JPH064162B2 - Hot rolling method for aluminum slabs - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for hot rolling an aluminum or aluminum alloy slab, and particularly to a method for greatly improving the yield and surface quality of a rolled plate.

[Conventional technology]

The slab made of Al or Al alloy has segregation caused by the casting process before hot rolling in order to suppress cracking and surface defects of the rolled material.
The upper and lower surfaces of the slab in the longitudinal direction, that is, the rolling surface, is chamfered for the purpose of removing so-called defective ingots such as oxides, columnar crystals, and molten metal boundaries.
Such a slab is generally subjected to a soaking treatment in a heating furnace and then passed through a continuous hot rolling facility including a row of rough rolling mills and a row of finish rolling mills to be processed into a desired sheet thickness.

However, during this hot rolling, the rolled material causes cracks (edge cracks) and surface defects at the plate edges in the width direction, and these cracks and surface defects are peeled off and rolled into a rolling roll or the like.
This caused problems such as scratching the roll. As shown in FIGS. 4 (a) to 4 (c), such peeling is performed by chamfering the upper and lower surfaces in the longitudinal direction of the ingot, and the rectangular slabs (9a) and (9b) on the side surfaces in the width direction are left. When the rolling is repeated to 10), the casting surface on the side surface of the rolled plate (12) rises as shown in Fig. 4 (b), and the raised portions (11a) (11b) (11c) (11d) finally become As shown in FIG. 4 (c), the cast surface remains on the rolling surfaces (13a) and (13b), that is, black skins (14a) (14b) (14c) (14d).

The edge cracks are due to defective ingots remaining at both ends in the width direction of the slab. Furthermore, as a result of three-dimensional deformation of the material to be rolled during hot rolling, as shown in FIG.
This is because the central portions (16a) and (16b) of the side faces of (12) are largely dented, and at the end of rolling, the two-layer plate shown in Fig. 4 (c), that is, the laminations (15a) and (15b), is generated. The defective ingot is particularly remarkable in the Al-Mn type and Al-Mg type aluminum alloys, and the latter, that is, the lamination occurs regardless of the material. Further, particularly in the case of a pure Al type slab, even if the above edge crack does not occur in the hot rolling process, it always occurs in the cold rolling process of the next process and causes a break of the plate during rolling.

In order to avoid this, conventionally, the defective ingot portion and the lamination portion on the side surface of the plate have been removed by a trimmer provided in the finishing rolling mill train. However, this trimming amount has a large proportion in the rolling production amount, and the yield in the rolling process is significantly reduced. Therefore, in order to reduce this trimming amount, after chamfering the four corners of the rectangular cross-section slab recently before hot rolling, the slab width direction rolling is performed by the vertical rolls provided in the rough rolling machine, and the longitudinal direction is roughened. A method for rolling is proposed by Japanese Patent No. 1060065.

As shown in FIG. 3 (a), four corners of a rectangular cross section are chamfered (2a) (2b) (2c) (2d) before hot rolling to form an slab (3) having an octagonal cross section. The side surface of the slab where the casting surface (4a) (4b) in the width direction remains is rolled by a vertical roll (not shown), and at the same time, it is rolled in the vertical direction as shown in Fig. 3 (b). The central portions (6a) and (6b) of the side surface of (5) do not largely dent, so that as shown in Fig. 3 (c), the rolling surface (7a)
Black skin does not appear at both ends in the width direction of (7b), and the length of the laminations (8a) and (8b) is small.

[Problems to be solved by the invention]

However, this method is basically peeling-off with the progress of rolling in order to leave the ingot defective portion, the peeling causes a surface defect due to indentation in the rolled material, and further peeling causes roll scratches when wound into a roll, As a result, unevenness was generated in the rolled material, which left a problem in terms of quality. Further, the lamination on the side surface of the plate has not been completely solved, and edge cracks during hot rolling or cold rolling are not completely eliminated, and it has been strongly required to reduce the trimming amount.

[Means for solving problems]

As a result of various studies in view of this, the present invention has found that it is effective to control the amount of black skin and the amount of lamination in order to eliminate edge cracks, and further studies on three-dimensional deformation of the slab during hot rolling. We have developed a hot rolling method for aluminum slabs that eliminates edge cracks during rolling by finding the relationship between slab cross-sectional shape, black scale and amount of lamination, and melts and casts aluminum or aluminum alloys to form ingots. and octagonal cross-section and scalped the entire surface of the ingot in a method of hot rolling was scalped, and the depth of the chamfered portion of the thickness of the cross-sectional dimension rolling direction at t _s, octagonal width direction Is defined as C and the length of the straight portion on the side is defined as A, the following expression is satisfied, and then the chamfered ingot is hot-rolled.

e ^{-1.169 x (C / A-0.225 x ts / 100 + 1.525)} <0.44 ... (1) [ ^Operation ] In the present invention, first, the entire surface of the ingot is chamfered and its sectional shape is first.
As shown in the figure, it is octagonal and its three dimensions (A and C in the figure)
And ts) are defined as in Expression (1).

To obtain an octagonal ingot by chamfering the entire surface,
First, an ingot with a rectangular cross section may be obtained, and the entire peripheral surface may be chamfered so as to have an octagonal cross section, or an ingot with an octagonal cross section may be obtained from the beginning, and this entire peripheral surface may be obtained. Each may be chamfered.

The left side is limited to less than 0.44 as in the above formula (1) because edge cracks occur on the side surface of the rolled plate when the left side is 0.44 or more. That is, when ts is large, or when A is large or C is small, the amount of deformation of the slab also increases, that is, the amount of lamination increases, and thus edge cracks are likely to occur.

The above equation (1) is derived as follows.

That is, in an ingot having an octagonal cross section as shown in FIG. 1, as shown in Table 1 of the following examples, the amount of lamination when various ts, A and C dimensions were variously measured was measured. , A, C and the amount of lamination were analyzed by a statistical method (multiple regression), and the following relationship was obtained.

As a condition that edge cracks do not occur in the rolled material when the ingot is rolled, the lamination amount may be about 8 mm or less (considered to be less than 8.2 mm) as shown in the following examples. Therefore, the above first equation is obtained by rewriting the above equation based on this relationship as follows.

∴e ^{-1.169 x (C / A-0.225 x ts / 100 + 1.525)} <e ^-0.824 = 0.44 Furthermore, the 8 faces in the longitudinal direction of the ingot are all ^chamfered by completely removing the black ^scale during rolling. This is because the edge cracks can be completely eliminated by combining the above conditions in this case.

〔Example〕

The present invention will be described based on examples in order to further clarify its effects.

First, a rectangular slab (10) as shown in FIG. 4 (a) is rolled to produce a rolled plate (12) as shown in FIG. 4 (c), which remains on the upper and lower surfaces (13a) (13b) of the rolled plate. Cast skin, that is, black skin (14a) (14b) (14c) (14
The influence of the amount (E) of d) and the amounts (L) of laminations (15a) and (15b) on the occurrence of edge cracks was investigated and shown in FIG. The symbols in FIG. 2 are evaluations of the degree of edge cracks generated in the rolled plate as follows.

○ mark: Very good (almost no edge cracks) △ mark: Good (some edge cracks) × mark: Poor (having edge cracks that make rolling impossible) Black as seen from Fig. 2 When the peel remained, edge cracks were almost generated and the subsequent rolling could not be performed. Even if the black scale is not on the upper and lower surfaces of the rolled plate, some edge cracks may occur or the black scale may remain on the side of the plate and have large cracks (cobbing). In this case, the lamination amount is about 8 mm. It can be seen that the edge cracks or the edge cracks do not occur if the following conditions are satisfied. Therefore, the condition that does not cause edge cracks on the rolled plate is that the amount of black skin of the slab, that is, the amount of casting skin, is zero and the amount of lamination is 8 mm
It would be good if the following slab shape was created.

That is, ingots having a rectangular cross section were obtained after melting the Al alloys shown in Table 1 so as to satisfy the formula (1), and the entire peripheral surface was chamfered to obtain an octagonal cross section as shown in FIG. Then, hot rolling was performed on a slab made of a chamfered ingot (1) in which the dimensions of each part were variously changed as shown in Table 1, and the presence or absence of edge cracking was investigated, and the results are also shown in Table 1. In addition, JIS 5182 in the table is 0.20 ~
It shows a 0.50% Mn-4.0 to 5.0% Mg-Al alloy.

As is clear from Table 1, when the value of the left side of the first expression is changed by the combination of the dimensions of C, A and ts, when the first expression is satisfied, no edge crack occurs. .

〔The invention's effect〕

Thus, according to the present invention, in the rolling, the amount of trimming in the width direction can be set to zero, the yield can be significantly improved, and further, surface defects such as edge cracks on the rolled plate can be drastically reduced. It has a remarkable effect.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment according to the present invention, FIG. 2 is a relational diagram showing the influence of black skin and an amount of lamination on edge cracks, and FIGS. 3 (a) (b) (c) and 4 FIGS. 3 (A), 3 (B) and 3 (C) are explanatory views showing a conventional rolling method, and FIGS. 3 (A) and 4 (A) show a slab before rolling, and FIG. ) And FIG. 4 (b) show a rolling process, and FIGS. 3 (c) and 4 (c) are perspective views showing the end of rolling. 1… Chamfered ingot 2a, 2b, 2c, 2d… Chamfer, 3… Octagonal section slab 4a, 4b, 9a, 9b… Cast surface 5,12… Rolled plate 6a, 6b, 16a, 16b… Center of side 7a, 7b, 13a, 13b… Rolled surface 8a, 8b, 15a, 15b… Lamination 10… Rectangular cross-section slab 11a, 11b, 11c, 11d… Casting surface ridge 14a, 14b, 14c, 14d… Black skin E… Black Amount of skin L ... Amount of lamination

Claims (1)

[Claims] 1. A method of melting and casting aluminum or aluminum alloy, chamfering the ingot, and then hot rolling, in which the entire surface of the ingot is octagonal in cross section, and the cross sectional dimension is the rolling direction. Where t _{s is} the thickness of the octagon, C is the depth of the chamfer in the width direction of the octagon, and A is the length of the straight portion of the side, the following formula is satisfied, and then the chamfering A method for hot rolling an aluminum slab, comprising hot rolling a lump. e ^{-1.169 x (C / A-0.225 x ts / 100 + 1.525)} <0.44