JPS6360051A - Production of thin cast strip - Google Patents

Abstract

PURPOSE:To surely cast strip as high temp. without any heating stage by cooling so as to remain non-solidified range having the specific % of thickness for the cast strip at the position of finish roll of guide roll group in a secondary cooling zone and also reduction-rolling so as to eliminate the non-solidified part at the finish roll. CONSTITUTION:The finish rolls 6a, 6b in the secondary cooling zone are pressed to downward by a cylinder 8 and at this part, the upper shell 9s of cast strip and the lower shell 10s of cast strip are brought into control with mutually and while non-solidified molten steel 11 is pushed back toward upstream side, both shells are welded in order and so perfect solidification is realized. In this case, the cast strip is cooled, so as to remain to <10% the thickness of cast strip as the non-solidified range at the position of finish rolls 6a, 6b, and also at this position, the upper part and the lower part shells are rolled under reduction by the cylinder 8, so as to eliminate perfectly the non-solidified part at this position.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for manufacturing thin slabs, particularly when the thickness is 3011 mm.
This is a proposal for a technology that is characterized by the method of cooling and rolling down when casting 779 steel plate as follows using a continuous thin slab casting machine.

(Conventional technology) What about metals, such as steel, that have been developed for the purpose of saving energy and equipment in processes? #In a slab casting device, it is effective to maintain the slab that comes out of the casting machine at a high temperature and feed it to the next rolling process.

This is because by keeping the temperature of the thin slab at a high temperature, the heating process necessary for rolling can be omitted. For this reason, heat retention technology for slabs has recently been attracting attention. However, in a thin slab VI production device such as a belt caster or block caster, which has endless long sides, if the contact between the belt (or block) and the slab shell is relatively good, the slab will not stay inside the mold. In this case, the surface temperature of the slab also decreases, so the enthalpy of the slab decreases, and the temperature drops too much by the time of the next rolling process.Then, the completely solidified position of the slab becomes outside the mold. It is possible to slightly control the heat retained in the slab by solidifying it in the secondary cooling zone by delaying it as described above.However, the latent heat of solidification occupies a large value in the heat retained in the slab. Average quality of slab in completely solidified area (retained heat W)
It is important to operate in a manner that maximizes the

For example, the conventional method disclosed in JP-A No. 60-87904 is to keep the thickness of the slab uniform by performing reduction rolling over several stages in a region where the unsolidified part of the slab exceeds 10% of the thickness of the slab. has been proposed, but in this case several stages of reduction are required to prevent cracking.

(Problems to be Solved by the Invention) The purpose of thin slab casting is: ■ To achieve a shape that is more similar to the final product, the rough rolling process can be omitted and equipment can be reduced;
■Energy saving can be achieved by omitting the rough rolling process, and ■Casting equipment is simple. Among these, the main purpose is energy saving. In the case of thin slab casting, the enthalpy of the slab itself is much smaller than that of conventional slabs, and as the enthalpy decreases rapidly over time, it maintains a high temperature state from casting to rolling. It is difficult to do so.

Considering that the latent heat of solidification of the enthalpy possessed by the slab is small, it is effective to use a layer that leaves at least a small unsolidified area before rolling.

However, in reality, the rolling and VT forming machines have to be in a one-to-one ratio, resulting in poor rolling efficiency.Therefore, the final solidification position of the slab is controlled to a constant position, closely following slight changes in operating conditions. It is an object of the present invention to make it possible to feed the slab at a high temperature without a heating process before rolling, by making it possible for the slab to be rolled and to maximize the enthalpy of the slab at this part. It is.

(Means for Solving the Problems) For the purpose of the upper part, the present invention solves the final solidification position of the slab.
Continuing to the mold part (by rolling down at the final roll of the secondary cold N1 band boat roll, the slab, which has been in an unsolidified state until then, is crushed and is always forced to completely solidify at this position. It is better to minimize the crushing cliff at this time, because crushing is effective in preventing internal cracking of the solidified shell inside the slab.

That is, the present invention employs a configuration based on the following points to achieve the above object.

Basically, the present invention provides a method for producing a thin cast piece using a continuous thin cast piece casting apparatus, which is made up of a pair of blocks or belts having endless long sides facing each other, and a mold part made of the blocks or belts. The slab that has left the slab is cooled so as to leave an unsolidified area of less than 10% of the slab thickness at the position of the final roll of the guide roll group in the secondary cooling zone, and this final cooling roll cools the slab. This is a method for manufacturing a thin cast slab, which is characterized by applying such a reduction that the solidified portion disappears.

(effect) Next, the method of the present invention will be specifically explained.

Figure 1 shows a twin-belt type continuous thin slab casting machine for steel, in which molten steel is transferred to top rolls 2a, 2b, bottom rolls 4 and 4.
a, 4b tension roll 3a.

A pair of opposing belts la supported by 3b.

It is fed from the upper side of the mold constituted by belts Ia and Ib, cooled while moving synchronously between belts Ia and Ib, thereby producing a solidified shell, and gradually growing to form slab 7.

In the case of the present invention, cooling conditions are adopted such that solidification of the slab core is not completed even at the positions of the bottom rolls 4a and 4b,
Cooling of the slab also progresses in the support rolls 5 that constitute the secondary cooling Ml zone following the mold.

The final day 6, located at the end of the secondary cooling zone section, is
The present invention has a slab rolling down mechanism as shown in FIG. That is, the last day - Rule 5a.

6b is forced downward by the cylinder 8, and at this part, the slab upper shell 9s and the slab lower shell 10s touch each other, and while pushing back the unsolidified part tA11 to the upstream side,
Achieve complete solidification by sequentially crimping.

In this case, the slab is not actively cooled at the support roll 5, but at the bottom roll 4a of the mold.

The surface of the slab 7 coming out from the support roll group 5 is reheated by heat supply from the internal unsolidified part, and the final part of the support roll group 5 (
It is necessary to control the cooling so that the enthalpy of the slab is maximized at the position of the final rolls 6a, 6b). At this position, the silonder 8 is operated to lower the upper and lower shells so that the unsolidified portions are completely eliminated.

It should be noted that unless the unsolidified thickness at the positions of the final rolls 5a and 6b is 10% or less of the slab thickness, the shell may crack during rolling and remain as a product defect.

(Example) In this example, a thin steel plate was produced by casting using the apparatus shown in FIGS. 1 and 2 under the following conditions.

・Casting speed 20m/min °Cold slab thickness 40n - width 1300n ・Distance from the bottom of the mold to the reduction roll 500m ・Steel type Low carbon aluminum killed steel (C/ 0.04%, Mn/ 0.30%, P/ 0
．． 015%, S/ 0.020%, Ai/ 0.04
0%) Figure 3 shows the relationship between slab reduction and internal cracking in such a casting example. As can be seen from this figure, when the slab pressure ratio increases, internal cracks occur and when the rolling reduction ratio increases to 10
%, it is clear that defects will occur to a degree that is problematic for R cotton products. Internal cracks were detected by S print and P (phosphorus) print. Therefore, in the case of the present invention, it was confirmed that it is important that the rolling reduction ratio be less than 10%.

On the other hand, the enthalpy of the slab 7 immediately after the final rolls 6a 1, 6b is shown in FIG. 4, and for example, the mold bottom rolls 4a, 4b/fi final day roll 6a.

The average temperature of the slab when extended to 6b is 1150°C, and 1190°C when rolled at the center of the length of the support roll 5 during unsolidified rolling. In comparison, in the method of the present invention, the temperature of the slab was 1280°C, and the enthalpy of the slab was significantly increased.

(Effects of the Invention) As explained above, according to the present invention, it becomes possible to directly roll a slab after continuous casting of a thin slab without heating it. Moreover, since the final solidification position can be specified, the casting speed can be increased, which is extremely effective in saving energy. Further, it is possible to maintain a constant thickness of the slab and to produce a slab without internal cracks.

[Brief explanation of the drawing]

Fig. 1 is a route map of the continuous casting machine for thin slabs, Fig. 2 is an explanatory diagram of the final roll reduction mechanism, Fig. 3 is a graph showing the relationship between reduction ratio and internal cracks, Fig. 4 is a comparison graph of the average temperature of the slab when various cooling conditions are adopted in the final roll section. 1a, lb...Belts 2a, 2b...Top rolls 3a, 3b...Dension rolls 4a, 4b...Bottom roll 5...Support rolls 5a, 5b...Final roll 7... Slab 8...Hydraulic cylinder 9...Upper solid layer...Lower solidified shell 11...Unsolidified portion Patent applicant: Kawasaki Steel Co., Ltd. Applicant: Hitachi, Ltd. Figure 3 Pressure "F'l (%) F? :(![115/i, l#nXf00 4th figure ε

Claims (1)

[Claims] 1. When manufacturing thin slabs using a thin slab continuous casting device consisting of blocks or belts with endless long sides facing each other, the slabs that have left the mold section consisting of the blocks or belts are , at the position of the last roll of the guide roll group in the secondary cooling zone, cooling is performed so as to leave an unsolidified area of less than 10% of the slab thickness, and the unsolidified area is eliminated by this final cooling roll. A method for producing thin cast slabs, which is characterized by applying a large reduction.