JP2002346603A - Yield improvement method in production of continuous casting billet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a yield improvement method in production of continuous casting billet to aim at utilization of a so-called top steel billet produced by continuous casting. SOLUTION: A top steel billet having a deviation in the longitudinal direction of a width and thickness which occurs at the final solidification stage of molten steel during continuous casting is used as a workpiece after the said deviation is eliminated by blooming.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the yield of continuously cast steel slabs. More specifically, the present invention relates to a method for continuously rolling a steel slab obtained by continuous casting of molten steel. This technology is used effectively as a material.

[0002]

2. Description of the Related Art Continuous casting of molten steel is generally performed as follows.

[0003] First, in a refining vessel (for example, a converter, an electric furnace, or the like), one charge of molten steel that has been refined and melted into a predetermined component is discharged to a ladle. Then, as shown in FIG. 2, the molten steel 2 held in the ladle 1 is an intermediate container called a tundish 3 (before the molten steel is poured into a mold,
The outer wall is injected into the cooling mold 4 via a dip nozzle provided at the bottom of the mold 4 via a container for performing a rectifying action).
In the mold 4, the molten steel in contact with the water-cooled outer wall forms a solidified shell. The molten steel is gradually cooled to obtain a long solidified solid 5. Eventually, the solidified body 5 is cut into a predetermined length by gas or the like to form a rectangular slab, a steel slab such as a bloom, etc., which is sent as a material to be rolled to a downstream rolling process, steel sheet,
After being processed into shaped steel, it is shipped to customers.

[0004] In such continuous casting, the solidified material contracts in the process of cooling and solidifying the molten steel. In particular,
The last end side of the solidified body shown in FIG. 2 (this part which finally solidifies is the top end in the mold 4 and is called a top) is free from load because there is no molten steel 2 thereon. Because of shrinkage, the amount of shrinkage is greater than the tip side of the solidified body (the leading end is referred to as the top on the basis of the above criteria). Therefore, even if there is no quality problem, the steel slab obtained in the portion located at the top (hereinafter referred to as top steel slab 8) has a thickness of 215 mm and a width of 2000 m, as shown in FIG.
Although the target is m, the difference between the maximum part and the minimum part (that is, deviation 9) occurs, resulting in a trapezoidal cube having a length of 500 to 1000 mm. Note that this length is a value excluding the so-called crop portion 10 that is cut off due to quality problems. The deviation 9 is about 10 to 40 mm in width and about 10 to 30 mm in thickness, and the weight of this trapezoidal cube is about 1 to 2 tons (as a yield of molten steel in continuous casting, 0.3 to 0.3 ton per molten metal for one charge). 0.6%).

[0005] Such a top steel slab 8 having a deviation 9 in width and thickness cannot be eliminated when the steel sheet is made into a steel sheet by a rolling mill that can be rolled only in one direction thereafter. Also,
At present, the current continuous casting technique cannot produce a top steel slab 8 having a thickness and a width that do not deviate from the bottom side.
Therefore, since the top steel slab 8 cannot be rolled as a material to be rolled in the same manner as the steel slab obtained in other portions, the top steel slab 8 often becomes scrap. That is, the yield of molten steel as a continuously cast steel slab (the amount of steel slab that became the material to be rolled / the total amount of continuously molten steel × 100) was 0.3 to 0.6% as described above.
Only declines.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of improving the yield of continuously cast steel slabs in which the so-called top steel slabs manufactured by continuous casting are effectively utilized in view of the above circumstances.

[0007]

Means for Solving the Problems The inventor has conducted intensive studies in order to achieve the above object, and has embodied the results in the present invention.

That is, according to the present invention, a top steel slab which has a deviation in the width and thickness in the longitudinal direction due to continuous casting of molten steel and has a deviation in the width and thickness in the longitudinal direction is eliminated by slab rolling, and the material to be rolled is removed. This is a method for improving the yield of continuously cast steel slabs, characterized in that the method is used for:

[0009] In this case, it is preferable that the above-mentioned slab rolling is performed with a reduction amount and a width reduction amount determined by the following formulas.

[0010] Reduction amount ≧ thickness deviation × 2 (1) Width killing amount ≧ width deviation × 2 (2) According to the present invention, deviations in width and thickness generated in the top steel slab are eliminated, and conventionally, scrap is removed. The top steel slab that has been used can be used as a rolled material for manufacturing a steel sheet.
As a result, the yield of the continuous cast steel strip is 0.3-0.6
% And the cost of steel sheet production is reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described along the history of the invention.

First, the inventor studied means for eliminating the above deviation of the top steel slab, and conceived of using a slab rolling mill. The ingot rolling mill is for turning a steel ingot originally having a taper in the longitudinal direction into a slab or a sheet bar (material for manufacturing a thin plate). Because it can be changed to It is also because the rolling capacity of the steel slab (the amount of reduction and the amount of width reduction) is larger than other rolling mills.

[0013] Then, using an existing slab mill, it was confirmed whether or not the deviation could be actually eliminated and formed into a rectangular shape using a top steel slab having various deviation values. As a result, the deviation could be eliminated in most cases (maximum width deviation of 40 mm, maximum thickness deviation of 30 mm), and the present invention was completed on the condition that slab rolling was performed.

[0014] The inventor also studied the amount of reduction and the amount of breadth required in the slab rolling, and determined them in the above (1).
Formula (2) The reason for this is that with a rolling reduction or width reduction less than twice the deviation, the deviation cannot be sufficiently eliminated because the unrolled portion remains.

[0015]

EXAMPLE A slab (steel type: 40K class) for producing a steel plate having a thickness of 215 mm was produced by continuous casting. The molten steel of the steel type was smelted in a 280 ton capacity top-bottom blow converter and continuously cast as shown in FIG. The dimensions of each slab obtained were as follows: width: 2000 mm, thickness: 215 mm, length:
There are 28 pieces of 3000 mm. At that time, a portion to be finally solidified has a length of 300 mm after cutting the crop, and its width and thickness are each 40 m in the longitudinal direction.
m and 30 mm deviations had occurred. This is equivalent to what was previously discarded as scrap under the direction of a rolling mill.

Therefore, the present invention was applied to this top steel slab and subjected to slab rolling.

The used bulking mill is the same as described above. As a result, width: 1920 mm, thickness: 155 mm,
It was a rectangular slab having a length of 4300 mm and no deviation. This steel slab is later sent to the rolling process,
When rolling was performed in the same manner as a steel slab having no deviation, it was possible to produce a steel plate having a shape comparable to that of a thick steel plate obtained from the same.

Based on these results, the present invention was applied when manufacturing thick steel plates having different steel types and thicknesses, and the results shown in FIG. 3 were obtained. From FIG. 3, it is clear that the yield of the continuous cast piece is improved by at least 0.3% compared with the conventional one according to the present invention.

[0019]

As described above, according to the present invention, the deviation of the width and thickness generated in the top steel slab obtained by continuous casting is eliminated, and the top steel slab which was conventionally made into a scrap is manufactured by a steel plate manufacturing. It can be used for rolled materials. As a result, the yield of the continuous cast steel strip is improved by 0.3 to 0.6% as compared with the conventional case, and the steel plate manufacturing cost is reduced.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a view for explaining dimensional deviations occurring in width and thickness in a top steel slab in continuous casting.
(B) is a side view.

FIG. 2 is a diagram illustrating a general continuous casting of molten steel.

FIG. 3 is a diagram showing a result of implementing the present invention in a yield.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ladle 2 Molten steel 3 Tundish 4 Mold 5 Solidified body 6 Cooling zone 7 Roller group 8 Top steel slab 9 Deviation 10 Crop part

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hirohide Uehara 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref.

Claims (2)

[Claims] 1. A top steel slab, which is produced in a final solidified portion by continuous casting of molten steel and has a deviation in width and thickness in a longitudinal direction, is used for a material to be rolled after the deviation is eliminated by slab rolling. A method for improving the yield of continuously cast steel slabs. 2. The method for improving the yield of continuously cast steel slabs according to claim 1, wherein the slab rolling is performed with a reduction amount and a width reduction amount determined by the following formulas. Reduction amount ≧ thickness deviation × 2 (1) Width kill amount ≧ width deviation × 2 (2)