JPS5870960A - Continuous casting method for steel - Google Patents

Abstract

PURPOSE:To make production of a high-temp. ingot for hot charging possible by controlling the static pressure of the molten steel in the unsolidified ingot to decrease bulging force and widening roll pitches to decrease the heat transfer of the rolls near the crater end. CONSTITUTION:In the stage of producing an ingot by drawing an unsolidified ingot 8 from the bottom end of a mold 10 which is open at both ends continuously, the vertical distance alpha between the final solidifying position 16 of said ingot 8 and the molten steel surface in said mold 10 is maintained in the range of the equation -1.4<=alpha<=3.0 (m), whereby the transfer heat of the rolls near the crater end 16 is decreased, and the temp. drop of the ingot is prevented. The ingots cut by a cutter 12 are conveyed in the state of high temp. to rolling stages. The static pressure of the molten steel is decreased and the pitches of rolls 15 are widened by the above-mentioned method within the range where the excellent quality of the ingots can be maintained. It is possible to decrease the transfer heat of the rolls and the radiation transfer heat between the rolls by providing a heat insulating installation 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method for steel, which is capable of casting slabs at a temperature of 1%.

An outline of a conventional continuous casting method using a mold with both ends open will be explained with reference to FIG.

Molten steel injected into a tundish 2 from a ladle 1 is injected into a mold 4 via a nozzle 3. The molten steel in the mold 4 is
The mold 4 is cooled by a guide roll 5 and a secondary cooling zone 6 provided next to the mold 4, and is then pulled out. The unsolidified slab, which has been cooled and has a solidified shell gradually thickened, is straightened horizontally by a straightening roll 7. After that, the completely solidified piece 8 is cut into a predetermined length by a cutting machine 9, and a product is produced. becomes.

In the continuous casting method described above, when the slab drawing speed is increased in order to improve the productivity of slabs, the crater end position moves in the drawing direction.

1, usually 6 to 10 for the solidified shell near the crater end
Since static pressure of Kg/cr/1 is applied, conventionally,
As shown in Fig. 2, the horizontal orbit O roll pitch of the slab is 114, and the cooling nozzle 1 installed between the adjacent rolls is
They are placed as close together as possible, leaving 4 spaces. If the roll pitch is far apart.

Since the above-mentioned large static pressure is applied to the solidified shell between the rolls, the bulging force becomes abnormally large, which causes problems in the quality of the slab and casting operations.

On the other hand, hot charging is becoming popular as part of energy conservation measures in recent years. This system combines seven existing continuous casting machines with the rolling process in a short time, prevents the temperature of the slab from decreasing from casting to rolling, and transports the slab as it is to the rolling process.

Generally, the heating rate i of slab removal in a continuous casting apparatus is expressed by the following formula.

Q - (hconv, tenri.and, +ThRa'
d, + ”spr,) (〒s'a)= h7ota
l (〒5-Ta) However, MConv: Natural convection heat transfer coefficient between rolls (average).

hco, d: Roll transfer heat transfer coefficient (average), “Ra
d, : radiant heat transfer coefficient between rolls (average), hs, r,
: Forced water cooling heat transfer coefficient (average), Ta: [side temperature, hTotal: Average heat transfer coefficient between rolls〒8: Slab surface temperature (average).

The inventors of the present application conducted a detailed investigation into the heat extraction situation of the slab near the crater end in the current continuous casting machine, and found that the above-mentioned K. The contribution of and , ζ-hRad, is extremely large, and is about the same size91, while h C
It was found that onv is less than 1 Orca+/hr°C, which is of an almost negligible order. That is, 900-1
In the case of slabs with a surface temperature of about 200℃, 'F'C
ona and “Rad” are each 50 to 100
w/m"hr'c and 60-100, (cal/m
It is about hr'C, and the total is about 110.
It was found to be within the range of ~200+c4/ihr'c.

Based on the above-mentioned facts, the inventors of the present application found that in order to cast high-temperature slabs using a continuous casting machine, it is necessary to perform not only inter-roll radiation transfer heat control but also roll transfer heat control. Ta.

Although it is possible to reduce the radiant heat transferred between the rolls by providing a heat insulating cover or the like on the track of the slab, it is not possible to reduce the heat transferred by the rolls.

This was not possible using conventional methods. For example, as an alternative method for casting high-temperature slabs, there is a method disclosed in Japanese Utility Model Publication No. 10442/1983. This is a system that controls radiation transmission by installing heat insulating plates between the rolls, but since it is aimed at seven existing continuous casting machines, the installation space for the heat insulating plates between the rolls is narrow and the space for installing the heat insulating plates between the rolls is limited by 40% at most. This method can only cover the slab to a certain extent, and it is not possible to manufacture the high-temperature slab that the inventors of the present application are aiming for.

Furthermore, roll transfer heat is not considered at all.

As a result of various studies based on the above-mentioned facts, the inventors of the present application have found that in order to reduce the roll transfer heat near the crater end, it is sufficient to widen the roll pitch. Problems arise due to bulging forces on the solidified shell in between. Therefore, it has been found that by reducing the bulging force, the roll pitch can be increased, which reduces roll transfer heat, making it possible to produce high-temperature slabs in a permanent manner.

This invention has been made based on the above knowledge, and provides a continuous steel casting method in which a slab is cast by pulling out an unsolidified slab from the lower end of a mold with both ends open while straightening the trajectory. , the vertical distance α between the final solidification position of the unsolidified slab and the molten steel surface in the mold is maintained within the range of the following formula, −1,4≦α≦3.0 (m). It is characterized by reducing the heat transferred from nearby rolls and casting high-temperature slabs.

In this invention, the reason why the vertical distance α between the final solidification position of the unsolidified slab and the molten steel surface in the mold is limited to the above-mentioned range will be explained.

Figure 3 shows the results when the amount of bulging between the rolls near the crater end and the amount of roll bending are the same as in the current continuous casting machine, and the melt-static pressure is reduced on the premise that good slab quality is maintained. Roll pitch ratio r, / L 0 and roll diameter ratio D
/D0 shows the relationship.

The current continuous casting machine mentioned above has a bending radius of 10.5 m.
This is a fully curved high-speed continuous casting machine, and in this case, the static pressure of molten steel near the crater end is approximately 7.5 Kg/cM, and the e-seal is installed near the crater end.

Roll hitchori. , roll diameter. Closed.

As is clear from Fig. 3, the static pressure of molten steel is 2 Kg/cA.
Below, in other words, if α is set to 3.0 m or less, the roll pitch can be increased and the roll diameter can be decreased, and as a result, the roll transfer heat described above is reduced.
It can be seen that it is possible to cast high-temperature slabs.

On the other hand, since atmospheric pressure is always acting on the molten steel in the mold,
The crater end position can be raised above the surface of the molten steel inside the mold until the static pressure of the molten steel balances with the atmospheric pressure.

Therefore, in this invention, the above α is −1,4≦α≦3.0 (
m).

Next, embodiments of the invention will be described.

The molten steel injected into the water-cooled control mold 10, which is open at both ends, is
Next, the unsolidified slab is pulled out along a curved trajectory while being cooled by the cooling zone 11, and after this, the unsolidified slab is straightened to -H flat, and then pulled out along a trajectory curved in the opposite direction to the curved trajectory, and finally It was corrected horizontally. The unsolidified slab 8 is completely solidified in the horizontal orbit, and then the gas torch 1
2 to a predetermined length. The hot slab cut into a predetermined length was transported following the rolling process.

In this case, the vertical distance α between the final solidification level dl 6 (crater end) of the unsolidified slab and the molten steel surface in the mold is 3.
It was set to 0m. Therefore, the static pressure of the molten steel near the crater end was reduced, and the roll pitch of the rolls 15 in this area was able to be widened, so the roll transfer heat was kept to a minimum.
Furthermore, since a strongly insulated equipment 13 with a large coverage ratio was provided between adjacent valley rolls, the slab could be transported to the rolling process while being kept at a high temperature.

FIG. 5 shows another embodiment of the invention.

The molten steel injected into the water-cooled mold 10, which is open at both ends, is
Next, the unsolidified slab is pulled out along a curved trajectory while being cooled by the cooling zone 11. After that, the unsolidified slab is straightened flat and then pulled out along a straight trajectory. The solidified slab is cut into a predetermined length by a gas torch 12. Amputated. The hot slab cut into a predetermined length was transported following the rolling process.

In this case, the vertical distance α between the final solidification position 16 (crater end) of the unsolidified slab and the molten steel surface in the mold is 1.07
It was set at 71. Therefore, similar to the embodiment shown in FIG.
The static pressure of molten steel near the crater end was reduced, and the roll pitch in this area was able to be widened, so the roll transfer heat was kept to a minimum.
The provision of a breaker made it possible to maintain the temperature of the slab at a high temperature while transporting it to the rolling process.

As explained above, according to the present invention, it is possible to cast high-temperature slabs by continuous piece making, so it is possible to roll the slabs without reheating them, which significantly reduces energy consumption. At the same time, useful effects such as the ability to greatly improve product productivity are brought about.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the conventional continuous casting method, Figure 2 is an explanatory diagram of bulging between roll pitches, and Figure 3 is a diagram showing the relationship between molten steel static pressure, roll pitch ratio, and roll diameter ratio. FIG. 4 is a diagram showing one embodiment of the method of the present invention, and FIG. 5 is a diagram showing another embodiment. In the drawing, ■...Ladle 2...Tandish 3.
... Nozzle 4 ... Mold 5 ... Guide roll 6 ... Secondary cooling zone 7 ... Straightening roll
8... Slab 9... Cutting machine 1o...
・Mold 11... Secondary cooling zone 12... Gas torch 13... Heat insulation equipment 14... Cooling nozzle 15... Roll 16... Crater end position Applicant Nippon Steel Tube Co., Ltd. Agent Keita Tsutsumi (Menu name), Figure 1 Figure 2 +4 14 14 Figure 3 Melt aS fold (Kgn 1 Figure 4

Claims (1)

[Scope of Claims] In a continuous steel casting method in which a slab is cast by pulling the unsolidified slab from the lower end of a mold with both ends open while straightening the trajectory, the final solidification of the unsolidified slab is performed. The perpendicular distance α between the position and the surface of the molten metal in the mold is maintained within the range of the following formula: -1,4≦α≦3.0 (m) This reduces the roll transfer heat near the crater end. , a continuous steel casting method characterized by casting a hot slab.