JPH0829325B2 - Thin plate manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has a thickness close to that of a product cast by a so-called synchronous continuous casting process in which there is no relative speed difference between a cast piece and an inner wall surface of a mold. The present invention relates to a method for cold rolling a slab to produce a thin plate.

[Conventional technology]

The conventional method of producing a thin plate using a continuous casting method, casting in a slab with a thickness of 100 mm or more while vibrating the mold in the casting direction, performing surface maintenance of the obtained slab, and heating in a heating furnace After that, hot rolling is performed with a hot strip mill consisting of a rough rolling mill and a finishing rolling mill row to form hot strips with a thickness of several mm, and further annealed as necessary, followed by descaling and cold rolling for final annealing. Was to do.

In such a conventional process, in order to hot-roll a slab with a thickness of 100 mm or more, a long hot strip mill is required, and a problem of using a large amount of energy for heating and rolling the slab was there.

With respect to this problem, research on a process for producing a slab having a thickness equal to or close to that of a hot strip by continuous casting is under way. For example, "Iron and Steel"'8
It is a synchronous continuous casting process with no relative velocity difference between the slab and the inner wall of the mold, such as twin roll method and twin belt method, as introduced in the papers featured in 5-A197 to '85 -A256. .

However, there remains an unsolved problem in manufacturing a thin plate product through these synchronous continuous casting processes.

[Problems to be Solved by the Invention]

When a thin plate is manufactured by adopting the process of continuously casting a slab (thin strip slab) with a thickness equal to or close to that of hot strip, which is being developed as a new process, from casting to product Since the process of (1) is shortened, there is a problem in the surface properties of the product.

The present inventors cast molten steel of various components by a twin roll continuous casting machine of an internal water cooling system to form a strip-shaped slab having a plate thickness of 2 to 5 mm, and after cold rolling this, a part is annealed and It was pickled to give a 2B product, and part of it was bright annealed to give a BA product. Further, a continuously cast slab having a thickness of 100 mm or more was hot-rolled and then cold-rolled to manufacture 2B products and BA products. As a result of a detailed comparison of the surface properties of these products, the products using a twin roll continuous casting machine were observed to have a fine crease-like undulation (roping) peculiar to this product.

The present invention, when producing a thin plate by cold rolling a thin strip slab having a thickness close to the product thickness cast by a synchronous continuous casting process without a relative speed difference between the slab and the mold inner wall surface, The object of the present invention is to provide a simple manufacturing method capable of obtaining a product free from the characteristic defects when subjected to this process, such as roping.

[Means for solving the problem]

In order to achieve such an object, the present invention has a thickness 10 obtained by a continuous casting machine in which the mold wall surface moves in synchronization with the slab.
It is intended to provide a thin plate manufacturing method for cold rolling a strip-shaped slab of mm or less using a roll having a Young's modulus of 30,000 kgf / mm ² or more.

[Action]

In the present invention, the continuous casting machine in which the mold wall surface moves in synchronization with the slab is a single roll method, a twin roll method, an internal method as described in "Iron and Steel"'85 -A200 to '85 -A203. The continuous casting machine performs a ring method, a roll belt method and a twin belt method, a moving mold continuous casting method, a method called a spray roll method, and the like.

The present inventors have found the cause of the above-mentioned peculiar roping observed in a product manufactured by cold rolling a thin strip-shaped slab cast by a twin roll continuous casting machine, and solving means thereof. Revealed.

That is, since such a strip-shaped slab has larger crystal grains than a hot strip, it was clarified that roping occurs due to the plastic anisotropy of individual crystal grains during cold rolling, and elastic deformation occurs. It was possible to prevent the occurrence of roping by suppressing the undulation that tends to occur on the surface of the thin plate by cold rolling with a difficult roll. The cause and the solving means are not limited to the case of using the twin roll continuous casting machine, and are also applied to the case of performing the various continuous casting processes in which the mold wall surface moves in synchronization with the slab.

 The present invention will be described in more detail below.

First, when manufacturing a thin plate from a strip-shaped cast piece obtained by the continuous casting machine, the thickness of the cast piece is set to 10 mm or less in order to reduce the load of cold rolling as much as possible.

Next, when the obtained strip-shaped cast piece was descaled and then cold-rolled, a roll having a Young's modulus of 30000 kgf / mm ² or more was used in order to suppress the occurrence of roping. Use of a roll having a Young's modulus of less than 30,000 kgf / mm ² makes it difficult to suppress the occurrence of roping. When cold-rolling a hot strip, since the crystal grains of the material before rolling are small, even if the plastic anisotropy of each grain is different, it deforms almost uniformly as a whole, so roping does not occur. In the case of a strip-shaped slab, since the crystal grains are large, the plastic anisotropy of each grain causes the amount of deformation in the plate thickness direction to become non-uniform within the plate surface, which appears as roping on the surface of the thin plate. The present inventors have previously proposed to suppress the occurrence of roping by cold rolling with a hard roll of Hv600 or more (Japanese Patent Application No. 1-59780), but with such a hard roll, before cold rolling. It was necessary to limit the materials of (1) to those that have taken measures to make them finer. According to the method of the present invention,
Since rolling is performed by a roll having a Young's modulus of 30000 kgf / mm ² or more and less likely to be elastically deformed, the occurrence of roping can be suppressed even for a material for which a grain refining means as in the previous application is not taken.

In the present invention, when the cold rolling is performed twice or more with the intermediate annealing interposed, a roll having a Young's modulus of 30,000 kgf / mm ² or more may be used in the first cold rolling. This is because in the second and subsequent cold rolling, recrystallization is refined by intermediate annealing. The cold rolling in the present invention may be performed in a temperature range in which coloring due to oxidation does not occur, and may be so-called warm rolling. After cold rolling to the product plate thickness, it is made into a thin plate product by a known means.

〔Example〕

Two kinds of Fe-Ni alloys and two kinds of austenitic stainless steel consisting of the components shown in Table 1 were cast into a strip-shaped slab of 2 to 5 mm by an internal water-cooled vertical twin roll continuous casting machine, and cooled. Hot rolled to produce sheet products. The Young's modulus of cold rolling rolls varies depending on the roll material.
000kgf / mm ² is SKD, 25000kgf / mm ² is powder HSS, 31000kg
f / mm ² is ceramics (Si ₃ N ₄ main component), 50000-64000kg
f / mm ² is tungsten carbide. The roping of the product was judged by the height of the swell measured by a roughness meter.

Nos. 1 to 6 of the invention examples shown in Table 2 have cold rolling ratios of 70 to
In the 95% range, cold rolling was performed using rolls having a Young's modulus of 30,000 kgf / mm ² or more, so roping did not occur. The height of the swell shown in the roping column of Table 2 is
If it is 0.2 μm or less, it is not judged as roping and there is no problem as a product.

In contrast, Comparative Examples Nos. 7 and 8 have a Young's modulus of 30,000 kgf / m
Since it was cold-rolled using a roll of less than m ^2, roping occurred.

[Effects of the Invention] According to the method of the present invention, when a thin strip-shaped slab having a thickness close to that of a continuously cast product is cold-rolled to produce a thin plate, the total reduction amount from the slab to the product is small. Since the problem of surface quality caused by this is solved, a hot strip mill becomes unnecessary, and a great effect can be obtained in process shortening and energy saving.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Ogawa 1-1-1 Edamitsu, Hachimanto-ku, Kitakyushu, Fukuoka Prefecture Inside the Nippon Steel Co., Ltd. 3rd Technical Research Laboratory (56) Reference JP-A-60-121010 ( JP, A)

Claims (1)

[Claims] 1. A thin strip-shaped slab having a thickness of 10 mm or less obtained by a continuous casting machine in which the wall surface of the mold moves in synchronization with the slab is cold-rolled using a roll having a Young's modulus of 30,000 kgf / mm ² or more. A method for manufacturing a thin plate, which comprises rolling.