JPH0714521B2 - Hot width rolling method for metal slabs - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot width rolling method of rolling a metal slab in a width direction with a vertical rolling mill, and more specifically, during hot width rolling of a metal slab. The present invention relates to a hot width rolling method for preventing the growth of front and rear end deformed portions that occur.

(Prior art) The feature of the hot width rolling method for metal slabs is that continuous casting slabs are targeted in proportion to the conventional slab rolling method for steel ingots. The ratio of plate width, that is, the roll gap shape ratio is as small as 0.1 to 0.2, and the repeated vertical roll width reduction amount per one time is as large as 200 to 300 mm. Therefore, a deformed portion called a fishtail is generated at the front and rear ends of the metal slab that is the material to be rolled, resulting in crop loss.

Many methods have been conventionally proposed for reducing the crop loss that increases with the width reduction amount. They are the methods that have been put to practical use in slabbing and those that have been applied. For example, as disclosed in Japanese Patent Publication No. 51-35383, it is possible to reduce the amount of reduction before leaving the rolling roll without allowing the material to be rolled to reciprocate in a schedule in which a predetermined amount of reduction is passed. Characteristic double-sided pass rolling method, and as disclosed in JP-A-57-81902, at least one end portion in the longitudinal direction of the material to be rolled is press-formed into a narrow width, and then a rolling mill at the subsequent stage And a press forming method of rolling.

(Problems to be Solved by the Invention) In any of these conventional techniques, the rolling efficiency is significantly reduced. That is, the double-sided pass rolling method usually requires two times of rolling in order to reduce one rolling amount during rolling,
Further, the press forming method requires a stop time for positioning the material to be rolled and the press operation process. Therefore, these methods cannot be applied to the width reduction vertical rolling mill which is made to realize the process of combining the continuous casting process and the rolling process, which can utilize the sensible heat of the continuous casting slab. When manufacturing various slabs in the width rolling process that directly connects the continuous casting process and the hot width rolling process, it is necessary to have a rolling efficiency that matches the capacity of the preceding and following processes, and the leading and trailing edges of the material to be rolled do not interfere with rolling time It is required to reduce the crop loss of the part.

It is an object of the present invention to provide an effective hot width rolling method for a metal slab that solves the above problems.

(Means for Solving the Problem) As shown in FIGS. 2 (b) and 6, the means of the present invention for solving the above-mentioned problem is to connect a vertical rolling mill to each of the front and rear of the horizontal rolling mill. Using the reversible rolling equipment installed, the width rolling of the metal slab is performed by the vertical rolling mill,
The width rolling metal slab dogbone leveling rolling is performed by a horizontal rolling mill, and after repeating this, thickness rolling to a predetermined target thickness is performed by a horizontal rolling mill in the final pass, and then width rolling is not performed. When manufacturing metal slabs of various widths, the maximum allowable rolling load of the vertical rolling mill, the maximum rolling speed at that time (maximum roll speed), and the slab rolling conditions (slab temperature, size, composition, etc.) Based on the maximum width reduction per vertical pass of the vertical rolling mill and the width reversal per horizontal rolling mill per dog bone leveling, the maximum reduction of width per single pass rolling of the reversible rolling mill Then, based on the target width reduction for obtaining the target width dimension of the metal slab, the rolling time of the total passes of the multiple passes of the maximum width reduction amount and the single pass with the width reduction amount less than the maximum width reduction amount is obtained. ,At this time To reduce the rolling speed of any of the multiple passes to increase the maximum width reduction per rolling of the vertical rolling mill to perform reversible rolling omitting passes less than the maximum width reduction. This is a hot width rolling method for a characteristic metal slab.

In the present invention, the total pass refers to a metal slab actual rolling pass in the reversible rolling mill, and the metal slab is supplied from one direction of the reversible rolling mill and the rolling completed slab is fed from the other direction as in the example of the present invention described later. In the case of paying out, the empty pass is not required because the final pass becomes the paying pass when the number of actual rolling passes is an odd number of passes, but when the actual rolling number is an even number of passes, the final pass is the opposite paying side of the reversible rolling mill. Therefore, the empty pass is set to the beginning (the embodiment of the present invention), the end, or the middle of the actual rolling pass. Further, when supplying the metal slab from one direction of the reversible rolling mill and paying out the rolling completed slab from the same direction, when the actual number of rolling passes is an even number of passes, the final pass becomes the payout pass, so no empty pass is required. However, in the case of an odd number of passes, the final pass is on the non-payment side of the reversible rolling mill, and therefore the empty pass may be handled in the same manner as described above.

(Operation) The operation of the present invention will be described below with reference to the drawings. Fig. 2 (a)
Is an example of a stand configuration of a width reduction rolling machine V ₁ -H-V ₂ that mainly rolls in the width direction. Vertical roll 2 with caliber (V ₁ )
The horizontal roll 3 (H) is arranged between the stands of 4 and 4 (V ₂ ). The metal slab 1 is reversibly rolled between the rolls 2, 3, and 4.

The rolling method is repeated V ₁ , H, V ₂ , V ₂ , H, V ₁ , V ₁ , H, ... And then the final odd pass is finished with V ₁ , H. this is
The V ₁ roll 2 and the V ₂ roll 4 are rolled in the width direction.
The so-called dog bone leveling rolling is carried out by rolling horizontally to the original thickness of the metal slab. This is because, in the widthwise rolling using a vertical roll with a caliber, when the locally increased thickness part becomes large, it bites out from the caliber, causing surface flaws on the slab and increasing the rolling power in the widthwise rolling. The amount that can be rolled will be significantly restricted. For this reason, it is necessary to take a rolling process to reduce the width by rolling again in the width direction after reaching the plate thickness locally increased by the horizontal roll to the same plate thickness as other parts or more. is there. By repeating this rolling process, rolling is performed to a target width dimension, and the final horizontal roll pressure is applied to finish to a target thickness dimension.

FIG. 2 (b) shows the slab width and the number of reversible rolling passes when rolling is performed at the maximum rolling speed to obtain a predetermined target thickness and width dimension and the maximum rolling load in the reversible rolling method shown in FIG. 2 (a). That is, the relationship of the number of passes generally called is shown. In the figure, when obtaining the target slab width dimension Wi from the original width slab dimension Wo, when Wi is in the range of W _2n-1 > Wi ≧ W _{2n + 1} , rolling is performed 2n + 1 times. (N is an integer) As a result, the shape of the metal slab is such that the fishtails 5 and 6 occur at the front and rear ends in the longitudinal direction as shown in FIG. 3, and the width center has a thinner cross-sectional shape than the width end. The hollow 7 causes the depression 7. Further, such phenomenon is not observed at the leading and trailing end portions, and the wide rolling reduction process exhibits complicated rolling behavior.

As a result of detailed investigations by the present inventors, there is a relationship with the reduction amount as shown in FIGS. 4 (a) and 4 (b). By increasing the reduction amount, the crop weight and the amount of depression in the central portion are increased. It was accompanied by a significant phenomenon. Therefore, the inventors have devised a method for increasing the reduction amount without impairing the rolling time under the number of passes determined by the maximum rolling speed and the maximum rolling load.

That is, the rolling load P can be reduced to one variable of the roll rotation speed N by the following procedure.

Mean deformation resistance Km is strain rate, temperature t, when the function determined by the carbon component ratio C of the rolled material sigma _f, f _m and m, Here, each function σ _f , f _m , and m is given by the following equation.

l = 0.41-0.07C ...... (4) m = (-0.019C + 0.126) t + (0.075C-0.05) ......
(5) Here, T is the absolute temperature of the rolled material, C is the carbon component percentage of the rolled material, ε is the logarithmic strain of the rolled material, and is the strain rate of the rolled material.

The strain ε and the strain rate are r, the rolling reduction, N is the roll rotation speed,
The roll radius is R and the strip width before rolling of the material to be rolled is h _{1, which} is given by the following equation.

The function σ _f forming the equation (1) is determined by the rolling temperature and the carbon amount, and the function f _m is also determined by the carbon amount and the rolling reduction.

Therefore, if the material to be rolled is determined and the rolling conditions are determined, σ _f ,
f _m is given by the constant. If this is expressed by a constant a ₁ , equation (1) becomes Substituting equation (8) into equation (9) Is determined as a constant when the material to be rolled and the diameter of the rolling roll are determined and the rolling conditions such as the rolling reduction and the width of the material to be rolled are determined.

Expressing this as a ₂ , equation (10) is km = 1.15 ・ a ₁・ a ₂・ N ^m …… (11) a ₃ = 1.15 ・ a ₁・ a ₂ km = a ₃ N ^m …… (12) The rolling load P is expressed as P = km · A · Q _p (13) by the rolling force function Q _p and the contact area A with the rolling roll. Since the rolling force function Q _p and the contact area A with the rolling roll are both constants obtained by the rolling conditions, the expression (13) can be expressed as a ₄ as follows: P = a ₃ N ^m · a ₄ ...... (14) If α = a ₃ · a ₄ , P = α · N ^m (15) Therefore, the rolling load P is expressed as a relation of the roll speed N.

As a result of various investigations by the present inventors on the rolling load and the roll rotation speed in the hot width rolling, as shown in FIG.
It was possible to express accurately with 0.1242.

FIG. 6 shows the knowledge obtained above in the relationship between the vertical roll rolling load and the vertical roll width reduction amount per pass. Point 8 in the figure indicates the maximum roll rotation speed Nmax and the rolling load limit value Pmax. Shows the maximum reduction amount ΔVmax per pass at this time, and point 9 in the figure indicates the rolling load P′max with respect to the maximum reduction amount ΔVmax when the roll rotation speed is reduced by ΔN, and the rolling load is as described above. From the formula Given in. Therefore, the maximum rolling amount ΔV′max with respect to the maximum rolling load limit Pmax when the roll speed is reduced
Is ΔVmax + ΔV, which can be seen to increase.

FIG. 1 shows the relationship between the target slab width Wi and the rolling time t.
When the number of rolling passes is an integer value, for example, odd number finishing, the number of passes is 1, 3, ..., _2n-1 , _{2n + 1} , while the finishing width is an arbitrary continuous numerical value. The rolling time becomes discontinuous at the slab width at the time of increasing. Boundary slab width Wmax of the number of rolling passes determined by maximum roll speed Nmax and maximum rolling load Pmax, and target slab width Wi ≧ Wmax
Assuming that the number of rolling passes is 2n + 1, the relationship between the target slab width and rolling time is as shown in diagrams 10 and 11 in the figure. The rolling time at the slab width Wmax increased from t _2n-1 to t _{2n + 1} because the number of passes increased. That is, the total number of passes in the actual rolling pass is 2n + 1, which is a combination of a plurality of passes 2n-1 with a maximum width reduction and a single pass 2 (including an empty pass) with a reduction amount less than the maximum width. When the roll rotation speed is reduced and rolling in the width direction is performed, the rolling load is reduced, so the slab width Wmax, which is regulated by the maximum rolling load, can be rolled to a narrower slab by increasing the maximum rolling reduction. Becomes possible,
This can be shown in diagram 12 in the figure. Therefore, if the rolling time is shorter than that shown in the diagram 11, rolling is possible without impairing the rolling efficiency. That is, if the slab width at the intersection of the lines 11 and 12 in the figure is W'max, the area of the slab width is Wmax.
≧ Wi ≧ W′max. The number of passes is 2 in the slab width area
It becomes n−1, and the single pass of less than the maximum width reduction amount is omitted. That is, it is a region in which the rolling speed is reduced and rolling is performed at the maximum width reduction amount.

(Example) Next, the Example of this invention is shown.

The rolling conditions are as shown in Table 1, and V ₁ (vertical roll) -H
(Horizontal roll) -V ₂ (Vertical roll) 3-stand reverse rolling method was used to produce a slab with a target slab size of 250 mm and 735/785 mm width from a continuously cast slab of 280 mm thickness and 1800 mm width.

Table 2 shows the rolling schedule when rolling with the maximum roll speed and the maximum rolling load. The roll opening of the horizontal roll was 250 mm for the final pass, and 280 mm for the other rolling passes. The rolling speed was set to 60 m / min in the final pass to perform the AWC short stroke, and 90 m / min in the other passes. In this case 5
The minimum slab width that can be rolled in a pass is 825 mm, which is a narrow 735 mm
In the case of, the number of paths is 7 as shown in the conventional method of Table 3 (a).
In this case, the vertical roll average rolling reduction is 116 mm per pass, and the rolling time is 3.6 min (min). According to the rolling schedule in the method of the present invention shown in Table 3 (b), the width of 73
When obtaining 5 mm, by reducing the roll speed by 40% and rolling, the average vertical rolling reduction is 14 per pass.
It becomes 8 mm and can be rolled in 5 passes, and the rolling time is 3.6 mi.
When n is set, the amount of reduction can be increased without hindering the rolling time. As a result, the crop loss was reduced by 8%, the amount of depression in the width center was improved by 25%, and the slab shape was made rectangular.

In the example (No. 2) shown in Table 4, the rolling speed was further reduced in the same pass when the target slab width of 785 mm was manufactured. As proposed by the present inventors in Japanese Patent Laid-Open No. 61-27102, the fishtail amount of the metal slab is different from that of the bite end and the bite end, and the bite end is different from the bite end. It is about 3 times that of the fishtail, and when the width reduction is performed with a vertical roll, the width reduction of the bite end is made larger than that of the bite-out end so that the fishtail Can be greatly improved. In Table 4 (b), compared with the conventional method of Table 4 (a), the number of rotations of the roll was reduced by 40% at the 4m portion of the slab biting end and 30% at other portions, and rolled. The rolling time was 3.4 min, and it was possible to increase the biting end reduction amount by 5 mm as compared with other parts without impeding the rolling time. As a result, the crop loss is improved by 10% and a great effect is obtained.

(Effect of the invention) The adoption of the yield improving rolling method by the conventional method to the width reduction rolling mill under the process of directly connecting the continuous casting step and the hot rolling step is impossible because the rolling time is significantly hindered. . According to the method of the present invention, even in rolling under the maximum reduction amount for the purpose of improving rolling efficiency, the maximum reduction amount can be further increased by reducing the rolling speed, and the number of passes can be reduced.
Therefore, the crop loss was improved without hindering the rolling time, and the yield was significantly improved. Furthermore, the amount of depression in the central portion of the slab width is reduced, and the rectangular shape is promoted.

[Brief description of drawings]

FIG. 1 is a drawing showing the relationship between the target slab width and rolling time,
FIG. 2 (a) is a drawing showing an example of a stand configuration of a width reduction rolling mill, FIG. 2 (b) is a drawing showing the relationship between the maximum rolling speed, the slab width at the maximum rolling load, and the number of reversible rolling passes,
FIG. 3 is a perspective view showing the shape of a metal slab rolled by a conventional method, FIG. 4 (a) is a drawing showing the relationship between crop weight and average width reduction per pass, and FIG. 4 (b). Is a drawing showing the relationship between the central depression and the average width reduction per pass, FIG. 5 is a drawing showing the relationship between vertical roll rolling load and vertical roll rotation speed, and FIG. 6 is roll rolling load and 1 pass. It is drawing which shows the relationship of the vertical roll width reduction amount per hit. 1 ... metal slab, 2,4 ... vertical roll, 3 ... horizontal roll, 5 ... tip fishtail, rear end fishtail, 7 ... width center hollow

Claims (1)

[Claims] 1. A dog-bone smoothing of a metal slab that has been width-rolled by using a vertical rolling machine to perform width rolling of a metal slab by using a reversible rolling device in which vertical rolling machines are connected in front of and behind a horizontal rolling machine. Rolling is performed by a horizontal rolling mill, and after repeating this, in the final pass, thickness rolling to a predetermined target thickness is performed by a horizontal rolling mill, and thereafter when manufacturing metal slabs of various widths that are finished without width rolling. Per pass of the vertical rolling mill based on the maximum allowable rolling load of the vertical rolling mill, the maximum rolling speed (maximum roll speed) at this time, and the slab rolling conditions (slab temperature, size, composition, etc.) The maximum width reduction amount per pass rolling of the reversible rolling apparatus is obtained from the maximum width reduction amount of the horizontal rolling mill and the width return amount per one dogbone leveling rolling of the horizontal rolling mill to obtain the target width dimension of the metal slab. To reduce the target width Based on this, the rolling time of the total passes of the plurality of passes of the maximum width reduction amount and the single pass with the width reduction amount of less than the maximum width reduction amount is obtained, and the rolling speed of any pass of the plurality of passes is reduced within this time. A method for hot width rolling of a metal slab, comprising performing a reversible rolling in which a maximum width reduction amount per rolling of a vertical rolling mill is increased to omit passes less than the maximum width reduction amount.