JPH0826406B2 - Method for producing Cr-Ni type stainless steel thin plate excellent in surface quality and workability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a so-called synchronous continuous casting process in which there is no relative velocity difference between a slab and an inner wall surface of a mold, and the slab thickness is set close to the product thickness by using a Cr-Ni type stainless steel. The present invention relates to a method for producing a thin plate, in which the structure is refined from the cast piece stage and MnS is precipitated to produce a Cr-Ni-based stainless steel thin plate having excellent surface properties and workability.

[0002]

2. Description of the Related Art Conventionally, in order to produce a stainless steel thin plate by a continuous casting method, a casting having a thickness of 100 mm or more is cast while vibrating the casting mold in the casting direction, and the surface of the obtained casting is cleaned. After heating at 1000 ° C. or higher in a heating furnace, hot rolling was performed by a hot strip mill consisting of a rough rolling mill and a finishing rolling mill row to obtain a hot strip having a thickness of several mm.

When the hot strip thus obtained is cold-rolled, the hot strip subjected to strong hot working is softened in order to secure the shape (flatness), material and surface texture required for the final product. The hot-rolled sheet was annealed for this purpose, and the scale on the surface was removed by grinding after the pickling step. This conventional process requires a large amount of energy for heating and processing the material in a long hot rolling facility, and it is difficult to say that the manufacturing process is excellent in terms of productivity. Also, the final product is
Since a slab with a thickness of 100 mm or more is manufactured by many processes, the texture develops, and it is necessary to consider the anisotropy when the product is pressed by the user. There were many restrictions on usage.

By the way, recently, in order to solve the problem that a long hot rolling facility, a large amount of energy, and a rolling power are required to roll a slab having a thickness of 100 mm or more into a hot strip, it has been recently continuous. Research on a process for obtaining a slab (thin band) having a thickness equal to or close to that of a hot strip in the casting process is underway. For example, the paper featured in "Iron and Steel"'85,A197-'85, A256 discloses a process for directly obtaining hot strip by continuous casting. In such a continuous casting process, when the gauge of the slab (strip) to be obtained is in the level of 1 to 10 mm, the twin drum system is used, and the gauge of the slab is in the level of 20 to 50 mm. Sometimes the twin belt method is being considered.

However, it is said that there is still a problem in the casting stage in these continuous casting processes, and it has not reached the stage where the problems concerning the material and surface properties of the product have been solved. "CAMP ISIJ" vol.
1, 1988, 1670 to 1705, the SUS304 sheet product manufactured by twin drum casting and single cold rolling process has a fine grain structure and lower elongation than the conventional process. It is described that the slab is annealed at a high temperature for a long time to eliminate the δ ferrite remaining in the slab.

In addition, "CAMP ISIJ" vol. Three
In (1990) P770, it was reported that orange peel-like surface defects were generated, and as a countermeasure against this, reducing the γ grain size before cold rolling was reported.

[0007]

In a process which is being developed as a new process and is premised on obtaining a slab (thin strip) having a thickness equal to or close to that of a hot strip by continuous casting. Since the steps from casting to products are simplified, the surface characteristics and workability of stainless steel sheet products are sensitively affected by the slab properties. That is, in order to obtain a product having excellent surface properties and workability, it is necessary to obtain an excellent cast piece.

The inventors of the present invention have already clarified a method of refining the γ grains of a cast piece as a method for preventing the occurrence of surface defects called the roping phenomenon or the above-mentioned orange peel phenomenon in a new process, and applied for a patent. Has come. Japanese Patent Application No. 63-221471, Method by cooling slab and hot rolling Japanese Patent Application No. 63-169095, cooling slab and 2CR method Japanese Patent Application No. SHO 63-221472, slab cooling and δ ferrite control Japanese Patent Application No. 63 -286680, slab cooling and δ-ferrite control Japanese Patent Application No. 1-1586, slab cooling and addition of fine-grained elements However, only with these methods, elongation of thin plate products, which is a characteristic of Cr-Ni stainless steel, It became clear that workability was insufficient.

The present invention has been made for the purpose of providing a simple manufacturing process capable of obtaining an austenitic stainless steel sheet free from surface defects such as roping and orange peel phenomenon and having good elongation and workability.

[0010]

The gist of the present invention is as follows. (1) Cr-Ni represented by 18% Cr-8% Ni steel
Using a continuous casting machine in which the mold wall surface moves in synchronism with the slab, the cooling rate during solidification is 100 ° C / se.
As c or more, it is continuously cast into a thin strip-shaped slab with a thickness of 6 mm or less and cooled, and during the cooling of the slab, it is held within a temperature range of 1250 to 900 ° C for 2 minutes or less and cooled to below 900 ° C. Rolling, annealing, pickling, and then pre-cold rolling applying a reduction rate of 60% or less, then annealing in a temperature range of 850 ° C. or higher and recrystallization to obtain an average grain size of γ grains of 50 μm or less. The surface characterized by being subjected to acid pickling, then cold rolling to a final thickness, and finally cold-rolling the obtained cold-rolled sheet, followed by pickling or bright annealing and temper rolling. A method for producing a Cr-Ni-based stainless steel thin plate excellent in quality and workability.

(2) Cooling below 900 ° C. results in 900-6
The temperature range between 00 ° C. is cooled at an average cooling rate of 10 ° C./sec or more, wound at 600 ° C. or less, and then pickled without annealing. A method for producing an excellent Cr-Ni-based stainless steel thin plate.

[0012]

The present inventors have found that the strip continuous casting method is used for C
Measures for improving elongation and workability in the r-Ni stainless steel thin plate manufacturing process were examined. As a result, in the case of a thin cast piece, MnS does not precipitate at the time of cooling and finely precipitates in the final annealing after cold rolling, which strongly suppresses grain growth, which results in a fine grain structure, which reduces elongation, It was revealed that the workability was deteriorated, and therefore it was confirmed that it is necessary to deposit MnS in a sufficiently large amount in the cast piece stage to render it harmless.

The present inventors have investigated an efficient method for this MnS precipitation. The slab was given a thermal history as shown in FIG.
(A) is a thermal history of a slab that is air-cooled after being cast by a twin roll for experiment, (b) is a thermal history of a slab that is strongly cooled with a water-cooled roll from immediately below the casting, and (c-1) is a roll immediately below the casting Thermal history of the slab, which was cooled and held at 1050 ° C for 15 seconds and then cooled,
Similarly, (c-2) shows the heat history of the slab that was cooled after being retained for 30 seconds, and (c-3) is the heat history of the slab that was cooled after being retained for 60 seconds.

After descaling these slabs, 1.5
Table 1 shows the product properties as a result of cold rolling to mmt, annealing at 1000 ° C., pickling, and cold rolling again to obtain a 0.6 mmt product. The elongation was significantly improved by holding at 1050 ° C for 15 seconds to 60 seconds. This effect has a temperature of 1250 ° C to 900
It was observed between ° C. > 1250 ° C or 90
If the temperature is lower than 0 ° C, the retention effect is small, and if the temperature exceeds 2 minutes, the effect is saturated. 1250 to 9 show these effects.
This is because MnS is precipitated and detoxified by holding it at a temperature of 00 ° C. for 2 minutes or less. On the short time side, the effect was recognized after 5 seconds or more.

Therefore, by combining these requirements with the roping countermeasures already clarified, it is possible to provide a method for producing a Cr-Ni type stainless steel thin plate having excellent surface quality and workability.

[0016]

[Table 1]

[0017]

[Example] 18Cr-8 shown in Table 2 prepared by a conventional method
Cr-Ni type stainless steel represented by Ni was cast by a twin drum method with an internal water cooling method to obtain cast pieces of 3 mmt and 4 mmt. The high temperature region just below the exit of the twin-drum casting machine was cooled by roll cooling in addition to air cooling. Between 1250 ° C and 900 ° C, hold the furnace at a constant temperature for 9 to 110 seconds, and then cool below 900 ° C with water to 600 ° C.
Was cooled at an average of 10 ° C./sec or more and wound up at 600 ° C. or less.

[0018]

[Table 2]

Thereafter, the slab was descaled by mechanical descaling and pickling without annealing, and pre-cold rolled by cold rolling. 30 for both 3mmt and 4mmt slabs
It was pre-cold rolled in the range of ˜50%, annealed at 1000 ° C. for 20 seconds or less, and then rapidly cooled. Thus, the slab was recrystallized and then cold-rolled by the main cold rolling to 0.6 mmt, and the final annealing was carried out in the usual manner to obtain 2B and BA products and temper rolling. The properties of the product thus obtained are shown in Table 3. The surface quality and mechanical properties of these products were very good.

In the comparative method, a slab cooled by air between 1250 and 900 ° C. is used and manufactured by the same process. The surface properties of the obtained product are improved, but the elongation and workability are poor.

[0021]

[Table 3]

[0022]

According to the present invention, an austenitic stainless steel thin plate excellent in surface properties and workability is obtained by a simple process of continuously casting thin strip-shaped slabs having a thickness close to the product thickness and directly cold rolling to produce a product. Can be obtained. Therefore, the technical effect of the present invention is extremely large in terms of economical efficiency and manufacturing purpose.

[Brief description of drawings]

FIG. 1 is a diagram showing a temperature history of a thin cast piece obtained by a continuous casting method.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hideki Oka, 3434 Shimada, Hitsu-shi, Yamaguchi Prefecture, Nippon Steel Co., Ltd., Hikari Steel Works, Inc. (72) Yuji Yoshimura, 3434 Shimada, Hikari-shi, Yamaguchi Prefecture, Japan Inside the Kogaku Steel Works

Claims (2)

[Claims] 1. C represented by 18% Cr-8% Ni steel
The cooling rate during solidification of r-Ni stainless steel was set to 10 by a continuous casting machine in which the mold wall surface moved in synchronization with the slab.
Continuously cast into a strip-shaped slab with a thickness of 6 mm or less at 0 ° C / sec or higher and cooled, and 1250 to 900 ° C during cooling of the slab.
Hold in the temperature range for less than 2 minutes, cool to less than 900 ° C, wind, anneal, pickle, then perform pre-cold rolling applying a reduction rate of 60% or less, then 850 ° C or more The average grain size of γ grains is 50
It is characterized in that after being made to be less than μm, it is pickled, then cold-rolled to a final thickness, and the obtained cold-rolled sheet is finally annealed, then pickled or bright annealed and temper-rolled. A method for producing a Cr-Ni-based stainless steel thin plate having excellent surface quality and workability. 2. Cooling below 900 ° C. is 900-600
2. The surface quality and workability according to claim 1, wherein the temperature range between ℃ is cooled at an average cooling rate of 10 ℃ / sec or more, wound at 600 ℃ or less, and then pickled without annealing. A method for producing an excellent Cr-Ni-based stainless steel thin plate.