JPH0620606B2 - Method for producing stainless steel sheet with excellent surface quality - Google Patents

Description

The present invention relates to a method for producing a stainless steel sheet having excellent surface quality, and in particular, there is no relative speed difference between a slab and a mold inner wall surface.
The present invention relates to a method for producing a stainless steel thin plate by cold rolling a thin strip slab having a thickness close to the product thickness cast by a so-called synchronous continuous casting process.

[Conventional technology]

In recent years, in the field of continuous casting of stainless steel, there has been a strong demand for the development of a technique for producing a thin strip-shaped slab having a final shape for the purpose of cutting down the production cost. In response to this requirement, for example, twin roll method (twin drum method), twin belt method, etc., such as those introduced in the papers featured in "Iron and Steel"'85 -A197 to '85 -A256 A synchronous continuous casting method in which there is no relative speed difference between the mold and the inner wall surface of the mold is known.

In these continuous casting methods, it is an important issue to stably maintain the surface quality of the slab at a high level.

That is, unlike the case of the slab manufactured by the conventional continuous casting equipment, these continuous casting methods are developed with the aim of obtaining a strip-shaped cast piece capable of reducing the degree of rolling in the subsequent steps. It was done. Therefore, if there is fluctuation in wall thickness or surface cracks in the thin strip,
This becomes a defect on the product surface, and there is a great risk that the commercial value will be significantly impaired.

Therefore, in order to prevent the occurrence of defects such as cracks in the thin strip slab, a circular (or oval) opening of uniform size is formed on the peripheral surface of the cooling drum as shown in FIG. There is a method of casting by forming a plurality of depressions (dimples) each having a predetermined depth (Japanese Patent Application Nos. 62-240479 and 62-24).
0481 and Japanese Patent Application No. 63-202962).

[Problems to be Solved by the Invention]

Although surface defects such as cracks can be prevented by the above method, when a recess is provided around the cooling drum and casting is performed, the recess of the cooling drum is transferred to the solidified shell surface of the slab as a recess. Due to the air gap created by these depressions, a rapidly cooled part and a slowly cooled part are generated in the slab, and the crystal grains become fine grains in the rapidly cooled part.
Coarse grains are formed in the slow cooling portion (Figs. 9 and 10), and uneven structure occurs on the surface of the slab. Also, grain boundary oxidation occurs at the crystal grain boundaries. This texture unevenness is shown, for example, in the surface texture photograph of the slab after pickling shown in FIG. When pickling a thin strip-shaped cast product having such unevenness in structure and grain boundary oxidation, oxides at the grain boundaries are removed, but the grain boundaries are etched into grooves (this is called microgrooves). Then, when cold rolling is performed, the surface of the thin plate after rolling becomes uneven in structure (12th
(Fig. 13, Fig. 13), this is uneven gloss on the surface of the product. A good gloss part corresponds to a coarse grain part, and a poor gloss part corresponds to a fine grain part.

The present invention is a method of producing a strip-shaped cast product by casting a strip-shaped cast product by a continuous casting machine in which the mold wall surface moves in synchronization with the cast product, in a method of producing a steres thin plate product by pickling and cold rolling, cracking of the cast product. Dimples on the wall of the mold for prevention
It is an object of the present invention to prevent the occurrence of uneven luster of a thin plate product after cold rolling, which is caused by uneven structure of a strip-shaped cast product caused by the above and microgrooves on the surface of the cast product after pickling.

[Means for Solving the Problems]

According to the present invention, according to the present invention, stainless steel including a step of performing cold rolling after casting thin strip slab by a continuous casting machine in which the mold wall surface moves in synchronization with the slab, and performing descaling by pickling. In the method for manufacturing a thin plate, the mold wall surface has a size of 0.1 mm or more and 1.0 mm or less, and the arrangement is characterized in that a random concave pattern is provided to form a random convex pattern on the thin strip-shaped slab surface. It is solved by a method of manufacturing a stainless steel plate having excellent quality.

[Work]

According to the present invention, the size of the dimples provided on the wall surface of the mold is 0.1 mm or more and 1.0 mm or less, and the arrangement is a random concave pattern, so these dimples are transferred as a convex pattern to the thin strip slab. . Therefore, the slab becomes a surface having a convex pattern in which the size, shape, and arrangement are random, and its structure is that in which coarse grains and fine grains are randomly arranged. When this is pickled, microgrooves appear at grain boundaries of random distribution. Therefore, since the structure of the surface of the thin plate after cold rolling becomes random, uneven gloss does not occur in the thin plate product.

The shape of the concave pattern on the mold wall surface in the present invention is preferably circular, elliptical, square, or the like. The size is 0.1mm
As above, it should be varied within 1.0mm. Size 0.1
If it is less than mm, the slow cooling portion becomes small and the slow cooling effect cannot be obtained. Further, if it exceeds 1.0 mm, the unit of the unevenness of the structure is large even if it is randomly arranged, and it becomes apparent as uneven gloss.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

Table 1 shows austenitic stainless SUS304 and ferritic stainless SUS430 made into strip strips by a twin roll continuous casting machine incorporating a cooling drum having dimples with a concave pattern, pickled, descaled, and cold rolled. The result of uneven surface gloss of the thin plate product manufactured by the above is shown.
As conditions for the dimples on the cooling drum, the shape, size,
Depth, gap and placement are indicated. FIG. 1 is an example of a random arrangement according to the present invention. In the example of the present invention in which the dimples on the wall surface of the mold have a random concave pattern, a random convex pattern is transferred to the slab as shown in FIGS. 2 and 3, and the texture of the slab has coarse grains and fine grains. It became one that exists at random. In the conventional example, the dimples on the wall surface of the mold are arranged in a regular concave pattern as shown in FIG.
As shown in FIG. 9 and FIG. 10, a regular concave pattern was transferred to the cast piece, and a structure in which coarse grain concave portions were regularly present was formed.

As shown in Table 1, the manufacturing method according to the present invention (No. 1 to N
The surface quality of the thin plate product obtained according to o.8) was good without uneven gloss, while the products obtained according to Comparative Examples (No. 9 to No. 12) had a slight uneven gloss. Or, the uneven gloss was large.

The surface changes before and after cold rolling are shown for Inventive Example No. 1 and Comparative Example No. 9. FIG. 4 is a surface schematic diagram having a random convex pattern of a slab of the invention sample No. 1 before cold rolling (after pickling). As shown in FIG. 5, no uneven gloss is observed on the surface circle of a thin plate which is 85% cold rolled. FIG. 6 is a schematic surface view of a slab of Comparative Example No. 9 before cold rolling (after pickling) having a regular concave pattern. This 8
On the surface of the 5% cold-rolled thin plate, uneven luster was observed as shown in FIG. 7 (uneven gloss C rank).

Microscopic observation of the surface of the thin plate after cold rolling reveals surface defects as shown in FIG. 13 due to microgrooves, and in the comparative example, it corresponds to the coarse grain portion having a regular distribution before cold rolling. Surface defects are regularly roughened, whereas in the examples of the present invention, since the structure before cold rolling is random, the density of surface defects after rolling is random.

[Effects of the Invention] As described above, according to the present invention, during the production of a thin strip slab,
Since the slab structure is randomized, it is possible to obtain a stainless thin plate having excellent surface quality without the appearance of gloss unevenness on the surface at the end of the subsequent cold rolling step.

[Brief description of drawings]

FIG. 1 is a view schematically showing a random concave pattern of dimples on the wall surface of a mold according to the present invention, and FIGS. 2 and 3 are schematic plane structure diagrams showing the structure of a slab according to the present invention and the same, respectively. FIG. 4 is a sectional structure diagram, FIG. 4 is a photograph of a surface metallographic structure of a slab having a random convex pattern according to the present invention after pickling (plate thickness 2.0 mm), and FIG. FIG. 6 is a photograph of the surface metallographic structure of a cold rolled sheet which was cold-rolled to a plate thickness of 0.3 mm (rolling rate of 85%). FIG. 6 shows an example of a cast sheet having a regular concave pattern according to the conventional method. FIG. 7 is a photograph of the surface metallographic structure after pickling (sheet thickness 2.0 mm). FIG. 7 shows the cold rolled sheet obtained by cold rolling the slab of FIG. 6 to a sheet thickness of 0.3 mm (85% rolling rate). 8 is a photograph of the surface metallographic structure, and FIG. 8 is a schematic view showing a regular concave pattern of dimples on the wall surface of the mold according to the conventional method. FIG. 10 is a schematic plan structure diagram and a cross-sectional structure diagram showing a slab structure according to the conventional method, and FIG. 11 is a slab after pickling (plate thickness 2.0 mm) according to the conventional method.
It is a photograph of the metal structure of the surface, and the rough part in the figure is the dimple corresponding part, and Figs. 12 and 13 show 50% cold rolled sheet (sheet thickness 1.0 mm) and 85% cold rolled sheet (sheet thickness, respectively). 11th of 0.3mm)
The surface metallographic photograph of the portion corresponding to the figure is shown.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigenori Tanaka 3434 Shimada, Hitsu-shi, Yamaguchi Pref., Nippon Steel Co., Ltd. Hikari Steel Works (72) Akio Kasama 3434 Shimada, Hikari-shi, Yamaguchi Pref. Kotsu Steel Works, Ltd. (56) References JP-A-62-254953 (JP, A)

Claims (1)

[Claims] 1. A method for producing a stainless steel thin plate, which comprises the steps of casting a strip-shaped slab by a continuous casting machine in which the wall surface of the mold moves in synchronization with the slab, descaling by pickling, and then cold rolling. , The size of the mold wall is 0.1 mm
A method for producing a stainless steel thin plate having excellent surface quality, characterized in that a concave pattern having a size of 1.0 mm or less and arranged randomly is provided to form a random convex pattern on the surface of the strip-shaped slab.