JP4669376B2 - Manufacturing method of thick steel plate with high flatness - Google Patents

Description

  The present invention relates to a method of manufacturing a thick steel plate for advantageously improving the shape of the thick steel plate obtained by rolling the thick steel plate, in particular, the flatness.

  In rolling thick steel plates, flatness defects are likely to occur in the latter pass where the thickness of the plate to be rolled becomes thinner. In this pass, the flatness failure is caused by a subsequent rolling mill called a shape adjustment pass. Rolling is performed at a predetermined rolling schedule with a constant crown ratio so that no rolling occurs. However, in actual rolling, there is an error in the rolling load or roll profile prediction and results, so the sheet crown of the material to be rolled Is different from the prediction, resulting in poor flatness. As a countermeasure, a method has been proposed in which shape control means such as work roll bending or pair cross rolling is used to prevent poor flatness by feedback control or feedforward control based on the steel plate profile and rolling load data. (Patent Document 1).

  Patent Document 2 discloses a rolling method using a temperature and plate crown measuring device and a process control calculation method for canceling out a thermal shrinkage difference (cooling strain) caused by a temperature deviation in the width direction of the material to be rolled during rolling. Has been proposed.

Japanese Unexamined Patent Publication No. 55-42167 JP-A-6-13532

However, the conventional method has the following problems.
In Patent Document 1, in order to measure the temperature in the width direction during online rolling, it is necessary to measure the temperature in a very short time between passes. Since the temperature does not recuperate and the temperature varies and the temperature deviation occurs in a very small region in the width direction, it can be easily assumed that there is a difference between the representative value of the measured temperature and the actual temperature distribution. Therefore, it has been industrially difficult to measure the actual steel plate temperature and thickness on-line and to give a desired strain to the steel plate based on the actual measurement values.

  In addition, a significant change in the crown ratio in the shape adjustment pass, particularly in the vicinity of the final pass, as in Patent Document 2, may deteriorate the rolling shape in the pass due to the loss of continuity from the rolling shape history so far. There was a possibility that it could lead to the cause of the trouble of threading.

  In addition, for materials for which accelerated cooling control is performed after rolling, a temperature control pattern in the width direction determined in advance must be performed regardless of the results during rolling, and the shape during rolling due to variations in material and predicted model accuracy. In some cases, defects could not be dealt with, and shape defects were sometimes promoted.

  The invention of the present application solves the above-mentioned problems, and in the initial pass schedule as much as possible, by defining the target rolling shape in consideration of the temperature deviation in the width direction, and building the shape, the final thickness of the thick plate after rolling to cooling It aims at providing the manufacturing method of the thick steel plate which can improve flatness.

  In response to the above problem, the inventors calculated the residual stress in the plate after cooling from the temperature distribution in the width direction of the rolled material after rolling. As a result, the inventors depend on only the width of the steel plate and aim at the final rolling. It has been found that the rolling shape changes. From this result, it is possible to modify the pass schedule according to the planned width of the steel plate before rolling, and to perform smooth rolling toward the target shape, and to significantly improve the flatness of the product after cooling. confirmed.

That is, the present invention is a method of manufacturing a thick steel plate having high flatness, and sets a target plate crown ratio change amount (ΔRc) for each planned width of the thick steel plate to be manufactured, and manufactures the thick steel plate. In this case, ΔRc is determined according to the above in accordance with the planned width of the thick steel plate, a pass schedule (rolling amount) in the final pass that can obtain the ΔRc is set, and rolling is performed according to the pass schedule. It is a manufacturing method of a thick steel plate with high flatness.
here,
ΔRc: Target plate crown ratio change amount (= Rc2-Rc1)
Rc1: Plate crown ratio before final pass (= (tc1-te1) / tc1)
Rc2: Plate crown ratio after the final pass (= (tc2-te2) / tc2)
tc1: Plate thickness at the center of the plate before the final pass
te1: Board edge thickness before final pass
tc2: Plate thickness at the center of the plate after the final pass
te2: Board edge thickness after the final pass

  Taking into account the temperature distribution of the steel plate that is the material to be rolled, the measurement of complex steel is carried out by rolling the steel plate from the initial pass in accordance with the target crown ratio change (ΔRc) determined in advance for each plate width. Enables the production of thick steel plates with high efficiency and excellent flatness without a calculation mechanism.

  In the method of manufacturing a thick steel plate, when performing controlled cooling after the rolling, the amount of sheet crown after the rolling is measured, and the cooling method of the controlled cooling of the steel plate is changed according to the measured amount of crown. , It may be combined with further residual stress control in the cooling control of the post-process.

  The method for producing a thick steel plate according to the present invention takes into account the residual stress due to cooling of the width end of the thick steel plate that is a rolled material, and performs rolling shape control and accelerated cooling control in a direction in which this residual stress is offset, It is possible to greatly improve the flatness defect that may occur after cooling. In particular, it is an extremely effective invention in the process of rolling to accelerated cooling used in high-grade varieties, which not only has a great effect on improving the quality of products, but also reduces the load on the refining process such as cold straightening. It enables smooth provision of high-quality plank products to the home.

  By feeding forward the results of the rolling shape to an accelerated cooling device in the subsequent process and performing width cooling control in the accelerated cooling device, it is possible to easily recover when a flatness defect occurs during rolling. That is, when the crown ratio change amount is more negative than expected, the edge mask is retracted in order to lower the temperature of the edge portion. Conversely, if ΔRc is shifted to the positive side, control is performed so that the edge mask is exposed and the temperature of the edge portion is increased. By these controls, the thermal strain of the thick steel plate works in a decreasing direction.

  In this invention, the residual stress distribution after cooling the thick steel plate is estimated in advance based on the temperature distribution in the width direction of the thick steel plate, which is a rolled material, and rolling is performed in a shape that cancels this residual stress. Without being affected by measurement time loss and measurement variations, the cooling distortion after cooling described above can be reduced, and the flatness can be effectively improved.

The present invention is described in detail below. As a result of investigating the temperature distribution in the width direction of the thick steel plate after the end of the final rolling pass, a temperature drop at the end compared to the center in the width direction was seen regardless of the plate thickness. The thermal residual stress applied after cooling the thick steel plate is expressed by the following equation (1).
σ = A (t, ΔT, W, ΔW) (1)
ΔT = B (t, W, Tpass)
ΔW = C (t, W, Tpass)
However,
σ: Residual stress t: Thick steel plate thickness ΔT: Temperature drop ΔW: Temperature drop width (This is the section of the edge portion (steel plate width direction distance) where the temperature is lower than the central portion of the thick steel plate)
W: Rolling width Tpass: Rolling time A, B, C: Constant

  In order not to generate the residual stress expressed by the above equation (1) after cooling, it is only necessary to add a shape in which the thick steel plate before cooling cancels the cooling strain, that is, the residual stress due to rolling in the direction to cancel the σ. Therefore, in the final pass of rolling, shape control means such as a pair cross is used to control the final shape of the rolling so that it can become a residual stress that cancels the residual stress.

The temperature distribution in the width direction of the steel plate, which is the material to be rolled, is determined and arranged in advance from the model calculation results. The results of the target crown ratio change (ΔRc) in the final pass and the wave height due to residual stress are shown in the figure. As shown in FIG. The “wave height” is indicated by the difference (mm) in the height direction between the highest point and the lowest point when a thick steel plate is placed in a flat (horizontal) location.
here,
ΔRc: Target plate crown ratio change amount (= Rc2-Rc1)
Rc1: Plate crown ratio before final pass (= (tc1-te1) / tc1)
Rc2: Plate crown ratio after the final pass (= (tc2-te2) / tc2)
tc1: Plate thickness at the center of the plate before the final pass
te1: Board edge thickness before final pass
tc2: Plate thickness at the center of the plate after the final pass
te2: Board edge thickness after the final pass

  Therefore, it was found that, unlike rolling with a constant crown ratio (change in crown ratio = 0), the wave shape can be improved by intentionally applying an appropriate crown ratio change in the final pass.

FIG. 2 shows the relationship between ΔRc and the wave height in the final pass according to the steel plate width of the thick steel plate that is the material to be rolled. As can be seen from FIG. 2, there is a large difference in the relationship between ΔRc and the wave height generation mode depending on the steel plate width. When the steel plate width is 4000mm, the region with low wave height is narrow, and at 2000mm, the region is wide. In other words, the wider steel plate width indicates that the prediction accuracy of the pass schedule in the final pass is stricter. Conversely, the narrower steel plate width indicates that the wave height is lower even if the prediction accuracy is somewhat worse. Yes. Further, the target value of ΔRc is the steel plate width 4000 mm, is a -0.025 (× ^{10 -2),} the steel plate width 2000 mm, is around -0.06 (× ^{10 -2).} Thus, the target ΔRc varies depending on the steel plate width.

Next, control cooling performed after rolling will be described.
For materials that require high strength and high toughness, accelerated cooling is performed online after rolling. A recent acceleration cooling device is provided with a width direction water amount control device (for example, an edge mask mechanism), which can apply a temperature deviation during cooling in the width direction and apply a residual stress (FIG. 3). ). In FIG. 3, 1 is a thick steel plate as a rolled material, 2 is an edge mask, and 3 is a water spray header.

  Considering the actually measured temperature deviation in the steel plate after rolling and the actual change in crown ratio, and controlling the edge mask in a direction to reduce the residual stress σ, even such high-grade materials can be cooled from rolling. Through this, it is possible to manufacture thick steel plates with low residual stress and excellent flatness.

  FIG. 4 is an explanatory diagram of a process for performing rolling according to an embodiment of the present invention. In FIG. 4, a pair cross device is applied to the shape control means, and a device having an edge mask is used as the acceleration cooling device.

  In FIG. 4, 11 is a thick steel plate as a material to be rolled, 12 is a work roll, 13 is an edge mask, and 14 is a thermometer. Before starting rolling, a target crown ratio change amount (ΔRc) is obtained by the process computer 15 according to the steel plate width of the thick steel plate 11, and a reduction pass schedule according to the target crown ratio change amount is set by the process computer 15. The cross angle of the work roll 12 corresponding to the schedule is set for each pass, and rolling is performed as much as possible according to the schedule. For the material (thick steel plate 11) for which accelerated cooling is performed after rolling, the necessary control amount of the edge mask 13 is determined by the process computer 16 from the crown results and temperature results after rolling, and the necessary mask amount by the edge mask 13 is determined. I set it.

  FIG. 5 compares the wave height distribution when the embodiment of the present invention is applied and when the conventional rolling method with a constant crown ratio is applied. According to the embodiment of the present invention, the wave height is greatly reduced as compared with the prior art. As a result, as shown in FIG. 6, it can be seen that the thick steel plate according to the embodiment of the present invention can be manufactured without applying the cold straightening process as compared with the conventional material.

  Although the present invention has been described with reference to an example in which a pair cross device is used as the shape control means, the present invention is not limited to the pair cross device, and other control means such as a roll bending device and a roll shift device may be used. good. Further, it goes without saying that the water amount crown mechanism may be used in a device other than the edge mask for the width direction water amount control mechanism in the acceleration cooling device.

  The present invention can be applied to the rolling of thick steel plates.

It is a graph which shows the relationship between target board crown ratio variation | change_quantity and a wave height. It is a graph which shows the relationship between the target crown ratio variation | change_quantity and wave height in the steel plate width of 4000 mm and 2000 mm. It is the front view which showed the state which is cooling the thick steel plate in the cooling device after rolling. It is the conceptual diagram which showed the rolling process to which the Example of this invention was applied. It is a graph which shows the generation frequency of the wave height in the Example of this invention and a prior art. It is a graph which shows the re-correction incidence in the Example and prior art of this invention.

Explanation of symbols

1 Thick steel plate 2 Edge mask 3 Water spray header 11 Rolled material (thick steel plate)
12 Work roll 13 Edge mask 14 Thermometer 15, 16 Process computer

Claims (2)

A method for producing a thick flat steel plate,
The target plate crown ratio change amount (ΔRc) is set in advance for each planned width of the steel plate to be manufactured,
When manufacturing the steel plate, ΔRc is determined according to the above according to the planned width of the steel plate,
A method of manufacturing a thick steel plate having high flatness, wherein a pass schedule capable of obtaining the ΔRc is set and rolling is performed according to the pass schedule.
here,
ΔRc: Target plate crown ratio change amount (= Rc2-Rc1)
Rc1: Plate crown ratio before final pass (= (tc1-te1) / tc1)
Rc2: Plate crown ratio after the final pass (= (tc2-te2) / tc2)
tc1: Plate thickness at the center of the plate before the final pass
te1: Board edge thickness before final pass
tc2: Plate thickness at the center of the plate after the final pass
te2: Board edge thickness after the final pass In the manufacturing method of the thick steel plate of Claim 1,
When performing controlled cooling after the rolling, the sheet crown amount after the rolling is measured, and the cooling method of the controlled cooling of the steel sheet is changed according to the measured crown amount. A method of manufacturing a steel sheet.

Images