JPH0360814A - Manufacture of stainless sheet excellent in surface quality - Google Patents

Abstract

PURPOSE:To obtain a stainless sheet excellent in surface quality by cooling a thin belt-like cast billet after casting in a specified temperature range and at a specified speed and performing a scrubber grinding process as the preceding and succeeding process of a descaling process by pickling. CONSTITUTION:The thin belt-like cast billet 5 is casted by moving synchronously the wall surface of casting mold, which is composed of cooling drums 3, with the cast billet 5. After descaling by use of a pickling tank 11, the billet is rolled in cold. Then, in the case of cooling of the thin belt-like cast billet 5 after casting, the billet is cooled at the speed >=10 deg.C/sec in the temperature range of 900-600 deg.C. As the preceding and succeeding process of the process where descaling is executed by pickling in the pickling tank 11, scrubber grinding process is performed by use of scrubbers 12. By this way, surface defects of sheet due to microgrooves can be reduced.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method of manufacturing a thin stainless steel plate with excellent surface quality, and in particular, a method for producing a stainless steel sheet with excellent surface quality, in particular a method for producing a stainless steel sheet with no relative velocity difference between the slab and the inner wall surface of the mold.
The present invention relates to a method of manufacturing a stainless-steel thin plate by cold rolling a thin strip having a thickness close to that of a product cast by a so-called synchronous continuous casting process.

[Prior Art] In recent years, in the field of continuous casting of stainless steel cavities, there has been a strong desire to develop a technology for producing thin strip-shaped slabs that are close to the final shape, with the aim of reducing production costs. In response to this request, for example, "Tetsu to Hagane""85-A197~'85
-As introduced in the paper featured in A256,
Synchronous continuous casting methods in which there is no relative speed difference between the slab and the inner wall of the mold are known, such as the twin roll method (twin drum method) and the twin belt method.

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

In other words, unlike the case of slabs produced by conventional continuous casting equipment, these continuous casting methods were developed with the aim of obtaining thin strip-shaped slabs that can be rolled to a lesser extent in subsequent processes. It is what was done. Therefore, if there is thickness variation or surface cracks in the thin strip slab,
This causes defects on the surface of the product, and there is a great danger that the product value will be significantly impaired.

Therefore, in order to prevent defects such as cracks from occurring in the thin strip slabs, a recess (of a predetermined depth) having a circular or oval opening of a predetermined size is formed on the peripheral surface of the cooling drum.
There is a method of forming and casting a plurality of dimples (Japanese Patent Application No. 62-240479, Japanese Patent Application No. 62-240481, and Japanese Patent Application No. 63-202962).

[Problem to be solved by the invention]

Although the above method prevents surface defects such as cracks, if casting is performed with depressions provided on the circumferential surface of the cooling drum, the richness of the cooling drum will be transferred as depressions on the solidified shell surface of the slab. The air gap created by this depression creates a rapid cooling zone and a slow cooling zone in the slab, and the crystal grains become finer in the rapid cooling zone.
In the slow cooling zone, the grains become coarse and uneven texture occurs on the surface of the slab. Furthermore, grain boundary oxidation occurs at grain boundaries. This texture unevenness is shown, for example, in the surface texture photograph of the slab after pickling shown in FIG. When a strip-shaped slab with such uneven structure and grain boundary oxidation is pickled, the oxides at the grain boundaries are removed, but the grain boundaries are etched into grooves (this is called anti-black groups). When cold rolling is then performed, the surface of the thin sheet after rolling becomes uneven in structure as shown in the photograph shown in FIG. 6, and this becomes apparent as uneven gloss on the surface of the product.

The present invention is a method for producing stainless steel sheet products by casting thin strip slabs using a continuous casting machine in which the mold wall surface moves in synchronization with the slab, pickling the strips, and cold rolling them. To prevent uneven gloss of thin plate products after cold rolling caused by micro groups on the surface of the slab after pickling and the uneven texture of the strip-shaped slab caused by the dimples provided on the mold wall to prevent this. The purpose is to

[Means to solve the problem]

According to the present invention, the above-mentioned problem can be solved by the process of casting a thin slab by a continuous casting machine in which the mold wall surface moves in synchronization with the slab, descaling it by pickling, and then cold rolling the stainless steel. In the steel manufacturing method, when cooling the ribbon-shaped slab after the casting, a temperature of 900 to 6
Stainless steel with excellent surface quality characterized by cooling in the temperature range of 00°C at a cooling rate of 10°C/sec or more and performing a scrubber grinding process as a pre-process and post-process of the descaling process by pickling. The problem is solved by a thin plate manufacturing method.

[For production]

According to the present invention, continuously cast thin strip-shaped slabs have a weight of 900 to
Since the temperature range of 600°C is cooled at a cooling rate of 10° (:/sec or more), the precipitation of Cr carbide at the grain boundaries is suppressed. Although there are irregularities with transferred dimples and structural unevenness as shown in FIG. 5, grain boundary oxidation is mild.

Scrubber grinding before and after descaling is done using 5iCAff.
Grinding is done by rotating a brush roll made by laminating and compressing disks made of nylon or the like containing abrasive grains such as izOs to a desired length, and grinding the concave portions of the irregularities on the surface of the slab to some extent. I can do it.

However, since it is not possible to uniformly grind the entire surface of the slab, oxide scale remains on the slab surface after scrubber grinding before descaling, and grain boundary oxidized portions also remain. However, the way they survive is random. When a cast slab is descaled by pickling, scale is removed and oxides in grain boundary oxidized areas are also removed, but micro groups are generated. When scrubber grinding is performed after descaling, the short black groups on the slab surface are ground and reduced, and their distribution becomes more random.

When cold rolling is then carried out, the frequency of surface defects based on microgroups on the surface of the rolled sheet is significantly reduced.
Its size and shape are random.

Therefore, uneven gloss does not occur on the surface of the thin plate product.

If the slab is cooled slowly after casting, which is outside the conditions of the present invention, the occurrence of Cr-deficient regions due to precipitation of Cr carbides at grain boundaries becomes significant, and grain boundary oxidation deepens. When this is pickled, the microglobes become deep and wide, so the occurrence of surface defects after cold rolling cannot be suppressed unless the amount of scrubber grinding is increased.

In addition, if the slab is cooled in a non-oxidizing atmosphere, grain boundary oxidation can be suppressed, but if the slab is cooled slowly, Cr carbide precipitation at the grain boundaries will not change, so a Cr-deficient region will also occur, and this can be removed by pickling. Microglobes are then similarly formed. The amount of scrubber grinding can be increased by installing brush rolls in multiple stages, but this is not practical.

In the present invention, it is preferable to perform mechanical descaling such as shot blasting before scrubber grinding before descaling.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic cross-sectional view illustrating a method for manufacturing a ribbon-shaped slab by continuous casting using a twin-roll method according to this embodiment.

As shown in Figure 1, the depth is 30 offshore and the size is 0 and 5.
A cooling drum 3 in which circular dimples with a diameter of mm were uniformly arranged was installed, and a thin strip-shaped slab 5 was cast. That is, for example, 5US304 injected from tandate 1
The molten steel 2 forms a pool between a pair of cooling drums 3. The solidified shells grown on the circumferential surface of each cooling drum 3 are pressed together at a kissing point 4 and formed into a thin strip-shaped slab 5.
It is sent out as a sheet, is wound up by a winding machine 8 via a pinch roll 6, a cooling device 7, etc., and is conveyed to the next process. Note that a cleaning brush 9, a drum coater 10, etc. may be arranged on the circumferential surface of the cooling drum 3. The pool of molten steel 2 and the vicinity directly below the cooling drum 3 are preferably cast in a non-oxidizing atmosphere such as nitrogen (N2) or argon (Ar). This suppresses the surface oxidation scale of the thin strip-shaped slab 5, thereby reducing the burden of descaling, which is a subsequent process. In addition, the cooling of the ribbon-shaped slab 5 before winding is performed at a temperature range of 900 to 600°C by 10"C/100°C to suppress sensitization.
Cooling was performed by gas blowing, water spray, etc. at a cooling rate of 2 seconds or more.

The rolled-up thin strip-shaped slab is descaled in a pickling tank 11 as shown in FIG. 2, and then cold-rolled into a product. In the example of the present invention, scrubbers 12 are installed before and after the pickling tank 11.
was used for grinding.

Sample material Nα1. using 5US304 as an example of the present invention. N
α2 and No. 3, and sample material No. 4 using 5US430, and sample material N using 5US304 as a conventional example [15, and sample material No. α6 and No. 7 and 5O5430 using 5US304 as a comparative example. For each of the sample materials Nα8 used, the slab thickness (M) was 900 ~
Table 1 shows the results regarding the rank of surface gloss unevenness after cold rolling, including the cooling rate (°C/sec) between 600°C, scrubber grinding conditions, pickling method, and cold rolling ratio (%). Scrubber grinding is performed by rotating a brush roll with a bottom shape made by stacking and compressing disks flocked with nylon containing abrasive grains, and checking the type of abrasive grains, the thickness of the nylon, the number of roll rotations, and the roll rolling load current. are shown in Table 1.

In the conventional example in which scrubber grinding was not performed, the surface gloss unevenness after cold rolling was large, and in the comparative example in which scrubber grinding was performed only before or after pickling, the gloss unevenness remained, although it was slight. On the other hand, in the example of the present invention in which scrubber grinding was performed before and after pickling, uneven gloss did not occur.

Conventional example No. 5 slab before cold rolling (pickling plate 2.0
As shown in FIG. 5, the surface (m+++ thickness) has coarse grain portions and fine grain portions, and micro groups are observed at grain boundaries. After cold rolling, surface defects caused by micro groups appear on the surface of the thin plate (0.3 mm thick), as shown in Figure 6, and defects occur in areas where the structure of the slab was fine-grained. The grains have become denser, and the parts that were coarse grains have become coarser. Such uneven texture on the surface of the thin plate results in uneven gloss. On the other hand, the slab of invention example No. 1 before cold rolling (
As shown in FIG. 3, on the surface of the pickled plate (2.0 mm thick), micro groups are observed at grain boundaries, but they are reduced by scrubber grinding before and after pickling, and their distribution is random. A thin plate (0.3mm thick) after cold rolling this
As shown in FIG. 4, the surface has significantly fewer surface defects caused by microglobes, and their size and distribution are random. Therefore, in the example of the present invention, uneven gloss does not occur.

[Effects of the Invention] As explained above, according to the present invention, during continuous casting of thin strip-shaped slabs, the slab is rapidly cooled to prevent sensitization, and by grinding with a scrubber before and after pickling, micro-groups can be removed. It is possible to significantly reduce the surface defects of the thin plate caused by oxidation and to make the distribution random, so it is possible to obtain a stainless steel thin plate with good surface quality and no uneven gloss.

[Brief explanation of drawings]

Fig. 2 is a schematic cross-sectional view illustrating a method of manufacturing a thin strip slab by continuous casting using the twin roll method according to the present invention, and Fig. 2 is a pickling process according to the present invention, and a scrubber before and after the pickling process according to the present invention. FIG. 3 is a schematic diagram showing the grinding process, and FIGS. 3 and 4 are photographs of the metallographic structures of a pickled plate and a cold-rolled plate of 5IIS304 according to the present invention, respectively, and FIGS. This is a photograph of the metallographic structure of a pickled plate and a cold-rolled plate of 5US304. 1...Tandishu, 2...Nongko, 3...
・Cooling drum, 4... Kissing point, 5... Thin strip shaped slab, 6 7... Cooling device, 8 9... Cleaning brush, (O... Drum coater, 1 12... Scrubber ...pinch roll, ...winding machine, 1...pickling tank,

Claims (1)

[Claims] 1. A thin stainless steel plate that includes the process of casting a strip-shaped slab using a continuous casting machine in which the mold wall surface moves in synchronization with the slab, descaling it by pickling, and then cold rolling it. In the manufacturing method of 900-6 during cooling of the thin strip-shaped slab after the casting,
Stainless steel with excellent surface quality characterized by cooling in the temperature range of 00°C at a cooling rate of 10°C/sec or more and performing a scrubber grinding process as a pre-process and post-process of the descaling process by pickling. Method of manufacturing thin plates.