JP2006000866A - Method for straightening thick steel plate with scale - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a straightening method of a thick steel plate with scale by which defects in shape in the flatness or the like of the thick steel plate with the scale can be straightened without peeling off the scale stuck to the surface of the steel plate. <P>SOLUTION: By this straightening method of the thick steel plate with the scale, the thick steel plate with the scale which is 4.5-120 mm thick and has the surface scale of 15-40 μm in scale thickness is straightened without peeling off the surface scale in the range of the elongation percentage of 0.2-0.5% by using a pair of upper and lower work rolls. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for correcting a thick steel plate with a scale, and more particularly to a method for correcting a thick steel plate with a scale that corrects the scale attached to the surface without peeling off the scale.

  In fields such as industrial machinery and bridges, inexpensive hot rolled steel plates with scales are used. For this reason, although a steel plate with a scale having good scale adhesion is manufactured by hot rolling, when the manufactured steel plate has a defective shape (flatness), correction is performed after hot rolling. .

  Generally, steel sheets are straightened by passing the steel sheets between the upper and lower straightening rolls using a straightening machine (roll leveler) in which a plurality of upper and lower straightening rolls sandwiching the steel sheets are arranged in a staggered pattern in the plate direction. And bending back is repeated to correct warpage and bending of the steel sheet (see, for example, Patent Document 1).

  Moreover, in the roll leveler, the applicable plate thickness range is limited, and even in the applicable plate thickness range, a plate shape defect that cannot be corrected by the roll leveler may occur. In order to improve plate shape defects, shape control technology in finish rolling has been developed, and further, steel plate rolling equipment equipped with a light rolling mill for the purpose of correcting plate shape defects in thick steel plates has been developed. As a light rolling mill, at least one of the upper and lower roll assemblies of the rolling mill has a mechanism for supporting the work roll by the divided reinforcing roll divided into three or more in the axial direction. , Each of which includes a load detection device, a reduction device, and a roll position detection device (see, for example, Patent Documents 2 and 3).

  Conventional straightening with a roll leveler is a relatively efficient straightening method. However, when a thick steel plate with a scale is straightened with a roll leveler, the scale on the surface of the steel plate is cracked and partially peeled off or the scale is strongly pressed. Will be left as indentations on the steel sheet, causing problems of dirt and wrinkles. That is, when a thick steel plate with a scale is corrected by a roll leveler, a steel plate with a beautifully attached scale on the steel plate surface cannot be obtained. Also, when shape control is performed with a rolling mill, the roll profile is optimized, or the plate shape control device such as roll bending device, roll cloth device, roll shift device is always set and controlled optimally for each rolling condition. Otherwise, since a good shape cannot be obtained, it is difficult to optimize the operating conditions within a short time for rolling a steel plate having a relatively short length.

  In these conventional straightening methods, when straightening a steel plate with a scale, consideration has been given to removing the scale that has been peeled off. At present, no specific correction method has been proposed.

JP 2000-202524 A Japanese Patent No. 2963261 JP 2000-102805 A

  In view of the above-described situation, the present invention provides a method for correcting a thick steel plate with a scale that can correct a shape defect such as flatness of the thick steel plate with a scale without peeling off the scale attached to the surface of the steel plate. This is a problem to be solved.

  The present inventor has studied a method of correcting a scale adhering to a steel plate surface without peeling off as a method of correcting a thick steel plate with a scale, and using a pair of upper and lower work rolls, an elongation of 0.2 to 0 The present invention was completed by finding that if the correction was made within the range of 5%, the surface scale could be corrected without peeling.

  The gist of the present invention is as follows.

(1) With a scale characterized by correcting a thick steel plate with a scale thickness of 15 μm or more using a pair of upper and lower work rolls without peeling off the surface scale within a range of elongation of 0.2 to 0.5%. Straightening method for thick steel plate.

(2) The method for correcting a thick steel plate with scale according to (1) above, wherein the thick steel plate has a surface scale with a thickness of 4.5 to 120 mm and a scale thickness of 15 to 40 μm.

  According to the present invention, it is possible to correct a defective shape after manufacturing a thick steel plate with a scale without correcting the surface scale, and to obtain a thick steel plate with a scale that is flat and has a beautiful surface without a scale peeling portion. be able to. When coated on a thick steel plate with a scale according to the present invention, a coated surface with a good appearance can be obtained, and when cutting with plasma or laser, good cutting properties can be obtained.

  The present invention will be described in detail below.

  A thick steel plate with a scale is used in industrial machines, bridges, and the like, but a thick steel plate with a scale having a good plate shape and excellent appearance and laser cutting properties is desired.

  Thick steel plates with scales are manufactured by hot rolling, but when manufactured by hot rolling, approximately 15% of poorly shaped material is generated, and a re-correction process is required for the poorly shaped material after hot rolling. In the re-correction process, correction is performed with a roll leveler and an oil press. However, since the correction is made flat by bending the steel plate, the scale that was evenly attached to the surface of the steel plate is peeled off. The part that has been peeled off is exposed to the surface, and the surface is dotted with scale peeling parts like "mandarin orange skin", the appearance is poor, the appearance after painting is poor, and the plasma and laser cutting properties are degraded. Let

  For this reason, it is necessary to obtain a thick steel plate with a scale by which the scale of the surface is not peeled off and is uniformly and beautifully adhered.

  In the present invention, attention is paid to correction in which plastic deformation is applied by rolling with a cluster type rolling mill in which a pair of work rolls and a backup roll (divided reinforcing roll) divided in the width direction are arranged in a housing. We thought that the exfoliation of the scale could be prevented during the correction, and we studied the conditions under which the scale does not exfoliate.

  FIG. 1 is a diagram showing an outline of a cluster type rolling mill.

  As a cluster type rolling mill, for example, as shown in FIG. 1 (a), a pair of upper and lower work rolls 1a and 1b are respectively divided by two reinforcing rolls 2a, 2b, 2c and 2d in the circumferential direction of the roll. As shown in FIG. 1 (b), each reinforcing roll is supported and divided into four or three in the roll axial direction, and is divided into seven in the axial direction for one work roll 1a. The reinforcing rolls 2a and 2b support the rolling reaction force.

  Each of the divided reinforcing rolls is provided with load detecting devices 3a and 3b for detecting a rolling reaction force acting on the divided reinforcing rolls, and rolling-down devices 4a and 4b having roll position detecting devices.

  In order to correct the plate shape, an optimum reduction position of the divided reinforcing roll is set, rolling by the rolling mill is started, and the reduction device of the divided reinforcing roll is controlled to perform rolling into a desired plate shape. Such a rolling mill and rolling control are known techniques. In the present invention, such a cluster type rolling mill is most preferable, but the invention is not limited to this, and other rolling mills can be used.

  In the present invention, a straightened steel plate with a scale was subjected to a straightening test using a cluster type rolling mill, and the conditions under which scale peeling could be prevented were investigated.

  The thickness of the thick steel plate with scale which is the subject of the present invention is about 4.5 to 120 mm, particularly about 4.5 mm to 90 mm. That is, as a steel plate with a scale, a steel plate of 4.5 to 120 mm is usually used, and when such a thick steel plate is manufactured by hot rolling, the scale thickness becomes 15 to 40 μm. When the scale thickness is 15 μm or less, the scale amount is insufficient. When the scale thickness is 40 μm or more, the scale becomes too thick and easily peels off.

  The material of the steel plate is not particularly limited, but JIS 400N steel, for example, SS400 steel or the like can be used.

  In the straightening test of the thick steel plate with the scale, it was found that there was a limit of elongation at which the scale could break.

As a sample for the correction test, a steel plate of SS400 (C: 0.175%, Si: 0.05%, Mn: 0.63%, Al: 0.10% contained) is a thick steel plate having a thickness of 8 mm and a scale thickness. Thick steel plates with scales having 15 μm, 19 μm, 26 μm, and 32 μm were prepared.
Moreover, as shown in FIG. 1, it is cold-rolled with a rolling mill having a pair of upper and lower work rolls (roll diameter: 400 mm), and the elongation is 0.2%, 0.3%, 0.4%, Correction was performed by changing the elongation rate to 0.5%, 0.6%, 0.7%, and 0.8%.

  Table 1 shows the test results, that is, the relationship between the scale thickness, elongation rate, and scale peeling state of the steel sheet with scale. In Table 1, ○ indicates that the scale amount after correction remains 98% or more of the surface scale amount before correction, and X indicates that the other scales are peeled off. This is the case when the amount is less than 98%.

  From Table 1, the thicker the scale, the weaker the elongation, and the higher the elongation, the more the scale peels off. That is, as the elongation increases, the amount of scale peeling increases, and the scale amount after correction remains 98% or more with respect to the scale amount before correction only when the elongation rate is 0.5% or less. It was determined that a good-scale steel sheet with no peeling was obtained.

  Further, regarding the flatness before and after correction, the wave height before correction of 50 mm or less could be reduced to 1 mm or less after correction.

  For straightening, an elongation rate of 0.2% or more is required, but when the elongation rate exceeds 0.5%, the scale attached to the surface of the thick steel plate with the scale will peel off. In the present invention, the elongation is in the range of 0.2 to 0.5%. In addition, the elongation in the rolling longitudinal direction was used as the elongation.

  In addition, when performing correction, if correction is performed at a temperature exceeding 300 ° C., scales are likely to be generated, and the flatness may deteriorate again in the subsequent cooling process. Or it is preferable to carry out cold.

  Hereinafter, the present invention will be described based on examples.

  As a test material, a steel plate having a thickness of 8 to 30 mm containing C: 0.184%, Si: 0.150%, Mn: 0.68%, Al: 0.20% in mass% by hot rolling. Manufactured.

  The obtained steel plate had a scale of 15 to 40 μm thick. Table 2 shows the plate thickness and scale thickness of the steel plate.

  As shown in FIG. 1, these steel plates are stretched from a steel plate having a high pre-correction wave height (mm) with poor flatness by a cluster type rolling mill having a pair of upper and lower work rolls (roll diameter: 400 mm). An orthodontic test was conducted to correct the rate within the range of 0.2 to 0.8%. These correction conditions and correction test results are also shown in Table 2.

  As shown in Table 2, all the inventive examples satisfying the requirement of the elongation rate of 0.2 to 0.5% defined in the present invention have a scale residual ratio of 98% or more, and the scale does not peel off. After correction, the wave height (mm) was low and the steel sheet was corrected to a flat plate with good flatness.

  In contrast, in the comparative examples with an elongation of 0.6 to 0.8%, the wave height (mm) after correction was low and the flatness was improved, but the scale peeled off during correction. As a result, the scale remaining rate was 81% or less.

  In addition, elongation rate is shown by (length after correction-length before correction) / length before correction × 100 (%).

  As shown in the above correction test, according to the present invention, it was confirmed that the correction of the shape defect after the production of the thick steel plate with the scale can be performed without peeling off the surface scale.

It is a figure which shows the outline | summary of a cluster type rolling mill, (a) is sectional drawing, (b) is a top view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Upper work roll 1b Lower work roll 2a, 2b, 2c, 2d Split reinforcement roll 3a, 3b Load detection apparatus of split reinforcement roll 4a, 4b Roll reduction apparatus of split reinforcement roll

Claims (2)

  A scaled steel plate having a scale thickness of 15 μm or more is corrected using a pair of upper and lower work rolls without peeling the surface scale within a range of elongation of 0.2 to 0.5%. Correction method.   2. The method for correcting a thick steel plate with scale according to claim 1, wherein the thick steel plate has a surface scale with a thickness of 4.5 to 120 mm and a scale thickness of 15 to 40 [mu] m.

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