JP2012218010A - Shape measuring method in hot rolling of steel sheet and steel plate, and hot-rolling method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a hot steel sheet and a hot steel plate, in which a plate waveform just after completion of rolling of the hot steel sheet and the hot steel plate is precisely measured and the plate wave form is freely made with a rolling mill based on the result.SOLUTION: In a measuring method for measuring the plate waveform after the completion of rolling of the hot steel sheet and the hot steel plate, positions in the sheet passing direction and the sheet width direction and displacement in the height direction are measured on the outlet side of the rolling mill as geometric values, and then, a profile, steepness and elongation strain difference are determined as the featured value of a shape. Further in the method, residual strain which is immanent in the steel plate when measuring is performed in addition to the measured featured value of a shape and it is superimposed on the measured featured value of the shape as the true featured value of the shape imparted from the rolling mill.

Description

  TECHNICAL FIELD The present invention relates to a method for producing hot thin and thick steel plates that accurately measure the plate wave shape immediately after the end of rolling of the hot and thin steel plates, and freely create the plate wave shape by a rolling mill based on the results. Is.

As a technique for measuring the shape of a steel plate, for example, as disclosed in Patent Document 1, a measuring device composed of a plurality of optical distance meters is installed on a steel plate conveyance line, and from a steel plate passing through this measuring device. There is a technique in which a distance from a light reflection state to a steel sheet surface is obtained and measured as a steel sheet height linked to a width position of the steel sheet and a sheet passing direction position of the steel sheet.
In addition, in Patent Document 1, for the shape control of the thick steel plate, an elongation strain difference is obtained based on data from a shape meter installed after the rolling mill, and an elongation obtained in advance by a calculation model in consideration of the shape dead zone. A technique for sequentially correcting a difference in strain difference and controlling a rolling shape is disclosed.
However, although the geometrical wave shape of the steel sheet can be measured with the technique disclosed in Patent Document 1, even if the wave shape is generated, the residual strain and residual stress inherent in the steel sheet are still present. Can not grasp.

Further, in Patent Document 2, an elongation strain difference is obtained based on data measured by a shape meter installed after a rolling mill, and differences in elongation strain obtained in advance by a calculation model taking into account a shape dead zone are successively determined. A technique for correcting and controlling the rolling shape is disclosed.
However, it is not described in Patent Document 2 how this shape dead zone equation is derived, and its definition is not clear. Even if the definition of the shape dead zone is clarified, the proposed shape control method is controlled by the crown change rate that removes the distortion component of the shape dead zone, and has nonlinearity. Has the problem of becoming complicated.

In Patent Document 3, when the strain distribution in the width direction of the steel sheet is known, the buckling equation is used to convert the distortion geometrically as a wave shape and the strain inherent in the steel sheet after buckling. A technique for separating and predicting the plate shape is disclosed. Since Patent Document 3 predicts a wave shape with a known width direction strain distribution, if the width direction strain distribution cannot be known, for example, to predict a subsequent shape such as after rolling. It is insufficient.
On the other hand, Non-Patent Document 1 shows a buckling model formulated with a triangular residual stress distribution (strain). The prediction technique disclosed in Patent Document 3 is modeled based on this Non-Patent Document 1.

JP-A-5-237546 Japanese Patent Laid-Open No. 9-295022 Patent No. 4262142

Journal of Japan Society for Technology of Plasticity: Plasticity and Processing, Vol. 28, No. 312 (1987-1) p58-66

  In view of the above problems, the present invention accurately measures the sheet wave shape immediately after the end of rolling of the hot and thin steel sheet and the thick steel sheet, and based on the result, the thin sheet is freely formed by the rolling mill, It aims at providing the manufacturing method of a thick steel plate.

In order to achieve the above object, the present inventor has extensively studied shape prediction by rolling. As a result, the following knowledge has been obtained.
As shown in Patent Document 3, the plastic strain distributed in the plate width direction of the steel plate is buckled, and can be divided into a strain that is geometrically converted as a wave shape and a strain that is inherent in the steel plate even after buckling. Are known. For this reason, even when trying to freely control the rolling shape by installing a shape meter that can obtain only geometric information after the rolling mill and performing feedback control based on the shape data acquired by the shape meter, A portion that does not take into account the residual strain and residual stress inherent in the steel sheet becomes an error, and therefore it is impossible to perform accurate shape control.

  Japanese Patent Laid-Open No. 2004-228688 assumes that the width direction strain distribution is known and uses the value to predict the wave shape. Therefore, in the technique disclosed in Patent Document 3, when measuring the strain distribution in the width direction by rolling, even though what appears as a wave shape can be measured, the strain inherent in the steel sheet is attenuated by creep, and the lattice It is difficult to measure directly from distortion or the like. In addition, it was questioned whether the value of this attenuation was accurate.

On the other hand, the present inventor conducted intensive research and found that the residual stress or residual strain applied by rolling can be accurately approximated with a simple model of the fourth order or less. A method to analyze the widthwise distribution of the inherent strain was developed.
Further, by comparing this analysis method with the measured value, it is possible to obtain a distribution in the width direction of the strain inherent in the steel sheet by correcting from the directly measured value. The gist of the present invention is as follows.

(1) The plate wave shape after the end of rolling of hot and thin steel plates and thick steel plates is measured as the geometric value of the plate feed plate direction, plate width direction position and height direction displacement on the rolling mill delivery side, and the shape feature amount In the measurement method for obtaining the profile, steepness, and elongation strain difference, in addition to the measured shape feature amount, the residual strain or residual stress inherent in the steel sheet at the time of measurement is obtained by analysis or measurement, and the measured shape feature amount is overlaid. A shape measuring method in hot rolling of a thin steel plate and a thick steel plate, characterized in that a true shape feature amount given from a rolling mill is obtained by combining.

(2) For the prediction of the residual strain or residual stress inherent in the steel plate at the time of measurement in the shape prediction method, the steel plate is divided into left and right by the plate thickness, plate width, tension and plate center of the steel plate, and the center portion is the origin. The residual strain width direction distribution assuming the superposition of the quadratic function distribution on the first to fourth order functions or trapezoids is determined using the buckling equation or FEM of the flat plate, and the buckling strain or buckling stress of the plate determined. Is the residual strain or residual stress, the shape measuring method in hot rolling of the thin steel plate and the thick steel plate according to the above (1).
(3) Based on the true shape feature value obtained in (1) or (2) above, the hot rolling of a thin steel plate and a thick steel plate that has a predetermined corrugated shape by feedback control using the shape forming mechanism of the rolling mill Rolling method.

  It is impossible to measure the residual strain and stress inherent in the steel plate no matter how the geometric shape measuring means represented by the shape meter is used. However, according to the shape measuring method according to the present invention (1), the residual strain or residual stress inherent after the generation of the wave shape that does not appear in the plate wave shape, and the shape obtained by the geometric shape measurement measured by the shape meter By superimposing the elongation strain distribution or the residual stress distribution as the feature amount, it is possible to determine a so-called “true” elongation strain distribution (true shape feature amount) with little error.

  Also, according to the present invention (2), the residual strain distribution is divided into left and right with the center as the center, a simple distribution function is defined with the center at the left and right as the origin, and the thickness, width, residual strain distribution, and tension are input. The strain distribution in the width direction that buckles can be obtained by the inherent buckling strain equation of the flat plate. This strain distribution in the width direction is a predicted residual strain distribution inherent in the steel sheet even after the corrugation occurs. The strain distribution as a shape feature obtained by geometric shape measurement measured with a shape meter and the above-mentioned predicted residual strain distribution. By superimposing the strain distributions, it is possible to determine a “true” elongation strain distribution (true shape feature amount) with less error.

  In addition, according to the present invention (1) and (2), it is possible to grasp the strain distribution applied to the steel sheet with high accuracy, and therefore, based on the true shape feature amount obtained in (1) or (2). It is possible to obtain a predetermined wave shape by feedback control using the shape forming mechanism of the rolling mill. That is, according to the present invention (3), the shape control amount corrected with the “true shape feature amount” is used when setting the reduction, so that a predetermined plate shape can be obtained with high accuracy.

It is the figure which showed preferable embodiment (reverse rolling) of Claims 1, 2, and 3 of this invention. It is the figure which showed preferable embodiment (tandem rolling) of Claims 1, 2, and 3 of this invention. It is a figure explaining the shape meter, the arithmetic unit, the control logic, and the shape control actuator. It is the figure which showed the example of distribution of the residual strain distribution assumed by this invention. It is the figure which showed the constraint conditions according to the conditions set when implementing an intrinsic buckling strain calculation. It is a figure of the wave shape measured with the shape meter. It is the figure which showed the center reference | standard elongation-strain difference distribution calculated | required by calculating the shape data obtained from the shape meter.

Hereinafter, a shape measuring method of a steel sheet and a shape control method using the shape measuring method according to an embodiment of the present invention will be described with reference to the drawings.
1 and 2 show preferred embodiments of claims 1, 2 and 3 of the present invention. There are various types of steel plate rolling equipment, but at least a finishing reverse rolling mill 1 for performing reverse rolling shown in FIG. 1 or a finishing tandem rolling mill 2 shown in FIG. 2 is an object of the present invention. Yes.
As the finishing reverse rolling mill 1 or the finishing tandem rolling mill 2, a four-high rolling mill having a mechanism for supporting a pair of work rolls with a pair of reinforcing rolls is often used. A multi-stage rolling mill may be used. Usually, a sheet passing roll 4 for passing a steel sheet is installed.

  A shape meter 3 is installed on the exit side of the rolling mill, for example, on the downstream side of the rolling roll, and the geometric sheet wave shape of the steel sheet immediately after rolling, that is, the wave height for each sheet passing direction and each sheet width position is measured. In the case of reverse rolling, in FIG. 1, the shape meter 3 is installed before and after the rolling mill, but the shape may be measured by installing only one of them. In the case of tandem rolling, the shape meter 3 is installed after the final stand, but it can also be installed on the rear surface of each stand.

Then, using this shape data, the profile, steepness, and elongation strain difference are obtained as shape features, and the plate thickness, width, tension, standardized residual strain and stress distribution are input in advance. Is also provided with an arithmetic unit 5 for calculating residual strain and stress inherent therein.
The arithmetic unit 5 may be provided in a shape meter, or a function may be provided in the process control 6 that controls the rolling shape. In any case, since the true residual strain is found from the result of the arithmetic unit 5, the result is received, and in order to obtain a predetermined shape, the shape is controlled using a shape control actuator 7 such as a load, a bender, a work roll shift, or a pair cross. Is controlled using a known shape control logic such as feedback control. The details of the arithmetic unit 5 are shown in FIG. The contents of the arithmetic device 5 will be described below.

Step 1
The geometric shape data measured by the shape meter shown in FIG. 4 or 5 is, for example, shape data having height information for each position in the plate passing direction and plate width direction as shown in FIG. Direction, y is the width direction, and z is the height direction).

Step 2
Thereafter, using the following formulas (1), (2), and (3) that define the line integral and strain, an elongation strain difference is calculated from the geometric shape with the plate width center as the origin (reference). The subscript i indicates the i-th position when the sheet passing direction is divided into N parts. The subscript j indicates the j-th position when the plate width direction is divided into M parts.
ε _j = (Σ (ds _ij ) −Σ (dx _i )) / Σ (dx _i ) (1)
ds _ij = √ (dx _i ² + dz _i ² ) (2)
Δε _j ′ = ε _j −ε _CENTER (3)

  When this calculation is executed, the shape data of FIG. 6 is converted into an elongation strain difference shown in FIG. 6 and 7 are based on the premise that the division in the plate width direction can be measured finely. However, when the shape meter has a total of three points, ie, the center part and the two edge parts, the accuracy is lowered but it depends on the quadratic function. An approximation may be used. In addition to the above-mentioned three points, if two points of the quarter part WS (work side) and DS (drive side) can be measured, it is determined by approximation by a quadratic to quartic function excluding the asymmetric component.

Step 3
The boundary of the intrinsic buckling analysis that is performed to estimate the residual strain inherent in the steel plate after buckling, assuming that the edge strain in the elongation obtained in Step 2 is a positive value if the edge is positive, and if it is a negative value, it is a medium wave. Determine the conditions and send this information to step 4.
Here, since the quarter wave is considered to be basically generated due to local elongation of the outermost edge portion due to edge drop to the ear wave, the inherent distortion is treated as an ear wave. At this time, the boundary condition of the strain inherent in the steel sheet is set to 0.

Step 4
Thickness, width, and tension information is collected in advance from the process control used in the rolling operation, and the maximum residual strain is determined based on the information on whether it is an ear wave or a medium wave based on the characteristics of the rolling shape obtained in Step 3 in advance. To determine the non-dimensional residual strain and constraint conditions. If an approximate wave pitch can be measured, the pitch may be directly input.
Here, as shown in FIG. 4, the dimensionless residual strain distribution has a center portion as the origin, an edge portion as a half-width position of the plate, and a maximum strain value of 1. The solid line is an ear wave, and the broken line is a medium wave condition. Although the distribution shape of the residual strain is shown from the first order to the fourth order, it has been confirmed by modeling so far that the accuracy is sufficiently good even by the fourth order or less by the present inventors.
In the rolling of a steel plate, an edge drop phenomenon occurs in which the steel plate is inevitably pushed out in the plate width direction by rolling at the edge portion, so that the strain in the region where the edge drop is generated does not extend in the rolling direction. As a result, when there is no plate crown, it is considered that a trapezoidal strain distribution is generated. A strain distribution with a roll crown or plate crown attached and the resulting embedded residual strain superimposed as a ± quadratic function distribution is used. It was used as the width direction distribution.

The constraint conditions corresponding to the conditions of each wave are shown in FIG. The said figure has shown the C cross section of the steel plate on the one side restraint state from a center part to an edge part, and the broken line has shown the image of the shape profile at the time of buckling.
Here, in the case of the ear wave condition, the width and height displacement of the center part is restricted and the edge part is not restricted, and in the case of the medium wave condition, the rotation of the center part around the plate direction axis is restricted and the edge part is in the height direction. In the case of only restraint and quota conditions, the center part restrains the width and height displacement, and the edge part also restrains in the height direction.

Step 5
Based on the data of step 4, FEM or flat plate proper buckling analysis is performed. More specifically, the inherent buckling analysis of the flat plate shown in Patent Document 3 and the large deflection analysis using the finite element method are performed, and the limit inherent buckling strain that causes elastic buckling when larger than this is obtained. The inherent strain is determined as a strain that remains (internal) in the shape even after buckling.

As for the inherent buckling analysis of a flat plate, a buckling model formulated by a triangular residual stress distribution (strain) shown in Non-Patent Document 1 is shown, and the discretized distribution follows Patent Document 3. In particular, in the case of Patent Document 3, analysis is possible even with a stress distribution in which residual stress is arbitrarily distributed in the width direction, and buckling analysis is also possible with residual stress discretized for each position in the plate width direction. It is formulated into
Based on these buckling equations, a distribution obtained by multiplying the longitudinal residual strain or longitudinal residual stress in the width direction, which has been made dimensionless in advance, by multiplying the width direction uniformly, and the wave pitch The stress or strain distribution for starting buckling is obtained for each time, and the wave pitch with the lowest buckling stress or strain distribution value is defined as the buckling wave pitch and determined as the strain or stress criteria for occurrence of buckling.
In this shape prediction, wave buckling may occur at a pitch that is actually shorter than theoretical buckling. In that case, it is also possible to obtain a wave buckling pitch from a shape meter and determine it as a criterion for strain or stress of occurrence of buckling corresponding to the wave buckling pitch.

  When a certain degree of rolling conditions are known, the results may be calculated in advance, the results may be tabulated, and the results may be determined by an interpolation function for the table. There are buckling modes from the first to the nth order regarding the buckling intrinsic strain width direction distribution, but basically buckling by rolling in the range of the hot rolling, the thickness of the thick steel plate, and the width of the plate which is the object of the present invention. The mode becomes so large that the corresponding intrinsic buckling strain enters the plastic region and theoretically does not exceed the second-order mode. Therefore, the calculation uses only first order results.

Step 6
The elongation strain difference distribution obtained in step 2 and the inherent buckling strain distribution obtained in step 5 are overlapped to determine the net residual strain distribution (true shape feature amount) applied to the steel sheet by rolling. This is calculated and executed for each WS and DS around the center.

Step 7
Based on the control logic such as PID control, how to move the shape control actuator to achieve a predetermined rolling shape using the net residual strain distribution (true shape feature value) applied to the steel plate Determine the value. When the true shape feature value is a residual strain distribution, this can be used as a correction value for the widthwise elongation distribution or the crown ratio. When the true shape feature value is a residual stress distribution, the entry side and / or It can be used as a correction value for the tension distribution on the delivery side.

Step 8
Based on the control command value determined in step 7, the shape control actuator 7 such as a bender, load, tension, pair cross, or CRS is moved to create a predetermined shape.
By executing a loop in which the above steps (STEP) are repeated while calculating net residual strain, a highly accurate shape can be created.
Here, the apparatus for calculating the net residual strain distribution may be provided individually, or may be provided in the process controller 6 as part of the shape meter 3 or control logic as shown in the broken lines and double lines in FIGS.

  Here, the difference between Patent Document 3 and the present invention will be described. In Patent Document 3, the residual stress and strain distribution of a flat plate to be evaluated are known. The known residual stress and strain distribution of the flat plate is determined by using the buckling equation of the flat plate and FEM, and the buckling limit residual strain or stress distribution that causes buckling if larger than this is obtained. Compared to the residual stress and strain distribution of the flat plate to be evaluated, if it is small, the flat plate does not buckle as it is, but is present in the flat plate, and if it is large, it buckles with the residual strain or stress present in the flat plate and appears in the shape. The shape is predicted by separating into residual stress and strain distribution converted from geometric displacement.

  On the other hand, according to the present invention, the residual stress and strain (true shape feature amount) of the flat plate to be evaluated are unknown, and this is being obtained. However, in claim 2 of the present invention, the geometric displacement deformed out of plane by the shape meter is grasped, and the sheet width center is set to 0 for the residual strain and stress distribution (true shape feature amount) applied by some analysis or rolling. It is modeled by a functional expression from the first to fourth order excluding the asymmetric component as a point or a function expression in which a quadratic function is superimposed on a trapezoid, and remains in the flat plate even after buckling using FEM or the buckling equation of the flat plate. The residual strain or stress distribution is obtained, and the residual stress or strain distribution of the flat plate to be evaluated is determined by superimposing the residual stress or strain distribution converted from the geometric displacement appearing in the shape.

Further, according to the first aspect of the present invention, as a method of obtaining the residual residual strain or stress, not only a method of obtaining by analysis but also a method of directly measuring is recognized.
In both Patent Document 3 and the present invention, the residual stress and strain distribution of the flat plate to be evaluated is based on the residual stress and strain distribution (buckling criterion) inherent in the steel plate after buckling and the geometric displacement that appears in the shape after buckling. The point which uses the point which has the relationship which superposed | superposed the residual stress and strain distribution converted is the same.

However, while Patent Document 3 is known because the residual stress and strain distribution (true shape feature amount) to be evaluated is obtained from the temperature distribution or the like, the present invention is a true shape feature amount generated by rolling. It differs greatly in that it cannot be given as known.
In addition, a residual stress and strain distribution converted from geometric displacement appearing in the shape was obtained using a shape meter to obtain the true shape feature amount, and the asymmetric component was removed from the residual strain and stress distribution applied by rolling. The objects and operations to be obtained differ greatly depending on the first to fourth order function expressions or the points modeled by a function expression in which a quadratic function is superimposed on a trapezoid.
Furthermore, in the present invention, since the rolling shape is controlled based on the true shape feature amount, a desired plate wave shape can be obtained.
The stress distribution described here is equivalent to the strain distribution multiplied by a uniform Young's modulus for the width and thickness.

Such an invention was carried out by reverse rolling of a thick steel plate as shown in FIG. 1 and tandem rolling of a thin steel plate as shown in FIG.
In reverse rolling, first, the shape is measured by the shape meter 3 immediately after the end of a certain intermediate pass, and the width direction elongation strain difference distribution is approximated by a quartic equation based on this shape data.
Next, it is determined whether this wave shape is a medium wave, an ear wave, or a quarter wave. At that time, not only one but also a combination of a plurality of waves such as a medium wave and an ear wave or an ear wave and a quarter wave may be present. Based on this, the arithmetic unit 5 solves the buckling equation, and the buckling limit, which is the solution, is defined as the residual strain distribution or residual stress distribution in the width direction inside the steel plate.

As described above, the residual strain distribution inherent in the steel sheet and the residual stress distribution inherent in the steel sheet are the difference between whether or not they are multiplied by a uniform Young's modulus, and are essentially the same. The residual strain distribution (residual stress distribution) inherent in the steel plate thus obtained and the strain distribution (stress distribution) converted from the shape measured by the shape meter 3 are added to obtain a true shape feature amount.
By correcting the bender force of the work roll bender, which is the shape control actuator 7, with this true shape feature amount after the next pass, the shape median ratio of the thick steel plate is compared with that using the conventional shape meter method. 15% improvement in reverse rolled thick steel plate.

On the other hand, in tandem rolling, first, the shape is measured by the shape meter 3 immediately after the top portion passes through the final stand, and the width direction elongation strain difference distribution is approximated by a quartic equation based on the shape data.
Next, as in the case of reverse rolling, it is determined whether this wave shape is a medium wave, an ear wave, or a quarter wave. At that time, not only one but also a combination of a plurality of waves such as a medium wave and an ear wave or an ear wave and a quarter wave may be present. Based on this, the arithmetic unit 5 solves the buckling equation, and the buckling limit, which is the solution, is defined as the residual strain distribution or residual stress distribution in the width direction inside the steel plate.

Similarly to the reverse rolling, the residual strain distribution (residual stress distribution) inherent in the steel plate thus obtained and the strain distribution (stress distribution) converted from the shape measured by the shape meter 3 are added. Together, the true shape feature value is obtained.
By correcting the bender force of the work roll bender, which is the shape control actuator 7, with this true shape feature value in real time at the final stand, the shape medianity of the thin steel sheet can be compared with the conventional shape meter method. The shape median of the hot-rolled steel sheet was improved by 20%.

DESCRIPTION OF SYMBOLS 1 Reverse rolling mill 2 Tandem rolling mill 3 Shape meter 4 Feeding plate roll 5 Arithmetic device 6 Process control 7 Shape control actuator

Claims (3)

The sheet wave shape after the end of rolling of the hot thin steel plate and the thick steel plate is measured as a geometric value on the delivery side of the rolling mill and the plate width direction position and the plate width direction position and the height direction displacement, and is profiled as a shape feature amount. In the measurement method for determining the steepness and the elongation strain difference, in addition to the measured shape feature amount, the residual strain or residual stress inherent in the steel sheet at the time of measurement is obtained by analysis or measurement, and is superposed on the shape feature amount. A shape measuring method in hot rolling of a thin steel plate and a thick steel plate, wherein a true shape feature amount given from a rolling mill is obtained at the same time.
Regarding the prediction of the residual strain or residual stress inherent in the steel plate at the time of measurement in the shape prediction method, the steel plate is divided into right and left by the plate thickness, plate width, tension, and plate center of the steel plate, and the primary portion with the center portion as the origin ˜4th order function or trapezoidal quadratic function distribution is assumed to be the residual strain width direction distribution using plate buckling equation or FEM to determine the buckling strain or buckling stress of the plate determined from residual strain. The shape measuring method in hot rolling of a thin steel plate and a thick steel plate according to claim 1, wherein the shape is a residual stress.
A hot rolling method for thin steel plates and thick steel plates that have a predetermined corrugated shape by feedback control using a shape-making mechanism of a rolling mill based on the true shape feature amount obtained in claim 1 or 2.

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