JPS59113964A - Continuous casting method - Google Patents

Abstract

PURPOSE:To produce a high-temp. defectless billet which can be immediately hot-rolled without passing the billet through a heating stage by making the surface temp. of the shell in the stage of straightening the billet lower on the top of bending than the bottom and making the shell on the short side higher than the top. CONSTITUTION:The shell surface temp. on the top side where tensile stress is generated is made lower than the shell surface temp. on the bottom side where compressive stress is generated to relieve the tensile stress of the top shell and to join the top and bottom shells in the stage of straightening of an unsolidified billet in a multipoint straightening and curving type continuous casting machine having a low machine height. The surface temp. of the shell on the short side where stress is transmitted is made higher than the surface temp. on the top shell to induce positively the shearing deformation of the shell on the short side and to accelerate further the relieving of the above-mentioned tensile strain, whereby the generation of internal crack is prevented and the defectless billet is obtd. The straightening started and completed by the above-mentioned method and further the high temp. defectless billet is handed over to a hot rolling stage with the recuperation of the unsolidified molten steel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a continuous casting method for casting high-temperature defect-free slabs necessary for a process in which a hot rolling mill and a continuous casting machine are directly connected without going through a heating process in the steel manufacturing process. It is about the method.

In recent years, continuous casting machines (hereinafter referred to as continuous casting machines) have been used in the steel industry.
The development of continuous casting machines has been remarkable, but on the other hand, the demands on continuous casting machines are also extremely large. Among these, the demand for energy conservation due to the recent rise in energy prices is significant. Especially in the continuous casting-rolling process, there is a particularly great need for energy saving by directly connecting the continuous casting machine and rolling equipment.

In the steel industry, the conventional continuous casting-rolling process can be roughly divided into three types shown in Figure 13 (al, (bl, (C1)).
Divided into processes. The process shown in Figure 13 la) has been widely practiced in the steel industry for some time. In addition, the hot charging process shown in Figure 13 (bl 5-) has been gradually put into practical use in the steel industry in recent years due to its remarkable energy saving properties.However, in the direct rolling process shown in Figure 13 (C1), the heating process Not only does this eliminate the need for energy, but also there is no need to install heating equipment, so its benefits are great, and its development is eagerly awaited.

In the direct rolling process shown in Figure 13 (C1), the continuous caster is required to have high productivity (high-speed casting), and the slabs cast by the continuous caster are defect-free, and furthermore, the continuous caster has no defects. A high temperature is an essential condition.

On the other hand, continuous casting machines can be roughly divided into vertical types, curved types, curved types with a vertical section, and horizontal types. The currently mainstream type and most commonly used is the curved continuous casting machine.

This curved continuous casting machine has a curved mold 1 as shown in Fig. 1.
The curved slab 2 that comes out of is guided into an arc shape by rolls 3,
The roll 4 straightens the bend.

It is used for casting.

6- In order to increase productivity (casting efficiency) with this curved continuous casting machine, it is necessary to increase the casting speed. The presence of a solidified phase is inevitable.

In addition, in order to obtain high-temperature slabs, the conditions for secondary cooling by injecting water into the slab from directly below the mold to at least the bending straightening point are slow cooling, and the water injection is completed immediately after the bending straightening completion point, so that the It is necessary to solidify and reheat.

Furthermore, the machine height of a curved continuous casting machine is restricted by the radius of curvature. When the machine height is high, the static pressure of molten steel increases. When the static pressure of molten steel increases, the amount of bulging of the slab increases, which causes internal cracking of the slab.

The arc radius R of this curved continuous casting machine is 3 to 13 m.
There are various types within this range, each with their own advantages and disadvantages. That is, when the arc radius R is increased, the machine height H becomes higher,
Due to the high static pressure of the molten steel, the amount of bulging between the rolls 3.3 becomes large, and when this bulging is corrected by the rolls 3, tensile strain is generated at the solidification interface, causing internal cracks.

Therefore, it is necessary to increase the cooling intensity in the secondary cooling zone or to use split rolls to reduce the roll pitch. However, if the cooling strength is increased, internal cracks can be prevented, but unsolidified bending cannot be straightened, and a high-temperature slab that can be used in the direct rolling process cannot be obtained. On the other hand, theoretically it is possible to obtain high-temperature slabs without internal cracks by using multi-segmented rolls and reducing the roll pitch, but in reality, there are problems with the maintenance of slab guide rolls, resulting in stable slabs. It is impossible to obtain high-temperature defect-free slabs.

For example, conventional technical measures taken to prevent internal cracks from occurring in slabs obtained by continuous casting include:
From the viewpoint of reducing bulging strain and corrective strain, measures have been taken to make the pitch of rolls that support and guide the slab after the mold denser to reduce the amount of bulging, thereby reducing bulging strain. In addition, the cooling in the secondary cooling zone is performed as strong cooling (water injection ratio of 1.0 to 9 or more) in order to improve the hot strength of the solidified shell.

Currently, in most continuous casting machines using curved continuous casting machines, unsolidified bend straightening is performed, for example, arc radius R: 10 to 13 m, casting speed: 0.7 to 2. c)
Continuous casting is carried out with specifications such as m7m, dense roll arrangement, and spray cooling. When molten steel is cast with a curved continuous casting machine having these general specifications, the bending straightening point will be located 15.7 to 20.4 m from the meniscus position. At this time, the surface temperature of the slab at the bend straightening point was 70
The temperature is 0~900℃, and the solidified shell thickness is about 80~120 m.
m (estimated). By the way, the cross-sectional dimension of the slab is 250.
When the width of the slab is 1800 mm, 70 to 90% of the slab thickness is occupied by the solidified shell. If the slab is bent and straightened in this state, internal cracks will occur even under today's advanced technology.

On the other hand, if the arc radius R is made smaller, the machine height H will be lowered,
The static pressure of the molten steel is reduced, the load on the rolls supporting the slab is reduced, the roll diameter is reduced, and the roll pitch can be made smaller compared to Takatsuki's continuous casting machine with a large arc radius R. This makes it possible to reduce the amount of bulging between rolls. Therefore, high speed, slow cooling,
This method is more suitable for obtaining high-temperature slabs through unsolidified straightening and reheating when comprehensively judged by taking into consideration the maintainability of the slab support guide rolls, equipment costs, etc.

However, at the stage of straightening the unsolidified slab, the tensile strain of the shell inside the arc increases. That is, the second
As shown in the figure, when the shell 8 has an unsolidified phase 6 and undergoes bending straightening during casting in the direction of the arrow 10, the shell 8 having a shorter length with respect to the neutral axis 7 of bending is the shell 9 having a longer length. This bending correction strain occurs as a result of compressive deformation, and the smaller the radius of the arc, the larger this bending correction strain becomes.

Methods for alleviating this correction distortion include: ① Using multiple correction points to disperse the correction distortion; and ③ Installing a drive roll in the area before the correction point (or correction band in the case of multi-point correction). There is a method using so-called compression casting in which the tensile strain generated in the upper shell is offset or alleviated by pushing the solidified shell and applying a braking force by a group of drive rolls after the straightening point (or straightening zone).

However, in a multi-point straightening curved continuous casting machine that uses multiple straightening points and disperses straightening molds, there is a limit to the length of the multi-point straightening band, and as a result, there is a limit to the number of straightening points. That is, in a multi-point straightening curved continuous casting machine, the straightening type εn associated with the n-th straightening is expressed by the following equation.

In the above formula, D: slab thickness, S: shell thickness, Rn-1p
The arc radius before the nth correction point, Rn; The arc radius after the nth correction point.

Here, to simplify the explanation, it will be considered that one correction is performed from the reference arc Ro from the mold. In Figure 3, point A
Considering the case of bending back from Ro to R+ (>Ro) at point B, point A is closer to the mold, that is, when the angle θ with the horizontal is smaller, the machine height after final straightening is lower. H is Δ
Only H becomes higher.

In actual cases, there will be multiple points (two or more), but the phenomenon is the same: the closer you start straightening to the mold, the higher the machine height becomes, making it more difficult to reduce the amount of bulging, resulting in bulging distortion. As is clear from the above distortion equation, there is also an influence of the shell thickness S, and the larger the shell thickness S, the smaller the correction mold becomes. Therefore, from the viewpoint of preventing internal cracks due to bulging distortion and reduction of the correction die, it is desirable to carry out correction from a point where the angle θ is as large as possible.

On the other hand, as a matter of course, the angle θ is smaller than 9o0, so the length of the straightening band is determined once the reference arc R8 and the height H of the continuous casting machine are determined, and once the roll diameter that supports static pressure is determined, the length of the straightening band is determined. The number of rolls that can be incorporated into the correction band is determined, and the number of correction points is also determined. In other words, as the arc radius R of the curved continuous casting machine becomes smaller, the number of correction points cannot be increased, even though the number of correction molds increases.
For example, a curved continuous casting machine with a machine height of about 3.5 m requires about 15 points of straightening at most.

However, such a number of correction points can only be obtained by controlling the roll position on the order of Q, l mm, and can only be considered on design drawings. In actual cases, there is a deviation from the reference position of roll alignment, and even if the best technology is used and strict management is carried out, a misroll alignment amount of Q, 5 am or less is unavoidable. Therefore, the number of effective straightening points is significantly reduced. For example, as described later, although the standard arc radius is 3 m and the number of straightening points is 15, the slab thickness is 250 mm and the casting speed is 1.5 m/m.
, A slab without internal cracks could not be obtained under the casting conditions of water injection ratio of 0, 5 liters and 7 kg. In addition, when the standard arc radius is made larger, the length of the straightening belt and the number of straightening points can be increased if the machine height is ignored, but as mentioned above, the degree of increase in the machine height is greater than when the standard arc radius is small. , the machine height increases, making it impossible to create a curved continuous casting machine with a low machine height.

By the way, according to the study results described later by the present inventors, it is possible to perform a direct rolling process, that is, direct rolling, as described later.
And assuming high productivity, the average temperature of the slab cross section at the end of the continuous casting machine needs to be about 118013-℃ or higher, and calculated from the current roll support mechanism, the standard arc radius of the continuous casting machine 6m or less, machine height 6
．． It was found that a distance of 5 m or less is desirable.

On the other hand, regarding the minimum machine height, if we are to obtain high-quality slabs using the current curved continuous slab casting machine, immersion type powder casting is a prerequisite. Radius RO is 250
For ynyn thick slabs, the length must be 3.0m or more,
Therefore, the machine height H (≧RO) is 3.0 m or more.

The above-described compression casting also has the following problems when applied to a small arc, multi-point straightening, low machine height curved continuous casting machine (hereinafter abbreviated as a low-head continuous casting machine).

Figure 4 shows the profiles of a low-head continuous casting machine and a large-arc, single-point straightening, high-machine, high-curve continuous casting machine (hereinafter referred to as the "high-head continuous casting machine").

A indicates an area in which a driving roll cannot be installed, B indicates an area in which a pushing drive roll can be installed, C indicates a horizontal brake zone, D indicates a multi-point correction zone, and E indicates a correction point. In other words, with the low head continuous casting machine 14-1, as shown in Fig. 4, the drive generation band B of the single circular arc portion to generate the required compressive force in the straightening band cannot be sufficiently secured, and the drive force generation area B is not large enough. Since the static pressure is smaller than that of the I-head continuous casting machine, the driving force generated per driving force roll is small, and a sufficient correction strain relaxation effect cannot be obtained.

Fact-based arc radius 5mR, compression casting with 15 points correction (c
As shown in Fig. 5, the distortion at the rear stage of the orthodontic belt was reduced by using the method (with PC), but the distortion at the front stage of the orthodontic belt could not be reduced.
Compression casting was carried out under the conditions of slab thickness 250 mm, casting speed 1, and 57717 m, but it was not possible to completely eliminate internal cracks. The total strain on the vertical axis in FIG. 5 is the total strain of corrective strain, bulging strain, and misroll strain.

As mentioned above, it is possible to obtain high-temperature slabs without internal cracks that enable the direct rolling process by continuous casting using a low-head continuous caster or by compression casting using a low-head continuous caster. Moreover, as mentioned above, in high-head continuous casting machines, there is no internal cracking to realize the direct rolling process due to the distortion caused by bulging between the rolls, and high-temperature slabs cannot be obtained. , it is necessary to try to alleviate the correction distortion by new technical means.

The present invention promotes relaxation of tensile strain in the upper shell by adjusting the temperatures of the upper and lower shells of the slab and the short side shells during straightening, thereby obtaining a slab without internal cracks.

Conventionally, it has been proposed in Japanese Patent Application Laid-Open No. 52-52126 to increase the shell strength, reduce the amount of tensile strain, and prevent internal cracks due to bending straightening by lowering the temperature of the upper shell than that of the lower shell during straightening. No. Publication, JP-A-55-5
115, etc., but as shown in the examples of these publications, the arc radius is 10.5 m, and it is a one-point straightening type I-head continuous casting machine, and as described later, the standard arc radius is 3. ~6m, multi-point straightening type low head continuous casting machine with a machine height of 6.5m or less, the inner shell surface temperature of the arc is 8.
It was not possible to prevent internal cracks only by setting the arc outer shell surface temperature to 50° C. and 1000111:.

That is, in the case of a low-head continuous casting machine, it has been found that internal cracks occur only under the condition of a temperature difference between the inner arc and the outer shell.

The present invention analyzes the behavior of the short side that connects the top shell and the bottom shell and transmits stress due to straightening, and by making the temperature of the short side shell higher than the temperature of the top shell, This was based on the new knowledge that it is possible to actively cause shear deformation of the short side shell, thereby alleviating the tensile strain of the top shell.

The gist of the invention is as follows.

(1) In a continuous casting method for bending and straightening a curved slab having an unsolidified phase using a multi-point straightening curved continuous casting machine with a low machine height,
When straightening the bend of an unsolidified slab, the surface temperature of the shell on the side where tensile stress occurs is lower than the surface temperature of the shell on the side where compressive stress occurs, and the surface temperature of the short side shell is lowered to lower the surface temperature of the shell on the side where tensile stress occurs. A continuous casting method characterized by starting and completing bend straightening at a temperature higher than the surface temperature.

17- (2) In a continuous casting method for bending and straightening a curved slab having an unsolidified phase using a multi-point straightening curved continuous casting machine with a low machine height,
When straightening the bend of an unsolidified slab, the surface temperature of the shell on the side where tensile stress is generated is lower than the surface temperature of the shell on the side where compressive stress is generated, and the surface temperature of the short side shell is lower than the surface temperature of the shell on the side where tensile stress is generated. A continuous casting method characterized in that bending straightening is started by raising the temperature to a higher level, the bending straightening is completed, and unsolidified heat is recuperated.

(3) In a continuous casting method of bending and straightening a curved slab having an unsolidified phase at a high casting speed of 1.5 m/min or more using a multi-point straightening curved continuous casting machine with a machine height of 6.5 m or less, Surface temperature TL of the (top) shell on the (inner) side where tensile stress occurs during bending straightening of a slab having an unsolidified phase; Surface temperature TF of the (bottom) shell on the (outside) side where compressive stress occurs
, the following (1) between the surface temperature 'rsO of the short side shell,
(2), (3), (4) maintain the relationships of equations, start the bending straightening, complete the bending straightening, and set the surface temperatures TL and TF at the point of completion of straightening to 800°C or higher to recover the unsolidified state. 18. The continuous casting method according to claim 1, further comprising: heating.

1000℃≧TL≧700℃ (1
)Tp (= Tt, +ΔT)41100℃...
...(2) 1100℃-'pt)ΔT≧60℃+,
('rL-soo℃) ・・・・・・(3) 1100℃
+-'(Tt-800℃))Ts≧1000℃+L(T
L-800℃) 3 ...... (4) (4) Unsolidified under a high-speed casting speed of 1.5 m/m or more in a multi-point straightening curved continuous casting machine with a machine height of 6.5 m or less In a continuous casting method for bending and straightening a curved slab having an unsolidified phase, the surface temperature TL of the shell on the side (inside) where tensile stress occurs (inside) (top surface), the side where compressive stress occurs ( Below (]) , (2)
, (3) and (4), start and complete the bending straightening while maintaining the relationships in equations (4), and set the surface temperatures TL and TF at the straightening completion point to 800°C or higher, and perform unsolidified reheating. A continuous casting method according to claim 1, characterized in that:

1000℃≧TL≧700℃ ・・・・・・(
1) Tp (= Tt, +Δ'i') 41100°C
・・・・・・(2) 200℃＋±('rL-soo℃
) ≧ ΔT) 60°C 10-! -(TL-800℃)5 ・・・・・・(3) 1100℃10-M(TL-800℃)4TS≧1000
℃+-u (TL-soo℃) 3 ...... (4) (5) Multi-point straightening curved continuous casting machine with a machine height of 6.5 m or less under high-speed casting speed of 1, 5 yl 7 ml or more. In a continuous casting method for bending and straightening a curved slab having an unsolidified phase, the surface temperature TL of the (top) shell on the side (inner side) where tensile stress occurs during bending straightening of the slab having an unsolidified phase,
Below (1) between the surface temperature TF of the (lower surface) shell on the side where compressive stress occurs (outside) and the surface temperature 'rsO of the shorter side shell.
, (2), (3), and (4), the bending straightening is started, the bending straightening is completed, and the surface temperatures TL and TF at the point where the straightening is completed are set to 800°C or higher, and the unsolidified state is maintained. The continuous casting method according to claim 1, characterized in that heat is recuperated.

1000℃≧TL≧880℃・・・・・・(1
)Tp (= Tt+ΔT)41100℃...
...(2) 1100℃back L)ΔT≧60℃+-! −
(TL-800℃) ・・・・・・(3) 1100℃+
-'(Tt-soo℃)≧'r5≧1000℃+-'(
Tt, -800°C) 3 (4) The continuous casting method of the present invention will be explained in detail below. First, the principle of relaxation of tensile strain in the top shell due to the temperature of the short side shell will be explained.

Although the short side 14 shown in Fig. 6 maintains the balance of stress on the upper and lower surfaces, it has traditionally been viewed as merely transmitting stress, and bending correction has been understood in a one-dimensional manner. . However, as shown in FIG. 6, when looking at the bending straightening three-dimensionally, the casting is performed in the direction of the arrow 11, and when straightening is performed at this point, a tensile stress indicated by 15.15' acts on the upper shell 12. 21- A compressive stress indicated by 16.16' acts on the lower shell 13, but at this time, the upper shell has a stress of 17°17
A deformation that attempts to narrow the width of the upper shell 120, indicated by 18°, and a deformation that attempts to widen the width of the lower shell 13, indicated by 18°18', occur. In this case, it is the short sides that may inhibit this deformation. That is, on the short side,
As a result, as shown in Fig. 7, shear deformation in the casting direction shown at 19.19' and shear deformation in the width direction shown at 20.20' occur, but the temperature of the short side shell is higher than that of the upper surface shell. If the stiffness is lower than that of the lower shell, the shell stiffness increases and this deformation becomes difficult to occur. The resulting tensions are shown at 15.15' and 1.6, 16'' in FIG.

The compressive stress increases and cracks occur due to tensile strain based on the tensile stress on the upper surface side.

In the present invention, taking the above phenomenon into consideration, we take a cooling difference between the upper and lower surfaces, and raise the temperature of the short side shell more than that of the upper shell.
By generating the shear deformation shown at 20' with a smaller stress, the tensile stress at 15.15' in Figure 6 can be reduced, making it possible to obtain a high-temperature slab without internal cracks. It is.

Because the short side is generally cooled in two directions (thickness direction and width direction) due to its shape, the temperature of the short side shell is generally lower and its rigidity is greater than that of the other upper and lower shells. This makes it difficult for shear deformation to occur.

In the present invention, the temperature of the short side is increased to promote shearing deformation in a plane parallel to the slab surface, and various methods can be considered for increasing the temperature of the short side. For example, if a drain plate is installed at a width slightly narrower than the slab width, an air curtain is installed, or multiple nozzles are installed in the width direction, the nozzle at the end of the slab is cooled according to the width of the slab. Examples include methods for draining water.

The present invention will be explained in more detail with reference to Examples.

The basic arc is 3m and the section from 3m below the meniscus to 7m (4
In a continuous casting machine with a machine height of 3.5 m that performs continuous multi-point correction at 15 points in a section (m section), a draining plate 21 as shown in FIG.
Steel type: medium-coal Al! -8t killed steel, slab size, 250mm thickness x 1500mm width, casting speed; 1
．． 5 m/min, water injection ratio: 0.3 to 0.5137 to 9
Casting was carried out under these conditions and the occurrence of internal cracks was investigated.

Figure 9 (al, (bl) shows the surface temperature of the upper surface (inner surface, 5th surface) of the slab on the straightened side and the upper and lower surfaces (inner surface).

The figures are organized and illustrated according to the surface temperature difference (outer surface, L/2 surface). Further, FIG. 10 shows the relationship between the surface temperature of the upper surface (inner surface, 5th surface) and the surface temperature of the shorter side of the slab on the straightening borrowing side at that time, using the presence or absence of a drain plate as a parameter.

Now, the surface temperature of the upper surface (inner surface, 5th surface) of the slab on the side where the straightening belt is entered is T.
L, lower surface (outer surface, 2nd surface) surface temperature TF, upper, lower (inner,
The surface temperature difference (outer surface, L, 2 surfaces) is expressed as ΔT (-Tp Tt,
), when a drain plate is installed, the surface temperature difference conditions on the straightening borrow side to obtain slabs without internal cracks are 700°C M Tt, l-1100°C from Fig. 9.

In the range of TF≦1100°C, the following is true.

700℃4Tt! x1oo°C TF≦1100°C ΔT = TF −'rL ΔT≧60°C 10°C (Tt −soo°C) In addition, when no draining board is installed, the following will occur.

700℃≦TL41100℃ TF〈1100℃ ΔT = TF −TL ΔT≧200℃＋” (Tt −800℃) The maximum values of the surface temperature TF and TL on the straightening side are determined to prevent the occurrence of internal cracks due to bulging between the rolls. It is determined from this point of view, and on the correction borrowing side, it is necessary to keep the temperature below about 1100 degrees Celsius.

In addition, the minimum value of the surface temperature Tp + TL on the straightening borrow side is:
The slab rolling temperature required in the rolling process in the direct rolling process, which is determined by this rolling temperature. It is determined by the surface temperature of the slab at the strip exit side), the cooling conditions in the straightening zone (whether or not the slab is recuperated, the amount of recuperation if it is the amount of recuperation, and the amount of cooling if there is no recuperation).
As will be described later, when the required machine end temperature is 1180° C., for example, without straightening zone reheating, it is necessary to raise the temperature at the straightening borrowing side to 800° C. + straightening zone straightening temperature C. or higher.

On the other hand, as shown in Fig. 10, the short side surface temperature Ts at the straightening start point (straightening borrowing side) changes greatly depending on whether or not a drain plate is installed. 100~ than the surface temperature TL of the inner surface, 5th surface)
The temperature will rise by 300℃, whereas if it is not installed, the temperature will rise by 10℃.
The temperature decreases by about 0 to 250°C.

In detail, if the surface temperature of the upper surface (inner side, L side) of the slab on the straightening side is TL, and the short side surface temperature is Ts, then when a drain plate is installed, there is a difference between the surface temperature TL and the surface temperature TS. ,
From Figure 10, 700℃4TL≦1100℃, TF≦1
In the range of 100°C, the following relationship holds true.

26- 1000℃+S (Tt, -800℃)〈TS≦1100
°C tenth ('rL-soo °C)3'r3 min = 1000 °C ten-(Tt, -80
0℃)TS max =1100℃+-(Tt, -s
oo℃)Ts min';;='r5=TS
maxAlso, if no draining board is installed, the following relationship will apply.

600℃+'-(Tt-800℃) 4'l"s≦7
00℃+100(TL-800℃) Ts min = 60
0°C ten heat (TL800°C) Ts max = 700°C
+-'(TL-800℃)TSmin≦TS4TS
From Figures 9 and 10, the short side shell is strongly cooled without installing a drain plate, and the short side shell temperature on the straightening side is lowered than the upper surface (inner surface, L surface) surface temperature.

In other words, on the straightening borrow side, the short side surface temperature Ts is the upper surface (inner surface, L surface) surface temperature Tt (700℃4TL≦1100
℃) to 600℃ 1,000 (TL-800℃)≦TS≦
If the relationship is 700°C ten mutually (TL - 800°C), the temperature difference conditions for the upper and lower surfaces (inner, outer, L, F surfaces) on the straightening borrow side will be necessary to obtain defect-free slabs without internal cracks. is ΔT≧200℃+−7−(TL−800℃), and on the other hand, the upper surface (inner surface, L surface) surface temperature TL is 700℃≦TL.
≦1100℃, lower surface (outer surface, F surface) surface temperature TF is T
Since F≦1100℃ and ΔT-TF TL, the upper surface (inner surface, L
Surface) The surface temperature TL is in the range of 700°C≦TL4880°C.

The temperature difference conditions and upper surface (inner surface, L surface) temperature conditions are 11
00℃-TL≧ΔT≧200℃+, (TL-800℃)
.

700°C≦TL≦880°C, and the condition is limited to a narrow range of conditions surrounded by points A-B-C shown in FIG. 9 (bl).

On the other hand, as shown in Figures 9 and 10, a drain plate is installed to slowly cool the short side shell and raise the short side shell temperature on the straightening side to be higher than the upper surface (inner surface, L side) shell temperature. On the side, the short side surface temperature TS is changed from the top surface (inner surface, L surface) surface temperature TL (700℃≦Tt, <Ts!1100℃+a
(Tt soo℃), the temperature difference condition for the upper and lower surfaces (inner, outer, L, F surfaces) on the straightening borrow side to obtain a defect-free slab without internal cracks is ΔT≧60℃
+100 (TL - 800℃), while the surface temperature TL of the upper surface (inner surface, L surface) is 700℃4TL≦1100℃, and the lower surface (
Since the surface temperature TF (outer surface, F surface) is restricted to TF≦1100°C and ΔT=TF−TL, the upper surface (inner surface, L surface) satisfies the above temperature difference condition and each surface temperature condition above.
The surface temperature TL is in the range of 700°C to 41000°C.

That is, the above temperature difference conditions and upper surface temperature conditions on the straightening borrow side to obtain a defect-free slab without internal cracks are as follows:
00℃-TL≧ΔT≧60℃1100 (Tt-SOO℃),
700℃4Tt 41ooo℃, Figure 9 (bl
The condition is expanded to a wide range of conditions surrounded by points A-D-E shown in FIG.

Furthermore, from Figures 9 and 10, a drain plate is installed and the short side shell is slowly cooled to raise the short side shell temperature higher than the upper surface (inner surface, L surface) surface temperature. The side surface temperature Ts is the upper surface (inner surface, L surface) surface temperature TL (700
℃〈TL61100℃), 1000℃ 10' (T
l-800℃)4Ts! 1100℃ 10” (TL-800
℃) By maintaining the relationship of 3, the short side shell is strongly cooled without installing a drain plate, and the short side shell temperature is adjusted to the upper surface (inner surface, L surface).
In other words, the short side surface temperature Ts on the straightening side is lower than the surface temperature.

L side) 600℃100 (Tt, -
800℃) 4'ps! 7 Q Q℃10” (T
t - 800℃), the minimum required temperature difference ΔT (2 Tp - Tt
), TL=('rL-soo℃) to ΔT-60
The temperature can be reduced to 10" (Ti, -800°C).

For example, the upper surface (inner surface, L surface) under the implementation conditions in which slabs without internal cracks could be obtained without installing a drain plate.
At the minimum surface temperature TL of 700°C, 30-ΔT is changed from 175°C to 40°C, and at the maximum value of 880°C, it is 22
It can be reduced from 0°C to 76°C. Also, temperature TL = 800℃
In this case, ΔT can be reduced from 200°C to 60°C. This shows that by maintaining the short side shell temperature higher than the top shell temperature on the straightening side, the tensile strain generated in the top shell can be effectively alleviated.

As described above, by slowly cooling the short side shell with the drain plate and raising the short side shell temperature higher than the top shell temperature on the straightening borrowing side, the gap between the upper surface (inner surface, L surface) and the lower surface (outer surface, 2nd surface) It is possible to reduce the temperature difference between the two, absorb operational variations, and stably ensure defect-free slabs. For example, if a drain plate is not installed, and the maximum surface temperature of the upper surface (inner surface, L surface) that can be taken to obtain a high-temperature slab is 880°C, the lower surface temperature Tp = 1100°C, and the temperature difference ΔT = 220°C.
The occurrence of internal cracks cannot be prevented unless the temperature is maintained. For example, if Tp exceeds 1100°C during operation, or if TL exceeds 880°C and the temperature difference ΔT becomes 220°C or less, internal cracks will occur.

On the other hand, when a drain plate is installed, if TL - 880℃ is constant, TF is 1100 to 956℃ (ΔT = 220 to 76℃
) Defect-free cast slabs without internal cracks can be obtained even if variations occur within the range. For example, TL is 700 to 900℃ (
Or, even if variations occur in the range of 800 to 900°C) and variations in ΔT occur in the range of 80 to 175°C (or 60 to 200°C), defect-free slabs can be reliably obtained.

Furthermore, as described above, by slowly cooling the short side shell with the drain plate and raising the short side shell temperature on the straightening borrow side higher than the upper surface shell temperature, the upper surface (inner surface, L surface) and lower surface (outer surface,
It is possible to reduce the temperature difference between the upper surface (inner surface, )
The surface temperature of the shell can be made higher, and as a result, it becomes possible to obtain a defect-free slab at a higher temperature, and the rolling conditions on the rolling process side in the direct rolling process are relaxed.

That is, as mentioned above, the surface temperature TF of the lower surface (outer surface, 2nd surface) on the straightening borrow side needs to be approximately 1100°C or less from the viewpoint of preventing internal cracks due to inter-roll bulging, and if there is no drain plate, Top surface (inner surface, L surface) surface temperature TL
The maximum value of is about 880 degrees Celsius, but when a drain plate is installed, it is about too much.

℃.

Specifically, when a drain plate is installed, it is impossible to obtain a defect-free slab without a drain plate, and the high temperature condition range that is preferable for obtaining a high-temperature slab is shown in Fig. 9. (b
), the temperature condition range surrounded by points C-F-E [88
0℃4Tt, ≦1000tl:, 1100tl knee TL
≧ΔT)60℃+s (Tt-800℃), TF(=T
L+ΔT)! A defect-free slab can be obtained at a temperature of 1xoo°C].

The above describes the casting results of a small arc with a standard arc of 3 m, a machine height of 3.5 m, a straightening band length of 4 m, a multi-point straightening type low machine height, and a curved continuous casting machine, and the slab surface temperature conditions on the straightening side. The relationship between the occurrence of internal cracks and the occurrence of internal cracks has been summarized and explained. Depending on the cooling conditions within the straightening zone, the surface temperature of the upper surface, lower surface, and short side of the cast slab on the straightening side will vary depending on the temperature within the straightening zone and the temperature outside the straightening zone. It changes on the side.

For example, depending on the cooling conditions in the orthodontic zone, ■ the temperature of each surface on the orthodontic side is maintained within the orthodontic zone, and the temperature of each surface on the outlet side of the orthodontic zone is maintained at the above borrowing side temperature, or ■ the temperature of each surface within the orthodontic zone is Gradually reduce the temperature of each surface on the belt exit side to be slightly lower than the temperature of each surface on the borrowing side, or regenerate heat within the straightening zone to make the temperature of each surface on the belt exit side higher than the temperature of each surface on the borrowing side. I can do it.

However, if the cooling conditions within the straightening zone are adjusted and the heat is recuperated within the straightening zone, if the top or bottom surfaces are within the straightening zone and reheating is performed at a surface temperature of 100°C or higher, tensile strain due to this reheating will occur. It was found that internal cracks occurred due to the addition of Therefore, the reheating within the straightening zone must be kept at 100° C. or lower, and the reheating step to obtain a hot slab for the direct rolling process is preferably carried out at a time when the total strain is low after straightening is completed.

Furthermore, for cooling within the straightening zone, it is preferable to adopt a flat cooling pattern that maintains the straightening borrow side temperature or a slope cooling pattern that gradually lowers the temperature within the straightening zone.

Figures 9 and 10 are examples of a reference arc of 3 m, but in the case of a reference arc of 6 m, there are advantages in reducing orthodontic strain by increasing the arc radius and reducing orthodontic strain with a high shell thickness, but on the other hand,
The roll diameter increases due to the increase in static pressure, and the increase in bulging strain due to the increase in roll pitch reduces the allowable amount of straightening strain in the total strain. As a result, the temperature conditions on the straightening borrowing side are It is almost the same as in Figure 10, and it was also found that the same phenomenon occurs when the casting speed is increased, and that almost the same conditions need to be satisfied.

Next, the temperature conditions on the straightening band exit side (straightening completion point) will be described. The lower limit temperature condition at the time of completion of straightening is determined from the temperature condition of direct rolling. FIG. 11 shows an example of a cooling pattern in a low-height continuous casting machine in a direct rolling process. In this cooling pattern example, the flat cooling pattern described above is adopted as the cooling pattern within the straightening zone, and unsolidified heat is regenerated in the horizontal portion after the straightening is completed.

The problem here is the occurrence of internal cracks due to unsolidified recuperation in the horizontal section, and as a result of investigating this limit value, it was found that internal cracks will not occur if the amount of recuperation at the surface temperature is 260°C or less. Understood. Therefore, the casting speed is 1.7rrymin,
The average cross-sectional temperature of the slab at the time of complete solidification under recuperation conditions of 260° C. or less in the horizontal portion is determined for each surface temperature at the point of completion of straightening and for each reference arc (no), as shown in FIG. 12.

Although there are slight differences depending on the steel type and rolling mill capacity,
Calculated from the rolling temperature, the average temperature of the slab cross section at the end of the continuous casting machine required is 1180°C, and as is clear from Figure 12, it is necessary to complete straightening at a surface temperature of 800°C or higher. Recognize.

Therefore, in order to obtain a high-temperature slab for the direct rolling process (average slab cross-sectional temperature at the end of the continuous caster of 1180°C or higher), the surface temperature of the upper and lower surfaces of the slab at the straightening strip exit side (straightening completion point) must be 8.
℃A must be above 00℃.

In addition, the relationship shown in Figure 12 is that the casting speed is 1.7771/mj
In the case of R, the temperature at the end of the continuous caster is dominated by the difference between the completely solidified position and the end of the continuous caster as long as the reheating process is used, and the casting speed is 1.5 @ / mm~2. O
It has been found that in the range of m/mm, it is almost independent of the casting speed.

The gist of the present invention detailed above is summarized as follows. In order to obtain high-temperature slabs of good quality without internal cracks for direct rolling, we use a low machine height continuous casting machine with less bulging, i.e. a low machine height multi-point straightening curved casting machine. During casting with a continuous casting machine, more specifically, when bending and straightening a curved slab with an unsolidified phase, in order to alleviate the tensile strain caused by straightening, the shell surface temperature on the side where tensile stress is generated during straightening is adjusted to lower the shell surface temperature on the side where compressive stress occurs. By starting and completing bending straightening by lowering the surface temperature of the shorter side shell and making the surface temperature of the shorter side shell higher than the shell surface temperature of the side where the above-mentioned tensile stress occurs, shearing on the short side is achieved. This continuous casting method is characterized by giving priority to deformation and reheating the unsolidified slab at least after completion of straightening in order to obtain a high-temperature slab.

Note that the continuous casting method of the present invention uses a 37- This method can also be implemented using a curved continuous casting machine.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the profile of a continuously cast slab being cast by a curved continuous casting machine, Figure 2 is an explanatory diagram of the principle that tensile strain occurs in the upper shell due to bending straightening, and Figure 3 is an illustration of the machine height. Fig. 4 is an explanatory diagram showing the problems encountered when performing compression casting in a low machine height continuous casting machine, and Fig. 5 is a schematic diagram showing the influence of the straightening band start position. An explanatory diagram showing the degree of reduction in strain when casting is performed, Fig. 6 is an explanatory diagram of the principal stress and principal strain when bending straightening is viewed three-dimensionally, and Fig. 7
The figure is an explanatory diagram of the shear stress component generated in the short side shell, Figure 8 is an explanatory diagram of the installation situation of the drain plate installed to increase the short side shell temperature, and Figure 9 (al and (b) is an illustration of the correction zone Figure 10 is an explanatory diagram of the influence of the upper and lower surface temperatures and the presence or absence of a drain plate on the occurrence of internal cracks, and Figure 1O is an explanatory diagram of the relationship between the upper surface temperature and short side surface temperature with and without a drain plate installed. The figure is a schematic diagram of the recuperative cooling pattern for producing high-temperature defect-free slabs, Figure 12 is an explanatory diagram of the relationship between the straightening completion temperature and the average temperature of the end slab cross section, and Figure 13 (al, (bl,
fcl is a chart showing the conventional continuous casting to rolling process. 1... Curved mold, 2... Curved slab, 3, 4...
・Roll, 6... Unsolidified phase, 7... Neutral axis of 110 degrees, 8... Top shell, 9... Bottom shell, 10... Casting direction (arrow), 11... Casting Direction (arrow) 12...Top shell, 13...Bottom shell, 14...Short side (shell), 15.15'...
Tensile stress, 16.16'...Compressive stress, 17.1
7'...Deformation that attempts to narrow the width of the upper shell, 18
．． 18'...Deformation that attempts to widen the width of the lower shell,
19.19'... Shear deformation in the casting direction, 20, 2
0'... Shear deformation in the width direction, 21... Drain plate,
22... Roll, 23... Patent attorney representing the nozzle patent applicant Tomoyuki Yafuki (and one other person) 39- Figure 1 Figure 2 Soichi-10 Figure 5 Roll N. Always6WJ nη'P1 Ku・1......necessary. Figure 7 Figure 8 Figure 10 Figure 111 Temperature TtC''C) Figure 11E Figure 12

Claims (1)

[Claims] 1. A continuous casting method for bending and straightening a curved slab having an unsolidified phase using a multi-point straightening curved continuous casting machine with a low machine height,
When straightening the bend of an unsolidified slab, the surface temperature of the shell on the side where tensile stress occurs is lower than the surface temperature of the shell on the side where compressive stress occurs, and the surface temperature of the short side shell is lowered to lower the surface temperature of the shell on the side where tensile stress occurs. A continuous casting method characterized by starting and completing bend straightening at a temperature higher than the surface temperature. 2. In a continuous casting method for bending and straightening a curved slab having an unsolidified phase using a low machine height multi-point straightening curved continuous casting machine,
When straightening the bend of an unsolidified slab, the surface temperature of the shell on the side where tensile stress occurs is lower than the surface temperature of the shell on the side where compressive stress occurs, and the surface temperature of the short side shell is lowered to lower the surface temperature of the shell on the side where tensile stress occurs. A continuous casting method characterized by starting bending straightening at a temperature higher than the surface temperature, completing the bending straightening, and recuperating unsolidified heat. 3. In a continuous casting method of bending and straightening a curved slab having an unsolidified phase at a high casting speed of 1.5 m/In1n or more using a multi-point straightening curved continuous casting machine with a machine height of 6.5 m or less, Surface temperature TL of the (top) shell on the side (inside) where tensile stress occurs during bending straightening of a slab having a solidified phase; Surface temperature T of the (bottom) shell on the side (outside) where compressive stress occurs
F, the following (1) between the surface temperature 'rs of the short side shell,
(2), (3), and (4), maintain the relationships of equations (4), start bending straightening, complete bending straightening, and set the above-mentioned surface temperatures TL and TF at 800°C or higher at the point of completion of straightening to recover the unsolidified state. The continuous casting method according to claim 1, characterized in that the continuous casting method is heated. 1000℃≧TL≧700℃・・・・・・(1)T
F (=TL + ΔT) 41100℃ ・・・・・・(2)
1100℃zuL≧ΔT≧60℃s (Tt 800℃
)・・・・・・(3) 1100℃+-u(TL-soo℃)≧TS≧1000
℃ ten pieces (Tr--soo℃) 3 ...... (4) 4. 1. Using a multi-point straightening curved continuous casting machine with a machine height of 6.5 m or less. In a continuous casting method of bending and straightening a curved slab having an unsolidified phase at a high casting speed of s m/m1tt or higher, the side (inside) where tensile stress occurs during bending straightening of the slab having an unsolidified phase ( The following (1) between the surface temperature TL of the top shell), the surface temperature TF of the (bottom) shell on the side (outside) where compressive stress occurs, and the surface temperature 150 of the short side shell,
(2), (3), and (4), maintain the relationships of formulas, start bending straightening, complete the bending straightening, and set the surface temperatures TL and Tp at the point of completion of straightening to 800°C or higher to recover the unsolidified state. The continuous casting method according to claim 1, characterized in that heating is performed. 1000℃≧TL≧700℃ (1
) Tp (=Tt, +ΔT) 41100°C...
・(2) 200℃ 10-! -(TL-800℃))ΔT≧
60℃+L (Tt 800℃) 5 ...... (3) 1100℃+z (Tl-800℃) 4 'rs =
1000℃+-fl (TL-soo℃) 3 ...... (4) 5. High-speed casting speed of 1.5 m/Ilrm or more with a multi-point straightening curved continuous casting machine with a machine height of 6.5 m or less In the continuous casting method of straightening a curved slab having an unsolidified phase by m-th degree, the surface temperature TL of the shell on the side (inner side) where tensile stress is generated during bending straightening of the slab having an unsolidified phase (top surface). , the following (]) between the surface temperature TF of the (lower surface) shell on the side where compressive stress occurs (outside) and the surface temperature TS of the short side shell.
(2), (3), (4) Maintaining the relationships of equations, start bending straightening, complete bending straightening, and set surface temperatures TL and TF at 800°C or higher at the point where straightening is completed, and perform unsolidified reheating. The continuous casting method according to claim 1, characterized in that: 1000℃≧TL)880℃・・・・・・(1
) TF (= Tt, 10ΔT) 41100℃...
...(2) 1100℃−T L≧ΔT) 60℃＋−(T
t, -800℃) ・・・・・・(3) 1100℃
+ (Tt 800℃)≧TS≧1000℃
t, -800℃) - ・・・・・・(4)