JP3239761B2 - Method of estimating stripped camber and method of manufacturing steel sheet with less stripped camber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating a strip camber of a steel sheet manufactured by accelerated cooling after hot rolling or hot straightening and a method of manufacturing a steel sheet having a small number of strip cambers based on the estimation. It is.

[0002]

2. Description of the Related Art The accelerated cooling method of water-cooling a steel sheet immediately after hot rolling can produce a thick steel sheet having high strength, high toughness and excellent weldability, and thus can produce various high-tensile steel sheets for shipbuilding and building materials. Has been put to practical use.

[0003] In such an accelerated cooling method, uneven cooling is likely to occur in the width direction of the sheet during the cooling process, and when uneven cooling occurs, complicated residual stress and large deformation occur in the steel sheet. Regarding deformation, the plate shape can be flattened by hot leveler straightening or other straightening means, and the flatness can be confirmed by a flatness meter or visually, but it is not possible to measure the residual stress inherent in the steel plate. Have difficulty.

[0004] In order to obtain a long material for manufacturing a long pillar for building a ship or a box column of a building material, a steel plate accelerated and cooled is often cut in a longitudinal direction with a width of about 300 mm to 500 mm. This is called stripping, and the separated boards are called stripping materials. Even if the steel sheet having the above-mentioned residual stress is cut, the residual stress is released even if the steel sheet has the above-mentioned residual stress, so that the strip member undergoes in-plane and out-of-plane bending deformation. Out-of-plane bending deformation can be easily corrected because the plate thickness is small, but the width of the strip is 300 mm to 500 mm.
Therefore, it is difficult to correct in-plane bending deformation, which is a major problem in the production of shipbuilding materials and building materials. Such in-plane bending deformation is called a strip camber.

[0005] Fig. 1 shows how a strip camber is generated. In FIG. 1, reference numeral 1 denotes a stripping material, and 2 denotes a stripping camber. The main cause of the stripping camber is
This is because the plate is not uniformly cooled in the width direction during the accelerated cooling process.In addition, in the case of the strip material at the edge portion of the steel plate, in addition to the above, the temperature of the edge portion before the accelerated cooling, except for the edge portion not adjacent to the edge portion (Hereinafter referred to as “general part”) because the residual stress in the longitudinal direction becomes uneven in the width direction. When the strip is released, the residual stress in the longitudinal direction is released, but since the distribution is uneven in the width direction, the longitudinal strain generated by the stress release is also uneven in the width direction, and the in-plane lateral bending of the strip material is caused. It happens. Therefore, in order to prevent the strip camber, means for controlling the cooling in the width direction and means for reducing the residual stress are effective.

[0006] The strip camber is easily generated by the strip material at the edge of the steel sheet. As a means for controlling the cooling in the width direction to reduce the size, there is a method of disposing shield plates at both edges of the steel sheet. FIGS. 2 to 4 are graphs for explaining a change in the edge camber distribution graph and the strip camber depending on the amount of protrusion of the shielding plate. The shielding plate protrudes in the width direction of the steel sheet to control the amount of water at the edge of the steel sheet and adjust the temperature distribution at the edge.
If the shielding plate is not used (or the projection amount of the shielding plate is small), the edge part has a temperature drop before accelerated cooling, and is further cooled during cooling. 2
, And a convex camber is generated outside the steel plate.
When the shielding plate is protruded inside the steel plate, the cooling water at the edge portion is shielded, so that the temperature distribution is flat. The camber gradually decreases and eventually no camber occurs (see FIG. 3). If the shielding plate is protruded further than that, a camber projecting inwardly of the steel plate is generated (see FIG. 4). Therefore, it is important to find an appropriate shield plate position where camber does not occur. As a means for controlling the cooling in the width direction, there is also a method of adjusting the discharge water amount density distribution of the cooling water in the width direction. If the discharge water density is made smaller at the edge than at the center of the steel sheet, the same effect as when the shielding plate is protruded is obtained. In this case, it is important to find a proper discharge water amount density distribution that does not generate camber. For these reasons, it is necessary to accurately and quickly estimate the strip camber of the steel sheet.

Japanese Unexamined Patent Publication (Kokai) No. 63-168209 discloses a method for obtaining a characteristic value of a steel sheet surface temperature distribution immediately after accelerated cooling and estimating a strip camber (hereinafter referred to as "prior art 1"). .

[0008] An "online prediction system for the amount of lateral bending in strip cutting of an accelerated cooling type steel sheet" (Kobe Steel Engineering Reports / Vol.41 No.4 (1991)) discloses a method for determining a stripping camber from a temperature distribution after straightening. A prediction method is shown (hereinafter referred to as “prior art 2”).

As a means for reducing the residual stress, a cold leveler or stress relief annealing is used.

[0010]

In order to properly perform the cooling control in the accelerated cooling process and the correction control in the next process, it is necessary to quantitatively, accurately and quickly grasp the strip camber. However, the method of estimating the strip camber from the characteristic value of the temperature distribution shown in Prior Art 1 has the following problems. That is, the temperature distribution of the steel sheet is complicated and greatly fluctuates in both the width direction and the longitudinal direction of the steel sheet, and particularly at the edge portion, turbulence of the cooling water flow easily occurs, and the temperature distribution pattern itself may change, It is extremely difficult to accurately estimate the strip camber from only the characteristic values of the temperature distribution.

In the method for predicting the strip camber from the post-straightening temperature distribution shown in the prior art 2, the thermal stress generated because the temperature unevenness occurring in the post-straightening steel sheet becomes uniform at room temperature. According to this estimation method, if the temperature unevenness after the correction is the same, the same camber is generated for any steel plate of any thickness. However, the present inventors have the knowledge that even if the temperature unevenness after correction is the same, the strip camber is considerably different if the sheet thickness is different. From this point, the accuracy of the estimation method of the prior art 2 is poor. it is obvious.

As a means for reducing the residual stress, it is effective to remove the residual stress by a cold leveler or to perform stress relief annealing. However, as described above, it is difficult to measure the residual stress of the steel sheet. In order to guarantee that the residual stress is not more than the value, after all, measures must be taken to reduce such residual stress in all steel sheets, which is very costly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a precise and quick method for estimating a break camber, and to suppress the break camber at low cost and based on the method. It is an object of the present invention to provide a method of manufacturing a steel sheet which can be performed.

[0014]

SUMMARY OF THE INVENTION In a steel sheet immediately after accelerated cooling, the surface temperature is low and the temperature in the center of the thickness is high. As time elapses, the heat in the central portion of the plate thickness flows to the surface, so that the temperature difference between the surface and the central portion gradually decreases. This process is called recuperation. During reheating, the temperature distribution on the surface is constantly changing. The recuperation is 15 for a 25 mm thick steel plate.
The process is completed in about 40 seconds for a steel plate having a thickness of about 50 seconds. After the completion of the reheating, the temperature distribution in the thickness direction becomes almost uniform, but the temperature distribution on the steel sheet surface remains clearly, and its time change is very slow and stable. After the completion of reheating, the time change of the internal stress is very slow and stable.

In the first invention of the present application, the temperature distribution on the surface of the steel sheet is measured as early as possible after the end of recuperation after accelerated cooling. In the manufacturing method in which the accelerated cooled steel sheet is straightened by a hot leveler, the straightening is usually performed after about 20 seconds for a 25 mm thick steel sheet and about 50 seconds for a 50 mm thick steel sheet after accelerated cooling. Has been completed,
The measurement may be performed before, after, or during the correction. Then, a large number of strips having a width of 300 mm to 500 mm are assumed on the steel sheet, and a camber of this virtual strip is estimated from the measured steel sheet temperature distribution. As a method for estimating this, it is assumed that the residual stress of the steel sheet at room temperature is caused by the uneven temperature occurring in the steel sheet after straightening becomes uniform at room temperature, and the stripping camber is estimated from the residual stress. Is known.

However, according to the study by the inventors, among the internal stresses generated by accelerated cooling and existing after the end of recuperation, non-uniform stresses in the width direction which are generated by non-uniform cooling and cause stripping cambers. If the hot leveler straightening is not performed, it remains as it is, and even if the hot leveler straightening is performed, most of it remains even after the straightening, and the strip camber caused by this internal stress when the steel sheet reaches room temperature is very It is clear that it is impossible to accurately predict the section camber without taking this into account. The present invention has been made based on these findings.

The gist of the first invention of the present application resides in the point that the steel sheet is subjected to accelerated cooling after hot rolling or hot straightening, and the temperature distribution of the steel sheet after the accelerated cooling is obtained. The surface temperature distribution of the steel sheet is measured after the recuperation is completed, which is substantially uniform in the thickness direction, and a camber when the steel sheet is cut after cooling on the cutting line set on the steel sheet is estimated. In the method, when a slice obtained by subdividing the strip material in the longitudinal direction is non-uniformly accelerated and cooled in the width direction, a change in the surface temperature in the width direction of the slice after the completion of the recuperation and the non-uniform cooling occur. The relationship of the slice with the curvature of the strip camber caused by the residual stress after cooling is obtained in advance by calculation means, and the surface temperature distribution in the width direction of the strip material is calculated from the surface temperature distribution of the steel sheet. Is calculated, and from the longitudinal distribution of the surface temperature change in the width direction of the strip material, the longitudinal distribution of the curvature of the strip camber after cooling the steel sheet is calculated using the relationship, and the longitudinal direction of the curvature is calculated. Calculate the deflection curve of the strip camber from the distribution, further calculate the camber deflection curve of the entire steel sheet that occurs when the surface temperature distribution of the steel sheet becomes uniform after cooling the steel sheet, and calculate the camber deflection curve of the entire steel sheet A method for estimating a strip camber, characterized by adding a minus sign to the deflection curve of the strip camber to obtain a camber of the strip material.

High-speed water is sprayed on the steel sheet during rolling for descaling, and roll cooling water stays.
For this reason, at the end of rolling, that is, at the start of accelerated cooling, the temperature of the steel sheet is often not uniform. The present inventors have found that such non-uniform temperature distribution at the start of accelerated cooling has a non-negligible effect on the strip camber, and have reached the following invention.

That is, the gist of the second invention of the present application resides in that when a steel sheet is manufactured by accelerated cooling after hot rolling or hot straightening, the steel sheet is produced at the start of the accelerated cooling and the accelerated cooling. After reheating, the temperature distribution of the steel sheet after cooling becomes substantially uniform in the thickness direction, the surface temperature distribution of the steel sheet is measured, and the steel sheet is cut after being cooled on a cutting line set on the steel sheet. A camber at the time of the start is estimated from the surface temperature distribution of the two steel plates at the start of the accelerated cooling and after the end of the recuperation.

The gist of the third invention of the present application resides in that at the start of accelerated cooling when a slice obtained by subdividing the strip material in the longitudinal direction is accelerated and cooled unevenly in the width direction. Using the width-direction surface temperature change of the slice as a parameter, the width-direction surface temperature change of the slice after completion of the reheating, and the slice camber of the slice caused by the residual stress after cooling generated by the uneven cooling. The relationship with the curvature of the steel sheet is calculated in advance by calculation means, and the longitudinal distribution of the surface temperature change in the width direction of the strip material is calculated from the steel sheet surface temperature at the start of the accelerated cooling. The longitudinal distribution of the width-direction surface temperature change of the strip material is calculated from the temperature, and the length of the two width-direction surface temperature changes at the start of the accelerated cooling and after the completion of the recuperation. From the directional distribution, determine the longitudinal distribution of the curvature of the strip camber after cooling the steel sheet using the relationship, calculate the deflection curve of the strip camber from the longitudinal distribution of the curvature, and further, the surface temperature distribution of the steel sheet Calculates the camber deflection curve of the entire steel sheet generated when the temperature becomes uniform after cooling the steel sheet, and adds a minus sign to the camber deflection curve of the entire steel sheet to the deflection curve of the stripping camber. 3. A method for estimating a strip camber according to claim 2, wherein a camber of the cut material is obtained.

According to a fourth aspect of the present invention, the amount of change in the surface temperature in the width direction is a gradient obtained by approximating the surface temperature distribution in the width direction by a least square method. The method according to claim 1 or 3, wherein a surface temperature gradient is used.

According to a fifth aspect of the present invention, the curvature of the strip camber caused by the residual stress after cooling generated by the non-uniform cooling is determined after the end of reheating or after the end of reheating. 5. The method for estimating a stripping camber according to claim 4, wherein the value is obtained from the surface temperature gradient in the width direction after and at the start of accelerated cooling using the following equation.

The general stripping material is as follows: C = ｛(− 17.65 + 0.326t) Tg + (− 1)
1.12 + 0.222t) Tgo｝ × 10 ⁻⁶ + αTg The left edge of the edge part strip is C = ｛(− 10.7 + 0.19t) Tg + (0.40−
0.0068t)｝ × 10 ^-6 + αTg The right edge of the edge strip is C = Ｃ (-10.7 + 0.19t) Tg- (0.40-
0.0068t)｝ × 10 ⁻⁶ + αTg where C: curvature of the camber (1 / mm) (the curvature that causes a camber convex to the left when viewed in the longitudinal direction is positive) t: plate thickness (mm) Tg: return Surface temperature gradient in the width direction after heat end (° C / mm)
(Positive when the temperature increases from left to right) Tgo: Surface temperature gradient in the width direction at the start of accelerated cooling (° C./m
m) α: Linear expansion coefficient (1 / ° C.) The present inventors succeeded in accurately and quickly estimating the strip camber of the steel sheet by the first to fifth inventions of the present application, and at low cost and reliably. In order to apply the present invention to a method for manufacturing a steel sheet capable of suppressing a strip camber, the following invention has been attained.

According to a sixth aspect of the present invention, a shield plate is disposed on both edges of a steel plate during accelerated cooling of the steel plate, and the shield plate projects or retreats in a width direction of the steel plate. The method according to claim 1, wherein the cooling is performed by controlling the amount of cooling water at the edge of the steel plate or adjusting the discharge water density distribution in the width direction to control the amount of cooling water at the edge of the steel plate. Estimating the strip camber of the steel sheet by any one of the methods, and controlling the protrusion amount of the shielding plate or controlling the discharge water amount density distribution of the cooling water based on the estimated value. This is a method for producing a steel sheet with less stripping camber.

According to a seventh aspect of the present invention, a camber of a steel sheet is estimated by any one of the first to fifth methods, and the estimated value is an allowable value. If the number exceeds the limit, a method for reducing the residual stress of the steel sheet is applied in a subsequent manufacturing process, thereby providing a method for manufacturing a steel sheet with less stripping camber.

[0026]

Next, the present invention will be described with reference to the drawings. The method for estimating the strip camber of the first invention of the present application will be described in detail.

First, the internal stress generated after the end of reheating after accelerated cooling is estimated. Since it is difficult to estimate this stress, the stress is estimated by performing a thermo-elasto-plastic analysis by the finite element method. For this purpose, high-precision analysis is required, and in particular, phase transformation (transformation from γ phase to α phase) must be precisely considered. When phase transformation occurs, transformation heat is generated, and the thermal conductivity changes due to the structural change, so that the temperature distribution and the time history change. The change in temperature affects the thermal stress, further causes transformation expansion, and changes the yield stress and the like due to the transformed structure, so that the internal stress is greatly affected by the phase transformation.

The present inventors have developed a thermal stress analysis system capable of precisely considering such a phase transformation phenomenon, and have succeeded in estimating the internal stress with high accuracy. In this system, a time-varying temperature is converted into a step-like surface temperature change based on a TTT diagram (isothermal transformation diagram), and the transformation behavior is tracked by joining the isothermal transformations. Fig. 5 shows the TTT diagram used for analysis (for steel types with a plate thickness of 50 mm or less)
6 and 7 show the thermal conductivity and the heat capacity. The heat capacity before transformation is that of the γ phase. When transformed at a certain temperature, the latent heat (shaded area) up to that point is generated as transformation heat, and thereafter becomes the heat capacity of the α phase. FIG. 8 shows the yield stress of each structure. These physical property values and material constant values are values corresponding to the fraction of each structure. In thermal stress analysis, it is necessary to be able to accurately express the transformation expansion that has a large effect on the widthwise non-uniformity of the stress distribution. FIGS. 9 to 11 show the delay (strain) when cooled at various cooling rates from 900 ° C. by an experiment using a processing for master and comparing with the calculation results under the same temperature condition. 9 to 11, the temperature at which the transformation expansion starts is written. When the cooling rate is high, the behavior in which the transformation shifts to the low temperature side and the transformation expands can be accurately reproduced in the calculation, and the two agree well.

As described above, the temperature and the stress from the start to the end of the accelerated cooling of the steel sheet and further from the start to the end of the recuperation were calculated by using the thermal stress analysis system capable of precisely handling the phase transformation phenomenon.

An analysis is performed on a model obtained by slicing the strip material shown in FIG. 12 in the longitudinal direction. Strip width is 500m
m. Cooling is the same on the upper and lower surfaces, and 1/2 in the thickness direction
The slice cut plane keeps a plane, and moves in parallel so that the integral value of the longitudinal stress on the cut plane becomes zero. The calculation is started from the initial temperature at the start of accelerated cooling and the initial transformation rate (estimated separately by calculation). FIG.
3 is multiplied by (1 + a) and (1-a) by the left and right edges of the slice model shown in FIG. Express the temperature of the accelerated cooling process,
Calculate the stress. Further, the reheating process after the accelerated cooling is calculated, and the surface temperature change in the slice width direction and the internal stress after the reheating is completed are obtained. If hot leveler correction is not performed, the calculation is continued as it is, thermal stress analysis is performed until the temperature of the slice becomes a uniform temperature at room temperature, the internal stress at room temperature,
That is, the residual stress is obtained.

When performing hot leveler correction, the internal stress of the slice before hot leveler correction is determined. After the completion of the reheating, the temporal change of the internal stress is slow, and the correction is usually performed after the completion of the reheating. Therefore, the internal stress after the completion of the reheating may be regarded as the internal stress before the correction. The internal stress after hot leveler correction is obtained by performing elasto-plastic analysis for simulating the correction process on the slice model having the internal stress before correction. Then, thermal stress analysis is performed on the obtained slice having the corrected internal stress until the slice temperature becomes a uniform temperature at room temperature, and the internal stress at room temperature, that is, the residual stress is obtained.

The curvature of the strip camber is calculated from the residual stress thus obtained. In the stress state at room temperature, when the boundary condition that the cut surface moves in parallel is released, the cut surface rotates around the axis in the thickness direction while maintaining the plane, and the slice deforms into a sector shape, but this is the slice. It is a sectioned camber. The inventors determined the curvature from the rotation angle of the cut surface. The moment around the axis in the plate thickness direction at the center of the slice due to the longitudinal stress may be calculated, and the moment may be divided by the bending rigidity to obtain the curvature.

In this manner, the relationship between the surface temperature change in the width direction after the end of recuperation and the curvature of the strip camber generated by the residual stress after cooling when the slice model is accelerated unevenly in the width direction. Ask for.

If the change in the surface temperature in the width direction after the end of recuperation is the same, the inventors of the present invention have the same curvature of the stripping camber after cooling obtained by the calculation means as that of the actual steel sheet. I found something.

At the steel sheet edge, at the start of accelerated cooling,
Because of the temperature drop shown in FIG. 4, the relationship between the surface temperature change in the width direction after recuperation in the strip material adjacent to the steel sheet edge and the curvature of the post-cooling strip camber is the general section not adjacent to the steel sheet edge. Fig. 1
Using the initial temperature and the initial transformation rate shown in 4, the calculation is performed separately from the general strip material.

The steel sheet surface temperature distribution after the completion of the reheating is substantially linear in the width direction in the case of a general sectioned material, and the gradient representing the linear approximation of this distribution can be used as an amount representing the width direction surface temperature change. it can. However, in the case of the edge strip material, the temperature distribution in the width direction after the end of recuperation becomes complicated as shown in FIG. The present inventors, even with such a complicated distribution, it is a least square approximation with a straight line,
It has been found that if the gradient of the straight line is adopted as a value representing the change in the surface temperature in the width direction, the degree of uneven cooling can be well expressed and corresponds one-to-one with the curvature of the post-cooling strip camber.

Furthermore, if the surface temperature gradient in the width direction after the end of reheating is the same, the curvature of the cut camber obtained by the calculation means after cooling is smaller than the actual cut material of the steel sheet. It was found that this was in good agreement with the present invention, leading to the fourth invention of the present application.

In the present invention, the gradient obtained when the temperature distribution measured as an amount representing the surface temperature change in the width direction is approximated by a least square approximation with a straight line is also used in the actual strip material. There is also an effect that noise included in the measurement value is eliminated.

The relationship between such a surface temperature gradient in the width direction of the stripping material and the curvature of the stripped camber after cooling was determined by a sheet thickness of 25 m.
FIG. 16 (plate thickness 25 mm) and FIG. 17 (plate thickness 50 mm) show the values calculated by using the thermal stress analysis system according to the representative steel type, accelerated cooling conditions and straightening conditions for steel plates of m and 50 mm. Such a relationship needs to be determined for various types of steel, the thickness of the steel sheet, the start and stop temperatures of accelerated cooling, and the correction conditions. It was found that the following equation can be used.

The general stripping material is as follows: C = {(− 17.65 + 0.326t) Tg + (− 11.12 + 0.222t) Tgo} × 10 ⁻⁶ + αTg (1) Equation (1) is used here. The entire three equations shown are shown.

The left edge of the edge strip is C = ｛(-10.7 + 0.19t) Tg + (0.40−
0.0068t)｝ × 10 ^-6 + αTg The right edge of the edge strip is C = Ｃ (-10.7 + 0.19t) Tg- (0.40-
0.0068t)｝ × 10 ⁻⁶ + αTg where C: curvature of the camber (1 / mm) (the curvature that causes a camber convex to the left when viewed in the longitudinal direction is positive) t: plate thickness (mm) Tg: return Tgo: widthwise temperature gradient at the start of accelerated cooling (° C / mm) α: linear expansion coefficient (1 /) ℃) The steel type, accelerated cooling condition and straightening condition are not included.
This is because these conditions are almost determined by the plate thickness. This formula can be applied to a strip width of 300 mm to 500 mm. Tgo is an amount to be included when considering a width-direction surface temperature change at the start of accelerated cooling described later.

The above relationships among various steel types, sheet thicknesses, accelerated cooling conditions, strip widths, and straightening conditions may be obtained and expressed in the form of a table. As described above, the relationship between the temperature gradient in the width direction after the reheating of the steel sheet and the curvature of the strip camber generated by the residual stress after cooling is obtained. This relationship holds for a slice of a strip having an infinitely small thickness in the longitudinal direction.

Next, a method of estimating a strip camber in an actual steel sheet using this relationship will be described. Application No. 1
In the present invention, the surface temperature distribution of the steel sheet is measured after the recuperation of the steel sheet accelerated and cooled. 300mm-5 width on this steel plate
Set a 00 mm strip line. FIG. 18 illustrates this. Reference numeral 3 denotes a dividing line, and reference numeral 4 denotes a dividing line. FIG.
In FIG. 8, one strip is shown for simplicity, but a number of strips are actually set in the width direction. FIG.
FIG. 8 also shows the contour line of the steel sheet surface temperature. As shown in FIG. 18, the strip material is subdivided in the longitudinal direction, and the temperature distribution on the dividing line is approximated by a straight line with least squares to calculate the temperature gradient in the width direction. Do this for all the dividing lines,
The longitudinal distribution of the temperature gradient in the width direction after the reheating of the strip is completed. Using the above relationship, the curvature of the strip camber after cooling the steel sheet can be obtained from the width direction temperature gradient after the end of recuperation. From this, the longitudinal distribution of the curvature of the strip camber after cooling the steel sheet can be obtained. By integrating this curvature distribution twice in the longitudinal direction, a deflection curve of the strip camber after cooling the steel sheet is obtained.

[0044]

(Equation 1) Here, v ₁ (x): deflection curve of the strip camber after cooling the steel sheet x: longitudinal coordinate of the strip material C ₁ (s): curvature of the strip camber after cooling the steel sheet at x = s According to the equation (2) shown, this integration is obtained by numerical integration using the interval between the dividing lines in the longitudinal direction as the section width.

V ₁ (x ₁ ) = 0 (3) ′ v ₁ (x _{j + 1} ) = v ₁ (x _j ) + h (x _j ) Δx + ｛1 / 3C ₁ (x _j ) + 1 / 6C ₁ (x _{j + 1} )｝ Δx ² (3) ″ h (x ₁ ) = 0 (3) ′ ″ h (x _{j + 1} ) = h (x _j ) + 1 / 2 ｛C ₁ (x _j ) + C ₁ (x _{j + 1} )｝ Δx (3) ″ ″ (j = 1,..., L−1) Equations (3) ′ to (3) ) '''' Is referred to as equation (3).

Here, x _j : x coordinate of the dividing line Δx: interval of the dividing line L: number of the dividing lines The above equation (3) gives a deflection curve when the lower end of the strip is fixed.

In this manner, the deflection curve of the strip camber after cooling the steel sheet is obtained. If the temperature distribution of the steel sheet after the end of recuperation reaches a uniform temperature after cooling, the entire steel sheet bends in the plane of the sheet, and when the bent steel sheet is cut, the stripping material returns to its original position by the amount of the horizontal bend. Cause camber. The present inventors have found that the strip camber can be more accurately estimated by considering this phenomenon. That is, the steel sheet temperature distribution is calculated by calculating the camber deflection curve of the entire steel sheet caused by a uniform temperature after cooling the steel sheet, and adding a minus sign to the deflection curve to the sectioning camber deflection curve after cooling the steel sheet. They add.
According to the study of the present inventors, this consideration improves the estimation accuracy of the strip camber by about 1 mm at maximum per 10 m of strip material. Usually, the allowable value of the strip camber is 5 mm per 10 m, so the contribution of the accuracy improvement is not small. However, when the calculation speed has to be given priority over the accuracy, the consideration of the entire steel plate camber is omitted. Is also good.

The camber of the entire steel sheet is calculated from the following equations (4) and (5) shown in equations (2) and (3).

[0049]

(Equation 2)

[0050]

(Equation 3) Here, v ₂ (x): camber of the entire steel sheet C ₂ (s): camber curvature of the entire steel sheet at x = s w: steel sheet width α: linear expansion coefficient y: coordinate in the steel sheet width direction T (s, y) ): Surface temperature distribution of steel sheet after completion of recuperation By adding the minus sign to the camber of the whole steel sheet to the above-mentioned stripping camber after cooling the steel sheet, the stripping camber can be more accurately estimated.

V (x) = v ₁ (x) −v ₂ (x) (6) The above equation (6) gives a deflection curve when the lower end of the strip is fixed. The strip camber is a deviation from a straight line connecting the upper end and the lower end of the strip material. This deviation, that is, the strip camber is obtained from the following equation (7) shown in Expression 4.

[0052]

(Equation 4) In the first invention of the present application, the strip camber is estimated as described above. The actual calculation is performed as follows. The deflection curve of the strip camber can be calculated from the following expression (8) shown in Expression 5 from Expressions (2) and (4).

[0053]

(Equation 5) Of the integrands, C ₂ (s) is determined in advance because it is the same for all strip members. C ₁ (s) is obtained from the strip material, and C ₂ (s) is subtracted therefrom to obtain the longitudinal integration.
That is, the numerical integration of Expression (3) is performed to obtain v (x). In this case, since the numerical integration is performed only once for each strip, the calculation efficiency is high. Such an operation is performed for each strip material.

At the start of accelerated cooling, the steel sheet may already have a temperature distribution due to descaling during rolling of the steel sheet, uneven cooling by roll cooling water, uneven peeling of scale, and the like. The present inventors have found that such non-uniform temperature distribution at the start of accelerated cooling has a non-negligible effect on the strip camber, and have reached the second invention of the present application.

The present inventors have found that, in the above slice model, if the temperature distribution that changes in the width direction at the start of accelerated cooling is calculated as an initial condition, this effect can be taken in accurately. Using the initial temperature that changes in the width direction as a parameter, the relationship between the change in the surface temperature in the width direction after the end of recuperation and the curvature of the strip camber after cooling is determined. In this case as well, as described in the first invention of the present application, a gradient when the width-direction temperature distribution is least-squares-approximated can be used as the amount indicating the width-direction surface temperature change.

FIG. 16 is a graph showing the results after the completion of reheating when the temperature gradient (Tgo) at the start of accelerated cooling is ± 0.04 ° C./mm in the case of a general strip having a thickness of 25 mm calculated by the thermal stress analysis system. 4 shows the relationship between the temperature gradient and the curvature of the strip camber after cooling. In the case of a steel plate having a thickness of 50 mm, as shown in FIG. 17, there is no influence of a change in surface temperature in the width direction at the start of accelerated cooling. The variation in the temperature drop at the start of the accelerated cooling at the edge portion is usually small and need not be considered. However, when the rolling pass schedule or the like is changed, the amount or pattern of the temperature drop may change. In such a case, it is necessary to recalculate the above relationship of the edge strip using such an initial temperature distribution. There is.

As a result of the study by the present inventors, the temperature gradient in the width direction after recuperation and the curvature of the post-cooling strip camber of the general sectioned material are considered in consideration of the temperature gradient in the width direction at the start of accelerated cooling. It can be understood that the relationship can be substantially expressed by equation (1).

Then, the temperature distribution of the steel sheet at the start of the accelerated cooling and after the end of the reheating is measured, and the temperature gradient in the width direction is calculated on the dividing line of the strip of the temperature distribution, and from these two temperature gradients in the width direction. If the curvature of the strip camber after cooling the steel sheet is obtained using the above relationship, it is possible to accurately estimate the strip camber. The process of obtaining the strip camber from this curvature is exactly the same as in the first invention of the present application.

The estimation accuracy of the strip camber according to the first invention of the present application was verified by performing a factory experiment. The experiment is 25m thick
The measurement was performed for two types of m and 45 mm, and the camber was measured by dividing the camber into six sections and compared with the estimated value according to the first invention of the present application. FIG. 19 (plate thickness 25 mm), FIG.
mm) shows the steel sheet size (mm) and the section line. The temperature distribution of the steel sheet was measured at the start of accelerated cooling and before hot leveler straightening.

Because of the temperature measurement, the temperature at the start and stop of the accelerated cooling was lowered by about 120 ° C. from that in the actual operation, so that the temperature gradient in the width direction after the completion of the recuperation under the accelerated cooling condition and the stripping camber after the cooling were completed. Was calculated again. FIG. 21 (plate thickness 25 mm) and FIG.
(Plate thickness 45 mm).

A series of procedures such as the above-described setting of the cutting line, calculation of the temperature gradient and curvature on the cutting material dividing line, and calculation of the cutting camber were all processed by a computer.
In FIG. 23 (plate thickness 25 mm) and FIG. 24 (plate thickness 45 mm),
A comparison between the measured value of the strip camber and the estimated value according to the first invention of the present application is shown (in the case of a plate thickness of 25 mm, the scale is changed by the strip material of the general portion and the edge portion). The two types of plots in the figure show the strip camber on the drive side (DS
□) and the free side (FS ▽). As shown in the drawing, the estimated value (Est · 1) and the measured value are in good agreement, and it can be seen that the accuracy of the estimation method of the first invention of the present application is very good.

Incidentally, as shown in the prior art, the strip camber is obtained only from the stress generated when the temperature distribution of the steel sheet at the time of straightening (after the end of recuperation) becomes uniform after cooling, and is compared with the actually measured value. Then, FIG. 25 (board thickness 25m
m), as shown in FIG. 26 (plate thickness 45 mm). FIG.
5. As is clear from FIG. 26, the accuracy of the conventional strip camber estimating method is very poor. In particular, in the case of an edge strip material, the estimated value is very large at a board thickness of 25 mm, and
In mm, the direction of the camber is reversed.

From these comparisons, it can be seen that the estimation method according to the first invention of the present application is far superior to the conventional method. In the steel plate having a thickness of 25 mm shown in FIG. 23, the camber estimation accuracy of the second and fifth strip members according to the first invention of the present application is slightly poor. The allowable value of the strip camber is usually 10
The accuracy is slightly insufficient because it is 5 mm per m. With these two strips, -0.02 ° C / mm at the start of accelerated cooling
There was a moderate temperature gradient. Therefore, the estimation method of the stripping camber was performed by using the estimation method according to the second and third inventions of the present application in consideration of the temperature gradient at the start of accelerated cooling. FIG. 27 shows a comparison between the estimated value and the actually measured value according to the second and third inventions of the present invention for a general strip. As shown in FIG. 27, it can be seen that the estimation accuracy of the No. 2 and No. 5 strip camber materials is greatly improved.

As described above, the use of the strip camber estimation method according to the second and third inventions of the present application further improves the accuracy compared to the first invention of the present application. As described above, according to the first to fifth aspects of the present invention, it is possible to accurately and quickly estimate a strip camber.

The present inventors applied the sixth embodiment of the present invention to apply the strip camber estimating method according to the first to fifth aspects of the present invention to camber control using an edge strip member in which camber is most likely to occur.
Invented the invention. As described above, the camber of the edge part stripping material, the shielding plate is disposed on both edges of the steel plate, and is projected or retracted in the width direction of the steel plate to adjust the amount of cooling water at the edge of the steel plate, or in the width direction. It can be suppressed by adjusting the discharge water amount density distribution of the cooling water and optimizing the edge part temperature distribution. As shown in FIGS. 2 to 4, the amount of protrusion of the shielding plate must be an appropriate amount without being too large or too small. However, conventionally, accurate estimation of the strip camber is impossible. As a result, it was difficult to find this appropriate amount online. The same is true when adjusting the discharge water amount density distribution in the width direction, and it has been difficult to find an appropriate water amount density distribution online. In the present invention, the strip camber can be accurately and quickly estimated only by measuring the temperature distribution of the steel sheet after the end of recuperation. Understand the relationship between the shielding plate or the cooling water discharge water density distribution in the width direction and the cutting camber during steel plate manufacturing, and from this relationship, do not generate the cutting camber or minimize the shielding plate protrusion amount or width direction The cooling water discharge water density distribution is found, and is fed back to the protrusion amount during accelerated cooling of the next steel sheet.

As described above, according to the present invention, the cutting camber is estimated with high accuracy and speed, and the shielding plate protrusion amount or the cooling water discharge water amount density distribution is controlled based on the estimated value. Can produce steel sheets with less noise.

The present inventors applied the seventh invention of the present application to apply the method for estimating the stripping camber of the first to fifth inventions of the present application to a method of manufacturing a steel sheet capable of suppressing the stripping camber at low cost and reliably. Reached.

In the present invention, the temperature distribution on the surface of the steel sheet at the start of accelerated cooling is measured, if necessary, after the completion of recuperation. And 300mm to 500mm width on steel plate
A large number of strips are assumed, and the camber of these strips is estimated from the measured temperature distribution by the estimation method according to the present invention. If this estimated value is less than or equal to a preset allowable value for all assumed strips, no means is taken to reduce residual stress. If there is a strip material that generates a camber exceeding the allowable value, means for reducing the residual stress is applied to the steel sheet in the subsequent manufacturing process. That is, specifically, cold leveling or warm leveling is performed, or stress relief annealing is performed.

As described above, according to the present invention, since the strip camber can be estimated with high accuracy and speed, it is possible to easily and surely select the steel sheet in which the strip camber exceeding the allowable value occurs. Since only the residual stress reducing means is applied to the steel sheet, the costly application of the residual stress reducing means can be suppressed to a necessary minimum, and a steel sheet having a strip camber below an allowable value at a low cost can be surely produced. Can be manufactured.

[0070]

Next, the present invention will be described with reference to embodiments. FIG. 28 is an explanatory diagram showing a production line of a steel sheet production facility incorporating the method for estimating a strip camber according to the embodiment of the present invention. As shown in FIG. 28, the steel sheet that has been hot-rolled by the finishing mill 5 is cooled by the accelerated cooling device 6 and straightened by the hot leveler 8. Before the acceleration cooling device 6 (upstream) and before the hot leveler 8 (upstream), the radiation thermometer 7 measures the temperature distribution on the steel sheet surface. The radiation thermometer 7 before (upstream) the hot leveler 8 may be arranged after (downstream) or inside the hot leveler 8. The measured temperature data is sent to the arithmetic unit 9 and the strip camber of the steel plate is calculated.

The arithmetic unit 9 receives temperature data of each point (256 points in the horizontal direction and 100 points in the vertical direction in the present embodiment) in the visual field of the radiation thermometer 7 and converts the data into a front plan view.
A steel plate edge is detected, and temperature data only for the inside of the plate is created. At this time, the steel plate edge is not a straight line, and the plate shape is also deviated from the rectangular shape. Therefore, the steel plate edge is corrected to have a rectangular shape having straight sides of the steel plate (see FIG. 18). Next, the steel sheet is divided into a number of grids, and data of grid point coordinates and grid point temperatures are created.

From this data, the longitudinal distribution of C ₂ (s) in equation (5), which is the camber curvature of the entire steel sheet, is calculated. This curvature is commonly used in the strip material. next,
The cutting line 3 is set on the steel plate as shown in FIG. 18 based on the cutting position data input in advance. This strip material is subdivided in the longitudinal direction, and the gradient at the time when the temperature distribution in the width direction is approximated by a straight line with least squares at each dividing line 4 is calculated. The calculation of the temperature gradient is performed using the coordinates of the grid points and the data of the temperature. In the case of estimating the strip camber according to the first invention of the present application, the calculation is performed on the temperature measurement data after the end of the recuperation. In the case of the invention, the measurement is performed on two temperature measurement data at the time of accelerated cooling and after the end of recuperation.

The relations obtained in advance by the calculation means, that is, FIG. 16 (plate thickness 25 mm) and FIG.
0 mm) or equation (1), and using this temperature gradient in the width direction, equation (2), which is the curvature of the strip camber after cooling the steel sheet.
The longitudinal distribution of C ₁ (s) is calculated.

C ₂ (s) is subtracted from C ₁ (s), and numerical integration of equations (8) and (3) is performed to obtain a camber deflection curve. Camber is calculated. In the arithmetic unit 9, such calculation is performed for all the strips to which the position data is input,
Those strip cambers are estimated.

As described above, such an estimation method according to the present invention has much higher accuracy than a known estimation method. The arithmetic unit 9 outputs a shielding plate protrusion amount instruction signal to a device 11 for moving the shielding plate 10 installed in the width direction of the steel plate to suppress the camber of the edge part cutting material. Since the maximum camber is generated substantially at the center of the strip, x = l / 2 from the equation (7), where (l: length of the strip)
Is calculated, and this is converted into camber per 10 m to determine the protrusion amount. The conversion is performed by multiplying the calculated camber by (10 / l) ² .

The amount of protrusion of the shielding plate 10 is controlled as follows. The relationship between the protrusion amount of the shielding plate 10 and the estimated camber value per 10 m (conventional results) is stored in a database for each plate thickness, steel type, accelerated cooling condition, and correction condition. As shown in FIG. 29, the data corresponding to the current steel sheet is linearly approximated to the data near the camber of zero, and the shielding when the first steel sheet is accelerated and cooled so that the camber becomes zero in this linear relationship. The protrusion amount of the plate 10 is determined. When manufacturing a large number of steel sheets having the same thickness, steel type, accelerated cooling condition, and straightening condition, as shown in FIG. 30, the second steel sheet has the same slope as the approximate straight line from the actual value of the first steel sheet as shown in FIG. A straight line is drawn, and the protrusion amount (point B) at which the camber becomes zero is determined. For the third and subsequent steel sheets, the amount of projection (point C) that sets the camber to zero is determined from the relationship between the amount of projection up to that point and the estimated camber value, and camber can be suppressed more reliably. Such control of the amount of protrusion of the shielding plate 10 is performed separately by the left and right edge portion cutting members.

The method of the present invention is different from the conventional method of fixing the amount of projection of the shielding plate, in that the camber of the edge portion stripping material is 50.
% To 80%. When controlling the discharge water amount density distribution in the width direction, the same as the control of the shield plate protrusion amount, using the ratio of the discharge water amount density of the steel plate center portion and the discharge water amount density of the edge portion instead of the shield plate protrusion amount. In the procedure, an appropriate ratio of the discharge water amount density at which camber does not occur is determined, and the discharge water amount density of the edge portion is determined from the ratio. Thereby, the camber of the edge portion stripping material can be controlled to the same degree as the control of the shielding plate protrusion amount.

After the completion of the hot leveler straightening, the steel sheet is sent to the transport branching machine 12. In the meantime, the arithmetic unit 9 determines whether to apply the residual stress reducing means based on the estimated value of the strip camber or not to use it. That is, it is checked whether the estimated camber value per 10 m of the stripping material is within the allowable range.

After it is determined whether or not the residual stress removing means needs to be applied to the steel sheet being transported, the signal is output from the arithmetic unit 9 to the transport branching machine 12. When the residual stress means is unnecessary, the steel sheet is transported to the cooling floor 13 as it is, and when necessary, it is once transported to the stock yard 14.

As a residual stress removing means, a stress relief annealing by a leveler 15 and a heating furnace 16 is prepared.
For extremely thick materials, stress relief annealing is performed within a temperature and time range that does not affect the material. For thin materials,
The residual stress is removed by the leveler 15. For medium thickness materials, leveling or stress relief annealing is performed.

Conventionally, the residual stress removing means has been applied to all steel sheets. However, according to the present invention, the number of steel sheets to which the residual stress removing means is applied is reduced, and the production cost is greatly reduced.

[0082]

As described above, according to the present invention, the strip camber of a steel sheet is quickly and accurately estimated and the amount of edge water during accelerated cooling is appropriately controlled. It can be manufactured, and the residual stress removing means is applied only to steel sheets whose stripping camber exceeds the allowable value by highly accurate estimation, so the number of times these costly means are applied is greatly reduced, and the cost is reduced. A steel sheet having a small cutting camber can be reliably manufactured, and thus an industrially useful effect is obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a strip camber.

FIG. 2 is a diagram illustrating a change in an edge portion temperature distribution graph and a strip camber according to a protruding amount of a shielding plate.

FIG. 3 is a diagram illustrating a change in the edge portion temperature distribution graph and the strip camber according to the amount of protrusion of the shielding plate.

FIG. 4 is a diagram illustrating a change in the edge temperature distribution graph and the strip camber according to the amount of protrusion of the shielding plate.

FIG. 5 is a graph showing an isothermal transformation diagram used in a thermal stress analysis that can precisely consider a phase transformation according to the present invention.

FIG. 6 is a graph showing temperature dependence of physical property values used in a thermal stress analysis which can accurately consider a phase transformation according to the present invention.

FIG. 7 is a graph showing temperature dependence of physical property values used in a thermal stress analysis which can precisely consider a phase transformation according to the present invention.

FIG. 8 is a graph showing the temperature dependence of the yield stress of each structure used in the thermal stress analysis according to the present invention.

FIG. 9 is a graph showing a comparison between a time history of a dilat and an experimental value under a processing for master experimental temperature condition calculated by a thermal stress analysis system according to the present invention.

FIG. 10 is a graph showing a comparison between a time history of a dilat and an experimental value under a processing for master experimental temperature condition calculated by a thermal stress analysis system according to the present invention.

FIG. 11 is a graph showing a comparison between a time history of a dilat and an experimental value under a processing for master experimental temperature condition calculated by a thermal stress analysis system according to the present invention.

FIG. 12 is a perspective view showing a slice model used in a thermal stress analysis according to the present invention.

FIG. 13 is a graph showing the temperature dependence of the heat transfer coefficient used in the thermal stress analysis according to the present invention.

FIG. 14 is a graph showing an initial temperature distribution of the edge portion strip used in the thermal stress analysis according to the present invention.

FIG. 15 is a graph showing the temperature distribution after reheating of the edge portion strip material used in the thermal stress analysis according to the present invention and its least square approximation.

FIG. 16 is a graph showing the relationship between the temperature gradient in the width direction after the completion of recuperation and the curvature of the strip camber after cooling used in the example of the present invention.

FIG. 17 is a graph showing the relationship between the temperature gradient in the width direction after the completion of recuperation and the curvature of the strip camber after cooling used in the example of the present invention.

FIG. 18 is a diagram illustrating a method for processing temperature data and estimating a strip camber according to an embodiment of the present invention.

FIG. 19 is a plan view illustrating a steel plate subjected to an accuracy verification experiment of the estimation method of the present invention.

FIG. 20 is a plan view illustrating a steel plate subjected to an accuracy verification experiment of the estimation method of the present invention.

FIG. 21 is a graph showing the relationship between the temperature gradient in the width direction after the completion of reheating and the curvature of the strip camber after cooling calculated for the accuracy verification experiment of the estimation method of the present invention.

FIG. 22 is a graph showing the relationship between the temperature gradient in the width direction after the completion of reheating and the curvature of the strip camber after cooling calculated for the accuracy verification experiment of the estimation method of the present invention.

FIG. 23 is a graph comparing an estimated value of the strip camber according to the first invention of the present application and an actually measured value in an accuracy verification experiment of the estimation method of the present invention.

FIG. 24 is a graph comparing an estimated value according to the first invention of the present application with an actually measured value in an accuracy verification experiment of the estimation method of the present invention.

FIG. 25 is a graph comparing an estimated value and a measured value of a strip camber according to the prior art in an accuracy verification experiment.

FIG. 26 is a graph comparing an estimated value and a measured value of a strip camber according to the prior art in an accuracy verification experiment.

FIG. 27 is a graph comparing an estimated value according to the second invention and a third invention of the application of the strip camber in an accuracy verification experiment of the estimation method of the present invention with an actually measured value.

FIG. 28 is an explanatory view showing a production line of a steel plate production facility incorporating the method for estimating a strip camber according to the embodiment of the present invention.

FIG. 29 is a graph illustrating a method for determining an appropriate protrusion amount of the shielding plate according to the embodiment of the present invention.

FIG. 30 is a graph illustrating a method for determining an appropriate protrusion amount of the shielding plate according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Strip material 2 Strip camber 3 Strip line 4 Dividing line 5 Finishing rolling machine 6 Acceleration cooling device 7 Radiation thermometer 8 Hot leveler 9 Arithmetic device 10 Shielding plate 11 Shielding plate moving device 12 Transfer branching machine 13 Cooling floor 14 Stockyard 15 Leveler 16 Heating furnace

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Kibe 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Takashi Uchimura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 11/00 C21D 9/52 B21B 37/00-37/78

Claims (7)

(57) [Claims] When producing a steel sheet after accelerated cooling after hot rolling or hot straightening, the steel sheet after the completion of recuperation in which the temperature distribution of the steel sheet after the accelerated cooling becomes substantially uniform in the thickness direction. A method for estimating a camber when the steel sheet is cut after cooling on a cutting line set on the steel sheet by measuring a surface temperature distribution of the steel sheet, comprising: The surface temperature change in the width direction of the slice after the end of the recuperation when unevenly accelerated cooling in the direction, and the curvature of the slice camber of the slice caused by the residual stress after cooling generated by the uneven cooling. Is calculated in advance by calculation means, and the longitudinal distribution of the width direction surface temperature change of the strip material is calculated from the surface temperature distribution of the steel sheet, and the width direction surface of the strip material is calculated. From the longitudinal distribution of the degrees change, the calculated longitudinal distribution of the curvature of the strip cutting camber after the steel plate cooled with a relationship, to calculate the deflection curve of the strip cutting camber from the longitudinal distribution of the curvature, further,
The camber deflection curve of the entire steel sheet, which is generated when the surface temperature distribution of the steel sheet becomes uniform after cooling the steel sheet, is calculated, and the camber deflection curve of the entire steel sheet with a minus sign is the deflection of the stripped camber. A method for estimating a stripped camber, wherein a camber of a stripped material is obtained by adding the camber to a curve. 2. When manufacturing a steel sheet by accelerated cooling after hot rolling or hot straightening, the temperature distribution of the steel sheet at the start of the accelerated cooling and after the accelerated cooling becomes substantially uniform in the thickness direction. Measure the surface temperature distribution of the steel sheet after the end of recuperation, the camber when the steel sheet is cut after cooling on the cutting line set on the steel sheet, at the start of the accelerated cooling and after the end of the reheat. Estimating from the surface temperature distribution of the two steel plates. 3. The recuperation as described above, wherein when a slice obtained by subdividing the strip material in the longitudinal direction is non-uniformly accelerated and cooled in the width direction, a change in the surface temperature in the width direction of the slice at the start of accelerated cooling is used as a parameter. The relationship between the widthwise surface temperature change of the slice after completion and the curvature of the slice camber of the slice caused by the residual stress after cooling generated by the non-uniform cooling is calculated in advance by the calculation means, and the acceleration is calculated. Calculate the longitudinal distribution of the width direction surface temperature change of the strip material from the steel sheet surface temperature at the start of cooling, and calculate the longitudinal distribution of the width direction surface temperature change of the strip material from the steel sheet surface temperature after completion of the recuperation. From the longitudinal distribution of the widthwise surface temperature change of the two strips at the start of the accelerated cooling and after the end of the recuperation, after cooling the steel sheet using the relationship The longitudinal distribution of the curvature of the strip camber is determined, the deflection curve of the strip camber is calculated from the longitudinal distribution of the curvature, and the surface temperature distribution of the steel sheet becomes uniform after cooling the steel sheet. Calculating a camber deflection curve of the entire steel sheet to be added, and adding a minus sign to the camber deflection curve of the entire steel sheet to the deflection curve of the strip camber to obtain a camber of the strip material. Item 2. A method for estimating a section camber according to item 2. 4. A width-direction surface temperature gradient, which is a gradient obtained by approximating the width-direction surface temperature distribution with a straight line by a least square method, is used as the quantity representing the width-direction surface temperature change. Method for estimating the cross section camber. 5. The curvature of the strip camber caused by residual stress after cooling generated by uneven cooling is calculated from the surface temperature gradient in the width direction after completion of reheating or after completion of reheating and at the start of accelerated cooling. The method for estimating a strip camber according to claim 4, wherein the method is obtained by using an equation. The general section cutting material is as follows: C = ｛(− 17.65 + 0.326t) Tg + (− 1)
1.12 + 0.222t) Tgo｝ × 10 ⁻⁶ + αTg The left edge of the edge part strip is C = ｛(− 10.7 + 0.19t) Tg + (0.40−
0.0068t)｝ × 10 ^-6 + αTg The right edge of the edge strip is C = Ｃ (-10.7 + 0.19t) Tg- (0.40-
0.0068t)｝ × 10 ⁻⁶ + αTg where C: curvature of the camber (1 / mm) (the curvature that causes a camber convex to the left when viewed in the longitudinal direction is positive) t: plate thickness (mm) Tg: return Surface temperature gradient in the width direction after heat end (° C / mm)
(Positive when the temperature increases from left to right) Tgo: Surface temperature gradient in the width direction at the start of accelerated cooling (° C./m
m) α: linear expansion coefficient (1 / ° C) 6. A cooling plate is disposed on both edges of a steel plate during accelerated cooling of the steel plate, and the shielding plate is protruded or retreated in a width direction of the steel plate to control a cooling water amount at an edge portion of the steel plate. In controlling the cooling water amount at the edge portion of the steel sheet by adjusting the discharge water amount density distribution in the direction of cooling water to cool the steel sheet, the strip camber of the steel sheet is estimated by any one of the methods of claims 1 to 5. And controlling the amount of protrusion of the shielding plate based on the estimated value or controlling the discharge water amount density distribution of the cooling water. 7. A method for estimating a strip camber of a steel sheet according to any one of claims 1 to 5, and in a case where the estimated value exceeds an allowable value, a method of manufacturing the steel sheet in a subsequent manufacturing process. A method for producing a steel sheet having a small number of strip cambers, characterized by applying means for reducing residual stress.