and adjusting the coiling temperature control to increase the accuracy of the injection control according to the position of the tip of the steel plate. The number of the main banks in the run-out table is determined by applying the temperature drop amount of the steel sheet by the spray of the horizontal spray during the calculation.

Further, according to the present invention, the upward movement of the leading end of the steel sheet can be prevented more efficiently, and the supercooled section of the leading end portion can be reduced.

Hot Rolling, Steel Plate, Horizontal Spray, Head Up Control, Water Cooling Drop, Air Cooling Drop,

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a hot rolled steel sheet,

Fig. 1 is a diagram showing the relationship between the resistance of the steel plate and the force applied by the horizontal spray.

2 is a process diagram of an annual rolling process to which a method of manufacturing a hot-rolled steel sheet according to the present invention is applied.

3 is a flowchart showing a manufacturing procedure of a hot-rolled steel sheet according to the present invention.

4 is a temperature distribution diagram of the hot rolled steel sheet produced by the conventional method.

5 is a temperature distribution chart of the hot rolled steel sheet produced by the present invention.

The present invention relates to a method of manufacturing a hot-rolled steel sheet, and more particularly, to a method of manufacturing a hot-rolled steel sheet capable of effectively reducing an upwardly directed tip while reducing supercooling of a steel sheet front end.                         

Typically, when a hot-rolled steel sheet subjected to a finish rolling process during hot rolling passes through a final stand, it is wound through a cooling process of a run-out table. At this time, a flying phenomenon in which the leading end of the hot-rolled steel sheet is raised due to the defective level of the table roll and the air resistance due to the high-speed running frequently occurs in the light clearance cooled by the run-out table, which causes quality defects and malfunctions have.

Therefore, it is necessary to prevent the flying phenomenon in the cooling step. To this end, a horizontal spray is horizontally sprayed on the rear surface of the final stand, and then only the front end is concentratedly sprayed in the course of the steel sheet, Down.

However, when the front end is prevented from being upwardly prevented by the horizontal spray as described above, the tip cooling effect by the horizontal spray and the cooling effect by the lamina bank in the run-out table are combined to cause unnecessary tip overcooling, And the location of the steel plate was not selected and the injection timing was not properly set according to the position of the steel plate. Particularly, since there is no tracking information for the position of the leading end of the steel sheet, the injection timing is manually determined, and thus the horizontal injection is performed after the leading end passes. In this case, the material failure due to unnecessary cooling of the steel sheet, There has been a problem of inducing the phenomenon.

More specifically, in the hot rolling process, the conventional cooling control method is a method in which the target finishing rolling temperature (or cooling inlet temperature) (hereinafter referred to as " FDT " And the target cooling output temperature (or the coiling temperature) (hereinafter, referred to as 'CT') are set, and the FDT and the CT are hit accordingly.

To this end, the air-cooling quantity is first calculated by using the target FDT, the target CT, and the target communication speed V, and the required number of coolants is calculated, and then the number of the weekly bins in the run-out table is determined. When the FDT and the passing speed are measured after the leading end of the steel sheet has passed through the finish rolling bar, the required number of cooling amounts are recalculated at regular intervals using the actual FDT and the actual passing speed instead of the target FDT and the target feeding speed, Is reset every predetermined period.

The general air-cooling drop amount (CT _air ) is given by the following equation (1).

Where a and b are coefficients, A is 0.6E-7, L is the distance from the FDT to CT to 114.7 m, H is the thickness of the steel plate, V is the throughput rate, and FDT is the FDT temperature.

Further, the other water-cooling required amount T _N is calculated by the following equation (2).

T_N = T_W = FDT - CT_air - CT

In the above, FDT is an actual value of FDT, CT _air is a temperature drop during _air cooling, and CT is a target temperature for coiling.

The water-cooled drop amount is obtained by calculating the temperature drop amount by water cooling per bank depending on whether or not each bank is used in the run-out table and obtaining the sum for all the banks. The water-cooled drop amount (T _w ) in the run-out table is represented by the following equation (3).

Where Cp is the specific heat of the steel plate, ρ is the density of the steel plate, Qiu and Qid are the heat fluxes of the I-th phase and the lower bank, respectively, where l is the length of the I-th bank, Hf is the thickness of the coil,

The upper and lower heat flux values of each bank used in Equation (3) are expressed by the following Equation (4).

Here, f0 is the heat flux correction coefficient of the i-th bank, Tiu is the water temperature correction coefficient of the upper bank, Tid is the water temperature correction coefficient of the lower bank, and fv is the passage velocity correction coefficient.

Particularly, the values of the heat flux correction coefficients applied at the tip of the steel plate (about 60 m from the tip of the steel plate) are shown in Table 1 below.                         

Bank number # 7 #8 # 9 # 10 # 11 # 12 # 13 # 14 Heat flux correction factor (f2i) 1.48 1.56 1.64 1.72 1.80 1.88 1.96 2.04

F0 for calculating the heat flux is represented by a coefficient value of C0 to C8 and a learning coefficient f1 as shown in Equation (5) below.

Here, Tw is the water temperature and Wf is the width of the steel sheet.

In the conventional hot-rolled steel sheet manufacturing process as described above, the learning coefficient f1 is stored when one steel sheet is finished and applied to Equation (5) when the next set of the same set is worked. However, when the upward spraying horizontal spray is applied, the supercooling interval of the tip portion becomes longer due to the supercooling effect of the tip due to the spraying, which has a bad influence on the material. Particularly, in cold rolled steel products, since a considerable part of the front end portion must be cut and used in a cold rolling mill, which is a back-end process, the cold rolling ratio is adversely affected.

SUMMARY OF THE INVENTION The present invention has been proposed in order to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a method and a device for determining the specifications of a nozzle by mathematically calculating a resistance of a steel sheet during operation and a force applied by a horizontal spray, Rolled steel sheet which is capable of effectively reducing the flying phenomenon while reducing the wear resistance of the hot-rolled steel sheet.

As a constituent means for achieving the object of the present invention described above, the present invention is characterized in that a finishing mill, a runout table and a winding machine are arranged in this order, and a horizontal spray is provided on the fourth bank of the run- A method for manufacturing a hot rolled steel sheet using a hot rolling equipment,

A spraying condition setting step of calculating a spraying speed and a flow rate of the horizontal spray by calculating a force due to the air resistance with respect to the upward part of the front end of the steel sheet so that a force larger than the force due to the air resistance is applied;

The amount of air-cooling from the rear end of the finishing mill to the intermediate thermometer and the amount of water-cooling down by horizontal spraying are measured for each steel grade and standard, and the amount of air-cooling reduction and the amount of water-cooling reduction by horizontal spraying are subtracted from the actual finish rolling temperature, Setting an intermediate target temperature for each standard;

Determining whether an incoming steel sheet is an upward control target;

If it is determined that the object to be controlled is the upward control object, the horizontal spray positioned at the rear end of the finishing mill final stand is turned on when the steel plate arrives at the stand No. 3 of the finishing mill, And a horizontal spray positioned at a rear end of the fourth bank of the run-out table is turned on when the second bank of the steel sheet reaches the bank and is turned off when the bank reaches the 10th bank, And

A cooling control step of controlling the cooling process of the run-out table by calculating a necessary number of cooling quantities and the number of main banks from the difference between the set intermediate target temperature and the target winding temperature,

And a control unit.

Hereinafter, a method of manufacturing a hot-rolled steel sheet according to the present invention will be described with reference to the accompanying drawings.

(JS-SPCC-S) has a thickness of 2.2 to 2.5 mm, a narrow width of 940 to 970 mm, and a non-oriented electrical steel sheet (JS- 50A470, 50A1300). This material is a material in which the leading edge is mainly raised when cooling in a hot rolling process, and information on the hot rolled material is received from an upper calculator (not shown) that controls the entire process of hot rolling to determine whether or not the manufacturing method according to the present invention is applied .

Hereinafter, a hot rolling manufacturing process for preventing the leading end upward and suppressing the overcooling will be described mainly with the above-mentioned material.

1) Setting spray rate and flow rate of horizontal spray

As shown in Fig. 1, the force F1 applied by the air resistance to the tip end of the steel plate 7 traveling at a predetermined speed is calculated by the following equation (6).                     

Here, CD is a resistance coefficient of 1.98, p is an air density of 1.25, V1 is an advancing speed of the steel plate 7, A is a contact area between the upwardly directed end of the steel plate 7 and air, X height of the front end portion ".

When water is sprayed to the tip of the steel plate 7 in the rolling direction by the horizontal spray 4,5, the force F2 applied to the tip of the steel plate 7 can be expressed by the following equations (7) and same.

Where G is the specific gravity of water, g is 9.8 as the gravitational acceleration, Q is the flow rate of water sprayed from the horizontal spray (4,5), V1 is the traveling speed of the steel plate 7, V2 is the horizontal Is the spraying speed of water at the spray (4,5), and [theta] is the spraying angle of the horizontal spray (4,5).

(6) and (7), the force (F2) by the horizontal spray (4, 5) is adjusted to be equal to or greater than the force F1 received by the air resistance By setting the spraying speed and spraying flow rate of the spray (4, 5), it is possible to prevent the leading edge of the steel plate (7) from rising on the runout table of the annual rolling process.

2) Spray position and point setting of horizontal spray                     

According to the present invention, two horizontal sprays (4, 5) and thermometers (8, 9) are arranged and used as shown in FIG. 2 for precise upward control and cooling control.

More specifically, in the hot rolling step in which the steel sheet is transferred from the finishing mill 6 to the winder 1, the finishing mill 6, the run-out table 2 and the winder 1 are arranged in this order, Thermometers 8 and 9 for measuring the temperature of the steel plate 7 are provided between the rear end of the rolling mill 6 and the bank 8 of the run-out table 2 and the bank 9 of the ninth bank 9, Two horizontal spray nozzles 4 and 5 are provided on the exit side of the finishing mill 6 and on the rear side of the fourth lamina bank # 4 of the runout table 2.

At this time, the horizontal sprays 4 and 5 are installed on the work side and the drive side, respectively, with respect to the width direction of the steel plate 7.

The injection timing of the horizontal spray nozzles 4 and 5 is controlled in the following manner in consideration of the distance between the installation position of the horizontal spray nozzles 4 and 5 and the finish air nozzle 6 and the passing speed of the steel plate 7 .

First, the horizontal spray 5 on the rear surface of the finish rolling mill 6 starts spraying at the time when the steel sheet 7 enters the stand F3 (not shown) at the front end of the finishing mill 6, The horizontal spray 4 installed on the rear surface of the fourth bank # 4 is terminated at the time of reaching the fourth bank # 4 of the run-out table 2, The injection is started when the tip of the steel plate 7 reaches the No. 2 bank # 2 and the injection is terminated when the steel plate 7 reaches the No. 10 bank # 10.

The injection start and end points are determined by tracking the forward position of the steel plate 7 in the hot rolling process on the basis of the materials to which the tip end upward prevention is applied to obtain the optimum injection time .

3) Calculation of the intermediate target temperature considering the amount of water-cooled drop by horizontal spray

As described above, when the two horizontal sprayers 4 and 5 are operated, the leading end of the steel plate 7 can be further water-cooled and subcooled by the water sprayed from the horizontal sprayers 4 and 5. [ In order to prevent this, according to the present invention, an intermediate thermometer 9 provided between the # 8 and # 9 banks of the run-out table 2 is used to measure the number of steel plates, The air-cooling-down amount from the thermometer 8 to the intermediate thermometer 9 is measured by the above-described equation (1).

Then, the obtained air temperature decrease amount CT _air , the intermediate temperature actual value MT ₀ obtained by the intermediate thermometer 9, and the actual FDT measured by the FDT thermometer 8 are substituted into the following equation (8) by the two water-cooling is obtained by _spraying drop _horizontal to the horizontal spray (4, 5).

MT_0 = FDT - CTair - Water-cooled descent _ Horizontal spray

Then, by applying the air-cooling of the drop in the water-cooling drop and FDT thermometer 8 by the horizontal spray (4, 5) to the middle thermometer (9) in the following equation (9), the steel type intermediate target temperature (MT _t) .

MT_t = FDT - CT_air - Water-cooled descent _ Horizontal spray

As a result, the temperature drop of the steel plate 9 by the horizontal spray 4,5 was as shown in Table 2 below.

Steel grade JS-SPCC-S JS-50A470 JS-50A1300 Thickness [mm] 2.3 2.5 2.7 2.0 2.5 Intermediate target temperature 63 ° C 80 ℃ 91 ℃ 55 ° C 74 ℃

The temperature drop due to the horizontal spray as shown in Table 2 by the above procedure should be obtained by experimenting a plurality of steel plates as described above before actual operation.

4) Calculating the water-cooling required amount (T _N ) of the run-out table for reaching the target winding temperature from the intermediate target temperature

(9) using the intermediate target temperature (MT _t ) of the steel grade obtained in the previous step and the target winding temperature (CT) set in accordance with the demand of the demand during the hot rolling step, (T _N ) to reach the target coiling temperature (CT) in consideration of the temperature drop amount of the steel sheet due to the cooling water.

T_N = MT_t - CT

As described above, when the water-cooling required amount T _N taking into consideration the cooling by the horizontal spray 4,5 is calculated, the water-cooled drop amount T _{W for each} bank in the run-out table 2 is calculated by the above- Can be obtained. The heat flux correction coefficient values for each bank used here are differently applied as shown in Table 3 below to calculate the temperature drop amount. Therefore, the material (eg, JS-SPCC-S, thickness: 2.3 mm) to which horizontal spray (4,5) injection is applied to the upstream prevention control target is reduced by 7% The heat flux correction factor is applied and the exempted material is prevented from unnecessary undercooling by spraying the horizontal spray (4,5) by applying the heat flux correction coefficient as shown in Table 1 to reduce the material deviation, So that the winding shape can be improved.

Bank number # 7 #8 # 9 # 10 # 11 # 12 # 13 # 14 Existing heat flux correction factor 1.48 1.56 1.64 1.72 1.80 1.88 1.96 2.04 Modified heat flux correction factor 1.23 1.45 1.55 1.62 1.72 1.80 1.86 1.92

FIG. 3 is a flow chart sequentially summarizing the method according to the present invention according to the rolling process sequence. From the equations (6) and (7) before the rolling operation, (301), and the temperature drop from the spray of the horizontal spray (4, 5) to the intermediate thermometer (9) according to the set conditions is measured without driving the run-out table for each steel type and standard, The intermediate target temperature is set (302) when horizontal spray is applied for each steel grade and standard.

After the above-described setting, when rolling is performed, it is determined whether the introduced steel sheet is the upward control target material (303, 304).

As a result of the above determination, if the incoming steel sheet is not the upward control target material, the horizontal spray (4,5) is not sprayed and the cooling control is performed according to the existing method (305,306). On the contrary, (307, 308) by applying the adjusted intermediate target temperature and the corrected heat flux correction coefficient (Table 3) after the injection of the heaters (4,5).

The above control is repeated until the rolling operation is stopped (309)

The spraying condition of the horizontal spray and the intermediate target temperature can be reset at regular intervals.

(Example)

2, the finishing mill 6, the runout table 2 and the winder 1 are arranged in this order on the basis of the rolling direction, and the rear surface of the final stand F7 of the finishing mill 6 and the rear surface 4 The target finish rolling temperature (FDT) is 910 ° C, the target finish rolling temperature is 910 ° C, and the target finish rolling temperature (FDT) The rolling temperature (CT) was measured from the steel sheet produced by the conventional manufacturing method and the manufacturing method according to the present invention by changing the measured value of the coiling temperature (CT) when the cold rolled steel sheet having a temperature of 680 캜 was rolled, 5.

As shown in FIG. 4, the supercooled section is widely spread at the tip end of the steel sheet in the past, resulting in material failure.

However, as a result of applying the present invention, as shown in FIG. 5, the supercooled section of the tip portion of the steel sheet compared to the conventional steel sheet significantly decreased.

Therefore, it can be seen that the method of manufacturing a hot-rolled steel sheet according to the present invention is very effective in preventing the tip portion from being upwardly directed while minimizing the supercooling degree of the steel plate front end portion by horizontal spraying.

As described above, in the present invention, by controlling the cooling rate at the tip of the steel plate by improving the hit ratio of the steel plate front end by horizontally spraying, effectively suppressing the upward movement of the steel plate front end, The improvement of the material and the improvement of the real rate are shown.

Claims (4)

A method of manufacturing a hot rolled steel sheet using a hot rolling apparatus in which a spray is arranged in the order of a finishing mill, a runout table and a winding machine, and a horizontal spray is provided on a fourth stage of a final stage stand of the finishing mill, A spraying condition setting step of calculating a spraying speed and a flow rate of the horizontal spray by calculating a force due to the air resistance with respect to the upward part of the front end of the steel sheet so that a force larger than the force due to the air resistance is applied; The amount of air-cooling from the rear end of the finishing mill to the intermediate thermometer and the amount of water-cooling down by horizontal spraying are measured for each steel grade and standard, and the amount of air-cooling reduction and the amount of water-cooling reduction by horizontal spraying are subtracted from the actual finish rolling temperature, Setting an intermediate target temperature for each standard; Determining whether an incoming steel sheet is an upward control target; If it is determined that the object to be controlled is the upward control object, the horizontal spray positioned at the rear end of the finishing mill final stand is turned on when the steel plate arrives at the stand No. 3 of the finishing mill, And a horizontal spray positioned at a rear end of the fourth bank of the run-out table is turned on when the second bank of the steel sheet reaches the bank and is turned off when the bank reaches the 10th bank, And A cooling control step of controlling the cooling process of the run-out table by calculating a necessary number of cooling quantities and the number of main banks from the difference between the set intermediate target temperature and the target winding temperature, Wherein the hot-rolled steel sheet has a thickness of 10 to 100 mm. The method according to claim 1, wherein the step

(Where CD is a resistance coefficient of 1.98, p is an air density of 1.25, V1 is the traveling speed of the steel sheet, and A is the contact area between the upwardly directed tip of the steel sheet and air) The force F1 due to the air resistance is obtained,

V is the jetting speed of the water in the horizontal spray, and? Is the jetting angle of the horizontal spray), V1 is the flow rate of water in the horizontal spray, V2 is the flow rate of the water in the horizontal spray, Wherein an injection angle or a flow rate is set so that a force F2 applied to the upward portion of the steel sheet larger than the force F1 is generated by the horizontal spray. The method according to claim 1, wherein the upward control target member (JS-SPCC-S) having a thickness of 2.2 to 2.5 mm, a narrow width material (width of 940 to 970 mm), and some non-oriented electrical steel sheet self-material (JS-50A470, 50A1300) Way. The method according to claim 1, wherein the cooling control step Wherein a water cooling required amount is calculated by applying a heat flux correction coefficient value reduced by about 7% to a value of a heat flux correction coefficient applied to a tip end of a general steel plate other than the material to be controlled upward.

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