JP2518795B2 - Soft austenitic stainless steel with excellent hot workability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft austenitic stainless steel which is excellent in hot workability, and is particularly suitable for use as a roofing material or the like which is subjected to a large bending angle such as bending. The present invention relates to a soft austenitic stainless steel having excellent workability.

[0002]

2. Description of the Related Art Conventionally, stainless steel has come to be widely used in various fields based on its excellent corrosion resistance and designability by maintaining a metallic luster. Is in the direction of further expansion. However, the austenitic stainless steel typified by SUS304 is harder than ordinary steel, particularly harder than the commonly used low carbon ordinary steel, and has a large work hardening, so that it is difficult to process. There is a problem of wanting. For example, according to JIS G4307, SUS304 has a hardness (Hv) of 200 or less and a tensile strength of 53 kgf / mm ² or more in a solution heat treatment state, whereas it is a typical thin plate forming material. In the case of ordinary steel cold rolled steel sheet and strip, according to JIS G3141, hardness (Hv) is 115 or less and tensile strength is 28 kgf /
As can be seen from the fact that it is at least ² mm ^2, it has properties such as higher hardness (Hv) than the above-mentioned ordinary steel cold-rolled steel sheet which has been often used. Incidentally, the hardness (Hv) of general commercial steel is around 160 and the tensile strength is around 70 kgf / mm ^2, and the austenitic stainless steel has properties very close to this.

For this reason, austenitic stainless steel has higher corrosion resistance than ordinary steel, but has a higher hardness, a higher tensile strength and a higher workability than ordinary steel cold-rolled steel sheet. Due to its mechanical property of large hardening, it has not been widely used like ordinary steel cold-rolled steel sheet. Because of its nature, the processing of austenitic stainless steel sheets often takes place mainly in factories, because it requires a special processing machine or requires a skilled technician. Under such circumstances, development of austenitic stainless steel that is soft and has low work hardening that can be easily worked has been required.

As an austenitic stainless steel having such properties, in JP-B-51-29085, C: less than 0.02%, Si: less than 0.1%, Mn:
2% or less, Cr: 16 to 26%, Ni: 8 to 24%, balance Fe and impurities inevitably mixed in, yield strength less than 18 kg / mm ² , hardness (Hv) 130 or less austenitic stainless steel. By reducing the contents of C and Si, which are solid solution strengthening elements, as described above, the yield strength when processed into a thin plate of 1.0 mm or less is less than 18 kg / mm ² , and the hardness ( Hv) is 130
I was able to do the following.

Further, in Japanese Patent Laid-Open No. 4-72038,
C: 0.05% or less, Si: 1.0% or less, Mn: 5.
0% or less, Ni: 9.0% or more and 15.0% or less, Cr:
15.0% or more and 20.0% or less, N: 0.04% or less, with the balance being Fe and inevitably mixed impurities, and having a chemical composition that simultaneously satisfies the two expressions,
Hardness (Hv) 130 or less and tensile strength 55 kgf /
austenitic stainless steel of mm ² or less, and Cu: 0.05% or less, Mo: 3.0 in addition to the above chemical composition
% Or less, Al: 1.5% or less, Ti: 0.5% or less, N
b: 0.5% or less, Zr: 0.5% or less, V: 0.5%
Hereinafter, an austenitic stainless steel containing one or more of B: 0.03% or less and REM: 0.02% or less and having the same properties as the above is proposed. This is to reduce the Cr content, increase the Ni content, and further add Cu and Mn content to lower the hardness and lower the work hardening.

[0006]

Although the above-mentioned soft austenitic stainless steel was able to reduce the hardness and the like, there were some problems in its practical use, and it was hot worked in particular. In that case, there was a problem in the workability. For example, in the austenitic stainless steel of Japanese Patent Publication No. 51-29085, the strength of the grain boundary is lowered because the content of the solid solution strengthening element is reduced, and defects called sliver are likely to occur during hot rolling. Further, the austenitic stainless steel disclosed in JP-A-4-72038 is
The addition of Cu causes segregation during solidification, which causes cracking during hot rolling. As described above, each of them has a problem in hot workability, and this problem must be solved in order to be used in a wide field. An object of the present invention is to provide an austenitic stainless steel having excellent hot workability that does not cause such a problem.

[0007]

In order to achieve the above-mentioned object, the present inventor has added various components to austenitic stainless steel and changed the composition of the austenitic stainless steel to make an alloy, and measure its properties. As a result of repeating the experiment of doing, the present invention was obtained on the basis of the knowledge described below. That is, the present invention has achieved the above object by the following means. (1) C: 0.02% or less, Si: 0.15% or less, M
n: 1.5% or less, Ni: 5 to 15%, Cr: 15 to 2
5%, Cu: 0.3-2.0%, Al: 0.001-
0.010%, B: 0.001 to 0.010%, N:
0.02% or less, O (oxygen): 0.01% or less, and satisfies (Al + B) /O=0.5 to 2.0, and balance Fe
And a soft austenitic stainless steel with inevitable impurities and excellent hot workability. (2) In addition to the soft austenitic stainless steel of the above item (1), Mo: 3% or less, Ti: 0.5% or less, N
b: Soft austenitic stainless steel excellent in hot workability, characterized by containing one or more of 0.5% or less.

The present inventors have obtained from the results of many experiments,
The knowledge on which the present invention is based is as follows. Addition of an appropriate amount of B can strengthen the grain boundaries and prevent the generation of three bars. The problem of low Si, that is, in order to prevent deoxidation failure, hot workability can be improved by adding an appropriate amount of Al according to the amount of oxygen. There is a specific range between the addition of Al and Si and the amount of oxygen that improves hot workability.

Further, the soft austenitic stainless steel of the present invention will be described in detail. First, the reasons for limiting each component will be described below. C, N: Since it is a solid solution strengthening element, if it is contained in a large amount, softening is hindered, so the content is made 0.02% or less. Si: It is added as a deoxidizing agent, but it is preferably 0.15% or less because it is more preferable from the viewpoint of softening. Mn: It is added to improve the workability, but if it is too much, the hot workability is deteriorated, so the content is made 1.5% or less. Ni: A major component of austenitic stainless steel. If it is less than 5%, it cannot be made into an austenite phase, and if it exceeds 15%, it becomes expensive, so it is made 5 to 15%. Cr: It is added from the viewpoint of corrosion resistance, but if it is less than 15%, the corrosion resistance is not sufficient, and if it exceeds 25%, it is not preferable from the viewpoint of softening, so it is made 15 to 25%.

Cu: An important element in terms of softening.
If it is less than 0.3%, the effect is not sufficient, and if it exceeds 2.0%, the solidification segregation becomes too large and it is difficult to improve the hot workability in the present invention as well.
%. Al: Si is added to compensate for the lack of deoxidation due to the reduced amount. If it is less than 0.001%, the deoxidizing effect is not sufficient, and if it exceeds 0.010%, the hot workability deteriorates due to the interaction between Cu and Al. B: It is an important element of the present invention. It is an element effective in improving hot workability and preventing sliver during hot rolling. If less than 0.001%, the effect is not sufficient,
If it exceeds 0.010%, softening is inhibited, so 0.00
It is set to 1 to 0.010%. O (oxygen): An element that is extremely harmful to hot workability. In particular, when the Si content is low as in the present invention, deoxidation failure tends to occur, and it is important to set the content to 0.01% or less.

(Al + B) / O: This is Al, B and O
It means that there is an appropriate range in the quantitative ratio with. Al is used only for deoxidation, excess Al is not preferred.
Further, B does not act effectively in the presence of oxygen, and (Al +
When B) / O is less than 0.5, the amount of solid solution oxygen increases and the hot workability deteriorates. When (Al + B) / O exceeds 2.0, solid solution Al is present, and the above-mentioned adverse effects of Al appear. In addition to the above elements, Mo, T
One or two or more of i and Nb can be added in the following amounts. These elements are effective for improving the corrosion resistance. If it exceeds the set range, workability deteriorates. Mo: 3% or less Ti: 0.5% or less Nb: 0.5% or less

[0012]

In the present invention, the addition of an appropriate amount of B can strengthen the grain boundaries and prevent the generation of three bars, but as in JP-A-4-72038, 0.03% of B is added.
Even below, it is not preferable for the content of about 0.020% to inhibit softening. Therefore, B is 0.001 to 0.001%.
The range is 0.010%. Even if B is in the above range, when (Al + B) / O is less than 2, Al in the deoxidizing material is insufficient, the amount of solid solution oxygen increases, the hot workability deteriorates, and the amount of Al increases. If solid solution Al exists, its A
Since the hot workability deteriorates due to the interaction between 1 and Cu, it is necessary to prevent both adverse effects. In the steel of the present invention, Mo: 3% or less, Ti:
Corrosion resistance can be improved by incorporating one or more of 0.5% or less and Nb: 0.5% or less.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to this embodiment. Example A molten steel having a composition of components shown in Table 1 was melted in an air induction furnace of 10 kg, cast into an ingot, hot-rolled, annealed, cold-rolled, heat-treated at 1050 ° C., and a plate having a thickness of 1.5 mm. Was manufactured. The properties of the board were measured. Its characteristics are second
Shown in the table. The hot workability was evaluated by the drawing value in the 900 ° C. ultrahigh temperature tensile test of the ingot.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

In Tables 1 and 2, for the comparative examples, those having a composition close to that of the stainless steel of the present invention were selected, and the amounts and ratios of Al, B and O (oxygen) were the same as those of the present invention. The different ones are mentioned so that the significance of the limitation of the amounts and the ratios of Al, B, O (oxygen) in the present invention becomes clear. Each of the obtained plates is made of austenitic stainless steel. According to Table 2, all of the steels of the present invention are soft and exhibit good hot workability, while No. Comparative steel No. 7 does not contain B, and No. 8 and No. Comparative Steel No. 13 does not contain Al or contains little Al, and therefore has a large amount of O. 9 and No. Comparative steel No. 14 has a small value of (Al + B) / O. The comparative steel of No. 10 has a large value of (Al + B) / O. 1
Comparative steel No. 1 has poor hot workability due to the presence of excess Al. No. The comparative steels of No. 12 contained a large amount of B, so that the grain boundary strength was improved and it was unsuitable from the viewpoint of softening. From the above points, the present invention is able to achieve the objects of having the above-described component composition, which is soft and improves hot workability.

[0018]

According to the present invention, it is possible to provide a soft austenitic stainless steel having excellent hot workability with high productivity, which is extremely useful in industry. This excellent hot workability means that the reduction value can be 90% or more during hot rolling, as described in Table 2, so that there is a sliver or edge crack in the hot rolled steel strip. Does not occur. Further, since it is soft, the number of times of rolling can be reduced during cold rolling, which improves productivity. Further, in the steel of the present invention, corrosion resistance can be improved by further containing one or more of Mo: 3% or less, Ti: 0.5% or less, and Nb: 0.5% or less. .

Continuation of front page (56) References JP-A-2-179850 (JP, A) JP-A-4-72038 (JP, A) JP-B-51-29085 (JP, B1)

Claims (2)

(57) [Claims] 1. C: 0.02% or less, Si: 0.15%
Hereinafter, Mn: 1.5% or less, Ni: 5 to 15%, Cr:
15-25%, Cu: 0.3-2.0%, Al: 0.0
01-0.010%, B: 0.001-0.010%,
N: 0.02% or less, O (oxygen): 0.01% or less,
In addition, a soft austenitic stainless steel that satisfies (Al + B) /O=0.5 to 2.0 and is excellent in hot workability composed of the balance Fe and unavoidable impurities. 2. The soft austenitic stainless steel of claim 1 further contains one or more of Mo: 3% or less, Ti: 0.5% or less, and Nb: 0.5% or less. A soft austenitic stainless steel with excellent hot workability.