JPH0314521B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a hot width rolling method for rolling a metal slab using a vertical roll with a caliber and a horizontal roll with a concave crown (hereinafter simply referred to as a horizontal roll). (Prior technology) Size consolidation of the width of metal slabs has been attempted with the aim of realizing a process that directly connects the continuous casting process, which can effectively utilize the sensible heat retained by continuous casting slabs, and the rolling process, which creates the product shape. . Therefore, in order to create the slab width necessary for the rolling process, a large width reduction is performed downstream of the continuous casting equipment. This metal slab is rolled in the width direction using a vertical rolling mill that incorporates so-called caliber vertical rolls with grooves, but when the width change amount is increased by increasing the amount of reduction in the width direction, the cross section of the slab changes. Localized areas of increased plate thickness called dogbones occur. As a hot width reduction rolling method for this purpose, for example,
The entire locally increased part of the plate thickness caused by the width rolling disclosed in Publication No. 117501 is rolled down with horizontal rolls to return it to the same thickness as the thickness of the metal slab before the width rolling, and then rolled again into a vertical caliber. The width rolling method for metal slabs involves repeated width rolling using mold rolls, and the continuous casting slab proposed in Japanese Patent Publication No. 58-55842, in which the amount of reduction at the center of the slab width is initially larger than the amount of reduction at the ends of the slab. There is a width reduction rolling method in which the material is rolled in the thickness direction with a distribution of reduction in the width direction, then rolled in the width direction, and then rolled in the thickness direction to achieve a uniform thickness. . (Problems to be Solved by the Invention) As proposed in the former prior art, the locally increased plate thickness at both ends of the plate, which occurs due to wide width reduction rolling, is horizontally rolled to the original thickness of the metal slab. When so-called dog-bone leveling rolling is carried out, when the thickened parts at both ends of the plate are stretched in the longitudinal direction, the central part in the width direction is also pulled in the longitudinal direction, causing a dent in the central part of the width. do. Compressive stress due to rolling does not act on this recessed portion, but is merely a tensile phenomenon, and the material is inferior in quality without undergoing plastic processing due to rolling, and many surface defects occur. In addition, if a rolling method is carried out in which rolling is performed in the thickness direction with distribution of the reduction in the width direction so that the reduction in the center of the slab width is larger than the reduction in the ends of the slab width, as in the latter prior art, In the process of the next large slab width reduction, the above-mentioned depression at the center of the width is further promoted. The problems of the above conventional technology will be explained with reference to the drawings. FIG. 2a shows an example of the stand structure of width reduction mills V ₁ and V ₂ , in which a horizontal roll 3 is disposed between the stands of vertical rolls 2 and 4 with calibers. The metal slab 1 is reversibly rolled by each roll 2, 3, 4. Figures 2b, c, and d illustrate the cross-sectional shape of the slab during the rolling process. That is, a continuous casting slab having a rectangular cross-sectional shape with original width w ₀ and original thickness h ₀ shown in FIG. 2b is rolled down in the width direction as shown in FIG. Amount △w ₁
When rolling is carried out, locally increased thickness portions (so-called dog horns) 5 are generated at both ends of the width of the metal slab. If this locally increased thickness portion 5 becomes large, it will cause surface flaws due to bite from the holes of the vertical roll with caliber and an increase in the rolling power for rolling in the width direction. These factors restrict the amount of width rolling that can be rolled, so as shown in Fig. 2d, the locally increased thickness is rolled down horizontally by the horizontal rolls 3, and the thickness h ₀ + h ⁺ is the same as the original thickness. The rolling process shown in FIGS. 2c and 2d is repeated such that the sheet thickness is set to h ₀ and width rolling in the sheet width direction is performed again using a vertical roll with a caliber to reduce the sheet width. In this case, as shown in FIG. 2d, the metal slab has a depression due to the shrinkage phenomenon at the center of the width of the plate, and the center of the width of the plate has a cross-sectional shape h ^- thinner than the ends of the width of the plate. After the width rolling is completed, the material is rolled to the target thickness _ho , as shown in FIG. 2e, using horizontal rolls. As a result, a recess thinner than the target thickness _ho is created in the central portion of the metal slab. This recessed portion is never rolled down during the rolling process, resulting in inferior material quality, and quality defects are concentrated in this portion. For this reason, in the width rolling process, which has conventionally been directly connected to the continuous casting process, metal slabs that reduce the so-called depression in the width center improve the material quality of the center part during width rolling without impeding rolling efficiency. A hot width rolling method has been strongly desired. The present invention provides an effective method for hot width rolling of metal slabs that solves the above problems. (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a method for hot rolling a metal slab to a finishing target thickness and width using a horizontal roll and a vertical roll with a caliber. A concave crown is formed at the center of the width, and the horizontal rolls with the concave crown are used to finish both sides of the slab width to a target thickness, and the center part of the slab width is rolled to a thickness greater than the thickness of both sides using the concave crown. After that, rolling is performed in the width direction using the vertical rolls, and then the locally increased thickness portion generated by the width direction rolling is rolled using a horizontal roll with a concave crown to the thickness of the metal slab before the horizontal roll rolling, The hot width of the metal slab is characterized in that rolling is repeatedly performed using the vertical roll and the horizontal roll with a concave crown to obtain the target finished width dimension, and then rolled to the target finished thickness dimension using the horizontal roll with the concave crown. The rolling method is used as a means. (Function) The present inventor has developed a vertical roll 2 with a caliber shown in FIG.
4 and the horizontal roll 3, the horizontal roll with a concave crown at the center, which is the part that rolls the central part of the metal slab width, rolls the central part of the slab width more than the rolling end part of the slab width. After rolling the metal slab with a reduction distribution in the width direction until the thickness on both sides of the width reaches the target finishing thickness, the local thickness increase caused by rolling in the width direction is After rolling with horizontal rolls to the thickness dimension and obtaining the target width of the metal slab by repeating this process, rolling is performed again with horizontal rolls to the target thickness dimension to obtain the desired shape.Continuously cast slab width As a result of rolling various slab width sizes of 750 to 1800 mm and thickness 250 mm from a fixed size of 1800 mm and thickness 280 mm, the following findings were obtained. That is, before rolling in the width direction, the horizontal rolls are used to roll the slab in the thickness direction so that the amount of reduction in the central part of the slab width is smaller than the amount of reduction in both sides of the slab width. As a result, a cross-sectional shape in which the central part of the slab width is thicker than both sides of the slab width can be obtained, and the depression in the central part that occurs during the dog-bone leveling rolling of subsequent width reduction rolling can be prevented. In order to carry out width direction rolling after rolling to 300 degrees, the entire width direction is subjected to plastic deformation by rolling, and the tensile phenomenon in the width reduction process is alleviated by making the central part of the slab width thicker than both sides of the width. This will reduce quality defects, and width rolling will be performed at a target thickness that is less than the original thickness of the metal slab, but the caliber side wall of the vertical roll will be filled with metal due to the formation of local thickened areas due to width rolling. However, even in subsequent rolling, since the locally increased thickness area is rolled to the original thickness, the bottom of the caliber, which has the same dimensions as the original thickness, is always filled with metal, and stable rolling can be performed. FIG. 3a shows the relationship between the depth of the depression generated in the central part of the slab width due to width rolling and the total width reduction amount for obtaining the target slab width finished by width rolling from the continuous casting slab width. The cross-sectional shape in which the thickness of the slab is thicker at the center of the slab width compared to both sides of the slab width does not cause the thinning phenomenon at the center of the width, compared to the conventional case where dogbone leveling is carried out every time the width is rolled without considering this. As a result, the depression at the center of the width is greatly improved. FIG. 3b shows an investigation of quality defects in the method of the present invention and the conventional method. As can be seen from the figure, in the method of the present invention, rolling is performed in the width direction after rolling to the target thickness using horizontal rolls, so quality defects are significantly improved not only at the center of the width but also at both sides of the width. Based on these findings, the inventor has determined that, under the structure of the vertical rolls 2 and 4 with calibers and the horizontal roll 3 shown in FIG. As shown in a, after rolling the metal slab 1 to the target thickness _ho on both sides of the slab width and ho ₊ △h ₀ (△h ₀ > 0) at the center of the width,
Rolling in the width direction is performed as shown in Fig. 1b, and the local thickness increase portion 5 generated by the width reduction amount △w ₁ is rolled up to the original thickness h ₀ of the metal slab by horizontal rolls 3 as shown in Fig. 1c. Roll in the thickness direction to achieve the target finishing thickness h _o
The increased plate thickness between and the original thickness h ₀ is left to fill the caliber bottom metal and perform stable rolling, and a horizontal reduction is applied to the peak part 7 of the locally increased thickness, and from then on, as shown in Fig. 1 b. A hot width rolling method was completed in which the width is changed to the target sheet width by repeating the rolling processes of , c and then rolled again to the target thickness using horizontal rolls. In addition, the behavior of the central part of the slab width due to the tensile phenomenon in the main rolling process is such that each time the peak part of the locally increased thickness is rolled, the central thickness of the slab width h _{o shown in Fig. 1c is}
+△h ₂ is smaller than the initial thickness h _o +△h ₀ (△h ₀ > △
h ₂ ), the initial roll reduction distribution is eliminated at the stage of obtaining the target plate width w _o shown in Fig. 1 d, and it is possible to obtain the finished target thickness h _o over the entire width direction, and the width center part dents are significantly improved. (Example) Next, an example of the method of the present invention will be shown. The rolling conditions are as shown in Table 1, and the continuous casting slab was 1800 mm wide and thick using the 3-stand reverse rolling method of V ₁ - H - V _2.
A target slab width of 860mm was manufactured from 280mm.

[Table] At the same time, the conventional rolling method was carried out as a comparative example, as shown in Table 2 a.
Rolling was carried out as described in Publication No. 117501. On the other hand, in the embodiment of the present invention, as shown in the rolling schedule shown in Table 2b, after rolling to the target thickness with horizontal rolls, the local thickness increase caused by rolling in the width direction is removed by horizontal reduction rolling. It was rolled to the original thickness dimension, and then rolled again in the width direction using grooved rolls to obtain the target width dimension, and then rolled to the target dimension.

[Table] Table 3 shows the results of both. As is clear from the comparison between the comparative example and the example in Table 3, the surface flaws of the slab are significantly improved, and the depression at the center of the width is also significantly reduced.

[Table] (Effects of the invention) The conventional rolling method for rolling a metal slab in the width direction under a process that directly connects the continuous casting process and the hot rolling process has a large depression in the center of the width and many quality defects. However, according to the method of the present invention, the quality of metal slabs can be improved without extending the rolling time,
Industrially very beneficial effects are produced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing changes in the cross section of a slab in the width direction during the width rolling process according to the method of the present invention, FIG. Figures b, c, d, and e are explanatory diagrams showing changes in the cross-section of the slab in the width direction during the width rolling process according to the conventional method. A graph illustrating the relationship between the slab width and the total width reduction amount to obtain the width-rolled finished target slab width. FIG. 3b is a graph illustrating the state of surface flaws when the conventional method and the method of the present invention are carried out. 1...Metal slab, 2...Vertical roll, 3...
Horizontal roll with concave crown, 4...Vertical roll,
5...Local plate thickness increase part, 6...Plate width center depression, 7...Local plate thickness increase part peak part.

Claims (1)

[Claims] 1. When hot rolling a metal slab to the finishing target thickness and width dimensions using a horizontal roll and a vertical roll with a caliber, a concave crown is formed in the center of the width of the horizontal roll, and the slab width is adjusted by the horizontal roll with a concave crown. Both sides are rolled to the target finishing thickness, and the central part of the slab width is rolled to a thickness greater than the thickness of both sides at the concave crown part, and then rolled in the width direction by the vertical roll, and then rolled in the width direction by the width direction rolling. The locally increased thickness of the plate is rolled using a horizontal roll with a concave crown to the metal slab thickness before the horizontal roll rolling, and rolling is repeated with this vertical roll and a horizontal roll with a concave crown to achieve the target width dimension. 1. A method for hot width rolling of a metal slab, which comprises rolling the slab to a target finishing thickness using a horizontal roll with a concave crown.