JPH035004A - Method for rolling reduction of unsolidified slab - Google Patents

Abstract

PURPOSE:To roll down an unsolidified slab at a high draft by using cross rolls for rolling reduction rolls inclusive of the rolling reduction rolls on the uppermost stream side. CONSTITUTION:The thin slab 8 which is continuously cast by a twin belt caster 3 and has the unsolidified layers remained therein is drawn by pinch rolls 6 and is rolled down by a thickness rolling reduction roll train 5A crossed in the same direction; thereafter, the slab section is molded to a rectangular section by a caliber edger rolls 11 and is drawn out by pinch rolls 6 via a guide roller train 5B. The elongation of the shell by the rolling reduction is decreased in this way and the rolling reduction of the unsolidified slab at the high draft is executed.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to thin cast slabs cast with a thin slab continuous casting machine such as a twin belt caster, and normally fixed mold continuous cast slabs. Regarding the unsolidified slab reduction method in which thickness reduction is performed while the inside is in an unsolidified state, more specifically, it is possible to prevent surface cracking of the slab, suppress the increase in internal cracks, and achieve high reduction rate unsolidified slab reduction. It is about how to achieve this.

(Prior art) Usually, when producing a hot rolled steel strip with a thickness of 1.5 to 5 mm,
First, continuous casting equipment is used to create a mold with a thickness of 200 to 300 mm and a width of 1 mm.
A slab of about 000 to 2QOOmm is produced, and this slab is cut into a length of about 10 m in a continuous casting line. The cut slabs are transported to the hot rolling process, heated to a predetermined temperature (1050 to 1200'C) in a heating furnace, and then subjected to continuous rolling or reverse rolling using several rough rolling mills. , rolled to a thickness of about 30 to 50 mm, and then rolled to a thickness of about 6
A hot-rolled steel strip with a thickness of 1.5 to 5 mm is finished using a continuous finishing mill with ~7 stands.

In addition, in recent years, with the development of continuous casting technology for thin slabs, such as twin belt casters, which is different from normal continuous casting, thin slabs with a thickness (40 to 80 mm) that is a fraction of the conventional thickness can be manufactured. became. As a result, when manufacturing the hot-rolled steel strip mentioned above, the conventional hot-rolling and rough-rolling process is no longer necessary, and the thin slab can be directly supplied to the hot-rolling process, which greatly reduces equipment costs. It brought about an effect.

Furthermore, in order to simplify the finish rolling process, it is necessary to manufacture thinner slabs. However, with the above-mentioned continuous thin slab casting technology, the necessity to change the width limits the hot water supply method, and furthermore, when thin slabs are continuously cast, the surface quality of the slab deteriorates due to this hot water supply method. There was a problem.

Therefore, continuous casting of thin slabs takes advantage of the fact that continuous casting is possible at a higher speed than normal continuous slab casting, and reduces the thickness difference (wedge amount) between the left and right edges, resulting in thinner hot-rolled slabs. A method of manufacturing a material for steel strip has been considered.

For example, as shown in FIG. 3, in a twin belt continuous casting machine (twin held caster) 3, molten metal 7 from a ladle 1 is injected through the tundish 2, and then the twin held caster 3 A rolling device 5 consisting of a rolling roll row 5^ in which horizontal rolls are arranged via a support roll row 4 and a guide roll row 5B is installed on the downstream side of the support roll row 4, and a rolling down device 5 consisting of a rolling roll row 5^ having horizontal rolls arranged therein and a guide roll row 5B is installed, and a thin slab 8 having an unsolidified portion inside is continuously rolled. By rolling it down, it is made into a thin steel strip for hot rolling. This hot rolling steel strip is taken out from the apparatus via pinch rolls 6.

In this method, as shown in FIG.
Even after rolling down with the rolling down roll 10 arranged at A, the unsolidified portion 7
This is a method in which unsolidified slab reduction (hereinafter also simply referred to as "unsolidified reduction") is performed so that . Therefore, the part that is actually rolled down by the rolling roll 10 is only the shell 9A at the width end, as shown in FIG. As shown, it only undergoes bending deformation, and the rolling load and torque during unsolidified rolling are much smaller than in conventional hot rolling.

Therefore, compared to hot rolling equipment that performs rolling after completion of solidification, unsolidified rolling equipment requires much less power, is a small equipment, and is a very inexpensive thickness rolling equipment. For example, the pinch roll 6 installed downstream of the rolling down device 5 can be used with several rolls shown in FIG. By pulling out the slab while performing light rolling, rolling of the unsolidified slab can be carried out.

(Problem B to be solved by the invention) However, when rolling down an unsolidified slab at a high reduction rate using a rolling down device 5 having horizontal rolls arranged as shown in FIG. Shell 9B (Figure 4(a)
) cracks occur in the slab, resulting in deterioration in slab quality or a breakout in which the shell 9B ruptures and the molten steel inside flows out.

Therefore, in reality, the unsolidified reduction is limited to a reduction ratio of about 10%.

Here, the deformation behavior of the slab under the pressure of the unsolidified slab is determined by the fourth method.
This will be explained using Figures (a) to (C).

First, as shown in FIG. 4(a), since there is an unsolidified part 7 inside the unsolidified slab, when this slab is reduced in thickness with the reduction roll 10, the shell at the width end Only 9A is compressively deformed and extends in the longitudinal direction of the slab (the fourth
Figure (b)).

On the other hand, as shown in FIG. 4(C), most of the shells 9B on the upper and lower surfaces of the slab are not compressed and deformed by the reduction roll 10, but are only bent, and are not subjected to elongation deformation in the longitudinal direction of the slab. This is caused by tensile stress in the longitudinal direction of the slab generated in the shell 9B due to the elongation of the shell 9^ at the width end. For this reason, if the rolling reduction rate of the unsolidified slab is increased, the tensile stress generated in the shell 9B on the upper and lower surfaces of the slab increases, and cracks in the width direction occur in the shell 9B at the center of the width.

Therefore, with the rolling down device 5 having horizontal rolls arranged as shown in Fig. 3, it is not possible to achieve a very large rolling reduction due to the occurrence of cracks in the shell 9B on the upper and lower surfaces of the slab. This did not result in a significant effect on the simplification of finishing rolling equipment.

Therefore, it is an object of the present invention to reduce the thickness of a thin slab cast by a continuous thin slab casting machine, without causing cracks on the surface of the slab, especially during unsolidified reduction in which the thickness of the slab is reduced while the inside of the slab is in an unsolidified state. The objective is to provide a method for reducing the unsolidified slab at a high reduction rate while preventing an increase in internal cracks in the slab. The purpose is to provide a method for realizing manufacturing.

(Means for Solving the Problem) Here, the present invention reduces the thickness of a thin slab cast by a continuous thin slab casting machine, for example, before the inside of the slab is completely solidified, and A method for rolling down an unsolidified slab, characterized in that cross rolls are used for the rolling down rolls including at least the most upstream rolling roll in unsolidified slab rolling that leaves an unsolidified layer inside the slab even after completion. .

According to a preferred embodiment of the present invention, the width end portion of the slab after the above-mentioned unsolidified reduction may be subjected to width reduction using a grooved edger roll disposed perpendicularly to the thickness reduction roll.

In addition, from another aspect, the present invention is a method for manufacturing a hot-rolling steel strip made of thin cast slabs, which employs the above-mentioned unsolidified slab rolling method.

(Function) In the unsolidified slab reduction method according to the present invention, each time the unsolidified slab is deformed into a diamond shape using cross rolls, the bending deformation of the shell at the width end is facilitated. It reduces the elongation of the shell in the longitudinal direction of the slab, reduces the tensile stress in the longitudinal direction of the slab that occurs in the upper and lower shells 9B of the slab as shown in Fig. 4, prevents cracks that occur in the upper and lower shells 9B, and This enables unsolidified pressure reduction.

Furthermore, when it is necessary to make the cross-sectional shape of the slab rectangular, after the thickness reduction, the width end portion of the slab is rolled down using a grooved roll edger.

What is called "cross roll" here is a type of normal two-high horizontal rolling mill, in which the upper and lower rolls are mutually moved in the horizontal plane from zero to zero.
They are crossed (skewed) by about 4 degrees. These cross rolls have recently been applied to finishing stands of hot rolling mills to control plate crowns, and in this case, a so-called pair cross rolling mill is known in which the backup roll and work roll of a four-high rolling mill are paired and the upper and lower pairs cross each other. It is being See Journal of the Japan Society for Plasticity Processing, "Plasticity and Processing", Vol. 28, No. 321, pp. 1067-1074.

One of the characteristics of this cross rolling is that shear forces in the width direction of the rolled material act in opposite directions on the upper and lower surfaces of the rolled material, causing the cross section of the rolled material to deform into a diamond shape. Normally, this rhombic deformation is not desirable for rolled materials, so for example, in a row of hot rolling finishing stands, this rhombic deformation can be prevented by sequentially setting the cross direction in the opposite direction for each stand.

Although it is desirable to drive the roll shaft of this cross roll, the effect of generating diamond-shaped deformation can be obtained even if the roll shaft is not driven.

Furthermore, as the cross angle (crossing angle of the upper and lower rolls) increases, the diamond-shaped deformation generation effect increases, but in this case, the upper and lower roll gap profile has a narrow gap at the center of the roll barrel and widens on both sides thereof. This results in a so-called convex crown roll, and if this roll is too large, the cross section of the rolled slab becomes a middle gate (minus crown) in the width direction. As a countermeasure against this problem, the roll may be ground so as to have a concave shape as an initial crown.

Regarding the application position of this cross roll, it is necessary to apply it to at least the thickness reduction roll on the most upstream side. This is because the shell thickness on the most upstream side is thinner and the slab thickness is thicker, so the cross rolls have a greater effect of generating diamond-shaped deformation in the cross section of the slab. There is a great risk that the shell will crack.

Furthermore, it is desirable to apply cross rolls to the downstream roll-down rolls, but even if the rolls are normal parallel rolls, if they have a certain rhombic cross section in the previous stage, this will have the effect of promoting rhombic deformation, so this is not necessarily the case. It doesn't have to be a cross roll.

It is also possible to cast the slab itself in a rhombic shape from the beginning, but in this case, the structure of the casting machine becomes complicated, and it becomes difficult to cool the slab uniformly, resulting in localized uneven cooling. Problems such as cracking and cracking occur.

A grooved edger roll 11 may be used to form the width end portions, thereby making it possible to form the slab into a rectangular cross section.

Embodiment An embodiment of the unsolidified slab rolling down method of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a schematic illustration of equipment for carrying out the method of the present invention. In FIG. 1, the same reference numbers as in FIG. 3 represent the same devices and equipment.

In this embodiment, on the downstream side of the twin belt caster 3, a slab support roll row 4, a thickness reduction roll row 58, a groove edger roll 11, a guide roller row 5B,
A continuous casting line in which pinch rolls 6 are sequentially installed is used to manufacture a hot rolling steel strip.

First, it was continuously cast using twin belt casters 3,
The thin slab 8 that leaves an unsolidified layer inside is pulled out by the pinch rolls 6 and passed through the thickness reduction roll row 5A, which is crossed in the same direction.
After being rolled down, the slab is shaped into a rectangular cross section by a grooved edger roll 11, and is pulled out by a pinch roll 6 through a guide roller row 5B.

Figure 2 shows the deformation of the thin slab 8 in the reduction roll row 5A.
It is shown schematically in a) and (b).

In the figure, the shearing force 1 generated by the cross roll reduction is applied to the upper and lower shells 9B-1 and 9B, as shown by the black arrows.
2, the direction is opposite, and the thin slab 8 is deformed into a diamond shape as a whole. Such deformation may be achieved by arranging cross rolls in opposite directions in order as described above, or by arranging and forming grooved edge rolls into a rectangular shape.

Next, using the apparatus as described above and shown in FIG.
The present invention will be described in detail in the case where unsolidified rolling is performed at a rolling reduction of 40% under the casting conditions shown in the table.

Table 1 2 In this example, the thickness reduction rolls were arranged in three rows (three stands) with rolls having a diameter of 300 mm at a cross angle of 2°. Each roll was ground into a parabolic shape with a diameter of -0.3 mm (middle profile) as an initial roll crown and was not driven. Thickness reduction amount is initial slab thickness 50mm
The slab thickness was 20 mm from 30 mm to the exit side, and the reduction was performed by 5 mm in the first stand and 7.5 mm each in the second and third stands.

Furthermore, at the end of unsolidified rolling, that is, the reduction roll row 5^
The target shell thickness h of the shell 9B on the upper and lower surfaces of the slab at the exit side of
Cooling of the slab was controlled so that s = 13 to 14 mm.

When we measured the elongation in the rolling direction of the center of the width of the slab after rolling the unsolidified slab, that is, the elongation of the shell 9B on the top and bottom surfaces of the slab, we found that the elongation was 0.8% with respect to the length of the slab before unsolidified rolling. Distortion had occurred. Moreover, no particularly problematic surface cracks were observed on the upper and lower surfaces of the slab.

On the other hand, under the same conditions as the unsolidified rolling described above, in the case of normal reduction rolls with the cross angle of the thickness reduction rolls set to 00, the elongation strain of shell 9B on the upper and lower surfaces of the slab is 2°6%, and the strain on the upper and lower surfaces of the slab is Cracks with a maximum depth of 5'mm and a length of about 50mm were observed, confirming the surface cracking prevention effect of the present invention.

The effect of preventing surface cracking according to the present invention described above will be explained with reference to FIG. 2. As described above, cracks on the upper and lower surfaces of the unsolidified slab during rolling down occur due to tensile stress acting on the upper and lower shells 9B due to elongation in the longitudinal direction of the slab due to rolling down of the shell 9 at the width end. Therefore, by reducing the elongation of the shell 9^ due to rolling, the tensile stress acting on the shell 9B can be reduced and cracking can be prevented. In the present invention, as shown in FIGS. 2(a) and 2(b), cross-roll rolling causes opposite width direction shearing forces to act on the front and back surfaces, so that the cross section after rolling is deformed into a diamond shape, and the shell 9A is simply It is only bent, with almost no elongation in the length direction. In particular, this effect becomes more pronounced as the shell thickness becomes thinner.

Therefore, compared to the conventional unsolidified slab reduction method,
The longitudinal elongation of the slab into the shell 9 due to thickness reduction is reduced, and cracking can be prevented.

For example, when the thickness reduction progresses only by bending deformation of the shell 9A, the elongation of the shell box becomes O, and cracking of the shell 9B can be prevented.

(Effects of the Invention) As explained above, the unsolidified slab rolling down method according to the present invention can reduce elongation due to shell rolling. Therefore, it is possible to realize unsolidified slab reduction with a higher reduction rate than in the conventional unsolidified cast slab rolling down method.

The unsolidified slab rolling method of the present invention can also be applied to unsolidified rolling of relatively thick slabs cast with a conventional fixed mold continuous casting machine.

According to the unsolidified slab rolling method of the present invention, rolling at a high rolling reduction rate is possible, so the hot rolling process can be simplified and inexpensive hot rolled steel strips can be manufactured.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of equipment implementing the unsolidified slab rolling down method according to the present invention; Figures 2 (a) and (b) are explanatory diagrams of the unsolidified slab rolling down method of the present invention: Figure 3 is a schematic explanatory diagram of equipment for carrying out the conventional unsolidified slab rolling method; and Figures 4 (a), [Yes]) and (C) respectively show the causes of cracking during unsolidified slab rolling. It is an explanatory diagram. 1: Ladle 2: Kundish 3: Twin
Belt caster 4: Slab support roll row 5: Unsolidified reduction device 5A: Thickness reduction roll row 5B guide roller row 6:
Pinch roller 7: Molten metal

Claims (2)

[Claims] (1) In an unsolidified slab reduction method in which thickness reduction is performed on a slab cast by a continuous casting machine before the inside of the slab completes solidification, and an unsolidified layer remains inside the slab even after the rolling is completed, A method for rolling down an unsolidified slab, characterized in that cross rolls are used for the rolling down rolls including at least the most upstream rolling roll. (2) Width reduction is carried out using a slotted roll edger arranged perpendicularly to the thickness reduction roll at the width end of the slab after the unsolidified slab is rolled down using cross rolls.
The unsolidified slab reduction method described.