JP2022146631A - Hot rolled coil production method - Google Patents

Abstract

To highly accurately predict a flatness of a hot rolled steel sheet in a coil to thereby improve the flatness thereof when winding the hot rolled steel sheet by a coiler in a hot rolling process and producing the coil.SOLUTION: A steepness of a hot rolled steel sheet in a coil is predicted on the basis of a tensile force when winding the hot rolled steel sheet by a coiler, a body crown generated on the hot rolled steel sheet after finish rolling, and the number of winding of the hot rolled steel sheet in the coil, the tensile force and the body crown are adjusted so that the predicted steepness becomes 2.1% or less.SELECTED DRAWING: Figure 13

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a coil by winding a hot-rolled steel sheet with a coiler in a hot-rolling process.

In the hot rolling process, the hot-rolled steel sheet after finish rolling is cooled to a predetermined temperature by a cooling device while being conveyed from the finishing mill to the coiler by the run-out table, and then wound up by the coiler to form a coil ( hot-rolled coil).

The coil manufactured as described above is once wound at a predetermined winding temperature and then transported to a coil yard, cooled to room temperature, and then shipped to a user or transported to the next process. At this time, when the coils to be shipped or conveyed to the next process are unwound for processing, the flatness of the hot-rolled steel sheet may be poor. In such a case, the threadability of the hot-rolled steel sheet is poor and meandering occurs, and problems such as drawing during working and rolling occur, so the shape must be corrected. However, since the shape (flatness) of the hot-rolled steel sheet is not known in the coil state, it is currently not possible to ship the coil with poor flatness. However, in this case, costs are incurred. Therefore, in order to transport only hot-rolled steel sheets with bad shapes to the refining process, it is required to adjust the flatness of the hot-rolled steel sheets wound into coils to within a standard value in advance. In addition, establishing a technology for reducing shape correction threading in the finishing process is an important technology especially in conventional mills, mini mills, and thin slab processes targeting hot finalization.

As a method for predicting the shape of a hot-rolled steel sheet, for example, Patent Document 1 describes a stress component that transforms the residual stress of a hot-rolled steel sheet (metal sheet) into a wave shape during buckling, and Disclosed is a method of predicting the shape of a hot-rolled steel sheet using stress components that are separated into residual stress components and converted into wave shapes. In addition, in this shape prediction method, the wavy shape of the hot-rolled steel sheet generated after finish rolling is corrected by, for example, the tension acting on the hot-rolled steel sheet when it is wound on a coiler. It is assumed that the temperature distribution in the width direction of the hot-rolled steel sheet in is generated as residual stress. Further, the flatness of the hot-rolled steel sheet is improved by controlling the temperature distribution in the width direction, for example, with an edge heater or an edge mask based on the result of shape prediction thus predicted.

Japanese Patent No. 4262142

However, when the present inventors investigated the shape of the steel sheet after the hot rolling process in detail, as disclosed in Patent Document 1, the residual stress (elongation strain difference) caused by the temperature distribution of the hot rolled steel sheet was used to It was found that there is a deterioration in flatness that cannot be clarified only by predicting the shape using It has also been found that the flatness of the hot-rolled steel sheet cannot be sufficiently improved only by controlling the temperature distribution in the width direction based on this shape prediction result. Therefore, there is room for improvement in accurately predicting the flatness of hot-rolled steel sheets and improving the flatness based on the prediction results.

The present invention has been made in view of the above circumstances. The purpose is to improve flatness.

In order to solve the above problems, the present inventors conducted extensive studies, and as a result, the mechanism of deterioration of flatness of hot-rolled steel sheets after the hot rolling process was elucidated. It was found that the tightening factor is caused by a combination of two factors. The first temperature factor is thermal strain caused by non-uniform temperature distribution in the width direction of the hot-rolled steel sheet immediately before being wound on the coiler, and this thermal strain becomes the elongation strain difference (residual strain). The second tightening factor is, for example, a crown generated in the hot-rolled steel sheet after finish rolling (in the present invention, defined as a body crown as described later). The tension is unevenly distributed in the width direction, and the inner circumference of the coil is plastically deformed due to tight winding due to the uneven tension distribution, causing plastic strain, and this plastic strain becomes the difference in elongation strain (residual strain). is a factor.

Of the two factors, the first temperature factor, which is exemplified by the shape prediction method disclosed in the above-mentioned Patent Document 1, has been conventionally considered as a factor of deterioration of flatness, and countermeasures have been taken. There is. On the other hand, the second cause of tight winding is that the present inventors newly discovered that deformation due to tight winding occurring in the cold rolling process also occurs in the hot rolling process.

As a result of further intensive studies by the present inventors, it was found that the flatness deterioration due to this tightening factor is the tension when the hot-rolled steel sheet is wound by a coiler, the body crown that occurs in the hot-rolled steel sheet after finish rolling, and the coil. It was found to be predictable based on the number of turns of the hot rolled steel. The details of this prediction method will be described later in the embodiment.

The present invention has been made based on such findings, and is a method for manufacturing a coil by winding a hot-rolled steel sheet with a coiler in a hot rolling process, wherein the steepness of the hot-rolled steel sheet in the coil is It is predicted based on the tension when the hot-rolled steel sheet is wound by a coiler, the body crown generated in the hot-rolled steel sheet after finish rolling, and the number of turns of the hot-rolled steel sheet in the coil, and the predicted steepness is 2.1. % or less, the tension and the body crown are adjusted.

According to the present invention, by predicting the steepness of the hot-rolled steel sheet using the above-mentioned three parameters of tension, body crown, and number of turns, it is possible to predict the flatness of the hot-rolled steel sheet, which deteriorates due to tight winding. . Furthermore, by adjusting the tension and body crown so that the predicted steepness is 2.1% or less, the flatness of the hot-rolled steel sheet can be improved.

Here, for example, Japanese Unexamined Patent Application Publication No. 2014-65935 discloses controlling the tension when winding the hot-rolled steel sheet, and discloses a low tension of 10 MPa, for example. However, Japanese Patent Application Laid-Open No. 2014-65935 does not disclose controlling the crown. Moreover, the control of the tension is originally intended to suppress the occurrence of surface defects in the hot-rolled steel sheet, and does not improve the flatness as in the present invention.

Further, for example, Japanese Unexamined Patent Application Publication No. 8-66701 discloses controlling the crown generated in a hot-rolled steel sheet after finish rolling, and discloses a low crown of 18 μm, for example. However, Japanese Patent Application Laid-Open No. 8-66701 does not disclose controlling the tension.

Thus, the prior art discloses controlling either tension or crown, but does not disclose adjusting both tension and crown (body crown) as in the present invention. It is a novelty that has never existed before.

但し、λ：前記コイルにおける熱延鋼板の急峻度（％）、α及びβ：調整係数、Ｕｔ：前記コイラーにより熱延鋼板を巻き取る際の張力（ＭＰａ）、Ｃｒ：仕上圧延後の熱延鋼板に生じるボディークラウン（μｍ）、Ｎ：前記コイルにおける熱延鋼板の巻き数 In the hot-rolled coil manufacturing method, the steepness of the hot-rolled steel sheet in the coil may be predicted by the following formula (1).

However, λ: steepness (%) of the hot-rolled steel sheet in the coil, α and β: adjustment coefficient, Ut: tension (MPa) when the hot-rolled steel sheet is wound by the coiler, Cr: hot-rolled after finish rolling Body crown (μm) generated on the steel sheet, N: Number of turns of the hot-rolled steel sheet in the coil

In the hot-rolled coil manufacturing method, the number of turns may be estimated from the thickness, width, and unit weight of the coil.

In the method for manufacturing a hot-rolled coil, the hot-rolled steel sheet wound around the coiler may have a temperature of 700° C. or higher before being transformed, during transformation, or after completion of transformation.

According to the present invention, the steepness of the hot-rolled steel sheet is predicted based on the tension when the hot-rolled steel sheet is wound by a coiler, the body crown generated in the hot-rolled steel sheet after finish rolling, and the number of turns of the hot-rolled steel sheet in the coil. By doing so, it is possible to predict the flatness of the hot-rolled steel sheet that deteriorates due to the tightening factor. Furthermore, the flatness of the hot-rolled steel sheet can be improved by adjusting the tension and body crown so that the predicted steepness is 2.1% or less.

It is explanatory drawing which shows the outline of the structure after a finishing mill of a hot-rolling equipment. It is explanatory drawing which shows the outline of a structure of a coiler. FIG. 2 is an explanatory diagram in an axial cross-section, showing an outline of the configuration of a mandrel; FIG. 3 is an explanatory view in a cross-sectional view in a direction perpendicular to the axis, showing the outline of the mandrel structure. FIG. 4 is an explanatory diagram showing the definition of steepness representing the degree of ear waves; It is a conceptual diagram explaining the mechanism of the flatness deterioration by a tightening factor. It is a conceptual diagram explaining the mechanism of the flatness deterioration by a tightening factor. It is a graph which shows the situation which caught the diameter reduction phenomenon of a mandrel. It is a graph which verifies the phenomenon that an ear wave is generated by a tightening factor. FIG. 4 is an explanatory diagram showing the definition of body crown; FIG. 4 is an explanatory diagram showing the steepness of the hot-rolled steel sheet at the inner periphery of the coil when the number of turns is 50, the tension is varied from 0 to 20 MPa, and the body crown is varied from 0 to 80 μm. FIG. 5 is an explanatory diagram showing the steepness of the hot-rolled steel sheet at the inner periphery of the coil when the number of turns is 70, the tension is varied from 0 to 20 MPa, and the body crown is varied from 0 to 80 μm. FIG. 5 is an explanatory diagram showing the steepness of the hot-rolled steel sheet at the inner circumference of the coil when the number of turns is 75, the tension is varied from 0 to 20 MPa, and the body crown is varied from 0 to 80 μm. FIG. 5 is an explanatory diagram showing the steepness of the hot-rolled steel sheet at the inner periphery of the coil when the number of turns is 100, the tension is varied from 0 to 20 MPa, and the body crown is varied from 0 to 80 μm.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

<Hot rolling equipment>
First, the configuration of the hot rolling equipment according to the present invention will be described. FIG. 1 is an explanatory view showing the outline of the configuration after the finishing mill 2 of the hot rolling mill 1. As shown in FIG.

The hot rolling equipment 1 includes a finishing rolling mill 2 for continuously rolling a steel plate H discharged from a heating furnace (not shown) and rolled by a rough rolling mill (not shown) to a predetermined thickness, and a steel plate after finish rolling. A cooling device 3 for cooling H (hereinafter referred to as a hot-rolled steel sheet H) to a predetermined temperature and a coiler 4 for winding the cooled hot-rolled steel sheet H are provided in the conveying direction of the hot-rolled steel sheet H in this order. A run-out table 5 for conveying the hot-rolled steel sheet H is provided between the finishing mill 2 and the coiler 4 . The hot-rolled steel sheet H rolled by the finishing mill 2 is cooled by the cooling device 3 while being transported on the run-out table 5, and then wound around the coiler 4 to be manufactured as a coil C.

A plate thickness gauge 6 for measuring the plate thickness of the hot-rolled steel plate H rolled by the finishing mill 2 is provided between the finishing mill 2 and the cooling device 3 of the hot rolling facility 1 . The plate thickness meter 6 can measure the plate thickness distribution in the width direction of the hot-rolled steel plate H and measure the body crown of the hot-rolled steel plate H.

FIG. 2 is an explanatory diagram showing the outline of the configuration of the coiler 4. As shown in FIG. In addition, the example of FIG. 2 shows the state of starting the winding operation in the coiler 4 . The coiler 4 has a pinch roll 10, a chute 11, a mandrel 12 and a wrapper roll 13.

In the coiler 4 , the hot-rolled steel sheet H is bent in the direction of the mandrel 12 by the pinch rolls 10 and passed through the chute 11 . Here, before the tip of the hot-rolled steel sheet H reaches the mandrel 12, the wrapper roll 13 is closed (in contact with the mandrel 12), and waits while rotating at a speed several percent faster than the steel sheet speed. is doing. When the hot-rolled steel sheet H reaches the mandrel 12 and the wrapper roll 13, the hot-rolled steel sheet H is sandwiched between the mandrel 12 and the wrapper roll 13 and wound. The diameter of the mandrel 12 can be expanded and contracted by the cylinder portion 24 as will be described later. When the tightening force is balanced, the wrapper roll 13 is opened and separated from the coil C.

3 and 4 are explanatory diagrams showing the outline of the configuration of the mandrel 12. FIG. As shown in FIG. 3, the mandrel 12 is segmented and has a mandrel segment 20, a wedge 21, a slide rod 22 and a wedge shaft 23. As shown in FIG. Of these constituent members, the slide rod 22 and the wedge shaft 23 constitute the cylinder portion 24 . By sliding the wedge 21 on the cylinder portion 24, the mandrel segment 20 slides radially along the wedge shaft 23 in an expanding or contracting direction.

Further, as shown in FIG. 4, the mandrel 12 has a gap A between the segment collar portion 25 and the wedge jaw portion 26, and when it rotates, the gap A disappears due to centrifugal force and the mandrel 12 expands. The segment-wedge portion 27 includes one pair of the mandrel segment 20 and the wedge 21, and four pairs of the segment-wedge portion 27 constitute the mandrel 12. FIG.

<Mechanism of deterioration of flatness>
The present invention predicts the flatness of the hot-rolled steel sheet in the coil manufactured by the hot rolling equipment configured as described above, and further improves the flatness based on the prediction result. The coiling temperature of the hot-rolled steel sheet varies depending on the material, but is in the range of approximately 100 to 800°C. The coils produced by the hot rolling equipment are conveyed to the coil yard, cooled to room temperature, and then unwound. . The flatness predicted in the present invention is the flatness of the hot-rolled steel sheet unwound from the coil (more specifically, the flatness of the hot-rolled steel sheet due to tight winding as described later). A wavy out-of-plane deformation called a selvage occurs at the widthwise end of the rolled steel sheet. Here, the deterioration of the flatness that occurs in many hot-rolled steel sheets is the edge wave, and the present invention intends to predict the edge wave and further improve it. In other cases, if the coiler shaft or pinch roll crown profile is convex and the winding tension is abnormally high, medium waves may occur in the center instead of the width direction ends. However, this is outside the scope of the present invention.

Note that FIG. 5 is an explanatory diagram showing the definition of the degree of steepness representing the degree of ear waves. The steepness λ is obtained by dividing the wave height H at the end of the hot-rolled steel sheet in the width direction by the wave pitch L, multiplying the result by 100, and expressing it in percent. The steepness λ is expressed by the following formula (2) using the elongation strain difference Δε.

Then, the present inventors conducted extensive studies and clarified the mechanism of deterioration of the flatness of the hot-rolled steel sheet after the hot-rolling process. In other words, the deterioration of the flatness is caused by the temperature factor that causes thermal strain due to the uneven temperature distribution in the width direction of the hot-rolled steel sheet, and the tightness of the winding due to the uneven tension distribution in the width direction that occurs during winding of the coiler. It has been found that two factors are combined to cause deformation and tightening factors. These two factors are described below.

(temperature factor)
The deterioration of the flatness due to the first temperature factor will be described. A hot-rolled steel sheet immediately before being wound on a coiler is subjected to thermal strain due to non-uniform temperature distribution in the width direction. This thermal strain becomes an elongation strain difference (residual strain), resulting in deterioration of flatness (deterioration of shape) of the hot-rolled steel sheet.

Deterioration of flatness due to temperature factors has been known for a long time. Investigation of prediction method” Akashi et al.). That is, when a hot-rolled steel sheet finish-rolled in a finishing mill is cooled by a cooling device while being transported on a run-out table, a difference in elongation strain occurs due to non-uniform temperature distribution in the width direction. However, before and after the hot-rolled steel sheet passes through the lower pinch rolls, the difference in elongation strain becomes almost zero due to the following correction action. For example, a hot-rolled steel sheet that has been tensioned by a coiler just before winding is threaded with an infinite curvature radius in the threading direction until just before the lower pinch roll. Due to the winding (surface contact), bending deformation is forcibly applied at the radius of the lower pinch roll, and after passage, the radius of curvature in the sheet threading direction becomes infinite again and corrected. When the temperature distribution in the width direction of the hot-rolled steel sheet during coiling is lowered to normal temperature during uncoiling, an elongation strain difference occurs in the hot-rolled steel sheet, resulting in deterioration of flatness.

(Tightening factor)
The deterioration of the flatness due to the second tightening factor will be described. For example, due to the crown generated in the hot-rolled steel sheet after finish rolling, the tension acting on the hot-rolled steel sheet when wound on the coiler is unevenly distributed in the width direction. The inner periphery is plastically deformed and plastic strain is generated. This plastic strain becomes an elongation strain difference (residual strain), resulting in deterioration of flatness (deterioration of shape) of the hot-rolled steel sheet.

Next, the mechanism of deterioration of the flatness due to tight winding will be described in detail with reference to FIGS. 6 and 7. FIG. 6 and 7, the symbol T indicates tensile stress and S indicates compressive stress.
(A) First, when the hot-rolled steel sheet is wound with a coiler at a constant tension, tensile stress acts on the hot-rolled steel sheet on the surface of the coil, but compressive stress acts on the hot-rolled steel sheet on the inner circumference of the coil near the mandrel. works.
(B) In addition, a general hot-rolled steel sheet has a crown with a convex shape at the central portion in the width direction. When another hot-rolled steel plate having a crown is further wound around the hot-rolled steel plate having such a crown, the central portion of the inner hot-rolled steel plate and the central portion of the outer hot-rolled steel plate come into contact with each other. For this reason, a larger compressive stress acts on the central portion in the width direction of the inner peripheral portion of the coil than on the end portions.
(C) In actual operation, the mandrel waits for the hot-rolled steel sheet to be conveyed at the standby diameter, and when the hot-rolled steel sheet is wound by a predetermined number of turns, the mandrel is further expanded (over-expanded). Then, when the pushing force of the cylinder portion that tries to expand the mandrel and the surface pressure from the coil are balanced, the expansion stops and the mandrel maintains a constant diameter. However, in reality, the tension of the hot-rolled steel sheet during winding, the thickness of the hot-rolled steel sheet, the frictional force between the hot-rolled steel sheets, etc., cause the tightening force to become excessive, and the pushing force of the cylinder part loses. , the diameter of the mandrel gradually decreases from the time point when the tight winding is completed. Due to such a reduction in the diameter of the mandrel, the hot-rolled steel sheet on the inner periphery of the coil must bear the tightening force of compression that should be applied to the mandrel.
(D) When the above phenomena overlap, the compressive stress in the inner peripheral part of the coil increases, especially in the center in the width direction. , deformation due to transformation plasticity and creep deformation will occur. As a result, the central portion in the width direction is apparently contracted and the end portions are elongated, resulting in the occurrence of ear waves.

FIG. 8 is a graph showing the state of the mandrel diameter reduction phenomenon in (C) above. The horizontal axis of FIG. 8 is the time from the start of coil winding. The vertical axis indicates the mandrel diameter (the radial distance of the outer surface of the segment) converted from the stroke amount of the cylinder portion. Point a is the point at which the mandrel starts winding the hot-rolled steel sheet, over-expands the mandrel after several windings, and stops the expansion once the tight winding force and the mandrel expanding force are balanced. After that, it can be seen that the mandrel diameter becomes smaller than the point a as the number of turns of the hot-rolled steel sheet in the coil increases with the passage of time and the tightening force on the inner periphery of the coil increases. It is known that the tightening amount of winding (mandrel diameter reduction amount) during winding is not constant but fluctuates for each coil.

FIG. 9 is a graph for verifying the phenomenon in which ear waves are generated due to tight winding in (D) above. The horizontal axis of FIG. 9 indicates the mandrel diameter reduction amount (MD reduction amount). The vertical axis indicates the steepness of the ear wave. It can be seen from FIG. 9 that there is a certain correlation between the mandrel diameter reduction amount and the steepness of the ear wave.

<Flatness Prediction Method and Flattening Method by Rolling Tightening Factor>
The above is the mechanism of deterioration of the flatness of the hot-rolled steel sheet, and the inventors of the present invention have found that the deterioration of the flatness is caused by a combination of the temperature factor and the tightening factor. Here, as described above, deterioration of flatness due to temperature factors is conventionally known, and countermeasures are taken. Specifically, for example, an edge heater installed in front of the finishing mill or an edge mask installed in the cooling device is used to control the temperature distribution in the width direction to be uniform, thereby improving the flatness of the hot rolled steel sheet. can be improved. Therefore, in the present invention, the flatness of the hot-rolled steel sheet, which deteriorates due to tight winding, is predicted, and the flatness is improved based on the prediction result.

(flatness prediction)
Based on the above-mentioned mechanism of deterioration of flatness due to tight winding factors, the present inventors found that as a countermeasure for improving flatness (improving shape), the first is the tension generated in the width direction after winding the hot-rolled steel sheet. The second is to reduce the tightening force to suppress the diameter reduction due to tightening of the mandrel. In order to reduce the first tension distribution difference, it is necessary to reduce the crown generated in the hot-rolled steel sheet. In order to reduce the second tightening force, it is necessary to reduce the tension when winding the hot-rolled steel sheet, and it is also necessary to reduce the number of turns of the hot-rolled steel sheet.

Here, in the present invention, the crown generated in the hot-rolled steel sheet after finish rolling is defined as body crown. As shown in FIG. 10, the crown of the hot-rolled steel sheet H is the difference between the thickness at the end (edge) in the width direction and the thickness at the central portion (center) in the width direction, and is the sum of the body crown and the edge drop. The body crown is the difference between the plate thickness at the edge and the plate thickness at a point 75 mm from the edge (hereinafter referred to as the 75 mm point). Edge drop is the difference between the thickness at the 75 mm point and the thickness at the center. Then, the crown of the hot-rolled steel sheet is defined as the body crown not including the edge drop.

但し、λ：コイルにおける熱延鋼板の急峻度（％）、α及びβ：線形多変量解析で言うところの相関係数であり調整係数である、Ｕｔ：コイラーにより熱延鋼板を巻き取る際の張力（ＭＰａ）、Ｃｒ：仕上圧延後の熱延鋼板に生じるボディークラウン（μｍ）、Ｎ：コイルにおける熱延鋼板の巻き数 The following formula (1) is derived based on such knowledge, and predicts the steepness of the hot-rolled steel sheet at the inner circumference of the coil as the flatness of the hot-rolled steel sheet due to the tight winding factor. The inner peripheral portion of the coil is a range of 200 m from the tip of the hot-rolled steel sheet. In actual operation, the shape of the hot-rolled steel sheet wound on the coil becomes flat within a range of 200 m or more from the tip. It is presumed that this is because when the tip of the hot-rolled steel sheet reaches the mandrel, tension is generated in the hot-rolled steel sheet and the shape is corrected. Therefore, in the present invention, the steepness of the hot-rolled steel sheet at the inner periphery of the coil is predicted. Note that the three parameters in equation (1), the tension Ut, the body crown Cr, and the number of turns N, can be measured and grasped in real time.

However, λ: steepness (%) of the hot-rolled steel sheet in the coil, α and β: correlation coefficient and adjustment coefficient in terms of linear multivariate analysis, Ut: when the hot-rolled steel sheet is wound by the coiler Tension (MPa), Cr: body crown (μm) generated in hot-rolled steel sheet after finish rolling, N: number of turns of hot-rolled steel sheet in coil

The tension Ut is the force (average tension over the entire length of the coil) that pulls the hot-rolled steel sheet when the hot-rolled steel sheet is wound by the coiler, and the magnitude of the tension can be grasped at the time of winding. When the tension Ut is small, the steepness λ becomes small and the hot-rolled steel sheet can be flattened. Note that the tension Ut is represented by a square root in the formula (1). This is because the tension Ut is considered to be in a linear relationship with the elongation strain difference Δε, and the steepness λ in Equation (2) is calculated from the square root of the elongation strain difference Δε.

The body crown Cr can be measured, for example, by a plate thickness gauge provided in the finishing mill and the cooling device shown in FIG. When the body crown Cr is small, the steepness λ becomes small and the hot-rolled steel sheet can be flattened. The body crown Cr is also represented by the square root in the formula (1) for the same reason as the tension Ut. Also, the body crown Cr is the average value of the body crown over the entire length of the coil.

The number of turns N can be grasped when the hot-rolled steel sheet is wound with a coiler. Specifically, for example, it can be estimated from the plate thickness, plate width, and unit weight of the coil, for example, it can be estimated by the number of turns N=(single weight)/(plate thickness×plate width). Alternatively, the number of turns may actually be counted. When the number of turns N is small, the steepness λ becomes small and the hot-rolled steel sheet can be flattened. Note that the number of turns N is also represented by the square root in equation (1) for the same reason as the tension Ut.

The adjustment coefficient α is a reference steepness (hereinafter sometimes referred to as a base steepness), which is the steepness when the tension Ut is 20 MPa, the body crown Cr is 80 μm, and the number of turns N is 100 turns. . Specifically, the adjustment coefficient α is determined by measuring actual machine data, and has a value of 0 (zero) to 10, for example. Also, the adjustment coefficient β is determined by measuring actual machine data.

但し、ａ１～ａ３：線形多変量解析で言うところの相関係数であり調整係数である、ｂ：定数である In the present embodiment, the steepness λ of the hot-rolled steel sheet is predicted by the formula (1), but it is not limited to this. The steepness λ may be predicted based on the three parameters tension Ut, body crown Cr, and number of turns N, ie calculated as a function of λ=f(Ut, Cr, N). Specifically, the steepness λ may be calculated by the following formula (3), or by calculating the difference by the following formula (1') obtained by modifying the formula (1).

However, a1 to a3: a correlation coefficient and an adjustment coefficient in terms of linear multivariate analysis, b: a constant

In addition, the elongation strain difference Δε as well as the steepness λ can be predicted based on the three parameters of tension Ut, body crown Cr, and number of turns N, that is, Δε = g (Ut, Cr, N) function can be calculated by Specifically, the elongation strain difference Δε is calculated by the following formula (4) or formula (5). Then, by inserting the elongation strain difference Δε calculated from these equations (4) and (5) into the above equation (2), the steepness λ can be calculated.
Δε=γ×Ut×Cr×N+b (4)
Δε=a1×Ut+a2×Cr+a3×N+b (5)
However, γ: Correlation coefficient and adjustment coefficient in terms of linear multivariate analysis

(Planarization method)
As described above, the functions f(Ut , Cr, N), g(Ut, Cr, N) (hereinafter referred to as a shape prediction function) can predict the flatness of the hot-rolled steel sheet, which deteriorates due to tight winding. Next, a method for improving the flatness of the hot-rolled steel sheet will be described based on this prediction result.

In order to improve the flatness of the hot-rolled steel sheet, the inventors set the steepness predicted by the shape prediction function to 2.1% or less. The steepness threshold of 2.1% is an allowable value for a product, that is, if the steepness is 2.1% or less, it can be said that the hot-rolled steel sheet is sufficiently flattened. As described above, the cause of the deterioration of the flatness is not only the tightening factor but also the temperature factor. It is assumed that

In order to reduce the steepness predicted by the shape prediction function to 2.1% or less, the three parameters, tension Ut, body crown Cr, and number of turns N, should be reduced. In other words, low tension, low crown, and low number of turns are good for flatness improvement. However, the number of turns N is predetermined according to the product, and is difficult to change in actual operation. Therefore, in the present invention, the tension Ut and the body crown Cr are adjusted so that the steepness predicted by the shape prediction function is 2.1% or less.

As described above, by calculating the steepness of the hot-rolled steel sheet at the inner periphery of the coil using the shape prediction function, it is possible to appropriately predict the flatness of the hot-rolled steel sheet, which deteriorates due to tight winding. Furthermore, by adjusting the tension Ut and the body crown Cr so that the steepness calculated by this shape prediction function is 2.1% or less, the edge waves of the hot-rolled steel sheet in the inner circumference of the coil are reduced. , the flatness can be improved. As a result of intensive studies by the present inventors, it was confirmed that the prediction result of the steepness by the shape function of the present invention and the steepness in the actual operation were in good agreement. It has been confirmed that by adjusting Ut and body crown Cr, the steepness of the hot-rolled steel sheet can actually be improved to 2.1% or less. Specifically, it is possible to improve the flatness to a level that does not require the coil to be transported to a refinement process to correct the shape. As a result, the manufacturing cost can be reduced, and the manufacturing period can be stabilized and shortened. In addition, it is possible to suppress flaws occurring on the surface of the hot-rolled steel sheet in the finishing process, thereby improving the yield of the product.

<Target hot-rolled steel sheets>
The flatness prediction method and flattening method based on the tight winding factor described above are particularly useful when the hot-rolled steel sheet to be coiled by the coiler is untransformed or is being transformed. For example, if the hot-rolled steel sheet is wound after the transformation is completed, the shape of the hot-rolled steel sheet does not deteriorate beyond that during winding. On the other hand, if the hot-rolled steel sheet to be wound around the coiler is not transformed or is being transformed, the hot-rolled steel sheet may be further deformed. In this respect, as in the present invention, if the tension Ut and the body crown Cr are adjusted so that the steepness predicted by the shape prediction function is 2.1% or less, the hot rolled steel sheet is untransformed or during transformation. Even if there is, the flatness of the hot-rolled steel sheet can be improved.

Further, for example, when the hot-rolled steel sheet is coiled at a high temperature of 700° C. or higher after the completion of transformation, the hot-rolled steel sheet may be deformed due to a creep phenomenon. Therefore, the flatness prediction and flattening method of the present invention is also useful when the creep phenomenon occurs during high-temperature winding.

<Specific Flatness Prediction Method and Flattening Method>
The flatness prediction method and the flattening method based on the winding tightening factor have been described above. Next, a specific example thereof will be described.

When winding a hot-rolled steel sheet with a thickness of 2.5 mm and a width of 1200 mm with a coiler, the tension Ut is varied from 0 to 20 MPa, the body crown Cr is varied from 0 to 80 μm, and the number of turns N is 50 to The steepness of the hot-rolled steel sheet at the inner peripheral portion of the coil was calculated from Equation (1) by varying the number of turns by 100 turns. The ranges of the tension Ut, the body crown Cr, and the number of turns N are assumed to be in actual operation. Also, the adjustment coefficient α (base steepness) in Equation (1) was set to 6, and the adjustment coefficient β was set to 0 (zero).

Calculation results of the steepness are shown in FIGS. 11 to 14. FIG. 11 shows the steepness when the number of turns N is 50, FIG. 12 shows the steepness when the number of turns N is 70, and FIG. 13 shows the steepness when the number of turns N is 75. , and FIG. 14 show the steepness when the number of turns N is 100 turns. Further, in FIGS. 11 to 14, shaded portions are portions where the steepness is 2.1% or less, and darker shaded portions are portions where the steepness is 1% or less. That is, the hot-rolled steel sheet can be sufficiently flattened by adjusting the tension Ut and the body crown Cr in the shaded portion.

Referring to FIG. 11, when the number of turns N is 50, the hot-rolled steel sheet can be flattened by winding the hot-rolled steel sheet with a tension Ut of 5 to 10 MPa. At this time, the body crown Cr is not particularly limited. Further, the hot-rolled steel sheet can be flattened by rolling the hot-rolled steel sheet with a body crown Cr of 0 to 40 μm, more preferably 0 to 25 μm. At this time, the tension Ut is not particularly limited.

Further, referring to FIGS. 11 to 13, in any case where the number of turns N is 50, 70, or 75, the hot-rolled steel sheet is wound with a tension Ut of 5 to 10 MPa, and the body crown Cr is 0 to 10 MPa. By rolling the hot-rolled steel sheet to 25 μm, the hot-rolled steel sheet can be flattened.

Referring to FIG. 14, when the number of turns N is 100, the tension Ut is 10 MPa, and the body crown Cr is 25 μm, the steepness of the hot-rolled steel sheet is 2.4%, which is slightly out of the allowable range. However, if the tension Ut is 5 to 10 MPa and the body crown Cr is 0 to 25 μm, the steepness of the hot-rolled steel sheet can be made generally within the allowable range, and the hot-rolled steel sheet can be flattened.

From the above, it can be said that the low tension Ut capable of flattening the hot-rolled steel sheet is 5 to 10 MPa and the low body crown Cr is 0 to 25 μm in actual operation. In fact, under the conventional operating conditions, for example, the number of turns N is 200 turns, the tension Ut is 20 MPa, and the body crown Cr is 70 μm, the steepness is 7%. On the other hand, under the operating conditions of the present invention (the tension Ut is 5 to 10 MPa and the body crown Cr is 0 to 25 μm), the steepness can be reduced to 2.1% or less, and the flatness of the hot rolled steel sheet can be improved. can.

The smaller the tension Ut, the smaller the steepness of the hot-rolled steel sheet, which is preferable for shape improvement. However, when the tension Ut is less than 5 MPa, the telescope phenomenon occurs, and the winding shape of the coil deteriorates, and it may not be possible to wind the coil stably. Therefore, the tension Ut is preferably 5 MPa or more.

Also, the smaller the body crown Cr, the smaller the steepness of the hot-rolled steel sheet, which is preferable for shape improvement. However, if the negative crown is less than 0 (zero) μm, the hot-rolled steel sheet meanders during threading, which may cause threading instability. Therefore, the body crown Cr is preferably 0 (zero) μm or more.

Although the embodiments of the present invention have been described above, the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive various modifications or modifications within the scope of the technical idea described in the claims, and these are also within the technical scope of the present invention. be understood to belong to

INDUSTRIAL APPLICABILITY The present invention is useful when manufacturing a coil by winding a hot-rolled steel sheet with a coiler in a hot-rolling process.

1 Hot rolling equipment 2 Finishing mill 3 Cooling device 4 Coiler 5 Run-out table 6 Plate thickness gauge 10 Pinch roll 11 Chute 12 Mandrel 13 Wrapper roll 20 Mandrel segment 21 Wedge 22 Slide rod 23 Wedge shaft 24 Cylinder part 25 Segment collar part 26 Wedge jaw portion 27 Segment-Wedge portion C Coil H Hot-rolled steel plate

Claims (4)

A method for manufacturing a coil by winding a hot-rolled steel sheet with a coiler in a hot rolling process,
The steepness of the hot-rolled steel sheet in the coil is predicted based on the tension when the hot-rolled steel sheet is wound by the coiler, the body crown generated in the hot-rolled steel sheet after finish rolling, and the number of turns of the hot-rolled steel sheet in the coil. death,
A method of manufacturing a hot-rolled coil, wherein the tension and the body crown are adjusted so that the predicted steepness is 2.1% or less. A method for manufacturing a hot-rolled coil, characterized in that the steepness of the hot-rolled steel sheet in the coil is predicted by the following formula (1).

However, λ: steepness (%) of the hot-rolled steel sheet in the coil, α and β: adjustment coefficient, Ut: tension (MPa) when the hot-rolled steel sheet is wound by the coiler, Cr: hot-rolled after finish rolling Body crown (μm) generated on the steel sheet, N: Number of turns of the hot-rolled steel sheet in the coil 3. The method of manufacturing a hot-rolled coil according to claim 2, wherein the number of turns is estimated from the thickness, width and unit weight of the coil. The hot-rolled steel sheet wound by the coiler according to any one of claims 1 to 3, wherein the temperature of the hot-rolled steel sheet is 700 ° C. or higher before or during transformation, or after completion of transformation. Production method.

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