JPS6141642B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dog-bone rolling method in which a flat steel slab is width-reduced to form a bulge at the side end portions to obtain a dog-bone-shaped steel slab in cross section.

With the recent development of continuous casting, it has become possible to mass produce slabs efficiently and economically. In order to make a section steel of a predetermined size, such as an H section steel, from this mass-produced slab, the width of the slab is rolled down to ensure the web height of the rough section of the H section steel, and to create a bulge at the side end. There is a method of forming a dog bone and performing dog bone rolling to ensure the flange width. The steel slab obtained by dogbone rolling is subsequently passed through a forming hole mold and a finishing hole mold to become an H-beam of a predetermined size. In dogbone rolling of such flat steel billet,
There is a remarkable tendency for the flat steel billet to fall to the left and right in the rolling direction. The main cause of this collapse is that the slab cannot be restrained from the left and right sides during width reduction, but it is also caused by the rolling mill and the rolling conditions around the rolling mill.

Looking at the way a steel billet that has been dog-bone rolled falls down, the angle of inclination tends to be large at the tip (top) and bottom (bottom), as will be described later, but the tip and back edges have metal flow in a fishtail shape and are tapered. It becomes tapered and an unsteady part is created which is narrower than the central part, and since this unsteady part does not fill the hole, the collapse at the start of width reduction is not corrected and is further exacerbated as rolling progresses. On the other hand, in the center, the metal flow is not as extreme as it is at the ends, so it fills the hole shape and is considerably corrected. If the inclination angle becomes large, uneven rolling will be performed at the bulge during dogbone rolling, which will cause flaws and will not be able to be caught in the subsequent forming hole. Even if the inclination angle is small, in the subsequent forming hole mold, uneven rolling is performed as shown in FIG. 12, so that down flaws f as shown in FIG. 13 are created.

According to the experience of the present inventors, if the inclination angle is not 2 degrees or less, caliber flaws (down flaws) will occur in the subsequent groove rolling. Therefore, steel billets with large inclination angles that exceed this angle and their parts will not be fully guided into the hole mold during subsequent shaping rolling, resulting in poor filling or caliber defects, so they will have to be scrapped and the production yield will decrease. decrease.

JP-A-56-117026 has already proposed a method for preventing collapse during dog bone rolling, which is harmful as described above. This proposal involves creating a groove in the center of the thickness of the slab using a roll with protrusions, and using this groove as a guide to prevent the slab from falling over, and has had some success. However, even with such a proposal, there are still a number of technical difficulties that must be resolved. In other words, an extra rolling pass is required to erase the groove once formed in the center of the slab thickness in the later stages of dog-boning rolling, and it is difficult to completely eliminate the groove in unsteady areas, which is one of the causes of product defects. .

In width reduction rolling, as described above, a tapered unsteady part is formed at the front and rear ends of the slab, which is thinner than the central part, but in this unsteady part, the protrusions and grooves do not engage with each other, and the guiding property is lost.

etc.

The present invention aims to provide a novel dogbone rolling method that solves many of the conventional difficulties. In dogbone rolling, a first inclined surface for preventing inclination that presses the corner of the side end of the rolled steel billet during width rolling is provided on both sides of the bottom of the hole having a width approximately equal to the thickness of the flat steel billet; A dogbone rolling method for a flat steel billet, characterized in that rolling is carried out using a box-shaped groove roll having a second slanted surface for expansion expansion that is steeper than the first slanted surface and is continuous on both sides of the first slanted surface. It is.

The present invention will be explained in detail below based on the drawings.

Figure 1 shows the roll hole arrangement G- used in the present invention.
1, G-2, G-3, and G-4 are shown. Hole type G-1
The box-shaped hole type generally used for width reduction is shown in broken lines, and is illustrated for easy comparison with the G-1 hole type used in the present invention.

Hole type G-1 of box-hole roll in the present invention
As shown in Fig. 2, in order to prevent the slab S from tilting during width reduction, the corner portion of the side end of the slab S is cut from the left and right on both sides of the hole bottom 1, which has a thickness approximately equal to the thickness of the slab S to be reduced in width. First inclined surface 2 to press evenly
and a second inclined surface 3 that is continuous on both sides of the first inclined surface 2. This second inclined surface 3 is
When the width of the slab S is reduced, the peak part P of the dogbone formed by being deformed by the first inclined surface 2 as shown in FIG. 3a becomes a sharp part. This is to enlarge the bulge of the dog bone. FIG. 3b shows how the slots of the slab are filled during dogbone rolling using the second inclined surface 3. The expansion of the bulge and the shaped state of the peak portion P are clear from FIG. 3b.

The inclination angle θ ₁ of the first inclined surface 2 needs to be at least 20 degrees in order to apply pressure evenly from left and right to effectively prevent the slab from tipping. In addition, the inclination angle θ ₂ of the second inclined surface 3 is set at θ ₁ in order to improve the acute angle shape of the peak portion P and form it into a shape that will not cause defects in the subsequent hole-form rolling process, while also aiming at expanding the bulge. ≠θ ₂
In addition, θ ₁ <θ ₂ and the angle range is preferably 65 degrees to 87 degrees.

Such dogbone rolling using the box-shaped hole type G-1 of the present invention is carried out as shown in FIG. First, as shown in a, the slab S is placed on the first inclined surface 2.
The upper and lower end corners of the slab are pressed evenly on the left and right sides, and the slab is rolled down widthwise while preventing the slab from tilting to form a steel piece with the cross-sectional shape (dogbone shape) shown in the figure. In this case, the width of the hole bottom 1 may be approximately the same as the thickness of the slab, but may be narrower or wider within the limit of 30 mm.

The reason why the width of the hole bottom is limited to ±30 mm of the slab thickness is that the lower limit is so that the center of the hole bottom and the center of the slab thickness do not deviate, and the upper limit is set so that the width of the bottom of the hole is not shifted from the center of the slab thickness. The reason is that this is the limit that does not reach the surface and tilt the slab.

Furthermore, the lower limit of the angle _θ1 of the first inclined surface is set to 20° because if it is less than that, the left and right restraining force will be weak and will not work effectively to prevent collapse. However, if _θ1 is too large, the dogbone generation efficiency will be greatly reduced and the required dogbone shape will not be obtained, so it is preferable to set the upper limit to about 55°.

The steel piece subjected to dogbone rolling on the first inclined surface 2 has an acute-angled peak portion P as shown in the figure.
If this peak portion P is applied to the subsequent molding hole as it is, it will cause flaws. Therefore, in the present invention, dogbone rolling is subsequently performed using the second inclined surface 3 to shape the peak portion P and further enlarge the bulge, which is shown in FIG. 3b. The reason why θ ₂ of the second inclined surface 3 is set to 65 degrees is that if it is less than this, the first
This is because the extended shape of the slope, that is, the acute angle shape of the peak part P, is not improved, and the upper limit of _θ2 is set to 87
The reason for this is that this is the limit of flaw occurrence due to the difference in circumferential speed inside the hole mold.

Fig. 3c shows the dog-bone steel piece of b further reduced in width using a box-shaped hole die (Fig. 1 G-2) to form an unfilled area 4.
It shows the state where it is filled with. This step c is required, for example, for H-section steel series with relatively large flange widths. That is, when the size becomes large, it is necessary to increase the flange width D _F of the dog bone, and to do so, the length of the first inclined surface 2 must be inevitably increased, and the unfilled portion 4 becomes larger. be.

Figure 4 is a cross-sectional view showing the collapsed state of a rough shaped steel piece made by dog-boning a slab.
θ is the angle of inclination. Figure 5 shows actually measured values of the inclination angles of the conventional method and the present invention, with the above inclination angle θ plotted on the vertical axis and the longitudinal position of the steel strip at the time of completion of dog bone rolling on the horizontal axis. . From this figure, it can be seen that in the conventional method (dogbone rolling using the dashed line in Figure 1), the collapse is large not only in the center but especially at the top and bottom, as shown by the broken line, but in the method according to the present invention, as shown by the solid line, the collapse is large. There is almost no inclination in the center, and the inclination angle at the top and bottom is extremely small, less than 0.5 degrees, which shows that it is significantly superior to the conventional method.

Figure 6 shows the shape of a steel billet at the initial stage of dogbone rolling.As shown in the figure, when dogbone rolling is performed, the flange width and web height become smaller toward the ends of the billet than at the center, as shown in the figure. An unsteady region D _A is formed. When such a steel billet is further dog-bone rolled, in the conventional method (using the dotted hole shape shown in Fig. 1), even if the center part of the steel billet collapses in the early stage of rolling, as a bulge is formed, it is restrained by the sidewalls of the hole shape. Since the inclination is corrected during rolling, the inclination angle is smaller than that of the top and bottom parts, but since the unsteady region D _A is tapered and narrow, the inclination at the initial stage of rolling remains. Therefore, according to the conventional method, as described above, the portions where the angle of inclination exceeds 2 degrees are cut and scrapped, which greatly reduces the yield.

In contrast, in the present invention, the corner portion of the slab side end is pressed evenly from the left and right from the beginning by the first inclined surface 2, and the unsteady area D _A is also pressed from the left and right to prevent tilting. Rolling can be carried out within a small tolerance range for the inclination angle of the rolled steel piece from the beginning to the end of rolling.
Therefore, since the material is well guided to the hole mold during the subsequent shape rolling, there is no filling defect and no caliber flaws occur. Furthermore, since there are no more than two folded parts to be cut off as scrap, the yield does not decrease.

As described above, according to the present invention, it is possible to roll with an extremely small angle of inclination over the entire length of the rolled steel billet during dogbone rolling, so the bulges are formed evenly on the left and right sides and no flaws occur. It does not become impossible to bite during subsequent groove rolling, and since the inclination angle is within a small range of 2 degrees or less, caliber flaws do not occur during groove rolling. Furthermore, since the angle of inclination is less than 2 degrees over the entire length including the leading end and the rear end, the yield can be improved with fewer truncated portions.

Example 1 A hot slab with a cross section of 250 mm x 1100 mm was processed into hole type G-1 using the roll pair shown in FIGS. 7 and 8.
(θ ₁ = 29°, θ ₂ = 80°), perform width reduction rolling with a reduction amount of 50 to 70 mm/pass, and then
Shape rolling was carried out to produce a rough shaped steel piece having a shape as shown in FIG. 9, with a web height W = 550 mm, a web thickness t = 75 mm, and a flange width F = 370 mm. The collapse during width reduction was as shown in Fig. 5, and there was no problem at all.

In this example, since the rolling object is relatively small in size, only one hole is required for width reduction, as shown in Fig. 1G.
-No need for a box-shaped hole like 2. For this reason, it is possible to provide holes of other sizes on one roll, and it can be seen that this is effective in reducing the number of rolls in stock.

Example 2 A hot slab with a cross section of 250 mm x 1400 mm was molded into a hole G-type using a pair of rolls shown in FIGS.
1 (θ ₁ = 25°, θ ₂ = 69°) with a reduction amount of 50 to 70 mm/pass, and then widening and shaping rolling of the dog bone part with a G-2 box hole type. Shape rolling was carried out using a hole size of G-4 to produce a rough-shaped steel piece having a shape shown in FIG. 9 with a web height W = 830 mm, a web thickness t = 100 mm, and a flange width F = 410 mm. As in Example 1, there was no problem with the collapse during width reduction.

[Brief explanation of the drawing]

Figure 1 shows the roll hole arrangement G- used in the present invention.
1 to G-4 are shown, and the broken line in the G-1 section shows a conventionally common box-shaped hole type. FIG. 2 is a detailed diagram explaining the above G-1, FIG. 3 is a diagram explaining width reduction rolling in the present invention, FIG. 4 is a diagram explaining the inclination angle θ during width reduction rolling, and FIG. An explanatory diagram of the inclination angle of the present invention and the conventional method, FIG. 6 is an overall diagram of the slab after width reduction, and FIG. 7 is an explanatory diagram of the roll hole arrangement used in Example 1.
Fig. 8 is a detailed view of Fig. 7 G-1, Fig. 9 is a cross-sectional view of a rough H-section steel piece, Fig. 10 is an explanatory diagram of the roll hole arrangement used in Example 2, Fig. 11 10 is a detailed view of FIG. 10G-1, FIG. 12 is an explanatory diagram of the uneven rolling situation in the forming hole mold, and FIG. 13 is an explanatory view of the down flaws caused by the uneven forming hole rolling. 1: Roll hole type bottom, 2: First inclined surface, 3: Second inclined surface, S: Slab.

Claims (1)

[Claims] 1. In dogbone rolling, in which a flat steel slab is width-reduced to form a bulge at the side end to form a dogbone shape, the steel to be rolled during width reduction is placed on both sides of the bottom of the hole, which has a width approximately equal to the thickness of the flat steel slab. It has a first sloped surface for preventing tilting that presses the corner part of the side end of the piece, and a second sloped surface for expanding the bulge which is continuous with both sides of the first sloped surface and has a larger slope than the first sloped surface. A dogbone rolling method for flat steel billets, characterized by rolling with box-shaped groove rolls.