JP3307229B2 - 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 strip camber.

[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. (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 portion than at the center portion of the steel plate, the same effect is obtained as when the shielding plate is protruded. 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. As a method for reducing the strip camber, Japanese Patent Application Laid-Open No.
No. 1 discloses a method of heating an edge portion at the time of correction by a hot leveler so that a temperature difference is 50 ° C. or less and strong leveling (plastic deformation rate is 0.5 or more) (hereinafter, “prior art 3”). ").

[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.

Further, as shown in Prior Art 3, the present inventors have found that if hot leveler correction is performed strongly, the strip camber becomes larger. The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a precise and quick method for estimating a cutting camber, and a low-cost and reliable cutting camber based on the method. An object of the present invention is to provide a method for producing a small number of steel sheets.

[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 end of the recuperation, 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. In addition, the time change of the internal stress is very slow and stable after the end of the recuperation.

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. And 300mm-500m width on steel plate
Assuming a large number of m strips, 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 after the straightening, and the strip camber caused by the internal stress after the straightening when the steel sheet reaches room temperature. Is very large, and it is clear that accurate prediction of the section camber cannot be performed 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 the slices obtained by subdividing the strip material in the longitudinal direction are accelerated and cooled non-uniformly in the width direction, the widthwise surface temperature change of the slices after the completion of the reheating, and the hot leveler after the accelerated cooling. When manufacturing by straightening a steel sheet, after the straightening, when manufacturing without performing the straightening, after the reheating is completed, the slice after cooling of the slice caused by uneven internal stress in the width direction. Can The relationship with the curvature of the strip material is determined 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 temperature change of the strip material is calculated. From the longitudinal distribution of, after straightening using the above relationship or when not straightening, to determine the longitudinal distribution of the curvature of the strip camber after steel plate cooling generated by the internal stress after the end of recuperation,
From the longitudinal distribution of the curvature, calculate the deflection curve of the strip camber after the steel sheet has been cooled due to the internal stress after the end of recuperation after straightening or if straightening is not performed on the strip material, Calculate the deflection curve of the strip camber generated when the surface temperature distribution of the steel sheet becomes a uniform temperature after cooling the steel sheet, and after the straightening curve of the strip camber is corrected, or when the straightening is not performed, the reheating is completed. A method for estimating a section camber, characterized in that a camber of a section member is obtained by adding the camber to a section camber deflection curve after steel sheet cooling generated by the internal stress later.

The gist of the second aspect of the present invention is that the surface temperature distribution of the steel sheet is measured at the start of accelerated cooling and after the end of recuperation, and after the steel sheet is straightened or not straightened. The longitudinal distribution of the curvature of the strip camber after cooling the steel sheet caused by uneven internal stress in the width direction after the end of recuperation, and the slice obtained by subdividing the strip material in the length direction into the width direction is not uniform In the case of accelerated cooling, the change in the width direction surface temperature of the slice at the start of accelerated cooling was used as a parameter, and the change in the width direction surface temperature of the slice after the end of recuperation. The relationship of the slice with the curvature of the post-cooling strip camber generated by the internal stress after the end of recuperation is determined in advance by calculation means, and the surface temperature of the steel sheet at the start of the accelerated cooling is determined. Calculate the longitudinal distribution of the width direction surface temperature change of the strip material from the cloth, and further calculate the longitudinal distribution of the width direction surface temperature change of the strip material from the steel sheet surface temperature distribution after the recuperation. The strip camber according to claim 1, wherein the camber is determined from the longitudinal distribution of the surface temperature change in the width direction of the two strips at the start of the accelerated cooling and after the end of the reheating. Is an estimation method.

According to a third aspect of the present invention, the curvature of the sliced camber after cooling of the slice, which is generated by uneven internal stress in the width direction after the correction, is determined as the end of reheating. After, or after completion of recuperation and at the start of accelerated cooling, the relationship between the surface temperature change in the width direction of the slice and the curvature of the sliced camber after cooling of the slice generated by uneven internal stress in the width direction before straightening. Previously obtained by the calculation means, obtained from the measurement of the surface temperature distribution of the steel sheet, after the end of recuperation, or from the width direction surface temperature change of the strip material after the end of recuperation and at the start of accelerated cooling, 3. The method for estimating a section camber according to claim 1, wherein a curvature of the section camber before correction is obtained using the relationship, and the curvature is obtained by multiplying the curvature by a residual rate having a value of 0 to 1. A.

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 distribution of the surface temperature in the width direction by a least square method. Using a surface temperature gradient, before straightening or when not straightening the curvature of the sliced camber after cooling of the slice generated by uneven internal stress in the width direction after reheating, after reheating, or 4. The method for estimating a stripping camber according to claim 1, wherein the width is determined from the surface temperature gradient in the width direction at the end of recuperation 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 The left edge of the edge portion strip is C = ｛(-10.7 + 0.19t) Tg + (0.40-
0.0068t)｝ × 10 ^-6 The right edge of the edge strip is C = {(-10.7 + 0.19t) Tg- (0.40-
0.0068 t)｝ × 10 ^-6 where C: before straightening or when no straightening is performed, after the cooling of the slice caused by uneven internal stress in the width direction after the end of recuperation (1) / Mm) (The curvature that causes a camber that is convex to the left when viewed in the longitudinal direction is positive) t: Plate thickness (mm) Tg: Surface temperature gradient in the width direction after completion of reheating (° 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) The present inventors succeeded in accurately and quickly estimating the stripping camber of a steel plate by the first to fourth inventions of the present application, and can suppress the stripping camber reliably and at low cost. The following invention was reached to be applied to a method for manufacturing a steel sheet.

According to a fifth 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 any one of claims 1 to 4, wherein cooling is performed by controlling the amount of cooling water at the edge of the steel sheet or adjusting the discharge water amount density distribution in the width direction to control the amount of cooling water at the edge of the steel sheet. 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 sixth aspect of the present invention, a stripping camber of a steel sheet is estimated by any one of the first to fourth 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.

According to the study of the present inventors, if hot leveler straightening is strongly performed to remove internal stress before straightening,
It became clear that the section camber became large. That is, it has been found that the stripping camber can be suppressed by minimizing the strength of the hot leveler correction.

After the steel sheet is subjected to accelerated cooling after hot rolling or hot straightening and then straightened by a hot leveler, the steel sheet can be straightened with a plastic deformation rate λ of 0.5 or less during the straightening .

[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 before the correction of the hot leveler after accelerated cooling or when the correction is not performed 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 change in the surface temperature in the slice width direction after the reheating and the internal stress are 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.

After the correction or when no correction is performed, the elastic strain corresponding to the internal stress after the completion of reheating is obtained, and the stress is obtained from the elastic strain and the elastic coefficient at room temperature. By calculating the curvature of the strip camber from the stress, the curvature of the post-cooling strip camber generated by the internal stress after straightening or when the straightening is not performed is calculated.

In the above stress state determined from the elastic modulus 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 plate thickness direction while maintaining the plane, and the slice is divided into a fan. It is transformed into a mold, which is a sliced 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, when accelerated cooling is performed non-uniformly in the width direction in the slice model, the change in the surface temperature in the width direction after the completion of the reheating and the correction in the width direction after the completion of the reheating. First, the relationship with the curvature of the post-cooling strip camber generated by uneven internal stress is determined.

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

However, in the case of performing hot leveler straightening, in order to simulate the straightening process, it is necessary to analyze not only the strip material but also the entire steel sheet in the width direction in consideration of the deformation of the leveler roll and the like. Further, in the actual operation, since the strength and the number of hot leveling are changed according to the deformation state of the steel sheet, the calculation must be performed under various correction conditions, which is difficult in terms of calculation cost.

The present inventors, as shown in the third invention of the present application, introduce the concept of the residual ratio of internal stress corresponding to the strength and the number of times of hot leveling. From the curvature, it was found that the curvature of the post-cooling strip camber generated by the internal stress after correction can be accurately estimated. That is, the elastic strain corresponding to the internal stress before the correction is obtained, the stress is obtained by using the elastic strain and the elastic coefficient at room temperature, and the camber curvature of the slice model is calculated from the stress, so that the correction before the correction is performed. The curvature of the cut camber after cooling caused by the internal stress is obtained, and the curvature of the camber after the cut caused by the internal stress after the correction is multiplied by an appropriate residual rate. Although the residual ratio is a value of 0 to 1, the residual ratio of 1 means that the internal stress before straightening that causes the strip camber remains even after straightening. This means that such internal stresses are completely eliminated by the correction. According to the study of the present inventors, it is known that the residual ratio has a value of 0.5 to 1.0 under normal correction conditions. The residual rate corresponds to the strength and the number of times of hot leveler correction, and is obtained by an experiment.

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 surface temperature distribution of the steel sheet after the completion of the reheating is substantially straight in the width direction in the case of the general strip material, and the gradient obtained when this distribution is approximated by a straight line is used as an amount representing the surface temperature change in the width direction. it can. However, in the case of the edge strip material, the surface temperature distribution in the width direction after the end of the reheating is shown in FIG.
It becomes complicated as shown in. The present inventors, even with such a complicated distribution, perform a least-squares approximation with a straight line and adopt the gradient of the straight line as an amount representing the change in the surface temperature in the width direction. They found that they could be expressed well and corresponded one-to-one with the post-cooling strip camber curvature, leading to the fourth invention of the present application. The relationship between the surface temperature gradient in the width direction of the strip material and the curvature of the strip camber after cooling due to internal stress before straightening or in the case where straightening is not performed due to the internal stress after the completion of recuperation, is shown by a steel sheet having a thickness of 25 mm and 50 mm. FIG. 16 and FIG. 17 show the results of calculations using the thermal stress analysis system under typical steel types and accelerated cooling conditions. Although such a relationship needs to be obtained for various steel types, the thickness of the steel sheet, the start temperature and the stop temperature of the accelerated cooling, as a result of examination by the present inventors, the following almost the fourth invention of the present application is described below. It turned out that it can be expressed by the formula.

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

The left edge of the edge strip is C = ｛(-10.7 + 0.19t) Tg + (0.40−
0.0068t)｝ × 10 ^-6 The right edge of the edge strip is C = {(-10.7 + 0.19t) Tg- (0.40-
0.0068t)｝ × 10 ^-6 where C: curvature of stripped camber (1 / mm) (the curvature that causes a camber convex to the left when viewed in the longitudinal direction is positive) t: sheet thickness (mm) Tg: reheat Surface temperature gradient in the width direction after completion (℃ / 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) 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, and strip widths may be obtained and expressed in the form of a table. Even in such a case, in the present invention, the change in the surface temperature in the width direction of the strip material is represented by a temperature gradient when the temperature distribution is approximated by a straight line with least squares.

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

As described above, the surface temperature gradient in the width direction after the reheating of the steel sheet and the curvature of the strip camber after cooling the steel sheet caused by the internal stress after the correction or when the correction is not performed. Ask for a relationship. This relationship holds for a slice of a strip having an infinitely small thickness in the longitudinal direction.

If the widthwise surface temperature gradient after the completion of the reheating is the same, the present inventors have performed the correction after the correction determined by the calculation means as described above. It has been found that the curvature of the strip camber after cooling the steel sheet caused by the internal stress is the same as that of the actual strip material of the steel sheet.

Next, a method for estimating the strip camber after cooling the steel sheet, which is generated by internal stress after the end of recuperation after the straightening of the actual steel sheet or when the straightening is not performed, using this relationship will be described.

In the first invention of the present application, the surface temperature distribution of the steel sheet is measured after the recuperation of the steel sheet accelerated and cooled. A cutting line having a width of 300 mm to 500 mm is set on this steel plate.
FIG. 18 illustrates this. 3 is the section line, 4
Indicates a dividing line. In FIG. 18, one strip is shown for simplicity, but a large number of strips are actually set in the width direction. FIG. 18 also shows contour lines 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 surface temperature gradient in the width direction. This is performed for all the dividing lines, and the longitudinal distribution of the surface temperature gradient in the width direction after the reheating of the strip is completed. Using the above-mentioned relationship, after straightening from the width direction surface temperature gradient after recuperation, or when not straightening, it is possible to determine the curvature of the strip camber after cooling the steel sheet caused by internal stress after recuperation. Since it is possible, after the straightening from the longitudinal distribution of the surface temperature gradient in the width direction of the stripping material, or in the case where the straightening is not performed, the longitudinal distribution of the curvature of the stripping camber after cooling the steel sheet generated by internal stress after the end of recuperation Can be requested.
When this curvature distribution is integrated twice in the longitudinal direction, a bending curve of the strip camber after cooling the steel sheet is obtained by the following equation (2) shown in Expression 1.

[0048]

(Equation 1) Here, v ₁ (x): the deflection curve of the strip camber after steel sheet cooling generated due to internal stress after straightening or in the case where straightening is not performed, and x: longitudinal coordinates C ₁ ( s): Curvature of strip camber after steel plate cooling generated due to internal stress after straightening at x = s or when no straightening is performed at the end of recuperation. It is obtained by numerical integration.

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) 3) "" is referred to as equation (3).

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

In this way, the deflection curve of the strip camber after the steel sheet is cooled, which is generated by the internal stress after the completion of the reheating, when the straightening is performed or when the straightening is not performed, is obtained. Next, a deflection curve of the strip camber generated when the temperature distribution of the steel sheet after the recuperation becomes uniform after cooling is calculated. This calculation method is represented by the following equation shown in Prior Art 2, Equation 2, Equation 3, Equation 4, and Equation 5.

[0052]

(Equation 2)

[0053]

(Equation 3)

[0054]

(Equation 4)

[0055]

(Equation 5) Here, v ₂ (x): deflection curve of the strip camber generated when the steel sheet temperature distribution becomes uniform after cooling after the end of recuperation C ₂ (s): camber curvature of the strip member at x = s w: Sheet width of steel sheet α: Linear expansion coefficient y: Coordinates in the steel sheet width direction T (s, y): Steel sheet surface temperature distribution after completion of reheat

[0056]

(Equation 6) C ₂₂ (s) is the curvature of the strip camber generated when the temperature distribution after the reheating of the strip material has reached a uniform temperature after cooling. In the present invention, it can be calculated from the surface temperature gradient in the width direction. In this case, C ₂₂ (s) = αTg (s) (6) where Tg (s): the surface temperature gradient in the width direction of the stripping material after the end of recuperation at x = s. Is small, but the latter is advantageous in terms of calculation time.

The inventors of the present invention have determined the deflection curve of the strip camber after the steel sheet has been cooled and the temperature distribution of the surface steel sheet after the heat recovery, which is caused by the internal stress after the heat recovery. Adding the deflection curve of the strip camber generated when the temperature becomes uniform after cooling,
It was found that the strip camber of an actual steel plate can be accurately estimated.

V (x) = v ₁ (x) + v ₂ (x) (7) where v (x) is the deflection camber deflection curve The above equation is obtained when the lower end of the stripping material is fixed. Give the deflection curve. 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 (8) shown in Expression 7.

[0059]

(Equation 7) 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 equation (8) from equations (2), (4) and (7).

[0060]

(Equation 8) Of the integrands, C ₂₁ (s) is a strip camber caused by the camber of the entire steel sheet, and is determined in advance because it is the same for all strip members. C ₁ (s), C
₂₂ (s) is obtained with a strip, and C ₂₁ (s) is added thereto, and longitudinal integration, that is, numerical integration of the equation (3) is performed.
Find 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 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 accurately captured. Using the initial temperature that changes in the width direction as a parameter, the surface temperature change in the width direction after the end of recuperation and the curvature of the stripping camber after cooling caused by internal stress after straightening or when straightening is not performed. Ask for a relationship. Also in this case, when performing hot leveler straightening, the curvature of the stripped camber after cooling generated by the internal stress before straightening is determined, and the remaining rate corresponding to the strength and the number of times of hot leveler straightening is calculated, similarly to the first invention of the present application. By multiplying by, the curvature of the cooled strip camber generated by the internal stress after correction can be accurately estimated. In addition, as the quantity representing the width-direction surface temperature change, a gradient when the width-direction temperature distribution is approximated by least squares can be used.

FIG. 16 shows that the temperature gradient (Tgo) at the start of accelerated cooling is ± 0.04 ° C. with a 25 mm-thick general sectioned material.
/ Mm shows the relationship between the temperature gradient after the end of recuperation and the curvature of the stripping camber after cooling, which is generated by internal stress before or after the end of the recuperation when no straightening is performed.
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 of the general strip was considered before and after straightening or when no straightening was performed in consideration of the temperature gradient in the width direction at the start of accelerated cooling. It was found that the relationship with the curvature of the post-cooling strip camber due to the internal stress after the end of recuperation 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 recuperation 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. After straightening or when straightening is not performed using the above relationship, the curvature of the strip camber after steel sheet cooling generated due to internal stress after the end of recuperation can be obtained 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.

A factory experiment was conducted to verify the estimation accuracy of the strip camber according to the first invention of the present application. 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. 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 is lowered by about 120 ° C. from the case of the actual operation, so that the temperature is generated due to the temperature gradient in the width direction at the time of the correction under the accelerated cooling condition and the internal stress before the correction. The relationship with the curvature of the strip camber after cooling was calculated anew. The result is shown in FIG.
(Plate thickness 25 mm) and FIG. 22 (plate thickness 45 mm). The residual ratio was set to 0.9 based on the results of other experiments.

A series of procedures such as the above-described setting of the cutting line, calculation of the temperature gradient and curvature on the dividing line of the cutting material, 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 actual value measured on the free side (FS ▽). The solid line (Est · 0) is the estimated value when the curvature C ₂₂ (s) is calculated using the equation (5), and the dotted line (Est · 0)・ 1)
This is an estimated value calculated using equation (6). As shown in the drawing, the estimated values (Est · 0, Est · 1) and the measured values 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.

By the way, as shown in the prior art, when the strip camber is obtained only from the stress generated when the temperature distribution of the steel sheet at the time of straightening becomes uniform after cooling is compared with the actually measured value, FIG. FIG. 26 (plate thickness 45 mm). As is clear from FIGS. 25 and 26, the accuracy of the conventional strip camber estimating method is very poor. In particular, in the case of the edge strip material, the estimated value is very large at a plate thickness of 25 mm, and the camber of the camber at a plate thickness of 45 mm. The direction 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 invention of the present application for a general sectioned material. 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 invention 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 fourth aspects of the present invention, it is possible to accurately and quickly estimate a strip camber.

The inventors of the present invention applied the fifth embodiment of the present invention to apply the strip camber estimation method according to the first to fourth 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, in the camber of the edge portion stripping material, the shielding plates are arranged at both edges of the steel plate, and the shielding plates are projected or retracted in the width direction of the steel plate to adjust the amount of cooling water at the edge portion of the steel plate. It can be suppressed by adjusting the discharge water amount density distribution in the width direction 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 distribution of cooling water discharge water amount density in the width direction and the stripping camber during steel plate manufacturing, and from this relationship do not generate the stripping camber, or the shielding plate protrusion amount or width that can be suppressed to the maximum The distribution of the cooling water discharge water density in the direction 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 strip camber is estimated with high accuracy and speed, and the protruding amount of the shielding plate or the cooling water discharge water density distribution is controlled based on the estimated value. It is possible to manufacture a steel plate with less noise.

The inventors of the present invention applied the sixth embodiment of the present invention to apply the method of estimating the strip camber of the first to fourth inventions to a method of manufacturing a steel sheet capable of reliably suppressing the strip camber at low cost.
Invented the invention.

In the present invention, the temperature distribution on the steel sheet surface is measured after the completion of the reheating or, if necessary, after the completion of the reheating and at the start of the accelerated cooling. And 300mm width on steel plate
Many strips of 500 mm 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 are strips that cause camber exceeding the allowable value,
For the steel sheet, means for reducing residual stress is applied in the subsequent manufacturing process. That is, specifically, cold leveling or warm leveling is performed, or stress relief annealing is performed.

As described above, in 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 is generated. 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.

Next, a hot leveler straightening method in the steel sheet manufacturing method of the reference invention will be described. The present inventors, by performing stress analysis from accelerated cooling to room temperature, the internal stress before hot leveler straightening has the function of suppressing the strip camber generated at room temperature, the stress distribution having such a function, It has been found that it is generated at a position somewhat in the center of the sheet thickness from the steel sheet surface, and if the stress distribution can be left after the correction, the camber at room temperature can be greatly suppressed, and the plastic deformation rate during hot leveler correction is reduced. The present invention has led to the correction of 0.5 or less.

In a slice model having a thickness of 25 mm,
Non-uniform cooling was performed at the left and right edges in the width direction at 1.07 times the heat transfer coefficient shown in FIG. 13 on the strong cooling side and 0.93 times on the weak cooling side, and stress was calculated (no correction). FIG. 31 shows the thickness direction distribution of the longitudinal stress at the left and right edges at room temperature. The stress at the intermediate position changes linearly substantially in the width direction. Taking the average value of this stress distribution in the thickness direction, the stress is compression on the strong cold side and tensile on the weak cold side. When this slice is cut, the strong cold side expands and the weak cool side contracts, so that a convex camber is generated on the strong cold side. However, FIG.
As shown in (1), the average value in the thickness direction of the stress distribution in the longitudinal direction before the correction is tensile on the strong cold side and compressive on the weak cold side. Therefore, if this slice is virtually cut before being corrected, a camber convex on the slightly cold side is generated. That is, if the fiber is cut before straightening, a camber in a direction opposite to the direction of the camber generated at room temperature occurs.

According to the study of the present inventors, it has been found that such phenomena are present irrespective of the plate thickness, the steel type, and the accelerated cooling conditions, though the degree thereof varies. This phenomenon means that the internal stress before correction has a function of reducing the camber at room temperature, that is, it has an effect of suppressing the camber at room temperature. 23 and 25 used in the description of the first invention of the present application, the camber estimated value of the edge portion stripping material is not taken into consideration, that is, the internal stress after straightening is not taken into account, that is, the internal stress before straightening disappears due to hot leveler straightening. The estimated value of the camber of the conventional method (Fig. 2
5) is very large, whereas the estimated value of the first invention in which the internal stress before correction is taken into consideration is considerably small, which also indicates that the internal stress before correction is suppressed by the camber at room temperature. It can be interpreted that there is.

The present inventors have found that such a camber suppressing effect due to the pre-correction internal stress exists from a position where the surface enters into the interior to some extent from the surface to the center of the plate thickness. Examining the pre-correction stress distribution in FIG. 32 as an example,
The pre-correction internal stress that causes the camber in the opposite direction to the room temperature camber, that is, the difference between the stress on the strong cold side and the stress on the weak cold side, did not exist on the plate surface, and entered about 20% of the half plate thickness from the surface. It exists from the position to the thickness center.

In the hot leveler straightening, a steel sheet is repeatedly bent and unbended to flatten the steel sheet. In this process, a plastic zone is generated from the steel sheet surface toward the inside. The ratio of the size of the plastic zone in the thickness direction to the steel sheet thickness is referred to as a plastic deformation rate. The internal stress in the area where plastic deformation occurs during straightening is almost eliminated, but in the elastic area inside the plate where plastic deformation does not occur, the stress distribution simply shifts to the tensile side or the compressive side, and the stress difference (phase difference) Distribution) remains as it is.

Accordingly, the camber at room temperature is suppressed by correcting the plastic deformation rate to a small value so that the inside of the plate, which has the effect of suppressing the camber at room temperature, stays in the elastic range.

As a result of the study of the present inventors, the plastic deformation rate at the time of hot leveler straightening was 0.5 or less, more preferably, the plastic deformation rate was changed depending on the sheet thickness.
In the following, it has been clarified that, by setting the thickness to 0.45 or less at a plate thickness of 50 mm, the effect of suppressing the strip camber according to the present invention is maximized.

As described above, according to the present invention, by setting the plastic deformation rate at the time of correcting the Hon Revela to 0.5 or less,
Since the pre-correction internal stress having the stripping camber suppressing effect can be left after the straightening, a steel sheet with less stripping camber can be manufactured.

[0085]

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 9. Before the acceleration cooling device 6 (upstream) and before the hot leveler 9 (upstream), the radiation thermometer 7 measures the temperature distribution on the steel sheet surface. The radiation thermometer 7 before (upstream) the hot leveler 9 may be disposed after (downstream) or inside the hot leveler 9. The measured temperature data is sent to the arithmetic unit 10, and the strip camber of the steel plate is calculated.

The arithmetic unit 10 takes in temperature data at 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, converts the data into a front plan view, An edge is detected, and temperature data only for the inside of the board 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 ₂₁ (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. When estimating the strip camber according to the first invention of the present application, the calculation is performed on the temperature measurement data at the time of correction, and according to the second invention of the present application. In this case, the measurement is performed on two temperature measurement data at the time of accelerated cooling and at the time of correction.

The relations obtained in advance by the calculation means, that is, FIG. 16 (plate thickness 25 mm) and FIG.
0 mm), equation (1) and the residual ratio, and the longitudinal distribution of C ₁ (s) in equation (2), which is the curvature of the steel sheet strip camber generated by the internal stress after correction from the temperature gradient in the width direction, is given by Is calculated. Further, the longitudinal distribution of C ₂₂ (s) at the dividing line 4 is calculated from Expression (6).

These three curvature distributions are added as shown in equation (9), and the numerical integration of equation (3) is executed to obtain a camber deflection curve, and the camber deflection curve is obtained from equation (8). Is calculated. In the arithmetic unit 10, such calculation is performed for all the strip members to which the position data is input, and the strip camber is 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 10 outputs a shielding plate protrusion amount instruction signal to the device 12 for moving the shielding plate 11 installed in order to suppress camber of the edge part stripping material in the width direction of the steel plate.
Since the maximum camber is generated almost at the center of the strip, the camber in x = 1/2 (1: strip length) is obtained from equation (8), and this is converted into camber per 10 m and projected. The amount is determined. The conversion is performed by multiplying the calculated camber by (10 / l) ² .

The amount of projection of the shielding plate 11 is controlled as follows. The relationship between the protrusion amount of the shielding plate 11 and the estimated camber value per 10 m (conventional results) is stored in a database for each plate thickness, steel type, and accelerated cooling 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 11 is determined. Same thickness, steel grade,
When manufacturing a large number of steel sheets under accelerated cooling conditions, in the second steel sheet, as shown in FIG. 30, a straight line having the same inclination as the approximate straight line is drawn from the actual value of the first steel sheet, and the protrusion at which the camber becomes zero is drawn. The quantity (point B) is determined. For the third and subsequent steel sheets, the amount of protrusion (point C) that sets the camber to zero is determined from the relationship between the amount of protrusion so far and the estimated value of the strip camber,
Camber can be suppressed more reliably. Such control of the amount of protrusion of the shielding plate 11 is separately performed by the left and right edge portion cutting members.

The method of the present invention is different from the conventional method of fixing the protruding amount of the shield 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 transfer and branching machine 13. In the meantime, the arithmetic unit 10 determines whether the residual stress reducing means is applied or not based on the estimated camber value. 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 10 to the transport branching machine 13. When the residual stress means is unnecessary, the steel sheet is transported to the cooling floor 14 as it is, and when necessary, it is once transported to the stock yard 15.

As a residual stress removing means, a stress relief annealing by a leveler 16 and a heating furnace 17 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 16. For medium thickness materials, leveling or stress relief annealing is performed.

Conventionally, the residual stress removing means has been applied to all the 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. In the hot leveler 9, leveling is performed so that the plastic deformation rate becomes 0.5 or less. As described above, the lower the plastic deformation rate, the greater the effect of suppressing the camber at room temperature due to the internal stress before correction. A flatness meter 8 is provided before and after the hot leveler 9 (upstream and downstream). The out-of-plane deformation of the plate is measured by the flatness meter 8 before (upstream of) the hot leveler, and the plastic deformation rate of the leveling is determined by the arithmetic unit 10 according to the degree. The value is always 0.5 or less, and preferably, the plastic deformation rate is changed according to the thickness of the sheet.
It is 0.25 or less at 5 mm, and 0.45 or less at a plate thickness of 50 mm. The out-of-plane deformation of the plate is measured by the flatness meter 8 on the rear surface of the hot leveler after the correction. If it is equal to or larger than the allowable value, the correction is performed again, and the correction is repeatedly performed until the correction falls within the allowable range.

In order to demonstrate the effect of the present invention, hot leveler straightening was performed with various plastic deformation rates on actual steel sheets, and the strip camber was measured. The test material has a thickness of 25 mm (2
5t) and 45mm (45t), width 2600mm,
The length was 12000 mm, and the strip width was 500 mm and the strip was cut into five strips. Table 1 shows the test results. Camber is shown as an absolute value.

[0098]

[Table 1] In the present invention, it was confirmed that by setting the plastic deformation rate to 0.5 or less, the strip camber was significantly suppressed.

By performing the hot leveling according to the present invention, the steel sheet requiring the residual stress reducing means has a plastic deformation rate of more than 0.5, compared to the case where the steel sheet is leveled at a plastic deformation rate of more than 0.5.
It was reduced by more than 0%, and the production cost was significantly reduced.

[0100]

As described above, according to the present invention, the following industrially useful effects are provided.

Since the strip camber of the steel sheet is quickly estimated with high accuracy and the edge water amount at the time of accelerated cooling is appropriately controlled, it is possible to manufacture a steel sheet with few strip cams, and to estimate the strip camber with high accuracy. Since the residual stress removing means is applied only to a steel sheet having a value exceeding the allowable value, the number of times of applying these means, which are costly, is greatly reduced.

By using the hot leveler straightening method of the present invention, the strip camber is suppressed, and the number of applications of the residual stress removing means is further reduced. As described above, it is possible to reliably manufacture a steel plate having a low camber at a low cost.

[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 the initial temperature distribution of the edge portion cut material used in the thermal stress analysis according to the present invention and its least square approximation.

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 shows the widthwise temperature gradient after reheating used in the embodiment of the present invention, and the curvature of the sectioning camber after cooling caused by internal stress before correction or after reheating when no correction is performed. 6 is a graph showing the relationship of.

FIG. 17 shows the widthwise temperature gradient after completion of reheating and the curvature of the sectioning camber after cooling generated by internal stress before or after completion of reheating, which is used in the embodiment of the present invention. 6 is a graph showing the relationship of.

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 at the time of correction calculated for the accuracy verification experiment of the estimation method of the present invention and the curvature of the stripping camber after cooling generated by the internal stress before correction.

FIG. 22 is a graph showing the relationship between the temperature gradient in the width direction at the time of correction calculated for the accuracy verification experiment of the estimation method of the present invention and the curvature of the stripping camber after cooling generated by the internal stress before correction.

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 of the strip camber according to the second invention of the present application and an actually measured value in an accuracy verification experiment of the estimation method of the present invention.

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 present invention 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.

FIG. 31 is a diagram showing the internal stress at room temperature and the strip camber calculated by the thermal stress analysis system according to the present invention.

FIG. 32 is a diagram showing an internal stress before straightening calculated by the thermal stress analysis system according to the present invention and a strip camber.

[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 Flatness meter 9 Hot leveler 10 Computing device 11 Shielding plate 12 Shield plate moving device 13 Transfer branching machine 14 Cooling Floor 15 stockyard 16 leveler 17 heating furnace

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI G05B 13/02 B21B 37/00 119D (72) Inventor Hiroshi Kibe 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72 Inventor Takashi Uchimura 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-8-90068 (JP, A) JP-A-58-163512 (JP, A) 62-197209 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21D 1/05 G05B 13/02 B21B 37/30 B21B 45/02

Claims (6)

(57) [Claims] When manufacturing a steel sheet by 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: When unevenly accelerated cooling in the direction, the width direction surface temperature change of the slice after the end of the reheating, and after straightening the steel sheet by a hot leveler after the accelerated cooling, after the straightening, after the straightening, When manufacturing without straightening, the relationship with the curvature of the sliced camber after cooling of the slice generated by uneven internal stress in the width direction after completion of the reheating is obtained in advance by calculation means. Calculating the longitudinal distribution of the surface temperature change in the width direction of the strip material from the surface temperature distribution of the steel sheet, and from the longitudinal distribution of the surface temperature change in the width direction of the strip material, after straightening using the relationship. Alternatively, if the straightening is not performed, the longitudinal distribution of the curvature of the strip camber after cooling the steel sheet generated due to the internal stress after the end of recuperation is obtained, and the straightening of the strip material from the longitudinal distribution of the curvature or from the longitudinal distribution of the curvature is performed. If straightening is not performed, calculate the deflection curve of the strip camber after cooling the steel sheet caused by the internal stress after the end of recuperation, and further, the surface temperature distribution of the steel sheet becomes uniform after cooling the steel sheet. Calculate the deflection curve of the strip camber generated due to the internal stress after the straightening of the deflection camber after the straightening or when the straightening is not performed. Method of estimating conditions cutting camber and obtains the camber of that steel sheet after cooling of the strip cutting camber deflection adds the curve strip cut material. 2. The surface temperature distribution of the steel sheet is measured at the start of accelerated cooling and after the end of reheating, and due to uneven internal stress in the width direction after the straightening of the steel sheet or after the end of reheating. The longitudinal distribution of the curvature of the stripping camber after cooling the generated steel sheet, the width of the slice at the start of accelerated cooling, when unevenly accelerated cooling in the width direction of a slice obtained by subdividing the strip material in the longitudinal direction, Using the surface temperature change in the direction as a parameter, the surface temperature change in the width direction of the slice after the end of reheating, and after the cooling of the slice caused by the internal stress after the end of the reheating after straightening or when straightening is not performed. The relationship with the curvature of the strip camber is obtained in advance by a calculating means, and the longitudinal distribution of the width direction surface temperature change of the strip material is calculated from the steel sheet surface temperature distribution at the start of the accelerated cooling. And further calculating the longitudinal distribution of the surface temperature change of the strip material in the width direction from the steel sheet surface temperature distribution after the completion of the recuperation, and calculating the two strips at the start of the accelerated cooling and after the completion of the recuperation. 2. The method for estimating a strip camber according to claim 1, wherein the relationship is obtained from the longitudinal distribution of the surface temperature change in the width direction of the cut material using the relationship. 3. The method of claim 1, wherein after the straightening, the curvature of the stripped camber generated after the straightening due to uneven internal stress in the width direction is adjusted after the completion of the recuperation, or after the end of the recuperation and at the start of the accelerated cooling. The relationship between the surface temperature change in the width direction and the curvature of the strip camber after cooling of the slice caused by uneven internal stress in the width direction before straightening is obtained in advance by calculation means, and the surface temperature distribution of the steel sheet is measured. From the end of recuperation, or after the end of recuperation, from the width direction surface temperature change of the strip material at the start of accelerated cooling, using the above relationship to determine the curvature of the strip camber before straightening, 3. The method according to claim 1, wherein the curvature is obtained by multiplying the curvature by a residual ratio having a value of 0 to 1. 4. A method of using a width-direction surface temperature gradient, which is a gradient obtained by linearly approximating the width-direction surface temperature distribution with a straight line, as an amount representing the width-direction surface temperature change, and The curvature of the sliced camber after cooling of the slice caused by uneven internal stress in the width direction after the end of recuperation, the width direction surface temperature after the end of recuperation, or after the end of recuperation and at the start of accelerated cooling. 4. The method for estimating a strip camber according to claim 1, wherein the slope is obtained from the gradient using the following equation. The general section cutting material is as follows: C = ｛(− 17.65 + 0.326t) Tg + (− 1)
1.12 + 0.222t) Tgo｝ × 10 ^-6 The left edge of the edge portion strip is C = ｛(-10.7 + 0.19t) Tg + (0.40-
0.0068t)｝ × 10 ^-6 The right edge of the edge strip is C = {(-10.7 + 0.19t) Tg- (0.40-
0.0068 t)｝ × 10 ^-6 where C: before straightening or when no straightening is performed, after the cooling of the slice caused by uneven internal stress in the width direction after the end of recuperation (1) / Mm) (The curvature that causes a camber that is convex to the left when viewed in the longitudinal direction is positive) t: Plate thickness (mm) Tg: Surface temperature gradient in the width direction after completion of reheating (° 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) 5. 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 retracted in the width direction of the steel plate to control the amount of cooling water at the edge of the steel plate or to control the width. In controlling the cooling water amount at the edge of the steel sheet by adjusting the discharge water amount density distribution of the cooling water in the direction, cooling of the steel sheet is estimated by the method according to any one of claims 1 to 4. And controlling the amount of protrusion of the shielding plate or controlling the discharge water amount density distribution of the cooling water based on the estimated value. 6. A method for estimating a stripping camber of a steel sheet by any one of the methods of claim 1 to 4, and when the estimated value exceeds an allowable value, the steel sheet is removed 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.