JPH0254161B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Field of Industrial Application The present invention relates to a hot rolling method for rolling a metal slab in the width direction with a vertical rolling mill having slotted rolls. The present invention relates to a horizontal rolling method for a locally increased thickness section. (b) Conventional technology In order to realize a process that directly connects the continuous casting process that can utilize the sensible heat retained by the continuous casting slab to the rolling process that creates the product shape, it is necessary to adjust the width of the continuous casting slab and the rolling process to the desired steel plate. The basic problem is that the difference between the width of the For this reason, continuous casting slabs are rolled in the width direction to change the slab width. The rolling of this metal slab in the width direction is carried out using a vertical rolling mill with grooves, but when the amount of reduction in the width direction is increased and the amount of width change is increased, the cross section of the slab changes to a localized thickened area called a dog bone. occurs. When this locally increased thickness increases, surface flaws occur due to the bite from the hole and the rolling power increases during widthwise rolling. As a hot width reduction rolling method for this purpose, for example, as disclosed in JP-A-55-117501, only the locally increased part of the plate thickness caused by width rolling is horizontally reduced and supplied. There is a method of width rolling a metal slab in which the width is rolled to the same thickness as the metal slab and the width rolling is repeated again using grooved rolls. (c) Problems to be Solved by the Invention The feature of the hot width rolling method for metal slabs is that, unlike the conventional blooming method for steel ingots, it targets continuously cast slabs, and roll contact during rolling is The ratio of arc length to average plate width, that is, the roll gap shape ratio is 0.1
It is small at ~0.2, and the amount of repeated width reduction per one time is large at 200 to 300 mm. For this reason, the width reduction force by the vertical rolls during width rolling does not propagate to the center of the width, resulting in localized plate thickness increase portions at both ends of the plate width. As presented in the prior art,
When this thickened part is horizontally rolled to the original thickness of the metal slab, so-called dog-bone leveling rolling, the thickened part occurs at both ends of the plate width, so a part of it is stretched in the longitudinal direction. However, a width return phenomenon that spreads in the width direction of the plate occurs where some parts are not restrained.
Therefore, the width change amount is the width reduction amount minus the width return amount due to dogbone leveling rolling, and the width change efficiency, that is, the ratio of the width change amount and the reduction amount, is 60.
~80%. In addition, the actual total width reduction amount, which is the difference between the original width of the metal slab and the target slab width, is 1.3 to 1.5 times the actual total width reduction amount, taking into account the amount of width return during dogbone leveling rolling. Furthermore, dog-bone leveling rolling using a horizontal rolling mill is compared to rolling a rectangular flat plate with the same area.
Large internal friction occurs not only in locally deformed parts but also in the central part in the width direction, which requires a rolling load that is 2 to 4 times larger, and in addition, the parts where the plate thickness increases at both ends of the plate width are longitudinal. Due to the shrinkage phenomenon in which the center portion in the width direction is also pulled in the longitudinal direction when stretched in the width direction, a depression with a depth of 10 to 20 mm is generated in the center width portion. Compressive stress due to rolling does not act on this concave area, but is simply a tensile phenomenon, so the internal quality is different from local deformation areas at both ends of the plate width. It becomes inferior in quality. For this reason, conventionally, in the width rolling process where the continuous casting process and the hot rolling process are directly connected, the heat applied to the metal slab reduces the rolling load and reduces the depression in the center area during width rolling without impeding rolling efficiency. A width rolling method was strongly desired. The present invention provides an effective method for hot width rolling of metal slabs that solves the above problems. (d) Means for Solving Problems The gist of the present invention is to provide a hot reversible rolling mill in which a vertical rolling mill is arranged in a skewer shape on the entry and exit sides of a horizontal rolling mill. Rolls with a groove shape are used in the rolling mill, and flat rolls are used in the horizontal rolling mill to roll the metal slab, which is the material to be rolled, to the target thickness and width dimensions. During horizontal reduction rolling of the increased plate thickness area, only a part of the increased plate thickness area is rolled, and the target width is obtained by repeatedly rolling the area in the width direction using grooved rolls, and then the target thickness is reduced using a horizontal rolling machine. A method for hot width rolling of a metal slab characterized by rolling it to a dimension. (e) Effects The effects of the present invention will be explained below with reference to the drawings. FIG. 2a shows an example of the stand structure of the 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. metal slab 1
is reversibly rolled between each roll 2, 3, and 4. Second
Figures b, c, and d illustrate the cross-sectional shape of the slab during the rolling process. That is, the width w ₀ shown in FIG. 2b,
A continuous casting slab with a rectangular cross-sectional shape of thickness h ₀ is
When the vertical rolls 2 and 4 with calibers perform rolling with a reduction amount Δw ₁ in the width direction of the metal slab as shown in FIG. 5 occurs. If this locally increased thickness increases, surface flaws may occur due to bite from the holes of the vertical rolls, and rolling power may increase due to width direction rolling. Since these factors regulate the width rolling amount, as shown in Fig. 2d,
Horizontally roll down the locally increased plate thickness using a horizontal rolling mill H,
The plate thickness h ₀ +h+ is brought to the same plate thickness h ₀ as the other plate thicknesses, and width rolling in the plate width direction is performed again to reduce the plate width, so-called Fig. 2 c and Fig. 2 d. Repeat the rolling process. In this case, as shown in FIG. 2d, the metal slab has a depression at the center of the width of the plate due to the shrinkage phenomenon, 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. Furthermore, a so-called width return phenomenon occurs in which the dogbone portion expands by _Δw2 in the width direction. still,
In this case, the width change rate is (w ₀ −w ₂ )/(w ₀ −w ₁ )
Or (Δw ₁ −Δw ₂ )/Δw ₁ . The present inventors have developed a method for the above-mentioned width rolling method, in which the local plate thickness caused by the width direction rolling is determined by the configuration of the vertical rolls 2 and 4 with calibers and the horizontal roll 3 shown in FIG. 2a. Only the peak portion of the increased portion is rolled using a horizontal rolling mill, and this process is repeated to obtain the target metal slab width. After that, rolling is performed in the thickness direction including the locally increased thickness portion to obtain the predetermined shape. Continuously cast slab width 1800mm, thickness 280mm by rolling method
Slab width (750~1800) mm, from a fixed size of mm,
As a result of rolling various slab width sizes with a thickness of 250 mm,
The following findings were obtained. In other words, metal slab surface flaws due to bite from the holes of a vertical roll with a caliber will not become bite defects if only the point at the locally increased thickness area is rolled using a horizontal rolling mill. As a result of investigating the rolling power of rolling mills and horizontal rolling mills, we found that the rolling power of vertical rolling mills is not much different, but the rolling power of horizontal rolling mills is significantly reduced. This can be significantly improved by reducing the thickness in the thickness direction, including the locally increased thickness area, after completion of the process. Figure 3 shows that the locally increased thickness caused by rolling in the width direction is not rolled down in the thickness direction to the original thickness with horizontal rolls, but only the pointed parts are rolled down, resulting in bite-out defects during rolling in the width direction in the next pass. This study investigated whether or not this occurs. That is, rolling can be carried out by setting the amount of reduction of the local thickness increase portion by the horizontal rolls and the amount of reduction in the width direction of the next pass within the area where no bite flaws occur as shown in FIG. FIG. 4 shows the relationship between the rolling power of the vertical rolling mill with a caliber and the horizontal rolling mill and the total width reduction amount for obtaining the width-rolled finished target slab width from the continuous casting slab width. The rolling power of a vertical rolling mill with a caliber is the rolling power required to re-roll in the width direction the amount of width return that occurs due to dogbone leveling by a horizontal rolling mill, and the rolling power required to roll again in the width direction due to dogbone leveling by a horizontal rolling mill. The amount of increase in rolling power due to the contact of the metal slab with the groove side wall of the vertical roll is not significantly different between the two, by rolling only with the dogbone generated without generating width return. The rolling power of the horizontal rolling mill is significantly reduced compared to dogbone leveling rolling when only the dogbone tip portion is rolled and dogbone rolling is performed after width rolling is completed. Accordingly, the rolling power of both the caliber-equipped vertical rolling mill and the horizontal rolling mill is improved. FIG. 5 illustrates the relationship between the depth of the depression generated in the central part of the slab in the width direction due to width rolling and the total width reduction amount for obtaining the target slab width after width rolling from the continuous casting slab width. Rolling of the dog bone point using a horizontal rolling mill does not cause thinning at the center of the width, and the thickness reduction including the dog bone is performed after width rolling is completed, compared to the case where dog bone leveling is performed after each width rolling. As a result, the depression at the center of the width is greatly improved. Based on these findings, the present inventors have developed the vertical rolls 2 and 4 with calibers and the horizontal roll 3 shown in FIG. 2a.
As shown in FIG _{. 1a} , under the structure shown in FIG. As shown in Figure b, the horizontal reduction amount Δh+ is applied only to the peak part 7 of the locally increased thickness area in the area where bite-out flaws do not occur at the next pass width reduction Δw ₃ shown in Figure 1c. We propose a hot width rolling method in which the width is changed to the target strip width by repeating the rolling processes shown in Figures 1b and 1c, and then the strip is rolled to the target thickness using a horizontal rolling mill. (f) 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.
An example of manufacturing a target slab size of 750 mm and thickness of 250 mm from 280 mm is shown below.

[Table] Table 2a shows the conventional rolling method used as a comparative example.
As shown in the rolling schedule,
- Rolling was performed as described in Publication No. 117501.

[Table] On the other hand, in the present invention, as shown in the rolling schedule in Table 2b, rolling is performed only on the point of the dog bone without performing the leveling rolling of the dog bone generated by rolling in the width direction in the horizontal rolling mill. . still,
The values in parentheses in Table 2 indicate the actual reduction amount taking into account width reversal, local thickness increases, etc. As is clear from the comparative example of the conventional method and the present invention method in Table 3, the rolling power of the vertical rolling mill with a caliber is approximately the same, but the rolling power of the horizontal rolling mill is significantly reduced by the present method. , and the recess at the center of the width is improved in width. In addition, the irregularities that occur at the leading and trailing ends have also been significantly improved.

【table】

[Table] (g) Effects The conventional rolling method for rolling a metal slab in the width direction under a process that directly connects the continuous casting process and hot rolling process requires the rolling power of the horizontal rolling mill and the depression in the center of the width. On the other hand, according to the method of the present invention, it is possible to reduce the rolling power of the horizontal rolling mill without interfering with the rolling time, and also to improve the internal quality of the metal slab because it is possible to improve the depression in the center of the width. has a beneficial effect.

[Brief explanation of the drawing]

Figures 1a, b, and c are explanatory diagrams showing changes in the cross-section of the slab in the width direction during the width rolling process according to the method of the present invention, and Figure 2a shows an example of the stand configuration of a width reduction mill that implements the method of the present invention. , Figure 2 b, c,
d is an explanatory diagram showing changes in the cross section of the slab in the width direction during the width rolling process according to the conventional method, and FIG. The graph shown in Figure 4 shows the relationship between the rolling power of the vertical rolling mill with caliber and the horizontal rolling mill, and the relationship between the rolling power of the vertical rolling mill with a caliber and the horizontal rolling mill, and the width rolling finish target and the total width reduction amount to obtain the slab width from the continuous casting slab width. The illustrated graph, Figure 5, is a graph illustrating the relationship between the depth of the depression that occurs in the center of the width direction of the slab due to width rolling, and the total width reduction amount that obtains the width-rolled finished target slab width from the continuous casting slab width. It is.

Claims (1)

[Claims] 1. In a hot reversible rolling mill in which a vertical rolling mill is arranged in a skewer shape on the entry and exit sides of a horizontal rolling mill, rolls with a groove shape are used in the vertical rolling mill, and flat rolls are used in the horizontal rolling mill. When rolling a metal slab, which is the material to be rolled, to the target thickness and width dimensions, when horizontal reduction rolling is performed on a locally increased thickness area caused by rolling in the width direction, a part of the area with increased thickness is rolled. 1. A method for hot width rolling of a metal slab, which comprises rolling the slab, repeatedly rolling it in the width direction using slotted rolls to obtain the target width dimension, and then rolling the slab to the target thickness dimension using a horizontal rolling mill.