JPS583442B2 - Direct hot rolling method and rolling equipment row for continuously cast slabs - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a rolling method in which slabs cast in a continuous casting machine are directly hot-rolled without being reheated at all, and the present invention provides a plate having uniform entrance and exit temperatures in the width direction of the finishing rolling machine. The present invention relates to a rolling method and a rolling equipment train for obtaining.

Generally, slabs cast by a continuous casting machine (hereinafter referred to as slabs) have a large temperature difference in the width direction (direction perpendicular to the casting direction) even immediately after casting.

As an example, FIG. 1 shows the width direction distribution of the average temperature in the thickness direction immediately after casting of a slab having a thickness of 250 mm and a width of 2000 mrIL.

In this slab, the width direction end and the center part direction from the width direction end 3
There is a temperature difference of 200 to 300°C between the 00mm position and the 00mm position.

Although there are slight differences depending on the casting conditions of the continuous casting machine, that is, the cross-sectional area of the slab, drawing speed, cooling conditions, etc., in the continuous casting machines currently in practical use, the widthwise center and end portions of the slab are roughly the same. There is a temperature difference of 150 to 300 degrees Celsius.

Further, the average temperature in the thickness direction of the central part in the dJ direction of the slab immediately after casting is 12500C to 1100C.

The drop in temperature of the slab immediately after casting is prevented by appropriate heat-retaining means, and this is controlled by a series of phase rolling equipment, a tandem finishing mill group, a cooling device for finish-rolled material, and a winding device. If the raw material is supplied to a continuous hot rolling machine, it is possible to roll it in the continuous hot rolling machine, but on the other hand, there is a large difference in finishing outlet temperature between the widthwise ends and the center part, and for this reason, 1] At the end of the direction, the temperature required due to the material (Ar3
It is extremely difficult to secure the following.

For this reason, conventionally, first, the ends of the slab, which have a large temperature difference in the width direction, are heated during the transfer path between the exit side of the continuous casting machine and the entrance side of the hot rolling machine, and the temperature at the end of the slab is heated. A method of installing a heating device for compensation, such as a heating furnace, a tunnel furnace, an induction heating furnace, etc., and a second method of heating the widthwise edge of the rough finished material on the table between the rough rolling mill and the finishing rolling mill. That is, methods of installing edge heaters, induction heating devices, etc. have been proposed.

However, both of the first and second methods require very large equipment, leading to increased equipment costs and running costs, and have drawbacks such as leaving many problems in maintainability.

Therefore, as a third method, the transfer route between the outlet side of the continuous casting machine and the inlet side of the hot rolling mill is sufficiently insulated, and the temperature is made uniform by recuperation between the two. A method has also been proposed in which the temperature at the ends in the width direction is increased to ensure the temperature at the ends in the width direction at the finish exit is Ar3 or higher, but research by the present inventors has shown that this method maximizes the recuperation effect during transfer. Even if estimated, the temperature difference between the end and the center before rolling (specifically, before rough rolling) is 50°C for reheating within 2 hours, where there is no practical problem in reducing the average temperature of the entire slab. The following can occur.If you want to roll this as it is and ensure the finish exit temperature at the widthwise end to be Ar3 or higher, the temperature at the center must be high, and the finish at the center The outlet temperature rises significantly and surface defects (scale eaves) increase significantly, making it difficult to produce finished products.

Of course, even if the temperature is kept for 2 hours or more, it is possible to maintain a temperature difference of 50° C. or less, but the overall temperature decreases, which is a practical problem.

The present invention compensates for the drawbacks of the conventional method as described above and provides a rolling method and device for obtaining a plate having a uniform finish exit temperature in the width direction, thereby making it possible to directly hot-roll a slab without reheating it. It makes it seem possible.

The gist of the present invention is to carry out a series of rolling passes in which width cutting is performed by an edger using flat rolls before finish tandem rolling, and immediately thereafter, the dogbone formed by the width cutting is rolled down by horizontal rolls. The purpose of this is to increase the temperature at the ends in the width direction, thereby obtaining a plate whose inlet and outlet temperatures of the finishing tandem rolling mill are uniform in the width direction.

Note that the term "uniformity in the width direction" as used in the present invention means the same level as that of ordinary reheated materials.

According to one embodiment of the present invention, if a slab with a temperature difference of about 130°C between the center and end portions is supplied to the inlet of a rough rolling mill, for example, by an unsolidified recuperative continuous casting method, etc. It is possible to obtain a plate with a uniform finish exit temperature in the width direction by direct rolling without any heat retention and reheating, while on the other hand, it is cast with a current continuous casting machine and has a temperature difference of about 200 to 300 °C immediately after casting. As for the slab, the above temperature difference can be reduced to about 130°C, which can be easily obtained by the recuperation effect of the slab due to the heat retention of the slab, by simply insulating and reheating it in, for example, a transfer route or a heat-insulating pit. In other words, by heat retention and reheating for a short time, a plate having a uniform finish exit temperature in the width direction can be obtained.

It is well known that horizontal roll rolling generally causes a slight increase in the temperature of the rolled material.

This temperature rise occurs because plastic work is applied almost uniformly to the rolled material in the roll axis direction that is rolled down by the horizontal rolls, and the temperature rises almost uniformly in the axial direction.

On the other hand, as shown in FIGS. 4a and 4b, the widthwise ends of the rolled material swell up in the thickness direction due to the widthwise rolling, forming a shape called a dock bone.

The shaded area in FIG. 4 indicates the bulge in the thickness direction of the width direction end portion formed in the slab after width reduction rolling.

Here, FIG. 4a shows the case of etching with a caliber roll, and FIG. 4b shows the case of etching with a flat roll (roll without caliber).

According to the implementation of the width reduction rolling of the present invention, for example, the thickness is 25.
0 When a slab with a width of 1,700 m/m is rolled to a height of 100 m/m, the maximum height hi of the dongbone and the length l from the width end to the maximum height h are 4 in the case of flat roll edging. 5. 5 0m/m. However, with Caliber Roll Edging, it was 30.70 m/m.

Conventionally, since the purpose of width reduction rolling was to adjust the width dimension, technical studies were conducted to prevent the above dogbone from occurring.Generally, when a dogbone occurs, the width returns due to horizontal roll rolling and width dimension adjustment is performed. Therefore, in order to suppress the occurrence of dog bones as much as possible, width rolling is performed using a force river roll.

For example, the Calibur Roll was developed in Japanese Patent Publication No. 47-36619, which eliminates the need to change the dimensions of the mold according to the width of the slab and improves the operating rate of the continuous casting machine. This method is used in rough rolling mills for changing the width of slabs.

On the other hand, as a means of increasing the temperature at the ends of a slab with a temperature distribution as shown in Figure 1, we reconsidered width rolling and found that the plastic work due to engraving increases the temperature only at the ends in the width direction of the casting. When the dogbone formed immediately after this etching is rolled down by horizontal rolls, the energy due to mechanical deformation of the slab is used to increase the temperature only at the widthwise edge where the thickness direction bulge is formed. healed,
It has been found that in slabs having the temperature distribution shown in Figure 1, the end temperature increases extremely efficiently.

Also, this edge temperature increase effect increases as the dogbone formed by flat roll etching, as shown in Figure 4b, is closer to the widthwise edge and is higher. It has also been found that dog bones with a low height and a long extension toward the center in the width direction are less effective because the energy due to mechanical deformation of the material is dispersed in the width direction.

Specifically, the amount of increase in temperature at the end of the slab when the same amount of width cutting is performed separately with a flat roll and a caliber roll, and the same amount of width reduction is performed immediately after each, is as follows: It was more than twice that of 1.

In other words, the caliber roll requires about twice the amount of width reduction than the flat roll method to obtain the same temperature raising effect, and this increases the amount of width reduction, leading to an increase in fish tails at the leading and trailing ends, and the rolling yield decreases.

This also means that the slab needs to be considerably wider than the width of the product plate.

Regarding the difference in the temperature increase effect between the flat roll method and the caliber roll method, the plastic work due to etching is carried out by the temperature increase only at the width direction edge, and the temperature increase
In addition to introducing the item of the maximum dog bone height position l into the quantity calculation formula, the maximum dog bone height h is also added to the calculation formula for the temperature rise at the widthwise end due to plastic work in the dog bone rolling pass.
By introducing the following items, we were able to find the following empirical temperature rise calculation formula that closely matches the actual results.

Now, for example, as shown in FIG. 5A, assuming that a pair of vertical rolls are performing width-cut rolling, the plastic work dw due to the etching at a very small amount ΔX in the rolling direction is as follows.

However, pm is the average rolling pressure, and H is the plate thickness.

The temperature increase Δθ due to this plastic work can be determined as follows, where C is the specific heat, r is the specific weight, a is the range of influence of the work, and A is the heat equivalent of the work.

Since this holds true, if we transform this, the temperature rise △θ will be calculated as follows: α in equation (1) is the ratio of the width b to the area of influence of work a, but the following α is used instead of this α. The actual temperature rise value was more consistent with the actual temperature rise value.

However, l is the highest height position of the dogbone, ΔB is the width reduction amount, and ΔB' is the width return amount.

Therefore, the amount of temperature increase △θ1 due to etching is becomes.

On the other hand, the temperature-L increase value △θ2 due to the dogbone reduction pass is However, α2 is It is.

The present invention was made based on the above knowledge, and it is found that when using a caliber roll, the effect of increasing the temperature at the edge by the same amount of width reduction is about 1/2 compared to using a flat roll, and the same amount of temperature increase can be achieved. If this is attempted, the amount of width loss will increase, the fish tail will be large, and the yield will be poor. Therefore, instead of using caliber rolls, in the present invention, we actively use flat rolls that form inconvenient dog bones when etching for the purpose of adjusting the width. The dogbone is formed very close to the end of the slab (i.e., the length l is made small) and high (
In other words, the height h is increased), and the mechanical deformation energy due to etching and the mechanical deformation energy of the dogbone due to the subsequent horizontal roll rolling are concentrated at the ends, effectively raising the temperature of the width direction ends where the temperature is lowest. This is to make the temperature in the widthwise direction of the slab uniform.

At this time, the temperature uniformity in the width direction is at the same level as before rough rolling of ordinary reheated material, that is, the temperature difference between the edges and the center is 1
The aim is to achieve a temperature of around 0°C.

The direct hot rolling method for continuously cast slabs of the present invention will be described below with reference to Examples.

A slab with a thickness of 250 m/m and a width of 1700 m/m was cast using a continuous casting machine, and the temperature distribution in the width direction shown in Fig. 2a was obtained as the temperature distribution immediately after casting.

Place this in a heat insulating device and keep it insulated from the surroundings for 30 minutes.
The temperature distribution after reheating is as shown in Figure 2b, and the temperature difference between the widthwise edges and the center, which was 220℃ immediately after casting, was 130℃.
has decreased to ℃.

In this state, the flat roll edger of the rough rolling mill is used to edge by an effective width reduction amount of 50 mm, and then the dogbone is rolled down by the horizontal roll (horizontal reduction amount is 10 m).
m) a series of passes (vertical roll-horizontal roll pass),
FIG. 3 shows the temperature distribution in the width direction of the slab after each pass when three passes were performed.

Figure 3 a, b, c, and d show the temperature distribution in the width direction before rolling, the temperature distribution after carrying out one pass of the above series, the temperature distribution after carrying out 2 passes of the above series, and the temperature distribution after carrying out 3 passes of the above series. The temperature distribution after the pass is shown.

As shown in Fig. 3C, there was also a temperature difference of 45°C between the edges and the center during two-pass rolling, but as shown in Fig. 3D,
Due to the three passes of rolling, the temperature at the edges in the width direction increases significantly,
The temperature difference with the center was 10°C, which was equal to the level of normal reheated material.

When similar rolling was carried out with an edger using caliber rolls, the temperature difference between the width direction edge and the center decreased from 130°C before rolling to 50°C, but compared to 10°C obtained with flat rolls. There was no difference in temperature.

The above series of flat roll edging and horizontal roll rolling was repeated three passes, and the slab with the temperature distribution shown in Fig. 3d was roughly rolled to a thickness of 30mm.
2. Stand finishing tandem rolling mill. When rolled to 5 mm, the end temperature at the outlet was 870°C, and the center temperature was 920°C.
of steel strip.

Note that Ar3 of this rolled material is 870°C. Rough and finish rolling were carried out under the same conditions, and the series of passes using the flat rolls described above was repeated for two passes, with the temperature distribution shown in Figure 3C being 840°C at the ends and 920°C at the center. After the above-mentioned series of passes, the temperature of the slab shown in FIG.

On the other hand, in the slab obtained by repeating the series of passes of 3 passes of caliber roll cutting and horizontal roll reduction using the caliber roll, the temperatures were 830°C at the ends and 920°C at the center.

Furthermore, when the width was removed by 150 mm in just one pass and the dogbone was subsequently rolled down, the temperature difference between the ends and center of the slab was as shown in Figure 3a, indicating that the slab had the pre-rolling temperature distribution. However, the temperature was 40°C for the Flat Roll Edger and 70°C for the Caliber Roll Edger.

In this example, the uniformity is not as high as that of ordinary reheated material, but if the temperature difference in the width direction of the slab supplied during main etching rolling is appropriate, the one-pass flat roll edger method described above can also be adopted. .

In the above example, the effective width reduction amount is 50 mm, and the temperature uniformity effect in the width direction, which is equivalent to that of ordinary reheated material, is obtained with 3 passes. The amount and number of passes are determined by the temperature distribution of the slab just before etching with flat rolls (particularly the temperature difference between the ends and the center, and the average temperature of the entire slab), the Ar3 temperature determined from the slab material, and the etching process. An appropriate value can be determined by taking into consideration the etching ability of the rolling machine, etc.

Further, if necessary, after finishing the rolling to make the temperature uniform in the width direction, the slab can be turned by 90 degrees and width-rolled using horizontal rolls.

Also, one pass is 50mm using the flat roll Edger method.
With the effective width reduction amount shown below, approximately 10 passes are required to obtain a temperature uniformity effect in the width direction to the same level as in Fig. 3d, and the average temperature of the entire slab decreases and the slab This is not preferable because the rolling time required to make the temperature uniform in the width direction increases.

Figure 6 shows a row of hot rolling equipment suitable for carrying out the method of the present invention on slabs supplied from a current continuous casting machine, and the mechanical deformation energy given to the ends of the slab is Since the number of deformations is approximately proportional to the number of deformations, a series of horizontal roll passes immediately after edging with flat rolls is executed to raise the end temperature and equalize the temperature in the width direction. An edging rolling mill 1, a rough rolling mill 2 for thinning and rolling a homogenized slab to a thickness that can be finished and tandem rolled, and a six-stand finishing tandem rolling mill 3 are arranged in this order.

The etching rolling mill 1 is composed of a pair of flat vertical rolls 4 and pairs of horizontal rolls 5 and 6 arranged before and after the pair of rolls 4. In the rolling pass in the direction of the rough rolling mill 2, the pairs of horizontal rolls are 5, the slab is pushed into the pair of vertical rolls 4, and the vertical roll pair 4 performs width-kill rolling, and the slab discharged from the pair of vertical rolls 4 has its dogbone rolled down horizontally by the pair of horizontal rolls 6.

Conversely, in the rolling pass in the direction away from the rough rolling mill 2, the horizontal roll pair 6 becomes the pushing roll, and the horizontal roll pair 5
becomes the roll for rolling down the dogbone.

By arranging the horizontal roll pairs before and after the vertical roll pair in this way, one horizontal roll pair can perform indentation rolling onto the vertical roll pair and a large amount of width loss can be achieved, while the other horizontal roll pair A dogbone formed by a pair of flat vertical rolls is rolled down immediately after being formed.

The rough rolling mill 2 is equipped with a vertical roll 8 in front of a pair of horizontal rolls 7, and the final width dimension adjustment is performed in this vertical roll 8.

In this way, an edging rolling machine dedicated to temperature compensation at the end of the slab,
By separating and arranging the rough rolling mill that mainly performs thickness reduction, the rolling time for compensating the temperature at the end of the slab, the rough rolling time, and the finishing rolling time by the finishing tandem rolling mill 3 can be harmonized very easily. Therefore, it is possible to effectively prevent a decrease in Ton/Hour due to the addition of the slab end temperature compensation rolling pass.

As detailed above, according to the method of the present invention, a steel strip having a uniform temperature in the width direction can be obtained without reheating a high-temperature slab cast by a continuous casting machine.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the temperature distribution in the width direction of a slab immediately after being cast in a continuous casting machine, and Fig. 2 is an explanatory diagram of the temperature distribution in the width direction of a slab used in an example of the present invention, where a is immediately after casting, b is is immediately before the start of rough rolling. Fig. 3 is an explanatory diagram illustrating the transition of temperature distribution during rolling according to the present invention, Fig. 4 is an explanatory diagram of a dog bone, and Fig. 5 is an explanatory diagram illustrating the temperature at the end of the slab due to width reduction rolling and horizontal roll rolling immediately after the rolling. FIG. 6, which is an explanatory diagram of the rise amount calculation formula, is a schematic diagram showing an embodiment of the rolling apparatus row of the present invention. 1... Etzink rolling mill, 2... Rough rolling mill, 3... Finishing tandem rolling mill, 4...
...Vertical roll pair, 5...Horizontal roll pair, 6...
...Horizontal roll pair, 7...Horizontal roll pair,
8... Vertical roll pair.

Claims (1)

[Scope of Claims] 1. In a rolling method in which a high-temperature slab cast in a continuous casting machine is transported to the hot rolling machine entrance equipment and directly hot rolled without being reheated at all, before finishing tandem rolling. Then, a series of passes were carried out in which a dog bone was formed at the edge in the width direction of the slab by width cutting using an edger using a flat roll, and immediately after, the dog bone formed by the width cutting was rolled down using a horizontal roll. 1. A method for direct hot rolling of continuously cast slabs, characterized in that the temperature at the ends in the width direction is increased by rolling, thereby obtaining a plate with uniform inlet and outlet temperatures in the width direction of a finishing tandem rolling mill. 2. An edzink rolling mill for raising the temperature at the end of a slab, which is equipped with a pair of flat-shaped vertical rolls, and a pair of horizontal rolls arranged before and after the pair of rolls at a distance shorter than the length of the slab; A direct hot rolling equipment train for continuously cast slabs consisting of a roughing mill with a pair of shafts arranged and a finishing tandem mill located behind the roughing mill.