KR20010064784A - Method for manufacturing cold rolled thin steel sheets - Google Patents

Abstract

PURPOSE: A method for manufacturing extreme-thick material cold rolled sheet is provided to prevent wrinkle due to swelling in the edge part by leveling width directional thickness profile of sheet and improve the shape quality. CONSTITUTION: In a method for manufacturing extreme-thick material cold rolled sheet in a 6-Hi stand to easily process continuous annealing, strip crown of stand outlet side satisfies a formula Ci=(-5.52 ε - 0.95561)Fw,i + (-1.284ε -0.24397)FI,i + (1.45ε+0.2397)δi + (0.15ε+0.03604)Pi-0.43615CH,i + 7.20308, wherein Fw,i is curvature force of each stand working roll, Fi,i is curvature force of each stand intermediate roll, and δi is displacement of each stand intermediate roll, and Pi is reduction force of each stand (i=1-5).

Description

Method for manufacturing cold rolled thin steel sheet

BACKGROUND OF THE INVENTION Field of the Invention The present invention generally relates to a method for preventing the occurrence of convex bulging (build up) edge wrinkles due to a change in the thickness profile in the continuous annealing process in the manufacture of an ultra-thick cold rolled steel sheet having a thickness of 1.6 mm or more. In the cold rolling process, which is the previous stage of the continuous annealing process, an edge drop (thickness reduction section) of a wide area is formed in advance in the width direction of the steel sheet to minimize the influence of the continuous annealing process. It is about.

In general, the cold rolled product is subjected to an annealing process that is gradually cooled after being heated to a predetermined temperature in order to soften the steel, adjust the crystal structure or remove the internal stress. At this time, based on the thickness of the cold-rolled product, for example 1.6mm thickness, the annealing process may be divided into an annealing process and a continuous annealing process.

In the manufacturing method of the ultra-thick steel sheet according to the conventional embodiment, the cold rolled steel sheet was produced as a final product in a batch annealing furnace (BAF). The annealing step is a step of performing a heat treatment called annealing by putting the cold rolled steel sheet into a furnace in a coil wound tightly and raising the internal temperature. At this time, since the external physical force on the steel sheet is completely excluded, the thickness profile at the time of cold rolling is maintained in the same state even if it undergoes an annealing process.

However, the product produced through the annealing process has a disadvantage in that the surface quality of the steel sheet is poor due to the gas atmosphere in the annealing furnace, so that a lot of quality defects occur, and mass production is impossible because the time required for the annealing takes much time. Therefore, the continuous annealing process is inevitable in terms of quality and mass production.

Steel plate of heavy material thickness has been working in continuous annealing process for a long time, but continuous annealing work of extreme thick material was not activated until recently and still had to be produced through an annealing process.

In other words, when working with ultra thick materials in the continuous annealing process, external physical forces such as roll crown (convexity of the center part), temper rolling conditions such as tension, rolling force and elongation on the steel sheet have a great influence on the surface of the steel sheet. For this reason, as shown in FIG. 1, it can be seen that the thickness difference 12 after annealing and after rolling has caused more thickness reduction at the center of the steel sheet than at the edge portion.

Meanwhile, as shown in FIG. 2, the 6-Hi 5 stand type cold rolling mill employing six rolls has an intermediate roll (IMR) between a back up roll (BUR) and a work roll (WR). The upper three rolls and the lower three rolls with the rolls inserted therein are arranged in six vertical stages. This rolling mill has the advantage that the thickness profile is very flat.

This can also be seen in the thickness profile 10 of the steel sheet after cold rolling as shown in FIG. 1. However, this advantage is advantageous for continuous annealing of the cold rolled steel sheet of thin thickness, but in the ultra-thick steel sheet, as shown in the thickness profile 11 after the continuous annealing, swelling (13, 14) occurs in the edge portion. This is because the thickness reduction amount of the edge portion is relatively small. This swelling is a fatal defect called edge wrinkles.

However, it is difficult to solve the above problem in the continuous annealing process. This is because, in order to solve these problems, it is well understood what adjustments are desirable in the continuous annealing process, but the interpretation based on the theoretical background for applying such adjustments to the actual process is still insufficient. Because there is.

Therefore, since the problem cannot be solved in the continuous annealing process, the defective steel sheets must be corrected again through a facility called a correction line, which increases the cost and reduces the error rate. And, even through the correction line, there is a limit to the correction of severe swelling. Accordingly, there is a need to solve the above problem in the cold rolling process, which is a previous step.

In order to solve the conventional problems as described above, the present invention relates to the intermediate roll displacement amount, the intermediate roll bending force, the work roll bending force and the pressing force, which are factors that greatly affect the thickness profile of the steel sheet edge portion in the cold rolling process. The purpose of the present invention is to provide a method for manufacturing ultra-thick cold rolled steel sheets in which cold rolling work conditions obtained through simulation are applied to actual field work, and operating conditions for cold rolling work in consideration of the change in thickness profile of the continuous annealing process are set. There is this.

That is, according to the embodiment of the present invention, when the ultra-thick cold rolled steel sheet is produced in the continuous annealing process, wrinkles are formed in the edge portion because the center portion is thinner than the edge portion of the steel sheet by an external force acting on the surface of the steel sheet. In order to prevent this problem, the purpose of the present invention is to provide a method for manufacturing an ultra-thick cold rolled steel sheet which can prevent the influence of the continuous annealing process in advance by making the thickness of the edge area of a wide area thin in the cold rolling process, which is a preliminary step of the continuous annealing process. have.

According to the present invention, in order to achieve the above object, the method for manufacturing the ultra-thick cold rolled steel sheet in the 6-Hi stand to facilitate the process of continuous annealing is a stand exit strip crown (C _i )

C _i = (-5.52ε- 0.95561) F _{w, i} + (-1.284ε-0.24397) F _{I, i} + (1.45ε + 0.2397) δ _i + (0.15ε + 0.03604) P _i -0.43615C _{H, i} + 7.20308, where Fw, i is the bending force of each stand work roll, Fi, i is the bending force of each stand intermediate roll, δi is the amount of displacement of each stand intermediate roll, i = 1 to 5).

1 is a graph showing a thickness profile of a cold rolled steel sheet according to a conventional embodiment.

Figure 2 shows a typical 6-Hi 5 stand cold rolling mill.

Figure 3 is a detailed view of the stand showing the displacement and the bending direction of the rolling roll.

4 is a flowchart for obtaining a thickness profile prediction model after cold rolling according to an embodiment of the present invention.

5 is a graph showing the results of a simulation according to an embodiment of the present invention.

Figure 6 is a graph showing the thickness profile of the cold rolled steel sheet according to an embodiment of the present invention.

<Description of Symbols for Major Parts of Drawings>

30, 35: reinforcement roll

31, 34: middle roll

32, 33: work roll

36, 37, 38, 39: displacement

40, 41, 42, 43: curved direction

44, 45: reduction amount

60: material steel sheet thickness profile

61: thickness profile after cold rolling by simulation

Hereinafter, with reference to the accompanying drawings illustrating a preferred embodiment of the present invention as follows, the same configuration adopts the same reference numerals.

2 is a schematic view of a typical 6-Hi 5 stand cold rolling mill. The raw material steel plate 20 is reduced in thickness while passing through the fifth stands 21 to 25 in the first stand, and is wound in the form of a coil 27. Immediately before winding, there is a profile measuring device called a shape measuring device 26 to measure the thickness profile in the width direction of the steel sheet.

As shown in FIG. 3, each stand has a shape in which six rolls are aligned, and the order from the top is the upper reinforcement roll 30, the upper middle roll 31, the upper work roll 32, and the lower work. Roll 33, the lower intermediate roll 34, the lower reinforcement roll 35 in the order. At this time, the middle roll (31, 34) has a left and right displacement function (40, 43) and the upper or lower curved function (36, 39), the work roll (32, 33) and the left and right displacement function (41, 42) and It has an upper or lower curved function (37, 38).

In the cold rolling process, the rolling factors to be considered for inducing the edge drop include the work roll bending force, the middle roll bending force, the middle roll displacement amount, the work roll displacement amount, the work roll diameter, the tension between the stands, the rolling reduction rate, the reduction force and the deformation resistance. There are many factors such as, roll material, roll crown (convexity), hot rolled steel crown. It is well known that among these factors, the middle roll displacements (40, 43), the middle roll bending force (36, 39), the work roll bending force (37, 38) and the pressing force (44, 45) are the most important influence factors. to be.

At this time, based on the various theoretical rolling models developed previously, the middle roll displacement amount (40,43), the middle roll bending force (36,39), the work roll bending force (37,38) and the reduction force (44,45) The model equation for predicting the steel plate thickness profile after cold rolling was calculated by performing calculation while changing). Here, Ci (i = 1-5) is the steel plate crown amount at each stand exit side.

First, stand 1;

_{C 1 = -2.362F w.1 - 0.56756F l.1} + 0.61333δ 1 + 0.07253P 1 - 12.2663

Stand 2;

_{C 2 = -2.28677F w.2 - 0.55309F l.2} + 0.59186δ 2 + 0.07206P 2 - 12.88662

Stand 3;

_{C 3 = -2.21582 w.3 - 0.53823F l.3} + 0.57221δ 3 + 0.07092P 3 - 13.0549

Stand 4;

_{C 4 = -1.92444 w.4 - 0.47422F l.4} + 0.49246δ 4 + 0.06498P 4 - 10.8368

5th stand;

C ₅ = -1.22751 _w.5 - it is _{3.4830 - 0.30532F l.5 + 0.31279δ 5 +} 0.0424P 5.

Where Ci is each stand exit strip crown (i = 1-5), Fw, i is each stand work roll bending force (i = 1-5), and Fi.i is each stand middle roll bending force (i = 1-5), delta i is each stand intermediate roll displacement amount (i = 1-5), and Pi is each stand rolling force (i = 1-5).

At this time, since the constant value is different for each stand, the final model was obtained by using the effect of the reduction ratio in order to integrate all the stand in one equation.

That is, C _i = (-5.52ε- 0.95561) F _{w, i} + (-1.284ε-0.24397) F _{I, i} + (1.45ε + 0.2397) δ _i + (0.15ε + 0.03604) P _i -0.43615C _{H , i} + 7.20308.

Using this model, several simulations were carried out by a calculation procedure as shown in FIG. This is a simulation for predicting the exit steel sheet thickness profile 58 after completion of the work up to the 5th stand when the entry hot rolled steel sheet profile 50 is arbitrarily set, and the cold rolling mill information 52 and the steel sheet information from the existing cold rolling mill control system. (53) and the cold rolling profile profile predictive model (51) based on the rolling information 54, the model obtains the thickness profile 55 of the stand repeatedly up to the 5th stand.

Meanwhile, FIG. 5 shows an optimal rolling condition obtained through the simulation of FIG. 4. Here, the first stand side profile 60 is set to a thickness profile immediately before the cold rolling mill, and is set in the form of a crown having a central portion of about 40 μm, which is a state of thickness of the most common form. The thickness profile after the simulation was 19.4 µm, as can be seen from the graph showing the final stand exit profile 61.

For example, when the simulation is performed under the conditions shown in Table 1, it can be seen that the thickness profile after cold rolling is thinner than the center portion.

Table 1

Cold rolling mill stand number One 2 3 4 5 Cold rolled steel entry hot rolled steel sheet size Thickness 6000 X 1231mm in width Cold rolled steel sheet thickness (mm) 4.740 3.663 2.930 2.430 2.357 Front tension (kgf / mm2) 3.4 4.2 4.2 4.3 0.3 Rear tension (kgf / ㎡) 1.5 3.4 4.2 4.2 4.3 Rolling force (ton) 986 1228 1086 1066 636 Working roll bending force (ton / chock) 41.4 37.8 31.2 24.6 21.0 Mid-roll bending force (ton / chock) 58.4 56.8 49.6 48.0 31.2 Intermediate roll displacement (mm) 300 300 300 50 20

At this time, the intermediate roll displacements 40 and 43, the intermediate roll bending forces 36 and 39, the work roll bending forces 37 and 38, and the pressing force 44 and 45, which are considered to be optimal by simulation, were obtained. The measured result is shown in FIG.

That is, referring to FIG. 6, as can be seen from the thickness profile 62 after cold rolling, it is understood that sufficient edge drops 64 and 65 are applied to the edge portion in the cold rolling process. And it turns out that the thickness profile 63 of the steel plate after continuous annealing has become very flat by this. These simulations and measurements were conducted on various sizes and materials. As a result, the following optimal working conditions were derived for each stand.

The optimum intermediate roll displacement is as follows.

(Thickness after cold rolling: 1.45mm or more, steel grade: whole)

division <900mm <1200mm <1500mm <1700mm ≥1700mm 1,2 stand 150 ~ 300mm 150 ~ 300mm 120 ~ 250mm 90 mm 40 mm 3, 4, 5 stand 100 ~ 1200mm 100 ~ 120mm 100 ~ 120mm 70 mm 40 mm

The optimum working roll curvature is as follows.

(Thickness after cold rolling: 1.85mm or more, width: whole, steel grade: less than 30)

division 1st stand 2nd stand 3rd stand 4th stand 5th stand Work roll curvature 50-65% 45-60% 38-46% 33-46% 30%

The optimum intermediate roll curvature is as follows.

(Thickness after cold rolling: 1.85mm or more, width: whole, steel grade: less than 30)

division 1st stand 2nd stand 3rd stand 4th stand 5th stand Middle roll curvature 11-13% 11-13% 11-13% 30-42% 25-30%

As described above, the ultra-thin material was produced by applying the intermediate roll displacement, the intermediate roll bending force, and the working roll bending force of the cold rolling mill. It was possible to prevent the wrinkles, and to improve the shape quality of the ultra-thick material.

The foregoing is merely illustrative of the preferred embodiments of the present invention and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without departing from the spirit and gist of the invention as set forth in the appended claims. It should be recognized.

Claims (3)

In the method of manufacturing a very thick cold rolled steel sheet in a 6-Hi stand to facilitate the process of continuous annealing, Stand exit strip crown (C _i ) is C _i = (-5.52ε- 0.95561) F _{w, i} + (-1.284ε-0.24397) F _{I, i} + (1.45ε + 0.2397) δ _i + (0.15ε + 0.03604) P _i -0.43615C _{H, i} + 7.20308, Where Fw, i is the bending force of each stand work roll, Fi, i is the bending force of each stand middle roll, δi is the amount of displacement of each stand middle roll, and Pi is the respective stand rolling force (i = 1 Ultra-thick cold rolled steel sheet manufacturing method characterized in that ~. The method of claim 1, wherein the rolling mill is 4 to 5 stands. The method according to claim 2, wherein the crown in the final stand exit thickness profile of the rolling mill is 19.4 ± 2㎛.