JPH062044A - Production of thin cast slab of ferritic stainless steel - Google Patents

Abstract

PURPOSE:To prevent the occurrence of cold rolling crack in a cast slab and to obtain a product sheet with high gamma-value at the time of producing a thin cast slab of ferritic stainless steel. CONSTITUTION:A ferritic stainless steel which has a composition consisting of, by weight, <=0.03% C, <=1.0% Si, <=1.0% Mn, <=0.040% P, <=0.030% S, 10.0-35.0% Cr, 6(C+N) to 1.0% Ti, =0.03% N, and the balance Fe with inevitable impurities, containing, if necessary, 0.3-5.0% Ni, and further containing, if necessary, one or >=2 kinds among 0.1-5.0% Mo, 0.2-1.0% Cu, 0.05-1.0% Al, and 0.1-1.0% V or further containing, if necessary, 0.0003-0.0030% B and satisfies gamma'p(gamma potential) <=0 is continuously cast into a thin slab. This cast slab after casting is cooled from solidification temp. down to 1250 deg.C at (50 to 500) deg./S cooling rate and coiled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ferritic stainless steel thin cast piece.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Unexamined Patent Publication (Kokai) No. 62-247029 has been disclosed as a technique for producing a ferritic stainless steel having excellent deep drawing characteristics by using a thin band casting method by rapid solidification. This technique produces thin cast pieces with a thickness of 10 mm or less, and then the cast pieces are heated from the solidification temperature to 1200 ° C.
To improve the ridging characteristics by cooling at a cooling rate higher than air cooling, and then from 1200 ° C to 1000 ° C at 30 ° C.
Cooling at a cooling rate of ℃ / sec or more, 1000 ℃ or less 70
The slab is wound up in a temperature range of 0 ° C or higher to improve the cold rolling property of the slab, the mechanical properties of the product, and the deep drawing property.

[0003]

The present invention pays particular attention to the deep drawing characteristics (pressability) in the above technique, and can produce a thin steel sheet having a pressability higher than the above technique, that is, a γ value of 1.20 or more. Aim to get. Another object of the present invention is to obtain a steel sheet which is further rich in cast piece toughness and excellent in intergranular corrosion.

[0004]

In order to achieve the above object, the present invention specifies the chemical composition of ferritic stainless steel and the cooling rate from the solidification temperature during casting to 1250 ° C. That is, the gist of the present invention is% by weight, C: 0.03% or less, Si: 1.0%
Below, Mn: 1.0% or less, P: 0.040% or less,
S: 0.030% or less, Cr: 10.0 to 35.0%,
Ti: 6 (C + N) to 1.0% and N: 0.03% or less are contained, Ni: 0.3 to 5.0% if necessary, Mo: 0.1 to 5.0% if necessary, Cu: 0.2-1.
0%, Al: 0.05 to 1.0%, V: 0.1 to 1.0
%, 1 or 2 or more or, if necessary, B: 0.0
003 to 0.0030%, balance Fe and unavoidable impurities, and a unique gamma potential (hereinafter referred to as γ′p) of the present invention, γ′p = 420C% + 470N% + 23Ni% + 9Cu
% + 7 Mn% -11.5 Cr% -11.5 Si% -12 Mo% -23
When continuously casting a ferritic stainless steel satisfying V% −49 Ti% −52 Al + 179 ≦ 0 into a thin-walled cast piece, the cast cast piece is cast at a temperature range from at least the solidification temperature to 1250 ° C. of 50 to 500 ° C./S. It is about to be cooled at the cooling rate of.

The present invention will be described in detail below along with its operation.

[0006]

First, the reason why the chemical composition of steel is limited as described above in the present invention will be explained. C adversely affects the workability and toughness of steel, so the content is made 0.03% or less. Since Si and Mn are effective as deoxidizing agents for steel, they are contained at 1.0% or less each. If it exceeds 1.0%, the mechanical properties deteriorate.

Cr requires a minimum of 10.0% to improve corrosion resistance and high temperature oxidation resistance, and if it exceeds 35%, toughness deteriorates and manufacturing becomes extremely difficult, so the range is 10 to 35%. And Ti has the property of combining with C and N to prevent grain boundary precipitation of Cr carbide and improving intergranular corrosion resistance, but if the content is less than 6 (C + N)%, the above properties cannot be obtained. If it exceeds 1.0%, the above characteristics are saturated and the workability is deteriorated. Therefore, the range is 6 (C + N) to 1.0%.

[0008] N, like C, deteriorates the workability and toughness of steel, so the upper limit of the content is made 0.03%. To further improve properties such as toughness, corrosion resistance, and workability,
In addition to the above chemical components, the following components are appropriately selected and contained. Ni is effective for improving the toughness of high Cr materials, but if its content is less than 0.3%, it is not effective, and 5.0%.
If it exceeds 1.0, gamma (γ) is generated in the high temperature range to deteriorate toughness and stress corrosion resistance, so 0.3 to 5.0%.
The range is.

Addition of Mo, Cu, Al and V is effective for improving the corrosion resistance, and one or more kinds are selected and contained. That is, since Mo has a remarkable effect of improving the corrosion resistance, Mo is contained in the range of 0.1 to 5.0%. If it exceeds the upper limit, the workability deteriorates and the cost increases. Cu is contained in the range of 0.2 to 1.0% in order to improve the corrosion resistance. If it exceeds the upper limit, γ is generated in the high temperature range and the toughness is deteriorated.

Since Al has characteristics similar to Ti,
It is contained in the range of 05 to 1.0%. V has the same characteristics as Ti, so V is contained in the range of 0.1 to 1.0%. Further, B is effective in improving the intergranular cracking property in hot and cold working, but if it is less than 0.0003%, the characteristic cannot be obtained, and if it exceeds 0.0030%, the characteristic is saturated. At the same time, hot workability deteriorates. Therefore, the content range is set to 0.0003 to 0.0030%.

In the present invention, the above chemical components are regulated so that the value of γ'p represented by the following formula is 0% or less. That is, γ'p = 420C% + 470N% + 23Ni% + 9Cu
% + 7 Mn% -11.5 Cr% -11.5 Si% -12 Mo% -23
When V% -49Ti% -52Al + 179≤0, it is possible to prevent the formation of martensite during cooling in the cast piece and improve the toughness of the cast piece.

Next, the cooling process from the solidification temperature, which is another feature of the present invention, will be described. The present inventors focused on fixing C and N in steel with Ti in order to improve the pressability of the product, and conducted the following experiment to obtain the most effective fixing means. Chemical composition: C: 0.010%, Si: 0.36%, M
n: 0.31%, P0.014%, S: 0.001%,
Ni: 0.10%, Cr: 16.45%, Ti: 0.2
5% (Ti / C + N = 12.3), A: 10.040
%, N: 0.0103%, balance Fe and unavoidable impurities, and molten steel regulated to γ'P = -15.1% was cast into a 3.0 mm thick slab by the twin drum casting method. .

When cooling the slab immediately after casting, it is cooled from the solidification temperature of the slab to 1250 ° C. at various cooling rates in the range of 50 to 800 ° C./S, and at a coiling temperature of 850 ° C. I wound up. Each of these coils was pickled with sulfuric acid, cold-rolled at room temperature to a thickness of 0.5 mm, finally annealed at a temperature of 880 ° C, pickled with salt and nitric acid electrolysis, and 2B.
The finished product plate.

Next, the γ value of the product plate corresponding to each cooling rate was measured and is shown in FIG. As is clear from the figure, the present invention provides a target for deep drawing γ
The product plate having a value of 1.20 or more is obtained at a cooling rate of 500 ° C./S or less. That is, from the solidification temperature to 12
By cooling the temperature range up to 50 ° C at a cooling rate of 500 ° C / S or less, C and N can be sufficiently fixed with Ti, which significantly improves the pressability and intergranular corrosion resistance of the product sheet. can do. The cooling rate is 50 ° C /
If it is less than S, heat-retaining equipment and heating equipment for the slab are required to obtain the effect of the present invention, and the structure of the casting machine becomes very complicated, which is not practical. Therefore, the winding temperature in the above temperature range is specified to be 50 ° C / S or more and 500 ° C / S or less.

In order to set the temperature range from the solidification temperature to 1250 ° C. to 50 to 500 ° C./S, for example, in twin-drum casting, the casting speed may be adjusted or the cooling capacity of the twin-drum may be adjusted. . As described above, according to the present invention, by setting γ'p to be 0% or less, the toughness of the slab is improved, and cold rolling can be performed without annealing.
Since the i content is 6 times or more of (C + N)%, intergranular corrosion after pickling can be prevented, and the cooling rate from the solidification temperature of the slab to 1250 ° C is 500 ° C / S or less. By doing so, a material for deep drawing can be obtained.

According to the present invention, the winding temperature is set to 200.
It became possible to select in a wide range of up to 1000 ° C.

[0017]

EXAMPLE A ferritic stainless steel having the chemical composition shown in Table 1 was melted, cast into a thin cast piece having a thickness of 3.0 mm by the twin drum method, and then the cooling rate from the solidification temperature to 1250 ° C. was measured. It was cooled by changing it as shown in FIG. Thereafter, the coil was descaled by shot blasting and nitric hydrofluoric acid pickling, cold-rolled to 0.5 mm with a cold rolling machine having a roll diameter of 50 mm, and subjected to a final annealing of holding at 950 ° C. for 30 seconds. Pickled (salt + nitric acid electrolysis), 2B
Finished product plate.

In each of the examples of the present invention, the γ value showed a deep drawability of 1.2 or more. In No. 9, martensite was generated because Ti was not added, the Charpy value was low, and the coil broke during cold rolling. In addition, severe intergranular corrosion occurred after pickling the cast slab. Sample No. 10 has a Ti content of (C +
It was only 4.2 times that of N), and similarly, intergranular corrosion occurred.
Sample No. 11 and 12 are 1250 from the solidification temperature of the slab.
The cooling rate up to ℃ was over 500 ℃ / S, γ value was 1.2 or less of the target value.

[0019]

[Table 1]

[0020]

As described in detail above, the ferritic stainless steel thin cast piece obtained by the present invention has excellent cast piece toughness and intergranular corrosion resistance, and has a high γ value ( 1.2 or more), the industrial effect thereof is great by improving the production yield by preventing rolling cracking of the slab and manufacturing a product plate with high added value.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a cooling rate from a solidification temperature of a cast piece to 1250 ° C. and a γ value of a product plate.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C22C 38/00 302 Z 38/28

Claims (4)

[Claims] 1. By weight%, C: 0.03% or less, Si:
1.0% or less, Mn: 1.0% or less, P: 0.040%
Hereinafter, S: 0.030% or less, Cr: 10.0 to 35.
0%, Ti: 6 (C + N) to 1.0% and N: 0.03
% Or less, the balance Fe and unavoidable impurities, and γ′p = 420 C% + 470 N% + 23 Ni% + 9 Cu
% + 7 Mn% -11.5 Cr% -11.5 Si% -12 Mo% -23
When continuously casting a ferritic stainless steel satisfying V% −49 Ti% −52 Al + 179 ≦ 0 into a thin-walled cast piece, the cast cast piece is cast at a temperature range from at least the solidification temperature to 1250 ° C. of 50 to 500 ° C./S. A method for producing a thin slab of ferritic stainless steel, which comprises cooling at a cooling rate of. 2. The method for producing a ferritic stainless steel thin cast slab according to claim 1, further comprising 0.3 to 5.0% by weight of Ni. 3. Mo: 0.1 to 5.0% by weight,
The ferritic stainless steel according to claim 1 or 2, containing one or more of Cu: 0.2 to 1.0%, Al: 0.05 to 1.0%, and V: 0.1 to 1.0%. Method for manufacturing thin steel slab. 4. The method for producing a thin cast piece of ferritic stainless steel according to claim 1, further comprising 0.0003 to 0.0030% by weight of B.