JPS5942561B2 - Hot rolling method - Google Patents

Description

Detailed Description of the Invention The present invention involves width reduction rolling to obtain slabs of various widths from continuously cast slabs of a constant size, then rough rolling, and then finishing rolling to obtain hot steel of various widths. The present invention relates to an improvement in a hot rolling method for obtaining a strip, and in particular provides a hot rolling force method that improves the rolling yield.

Normally, the slab width in hot rough rolling is 50 to io.

A pressing force is applied to this slab in the width direction by an edger of a rough rolling mill to make the width of the slab wider than the width of the finished product by rnm, thereby obtaining a finished product.

When this width reduction is performed, the slab produces so-called fish tails in the top and bottom parts of the slab, where the width ends bulge in the rolling direction, as shown in Figure 2, and the width ends of the slab in the cross section as shown in Figure 2. The width of the plate becomes locally thicker, resulting in a so-called tongue bone shape.

During the next rough rolling in the sheet thickness direction, this portion produces medium corrugations and the aforementioned fish tails are promoted.

These fish tails sometimes interfere with the passing of the sheet in the next finishing mill and the removal of ash, and even if it is successfully rolled in the finishing mill, it will not become a finished product and will be cut off, so it is usually done before entering the finishing mill. A decrease in yield is unavoidable since the cutting is performed using a shear.

In addition, recently, slabs have been made by continuous casting, and in this case, there is a tendency to reduce the number of types of molds used to simplify continuous casting. In order to get
It has become necessary to carry out the above-mentioned width killing forcefully.

For this reason, in addition to the edger of the existing rough rolling mill, a medium-reduction rolling mill dedicated to width reduction of slabs has been installed in hot rolling equipment.

For example, Fig. 3' shows an example of the configuration of this type of dedicated machine, where 1 and 1 are left and right vertical rolls equipped with calibers 2 and 2 to restrain the growth of dog bones during wide-width reduction; ，
3 is the top for erasing the dogbone placed adjacent to vertical roll 1,1.

On the lower horizontal rolls, 4 indicates the slab that is rolled at medium pressure by the calibers 2 and 2 mentioned above.

For example, Fig. 4 shows that in the rolling equipment shown in Fig. 3, a rectangular slab is rolled to a medium reduction with calibers 2 and 2 of vertical rolls 1 and 1, and then dog-boned in horizontal rolls 3 and 3 (the gap between the horizontal rolls is In one drawing, lc is the fishtail length, Sc is the fishtail area, ΔW is the width drop, 1w is the width drop, and Sw is the width drop. Indicates area.

The slab that has been subjected to medium reduction rolling and dog bone leveling rolling in FIG. 4 is then rolled in the thickness direction at a reduction rate of about 80% in a rough rolling mill to form a bar of a predetermined thickness.

Thereafter, the front and rear end portions of the bar, including the fishtail portion, are cut off by a shear to a width smaller than the width of the desired product (width of the central portion in the longitudinal direction of the bar).

The present inventors conducted various studies on the crop loss reduction measures mentioned above, and found that fish tails make it difficult for the deformed region of the slab caused by the vertical rolls to penetrate to the center of the slab width, and that both ends of the slab width extend more than the center of the slab. Therefore, we focused on the point that the formation of fishtails could be reduced if the deformed region by the vertical rolls penetrated to the center of the slab width direction.

When slabs of the same size are subjected to medium reduction rolling with the same amount of reduction, in order to make the deformed area by the vertical rolls penetrate to the center of the slab width direction; this is the conclusion that it is better to increase the diameter of the vertical rolls. reached.

Therefore, when slabs of the same size are rolled with the same amount of reduction and medium reduction, we conducted various experiments and studied the relationship between the diameter of the vertical roll, fishtail, and width drop. When performing medium reduction rolling, crop loss can be improved by using large diameter vertical rolls with a diameter of 1.5 mφ or more, compared to the conventional vertical rolls with a diameter of about 1 m. It has been found that the rolling yield can be improved.

That is, the inventors first determined that the thickness was 250 mm and the radius was 2000 mm.
A rectangular slab with a cross section of mm is 1000 Bφ in diameter and 1500 mm in diameter.
mmφ, 2000mmφ, 3000mmφ, 4000m
mφ vertical roll, width reduction amount 150 (mm/1 pass),
When the fish tail area S in Fig. 4 is reduced by 300 mm/2 passes and subjected to dog bone leveling rolling,
We investigated how c changes.

This investigation force method uses a hot model mill to create a model slab by reducing the dimensions of the rolled material while keeping the mill's roll diameter constant, and then rolling it to create a model slab. The area was measured.

The measurement results of this model slab are as follows:
L, converted to the fishtail area of a slab with a width of 1650 mm in cross section, and if this fishtail area is cut and removed, the yield loss and crop weight due to fishtail in a slab with a unit weight of 22tIXL, thickness of 250m11L and width of 2000mm is calculated as 6. What I wrote,
It is shown in FIG.

From the results of this experiment, the influence of the roll diameter on crop loss is as follows: ke) In the roll diameter range of 1 to rrLφ, the larger the roll diameter, the more the crop loss decreases.

(2) The larger the width reduction amount, the greater the effect of reducing crop loss due to increasing the roll diameter.

There was found.

For details, 300rIL1rL width pressure [150(rn7I
In the case of 2 passes], the conventional roll diameter 1
For mφ, the crop loss is 61%, but when the roll diameter is 1.5mφ, it becomes 0.80%, and the reduction effect is 0.81%.
For mφ, the crop loss is 0.89%, but when the roll diameter is 1.5 mφ, it becomes 0.66%, which has a reduction effect of 0.23%.

Also, when the roll diameter is 2 mφ under a pressure of 300 mm width, the crop loss is 0.66%, and when the roll diameter is 2 mmφ under a pressure of 150 mm width, the crop loss is 0.66%.
In the case of φ, the crop loss is 0.44%.

Furthermore, in the case of a 300mm width rolling roll diameter mφ, the crop loss is 0.4%, and for a 150mm width rolling roll diameter 4mφ.
In this case, the crop loss is 0.33%.

Next, in order to investigate the effect of slab size on crop loss, we used the same research method as above to investigate the effect of slab size on crop loss.
5mm, 1650, thickness 250mm, 370m11L
, 100-3001 for slabs of 470rn11L
The fishtail area was investigated when width reduction rolling was performed by n1n and dogbone leveling rolling was performed.

Figure 6 shows the effects of this investigation.

This study shows that the effects of slab size on fishtail area and crop loss are as follows: (1) The effect of slab thickness is small.

(2) The influence of slab width is significant.

(3) Even with the same amount of width reduction, the larger the slab width, the larger the crop loss.

became clear.

As described above, it was found that for the same width reduction amount, the larger the roll diameter, the more the crop loss decreases, whereas the larger the slab width, the more the crop loss increases.

Therefore, in the case of the same width reduction amount, the projected length of the contact arc between the slab and the vertical roll changes depending on the roll diameter, and the average plate width (the width of the entrance side of the vertical roll and the width of the exit side of the vertical roll) changes depending on the size of the slab width. The results shown in FIGS. 5 and 6 are organized as shown in FIG. 1 using the parameters determined by the ratio to the average value, that is, the rolling shape ratio.

Here, the rolling shape ratio refers to the width of the slab before width rolling, as shown in FIG.

, the slab width after width reduction is Wl, width reduction amount ΔW = Wo-W
1. When the radius of the vertical roll is R, the projected length of the roll contact arc 1 d = J drunk W and the average rolling Wo + W 1 ΔW width Wm 2 □ 2 W.

-ratio to one ld/Wm2 It is a parameter expressed as

The horizontal axis of FIG. 7 is [1/(rolled shape ratio)]−=(W
m/ld).

From FIG. 1, it was found that the rolling reduction condition for almost eliminating fish tails was Wm/ld of 1.5.

As described above, when the material inside (slab width) is fixed and the lowering amount is fixed, fishtail can be eliminated if Wm/ldki 1.5 is satisfied.

Here, for example, if the thickness is 250 wings, the width is 1650 mm, and the lowering amount is 150 mm, calculating the roll radius R that satisfies Wm/ld of 1.5, R = 7350 mm, and the diameter 2R = 14700 mm, which is 15 m.

In other words, if a vertical roll with a diameter of about 15 m is used when rolling a slab with a thickness of 250 blades and a width of 1650 mm in one pass with a 150 mm width, the average rolling width Wm/roll contact arc length 1d = 1.5, resulting in fishtail. The area becomes zero.

Note that the maximum roll diameter is preferably about 4 mφ in consideration of the vertical rolling mill structure, particularly the stand configuration, and the torque transmission yarn, and from the maximum constraints on rolling load and rolling torque.

Next, the reason why the minimum roll diameter employed in the present invention is limited to 1.5 mφ will be explained.

The first reason is that, as is clear from the experimental results shown in FIG. 5, if the roll diameter is 1.5rrLφ or more, it is possible to greatly reduce the amount of fishtail and scolding broth.

For example, under a pressure of 300 mm as shown in Fig. 5, when the roll diameter is 1 mφ, the crop loss is 1.61%, but when the roll diameter is 1.5 mφ, the crop loss is 0.8%, and the crop loss is 0.81%. %, or about 50%.

Also 4. At Omφ, the chloraf relaxation decreases to 0.4%,
Crop loss 1.6 when using conventional 1rrLφ
1%, it decreases by 1.21%, or about 75%.

For this 1.21% glue reduction loss reduction effect, 10
The 0.81% reduction effect at 0 mφ becomes about 67% reduction effect.

The second reason will be discussed next.

As mentioned above, the top and bottom parts of the slab after medium pressure rolling with vertical rolls and leveling rolling with dog bones have a width larger than the width Wmax of the middle part in the longitudinal direction of the slab, in addition to the fishtail part mentioned above, as shown in Fig. 4. There is a narrow width drop, and the minimum width of this width drop is Wm1n (width of the base of the crop)
and the above maximum medium Wmax (Wmax - Wmin
) is called the width drop ΔW.

By the way, by rough rolling without medium reduction rolling, the width A as shown in Fig. 9 is obtained.
When a horizontal reduction is applied to a rectangular slab of length V and length L, the ninth
As shown in Figure B, it is well known that the end portions of the slab are wider than the central portion in the longitudinal direction.

According to the investigation results of the present inventors, the difference ΔW' in the amount of medium corrugation between the central part and the end part of the slab shown in FIG. The thickness is 15
When a slab of 0 to 350 mm was roughly rolled to a thickness of 35 to 501 rLTL (that is, under normal rough rolling conditions of about 80% rolling reduction) to form a bar, Δw'=so.

This fact indicates that if it is possible to suppress the width drop ΔW of the crop root in the slab after medium pressure rolling with the vertical rolls and dog bone leveling to 80 mm or less, the crop cut off with the shear after rough rolling can be This means that only the part corresponding to the fish tail part of the slab after level rolling can be used as the reduction rolling dog bone.

If the difference in the amount of width expansion between the center and end portions in the longitudinal direction of the slab is smaller than the width drop of the slab after the above-mentioned medium reduction and dog bone leveling rolling, rough rolling corresponding to the width drop of the slab is performed. Since the top and bottom parts of the latter bar are also less than the width of the bar (less than the middle part in the longitudinal direction of the bar), the shear can be further cut away.

In order to prevent this part from being cut off, automatic plate width control was used to conventionally make the gap between the vertical rolls at the top and bottom sections larger than at the middle section when rolling slabs under medium pressure using vertical rolls with a diameter of 1 mφ or more. However, the reality is that this requires an expensive automatic handling width control device.

Therefore, the present inventor investigated the relationship between the vertical roll diameter and the width drop and found that when slabs of the same size are rolled with the same amount of roll reduction and medium reduction, the larger the vertical roll diameter, the smaller the width drop. There was found.

Furthermore, as a result of investigating the influence of slab dimensions on width drop, it was found that when the same roll diameter is used for medium reduction rolling with the same amount of roll reduction, the effect on the slab is small, but the influence of slab width is large, and the larger the slab width, the more the width decrease. The quantity turned out to be large.

What should be noted here is that for slabs of various widths up to 2,000 mm, which is the maximum slab width commonly used, if a vertical roll with a roll diameter of 1.5 mφ or more is used, what kind of roll can be used? Even if you take the lower amount, the width drop is still 80m.
The point is that it can be less than m.

For example, in Figure 10, a slab with a cross-sectional thickness of 250 mm and a width of 1650 mm is rolled down by vertical rolls with diameters of 1, 1.5, 2, 3, and 4 mφ for a maximum of 6 passes with a constant rolling amount of 159 mm per pass, and a dog bone is formed. It shows the width drop ΔW of the slab after smoothing rolling.

FIG. 11 shows the results of a similar investigation of the width drop ΔW for a slab with a cross-sectional thickness of 250 mm and a width of 2000 mm.

From the results of the above io and i in the figure, when the conventional roll diameter lrnφ is 2000 mm wide, the total width reduction is in the range of 100 to 500%, and when the width is 1650 mm,
When the total width reduction is in the range of 150 to 450, the difference in the width expansion between the central part and the end in the longitudinal direction of the slab that occurs in normal rough rolling becomes a width drop of more than 80 mm, but on the other hand, when the roll diameter is 1 For vertical rolls of 5 mφ or more, the width drop should be 80 dragons or less regardless of the total width reduction for slabs of various widths up to 2000 mm, which is the maximum slab width currently in common use. Therefore, the crop cut off by the shear after rough rolling can correspond to the fin tail portion of the slab after medium pressure reduction dogbone flattening rolling.

In other words, if medium reduction rolling is performed using vertical rolls with a roll diameter of 1.5 mφ or more, the width drop can be reduced to 80Tt11L or less, and when the bar is formed by subsequent rough rolling with a reduction rate of about 80%. , the width of the crop root becomes wider than the width of the central part of the slab by about 80 m1tt, and the width of the crop root of the bar becomes slightly wider than the width of the central part of the bar (finished product width).

Therefore, the crop that is cut off in the jar prior to finish rolling is
It is possible to use only the portion corresponding to the fishtail portion of the slab after the dogbone leveling rolling.

Note that the wide portion near the crop root of the bar can be easily smoothed into the product at the center in the longitudinal direction of the bar using, for example, an edger roll of a rough rolling mill.

As described above, if the vertical roll diameter is 1.5 mφ or more, width drop loss can be effectively prevented during medium reduction rolling without performing the above-mentioned automatic strip width control, so in the present invention, the minimum roll diameter is set to 1.5 mφ or more. The diameter is limited to 5 mφ or more.

(Example) Width 1650 mm, thickness 250 mm, length 6838 r
When a slab of rtrrt is medium-reduced to a thickness of 300 nm using a vertical roll and then roughly rolled into a bar with a thickness of 50 mm, the vertical roll has a diameter of 1 mm. Omφ
(Conventional method), 1.2mφ (comparative example), 1.5mφ, 2.
Table 1 shows the crop loss (fish tail loss, plus width drop loss) in the above bar when medium pressure rolling is performed using vertical rolls of 0rrLφ, 3.0mφ, and 4.0mφ (method of the present invention). show.

As is clear from this first coating, the method of the present invention can reduce the head loss by 1.4% or more compared to the conventional method, and can also completely eliminate the width loss.

As described in detail above, the present invention involves rolling a slab with a roll under medium pressure, and the roll has a diameter of 1.5rrL.
It is characterized by using a roll with a large diameter of φ or more, and can improve crop loss and improve yield.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams of the deformation characteristics of slabs during width reduction during hot rolling of slabs, Figure 3 is an explanatory diagram of the configuration of a medium reduction rolling mill exclusively for width reduction, and Figure 4 is 5 to 11 are explanatory views of the method of the present invention, and FIG. 5 shows the roll diameter and Figure 6 is a chart showing the results of investigating the relationship between width reduction and cropping. Figure 7 is the average plate width/contact arc projected length and the head knob. Figure 8 is an explanatory diagram of the contact arc projected length/average plate width, that is, the rolling shape ratio, and Figures 9A and B are local hits that occur when a thickness direction reduction is applied to the slab. FIGS. 10 and 11, which are explanatory diagrams of the waving phenomenon, are explanatory diagrams of the relationship between the total width reduction amount and the width drop amount. 1...Vertical roll, 2...-h') bar, 3...Horizontal roll, 4...Slab,
lJc...Fishtail length, Sc...
... Fish tail area, ΔW ... Width drop, 1
w...width fall length, Sw...width fall area.

Claims (1)

[Claims] 1. A hot rolling force method characterized in that when a slab is width-reduced by rolls, a large-diameter roll of 1.5 mφ or more is used as the roll.