JPH01138048A - Method for continuously casting cast slab - Google Patents

Abstract

PURPOSE:To increase the max. casting velocity by rapidly cooling one or more positions of long side surface in a cast slab more then the other position, adjusting the casting velocity, perfectly solidified part corresponding to forced cooled part before the machine end and making position behind the machine end of crater end position except the forced cooled part. CONSTITUTION:By varying width directional distribution of spraying water for secondary cooling so as to force the cooling at a part of long side surface, e.g., the forced cooling position 9 of width center part than the other position, before the machine end, the crater end position of the forced cooled part 9 is controlled to become almost the same position as the machine end position. Behind the machine end, the non-solidified part 3 is divided into two to width direction. In such a way, as it is acted that perfectly solidified position at Wc position of the forced cooled part in the cast slab prevents bulging of the solidified shell caused by molten steel static pressure, even if the crater end exists behind the machine end, the bulging of the cast slab can be suppressed. By this method, the increase of the max. casting velocity can be obtd. by only variation of the secondary cooling water distribution to the width direction without extension of the machine end of the continuous casting machine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a continuous casting method for steel slabs, and more particularly, to a method for obtaining slabs at a temperature that allows direct rolling or direct charging into a heating furnace.

[Prior art] Conventionally, in order to obtain high-temperature slabs, basically
As shown in 2-64462, perform unsolidified recuperation and adjust the casting speed or adjust cooling so that the crater end (completely solidified end) is at approximately the same position as the machine end or within the machine end. is a common method. The machine end here refers to the final support roll position of the continuous casting machine.

Furthermore, as in JP-A-57-17360, by making the width direction profile of the unsolidified portion, that is, the peripheral shape of the unsolidified portion in the cross section of the slab, into a dogbone shape, the both ends of the slab, which are easily cooled, can be heated to high temperatures. Efforts have also been made to maintain the temperature.

In any case, the conventional method for manufacturing high-temperature slabs is to place the crater end close to or within the end of the machine.

The reason for doing this is to prevent so-called bulging, in which the solidified shell swells due to the static pressure of the molten steel, if the crater end extends beyond the machine end.

Therefore, the casting speed is almost limited by the machine length (distance from the mold surface to the final support roll supporting the slab), and the maximum casting speed VmaX is given as shown in equation (1) below.

V max = L / (d / 2 k s )
2-- (1) Here, L is the machine length, d: slab thickness, ks: solidification rate constant.

As is clear from the above equation (1), in order to increase v max, it is possible to strengthen the cooling of the slab within the end of the machine and increase the thickness of 5, but it is possible to obtain the desired high-temperature slab. I won't be able to do that.

One possible way to further increase v max is to extend the machine length, but this requires major modification of the continuous casting machine.

From the above, v m to obtain high-temperature slabs with the current continuous casting machine
Currently, ax is determined by the captain.

Therefore, there is naturally an upper limit to the maximum temperature of the high-temperature slab that can be obtained.

[Problems to be Solved by the Invention] The present invention solves the problem of the maximum casting speed v max and the maximum slab temperature θmax, which were conventionally determined by the captain, without requiring major modifications.
The object of the present invention is to provide a casting method that increases θmax.

[Means for Solving the Problems] The present invention provides a secondary cooling zone in the support roll zone for preventing bulging of the slab during continuous casting, in which one or more parts of the long side surface of the slab are cooled from other parts. In addition to adjusting the casting speed, only the strongly cooled part is completely solidified at approximately the same position as the machine end or within the machine end, while the crater end position of the unsolidified part that is not strongly cooled is set at the machine end. By casting in the following manner, it is possible to make vmax and θmax larger than before.

[Operation] FIG. 2 shows a vertical cross-section of a continuously cast slab l passing through the final support roll 5 (end 6) of the continuous casting machine while being drawn out in the direction of arrow 10.

Conventionally, as shown in FIG.
Or, it is cast so that it is located upstream of it, that is, within the end C. In this case, the final support roll 5 prevents the solidified shell of the slab from bulging due to the static pressure of the molten steel.

However, when the crater end 7 extends downstream from the machine end 6 and comes out after the machine end as shown in B, there are no rolls to support the slab, so the solidified shell cannot withstand the static pressure and swells. This will cause bulging 8. If the swelling speed is higher than the growth speed of the solidified shell, the swelling will continue to expand without stopping, making it impossible to continue casting.

On the other hand, as shown in Fig. 1(b), within the end of the machine, a part of the long side surface of the slab, for example, the strongly cooled part 9 at the center of the width, is forcibly cooled more strongly than other parts. By changing the widthwise distribution of the secondary cooling spray water, if the crater-end position of only the strong cooling section 9 is controlled to be within the machine end or at almost the same position as the machine end, from the machine end onwards, the As shown in FIG. 1(b), the unsolidified portion 3 is divided into two parts in the width direction.

The place to be strongly cooled does not need to be limited to the central part in the width direction, and it may be cooled so that the unsolidified part 3 is divided into three or more parts in the width direction, for example, as shown in FIG. 3(C). In this way, the completely solidified part of the WC part, which is the strongly cold part of the slab, acts to prevent the solidified shell from expanding due to the static pressure of the molten steel, so the crater end is located after the machine end. It is also possible to suppress the bulging of the slab.

The amount of bulging in the case of the present invention will be compared with that in the case of the conventional method in which the crater end is located after the end of the machine.

Generally, the bulging of a slab is regarded as a deflection behavior due to support beams fixed at both ends, and the maximum bulging amount σmax can be estimated using the following equation (2).

Here, P: Static pressure of molten steel, (kg/cm") Wl: Width of unsolidified part (cm) E: Average Young's modulus of solidified shell (kg/c rri")
)ds Thickness of solidified shell (cm). If the width of the slab is W, and the distance from the end face of the slab to the unsolidified area is We, the conventional width W1 of the unsolidified area is as follows (3
) is expressed by the formula.

W 1=W-2W e −・= (3)
Further, the width W2 of the unsolidified portion in the case of the present invention is expressed by the following equation (4).

W2= (W-2We-nWcl/(n+1)-
...(4) Here, n is the number of places to be strongly cooled in the width direction.

Now, assuming that n=1, W=1200 mm, and W cm 230 mm, and assuming that We has the same solidification rate from the short and long surfaces, we can calculate We as the length covered by solidification from the short surface. can be estimated to be the slab thickness of 2"" 163mm. Therefore, W1 = 874mm, W2 = 322mm, and W 2 = W 1 / 2.71 ・
...(5). From equations (2) and (5), f
fmax is reduced to 1/(2,71)4, that is, approximately 1/54, compared to 1 in the conventional method. A trial calculation for the case where n=2 results in an even smaller value of 1/318.

In addition, when the amount of bulging is controlled by the distance from the aircraft end to the crater end in degrees Celsius, W in equation (2),
11 can be replaced with °C.

In the case of billet slabs, the cross section is small and the length of the negative side is short, so Crmax is dominated by Wl rather than a. In the case of slabs, in the conventional method, ffmax is controlled by °C rather than Wl, but in the case of the present invention, W or is shorter than in the conventional method due to the solidification of the We part, so as in the case of billets (Tmax
As a result of experiments, it has become clear that x is dominated by WR rather than by °C.

Therefore, it is possible to dramatically reduce σmax compared to the conventional method, and the bulging speed can be kept lower than the growth speed of the solidified shell, so casting can be performed with the crater end positioned after the machine end. There is no need to worry about bulging.

By performing such a casting method, it is possible to cast the crater end by ρ after the machine end, so
The maximum casting speed VmaX can be made larger than the value shown by equation (1) above.

Its value is given by equation (6).

Vmax = (L0℃) / (d/ 2 k s
) 2...(6) In other words, the method of the present invention makes it possible to increase i/(a/2ks) more than 1Tla× in the conventional method.

Now, if d = 260 mm, L = 36.2 m, and j2 = 4 m, the conventional method v m
ax is 1.68 m/min, but in the present invention it is 1.86 m/min.
/min, making it possible to increase the speed by 0.186m/min. This leads to a productivity increase of 10.7%.

In order to increase productivity by 1000% using the conventional method, the length of the aircraft would have to be extended by an additional 4 m, and the cost of modification would be enormous. However, according to the present invention, it is only necessary to change one or more locations in the width direction distribution of the secondary cooling water to provide strong cooling, so there is no need for major modification of the continuous casting machine.

On the other hand, the present invention, which completely solidifies after the machine end, can produce slabs at a higher temperature than the conventional method due to the effect of increasing the maximum casting speed and recuperating unsolidified heat.

[Example] Example 1 Conventional low carbon Aρ quilt steel slab slab 260mm thick x 12
For casting 40 mm width, the maximum casting speed was 1.6 m/min using a continuous casting machine with a machine length of 36.2 m.

When we cast a 150mm section at the center of the slab width throughout the secondary cooling zone with 20% more cooling water than other sections, we were able to increase the maximum casting speed to 1.8m/min, which was faster than conventional casting. The cross-sectional average temperature after cutting one piece was 1105℃ to 1205℃.
It was possible to raise the temperature to ℃.

At this time, a non-contact electromagnetic ultrasonic meter was installed at a position 2 m from the end of the machine to detect the position of the unsolidified part in the width direction of the slab. As a result, the width center part was completely solidified with a width of 340mm,
It was found that a width of about 200 mm on both sides was unsolidified, and it was found that the cross-sectional shape was as shown in FIG. 3(b).

Example 2 Same steel type and same continuous casting machine as Example 1, slab size 230m
The maximum casting speed for m thickness x 1000 mm width was 2.05 m/min, but the unsolidified part was detected in the width direction using a non-contact electromagnetic ultrasonic meter 1 m before and after the machine end, and the central crater end was detected at the machine end. Positioned within 1m in front and back, 200m in width center
When part m was cast by increasing the amount of secondary cooling water by 30%, the maximum casting speed could be increased to 2.30 m/min, and the average cross-sectional temperature of the slab increased from 1245°C to 1312°C.

Example 3 A slab with a thickness of 260 mm and a width of 2000 mm was cast under the conditions of Example 1. However, the strongly cooled part of the slab in the width direction was set at a position of 300 mm to 450 mm on both sides from the width center part. The value of the unsolidified area in the width direction of the slab at a position 2 m from the end of the machine is found in a total of 3 locations with a width of approximately 200 mm, at the center of the width and on both sides thereof, with a fully solidified area 300 mm wide in between. It was confirmed that the cross-sectional shape was as shown in FIG. 3(C).

As a result, the maximum casting speed is 1.55 m/min to 1.75 m/min.
m/min.

[Effects of the Invention] The maximum casting speed, which is approximately determined by each continuous casting machine, can be increased by changing only the widthwise distribution of the secondary cooling water without extending the machine end of the continuous casting machine.

In addition, since it can be cast in an unsolidified state at a position after the machine end, it becomes possible to increase the productivity of high-temperature slabs and manufacture them.

Therefore, the present invention has an effect that greatly contributes to the implementation of the direct rolling method and the direct rolling method of slabs.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the position and shape of the crater end of the slab near the machine end and after the machine end when the present invention is implemented, and Figure 2 is the crater end near the machine end when casting using the conventional method. Figure 3 is a cross-sectional view of the unsolidified slab near the machine end, where (a) is the conventional method, (b)
) and (c) show the case of the method of the present invention. 1... Slab 2... Solidified part 3 - Unsolidified part 4... Support roll 5... Final support roll, 6... Machine end 7... Crater end 9... Strong Cold section

Claims (1)

[Claims] 1. During continuous casting, one or more parts of the long side surface of the slab are cooled more strongly than other parts, and the casting speed is adjusted so that the unsolidified part corresponding to the strongly cooled part is completely solidified at least within the machine end, and the above-mentioned A continuous casting method for slabs, characterized in that the crater end position other than the strongly cold part is cast after the machine end.