JPH0673451A - Production of cr-ni stainless steel thin sheet excellent in workability - Google Patents

Abstract

PURPOSE:To provide the method for producing a Cr-Ni stainless steel thin sheet excellent in workability by a thin sheet casting process. CONSTITUTION:A Cr-Ni stainless steel thin slab case and whose sheet thickness is regulated to <=6mm is coiled in the temp. range of 60 to 790 deg.C, is thereafter reheated to the temp. range of 900 to 1200 deg.C for 20sec to 120min without reducing the slab temp. to <=60 deg.C and is thereafter subjected to cold rolling-annealing- pickling. By subjecting the slab coiled at 60 to 790 deg.C reheating to 900 to 1200 deg.C without executing cooling, MnS is coarsely deposited. The coarsely deposited MnS is harmless one which does not exert adverse influence such as the inhibition of the growth of recrystallized grains at the time of cold sheet annealing. By rendering MnS harmless, the production of the Cr-Ni stainless steel thin sheet product having good workability is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls precipitation of MnS in a cast ribbon in a process for producing a Cr-Ni stainless steel sheet by casting a ribbon having a thickness close to the product thickness.
The present invention relates to a process for producing a Cr-Ni-based stainless steel thin plate having good workability.

[0002]

2. Description of the Related Art In recent years, in order to save energy, reduce costs, and improve product quality, continuous casting has been carried out to research a process of casting a slab having a thickness equal to that of a hot rolled sheet and omitting the hot rolling step. There is. For example, "Heat and Steel"'85, Al97-A
A paper featured in 256 discloses a process for directly obtaining hot rolled sheet equivalent material by continuous casting.

The research and development of this process is mainly carried out on Cr-Ni type stainless steel (SUS304).
AMP ISIJ "vol. 3 (1990), 212, the general condition of the test on an actual scale is reported. However, it is known that the SUS304 thin plate product manufactured by this process has a fine grain structure and has a lower elongation than the thin plate product manufactured by the conventional process. For example, "CAMP ISI
J "vol. 3 (1990), 769, and as a countermeasure, 1
It has been reported that the elongation of the product (cold-rolled annealed sheet) is improved by eliminating homogenizing heat treatment at 150 ° C. for 3 hours to eliminate δ ferrite.

A method of improving elongation by winding a cast piece at 1200 to 800 ° C. has also been investigated (Japanese Patent Application No. 2-6371).

[0005]

However, such high-temperature and long-time heat treatment not only lowers the productivity but also has many problems such as the scale of the slab coil outer winding grows thick and the yield decreases. It was Further, setting the winding temperature to 800 ° C. or higher is not easy because the heat resistance of the winding machine is difficult.

As a result of the research conducted by the present inventors, it has been clarified that not only δ ferrite but also MnS finely precipitated in a cast slab or a cold rolled annealed sheet is the cause of grain refinement of a thin plate product. The effect of inhibiting grain growth by such fine precipitates is extremely large, and as a result, the crystal grains of the product become small and the workability deteriorates. Therefore, in order to improve the workability of the product, it is necessary to coarsely precipitate the precipitates and prevent the precipitation of fine precipitates. Only δ ferrite can be eliminated by heat treatment at high temperature for a short time, but finely precipitated MnS
It was also found that heat treatment at high temperature for a long time is required to coarsen the alloy.

Therefore, the present invention was constructed by investigating and researching a method for coarsening precipitates by a short-time heat treatment to produce a thin plate product having good workability.

[0008]

[Means for Solving the Problems] Generally, a slab that is wound at 850 ° C. or less is in a solid solution state in which MnS cannot be sufficiently coarsely precipitated during winding and during a cooling process after winding. Therefore, if a slab cooled to room temperature is cold-rolled and annealed as it is, MnS finely precipitates due to cold work strain during annealing and inhibits the growth of recrystallized grains, so that the product has a fine grain structure,
Workability is significantly reduced.

Further, since many twins enter the grains in the cooling process (about 60 ° C. or less) in the slab cooled to room temperature, in the process of reheating and coarsely depositing MnS, twins serve as nuclei to form MnS. Since it precipitates finely, it is not easy to coarsen MnS (FIG. 1). Therefore, the present inventors
By reheating the cast slab wound at the temperature below to 60 ° C or lower and keeping it at 900 to 1200 ° C, 2
In a short time of 0 seconds to 120 minutes, MnS was coarsened, and a technology for producing a thin plate product having good workability when cold rolled and annealed to form a thin plate product was established (Fig. 1).

S obtained by coarsening MnS by the process of the present invention
Cold-rolled annealed products produced from US 304 thin slabs have good workability with or without slab annealing, pickling, cold-rolled sheet annealing, pickling and temper rolling.

[0011]

EXAMPLE Austenitic stainless steel based on 18% Cr-8% Ni steel shown in Table 1 was melted and a thin cast piece having a plate thickness of 2.5 mm was cast by an internal water-cooled twin drum casting machine. . The slab is wound in a temperature range of 200 to 950 ° C., cooled to various temperatures, and then reheated to 900 to
After keeping the heat in the temperature range of 1200 ° C for 20 seconds to 120 minutes, cooling to room temperature and descaling, cold rolling, pure annealing, pickling,
The temper rolling was carried out under various conditions, or omitted to obtain a thin plate product.

As a comparative example, a slab cooled to room temperature (20 ° C.) was reheated under the same conditions and a thin plate product was prepared by the same method (Table 2). As a result of examining the mechanical properties of both thin plate products, Table 3
As shown in (4), the thin plate manufactured by the present invention showed good elongation, but the thin plate product manufactured by the comparative example had low elongation.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016]

According to the present invention, Cr-having excellent workability
Ni-based stainless steel sheet may be provided.

[Procedure amendment]

[Submission date] September 7, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Added

[Correction content]

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between a heat pattern of a slab and a precipitation behavior of MnS.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eimar Takeuchi 3434 Shimada, Hikari City, Yamaguchi Prefecture Shin Nippon Steel Co., Ltd.

Claims (4)

[Claims] 1. Cr- represented by 18Cr-8Ni steel
A thin strip having a plate thickness of 6 mm or less is cast from Ni-based stainless steel and wound in a temperature range of 60 to 790 ° C., and then the slab temperature is lowered to a temperature range of 900 to 1200 ° C. without lowering the slab temperature to 60 ° C. or less. Reheated from 120 seconds to 120 minutes and then cooled, the cast ribbon is annealed, pickled, cold rolled, then annealed-pickled,
Alternatively, a method for producing a Cr-Ni-based stainless steel thin plate having excellent workability is characterized by performing bright annealing to obtain a thin plate product. 2. A Cr- represented by 18Cr-8Ni steel.
A thin strip having a plate thickness of 6 mm or less is cast from Ni-based stainless steel and wound in a temperature range of 60 to 790 ° C., and then the slab temperature is lowered to a temperature range of 900 to 1200 ° C. without lowering the slab temperature to 60 ° C. or less. Reheated from 120 seconds to 120 minutes, and then cooled, the cast strip is pickled, cold-rolled, and then annealed-pickled or bright annealed to obtain a thin plate product, which is excellent in workability. -A method for manufacturing a Ni-based stainless steel thin plate. 3. A Cr- represented by 18Cr-8Ni steel.
A thin strip having a plate thickness of 6 mm or less is cast from Ni-based stainless steel and wound in a temperature range of 60 to 790 ° C., and then the slab temperature is lowered to a temperature range of 900 to 1200 ° C. without lowering the slab temperature to 60 ° C. or less. Reheated from 120 seconds to 120 minutes and then cooled, the cast ribbon is annealed, pickled, cold rolled, then annealed-pickled,
Alternatively, a method for producing a Cr-Ni-based stainless steel thin plate having excellent workability, which comprises performing bright annealing and then temper rolling to obtain a thin plate product. 4. A Cr- represented by 18Cr-8Ni steel.
A thin strip having a plate thickness of 6 mm or less is cast from Ni-based stainless steel and wound in a temperature range of 60 to 790 ° C., and then the slab temperature is lowered to a temperature range of 900 to 1200 ° C. without lowering the slab temperature to 60 ° C. or less. It is characterized in that a thin strip product is obtained by pickling and cold rolling the cast strip that has been reheated for 120 minutes from 120 seconds, and then performing annealing-pickling or bright annealing, and then temper rolling. And a method for producing a Cr-Ni-based stainless steel thin plate having excellent workability.