JPH073404A - Austenitic stainless steel excellent in cleanliness and weldability - Google Patents

Abstract

PURPOSE:To obtain an austenitic stainless steel minimal in gas adsorptivity and excellent in weldability and in cleanliness by incorporating specific amounts of B and N into an austenitic stainless steel. CONSTITUTION:An austenitic stainless steel having a composition containing, by weight, <0.2% C, <1% Si, <2% Mn, <0.025% P, <0.004% S, <0.1% Sol.Al, 15-25% Cr, and 6-30% Ni is used. Further, 0.003-0.015% B, 0.08-0.12% N, and 0.001-0.01% Ca+Mg are incorporated, or further, 0.001-0.01% Mo+Mg is incorporated. This austenitic stainless steel material is heated up to 650-900 deg.C in vacuum or in a nonoxidizing atmosphere to precipitate BN having high gas adsorption resistance at >=90% of the surface, by which the austenitic stainless steel material free from release of adsorbed gas from the surface in ultrahigh vacuum or in a high purity gas atmosphere, having high-cleanliness surface, and excellent in weldability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a container, a flange, which is used in a high vacuum, ultra high vacuum or high purity gas atmosphere used for semiconductor manufacturing equipment, physics and chemistry equipment, food equipment, medical equipment, particle accelerators and the like. The present invention relates to an austenitic stainless steel having excellent cleanability and weldability used for valves, valves, bellows, piping and the like.

[0002]

2. Description of the Related Art Stainless steel such as SUS304 and SUS316 is used for containers, pipes, valves, valves, flanges and the like which constitute vacuum devices such as semiconductor manufacturing equipment, physics and chemistry equipment, particle accelerators and the like.

In such a high-vacuum or ultra-high-vacuum device or a high-purity gas atmosphere device, the gas adsorbed on the surface of the steel material constituting the device is discharged to the vacuum device or the like. Therefore, these devices are made of the above-mentioned austenitic stainless steel, or, in order to be used as parts, perform a baking treatment under vacuum to sufficiently remove the gas adsorbed on the surface of the stainless steel, Degas. Since this baking process requires several tens of hours or more at several hundred degrees, it is desired to shorten the baking process time.

As a countermeasure against this, Japanese Patent Publication No. 62-39234
In the publication, a method of depositing boron nitride having high gas adsorption resistance on an austenitic stainless steel surface layer is proposed. This is characterized in that an austenitic stainless steel material added with boron (B), nitrogen (N), and cerium (Ce) is heated in a vacuum to deposit boron nitride on the surface thereof. Further, Japanese Patent Laid-Open No. 2-576675 discloses a steel material containing B, N, and calcium (Ca) and magnesium (Mg).
Vacuum degree of 0 ^-5 Torr or less, or purity 99.99
% To 650 to 850 ° C. in an inert gas atmosphere
A steel material having boron nitride deposited on its surface by heating at a temperature of 1 has been proposed.

Further, in Japanese Patent Laid-Open No. 3-042367, 0.005 to B is added to austenitic stainless steel.
0.05% and N of 0.08 to 0.3%, and this steel in hydrogen or in a mixed gas in which 1% or more of the total pressure of hydrogen is added to an inert gas atmosphere such as nitrogen or argon,
A manufacturing method has been proposed in which boron nitride is deposited on the surface of the steel by heating at a temperature of 600 to 900 ° C.

[0006]

SUMMARY OF THE INVENTION The present invention provides a container and a flange for use in a high vacuum or ultra high vacuum or high purity gas atmosphere used in the above-mentioned semiconductor manufacturing apparatus, physicochemical equipment, food equipment, medical equipment and the like. , Which is a material for valves, valves, bellows, pipes, etc., and is clean both in terms of internal quality and surface properties, that is, austenitic stainless steel with excellent cleanliness and with excellent weldability. Intended for series stainless steel.

In the above-mentioned prior art, since the addition amount of B is large, a low melting point compound is generated in the austenitic stainless steel, and hot cracking of the weld heat affected zone is likely to occur. In addition, since the N content is large, blowholes are generated during welding and remain in the weld metal. As a result, when used as a vacuum container, it becomes a gas adsorption point and sometimes causes gas leakage. Also becomes.

Therefore, in the present invention, as described above, it is particularly clean with respect to inclusions internally, and is clean in that boron nitride is deposited on the surface and gas adsorption is small, and these devices are manufactured. In this case, welding is usually performed, but the object is to provide an austenitic stainless steel having excellent weldability in that no defects are generated in this weld.

[0009]

In order to solve the above-mentioned conventional problems, the present inventors have repeatedly studied the amounts of B and N added in austenitic stainless steel, especially from the viewpoint of weldability, and Suppressing the occurrence of welding defects in the welding conditions used for the production of containers and the like, and examining the amount of addition in the range that completely completes the deposition on the surface of boron nitride having resistance to adsorbed gas, the present invention completed.

The gist of the invention is as follows. (1) The invention of claim 1 has the following component composition (component composition is w
t%) and is excellent in cleanliness and weldability. C: 0.2% or less, Si:
1% or less, Mn: 2% or less, P: 0.025% or less, S: 0.00
4% or less, Sol.Al: 0.1% or less, Cr: 15-25%
It contains Ni: 6 to 30%, B: 0.003 to 0.015%, N: 0.08 to 0.12% Ca + Mg: 0.001 to 0.01%, and the balance is Fe and inevitable impurities.

(2) The invention of claim 2 is an austenitic stainless steel having the following composition (the composition of the composition is wt%) excellent in cleanliness and weldability. C: 0.2%
Or less, Si: 1% or less, Mn: 2% or less, P: 0.025
% Or less, S: 0.004% or less, Sol.Al:0.1% or less, Cr: 1
5 to 25% Ni: 6 to 30%, B: 0.003 to 0.015%, N:
Contains 0.08 to 0.12% Mo + W: 3% or less, Ca + Mg: 0.001 to 0.1%, and the balance
Consists of Fe and inevitable impurities.

(3) The invention of claim 3 is an austenitic stainless steel excellent in cleanliness and weldability having the following characteristics (the composition of the components is wt%). (A) An austenitic stainless steel having the chemical composition according to claim 1 or 2, wherein (b) boron nitride is deposited on the surface of the stainless steel in 90% or more of the surface.

[0013]

The reason for limiting the component composition (the component composition is wt%) of the present invention will be described below. Cr: 15 to 25%. Cr is an element effective in corrosion resistance and oxidation resistance. However, if the Cr content is less than 15%, sufficient corrosion resistance and oxidation resistance are not exhibited. On the other hand, Cr is 2
If it exceeds 5%, it is necessary to increase the Ni content in order to obtain the austenite single phase, which increases the cost of the steel material,
Further, from the viewpoint of corrosion resistance and oxidation resistance, the above range may be used.
Therefore, the content of Cr is set to 15 to 25%.

Ni: 6 to 30% Ni is necessary as an austenite phase forming element. However, Ni
If the content is less than 6%, the austenitic single phase is not obtained. On the other hand, Ni is an expensive metal, and even if it is added in an amount of more than 30% with respect to the above-described amount of chromium added, the cost is increased but the effect is saturated. Therefore, the amount of Ni added is 6 to
30%.

B: 0.003 to 0.15% B is an essential element for precipitating boron nitride on the surface of the steel material. However, if the amount of B added is less than 0.003%, the amount of boron nitride deposited is insufficient. On the other hand, when 0.015% or more is added, the amount of the low melting point compound that causes grain boundary cracking during welding increases, and hot cracking of the weld metal and hot cracking in the heat affected zone are likely to occur. Therefore, the content of B is 0.
003 to 0.15%.

N: 0.08 to 0.12%. N is an essential element of boron nitride deposited on the surface of steel. However, if the N content is less than 0.08%, the amount of boron nitride deposited is not sufficient. On the other hand, if added in excess of 0.12%, in welding that is usually performed for manufacturing vacuum equipment, blowholes are generated and remain in the weld metal under normal welding conditions, and it is difficult to weld without defects. Therefore, the content of N is set to 0.08 to 0.12%.

Ca + Mg: 0.001 to 0.01%. The amount of Ca + Mg added is S which hinders the precipitation of boron nitride.
Is required to fix as sulfide, Ca and M
g has the same action and effect. When the amount of Ca + Mg is less than 0.001%, the boron nitride precipitation area is 40% or less, which is insufficient. On the other hand, if it exceeds 0.001%, the deposition area ratio of boron nitride sharply increases and reaches an area of almost 100%. However, when the amount of Ca + Mg exceeds 0.01%, the occurrence of scratches on the surface of the steel material is observed during hot rolling, and the fixing action of S is also saturated,
The total content of one or two of Ca and Mg is 0.00
It is limited to 1 to 0.01%.

C: 0.2% or less. C is a component effective for stabilizing and strength of the austenite phase, but 0.2
%, The hot cracking of the weld zone and the intergranular corrosion of the HAZ zone are likely to occur. Therefore, the C content is 0.2% or less. In this case, C may be 0%.

Si: 1% or less. Si is a very effective element for improving the deoxidizing action and the corrosion resistance during the melting of austenitic stainless steel, but it is a strong ferrite forming element, and if it is added in excess of 1%, a ferrite phase is easily formed. , Adversely affect the stability of the organization. Therefore, the addition amount of Si is set to 1% or less.

Mn: 2% or less. Mn has a deoxidizing action and an S fixing action, and is an effective component for stabilizing the austenite phase, but the amount thereof is 2% or less. On the other hand, if added in a large amount, the corrosion resistance and the oxidation resistance are deteriorated, so the content is made 2% or less.

P: 0.025% or less. When the content of P is high, the precipitation of boron nitride is suppressed and the weldability is impaired. Therefore, the P content is 0.025% or less.

S: 0.004% or less. Similar to P, S is concentrated on the surface when the steel of the present invention is heated in a vacuum, which hinders the deposition of boron nitride on the surface. Therefore,
The content of S is 0.004% or less. Since the steel of the present invention is intended to be a highly clean steel, if the S content is high, most of it becomes inclusions in the steel and impairs cleanliness. From this point as well, S
Content is 0.004% or less.

Sol. Al: 0.1% or less. Al
Is an element necessary for deoxidizing the steel of the present invention. The permissible limit for deoxidation is 0.1% or less. On the other hand 0.1
If it is contained in an amount of not less than 100%, a large amount of Al ₂ O ₃ is generally generated and the cleanliness of steel is impaired. Therefore, Sol. The upper limit of Al is 0.1% or less, and preferably 0.03% or less. The above is the reason for limiting the component composition of claim 1.

Mo + W: 3% or less. Mo and W
Is 1 when improving heat resistance or corrosion resistance.
One kind or two kinds can be added in combination. However, if the total content of these elements exceeds 3%, the so-called austenite phase stability decreases and the effect of addition saturates. Therefore, the total content of one or two of Mo and W is 3% or less (claim 2).

The above-mentioned stainless steels according to claims 1 and 2 are austenitic stainless steels according to the present invention which are excellent in cleanliness and weldability by themselves. Further, the surface of the stainless steel is clean. There is at least 90% of the surface to be used as a steel material for vacuum equipment.
It is necessary that the above-mentioned boron nitride is precipitated in an amount of at least%. When 90% or more of the surface is covered with boron nitride, the surface is prevented from adsorbing air and other gases as described above, and therefore, it can be applied to the vacuum device described above. The heat treatment conditions for depositing boron nitride on the surface of the stainless steel of the present invention will be described below.

The amounts of B and N which are dissolved during the solution treatment of the pretreated steel material for precipitating boron nitride have a great influence on the amount of boron nitride deposited on the surface. The boron nitride referred to here is presumed to be mainly BN in the analysis result by the scanning Auger electron spectroscopy, but it is also presumed to include various bonding states of B and N. The solution treatment temperature of 1010 ° C. or higher is sufficient when Mo and W are not added, but 1040 ° C. or higher is necessary when Mo and W are added. It is desirable to carry out at a higher temperature because the amount of solid solution can be increased and the supersaturation amount of B and N at the precipitation treatment temperature increases. The upper limit of the solution treatment temperature is not particularly limited, but may be determined in consideration of energy consumption for heating, productivity, and the like.

Austenitic stainless steel usually forms a thick passive oxide film by heating in the atmosphere. Further, in the atmosphere, various impurities are adsorbed on the surface of the steel material and polluted. If the passive oxide film is thick or if the contamination due to the adsorption of impurities is significant, the surface deposition of boron nitride may be hindered. Therefore, it is desirable that the surface of the steel material be polished in advance by a method such as buffing, electrolytic polishing, or chemical polishing to remove the thick passive oxide film and contamination with impurities, and then heated in a non-oxidizing atmosphere.

Conditions for Precipitating Boron Nitride on the Surface Austenitic stainless steel forms an oxide film mainly composed of Fe or Cr when heated in an atmosphere in which oxygen is sufficiently present. This oxide film inhibits the deposition of boron nitride on the surface. For this reason, it is necessary to perform the heating for depositing boron nitride in a vacuum, an inert gas atmosphere, or a reducing gas atmosphere.

However, when the degree of vacuum and the purity of the inert gas and the reducing gas are insufficient, oxygen as an impurity causes F 2
Even if the oxide film mainly composed of e is not formed, an oxide film containing chromium is formed, which also hinders the deposition of boron nitride on the surface. Therefore, in order to deposit boron nitride on the surface, a vacuum degree of 10 ^-5 Torr or less in a vacuum,
Alternatively, in the case of an atmosphere of an inert gas or a reducing gas, the treatment is performed in an inert gas having a purity of 99.99% or more, or a mixed gas of hydrogen and an inert gas.

The heating temperature for the deposition of boron nitride also greatly affects the deposition of boron nitride. If the heating temperature is less than 650 ° C., the diffusion rate of B and N to the surface is slow, boron nitride particles are formed in the steel before reaching the surface, and boron nitride is not formed on the surface. Further, when the heating temperature exceeds 900 ° C., the solid solution amount of B and N at the precipitation temperature increases, and as a result,
The supersaturated B and N involved in surface precipitation are reduced, and it becomes difficult to form a boron nitride film on the surface. Therefore, in order to deposit boron nitride on the surface of the steel material, 650 ° C to 900 ° C
Heat in the range.

A heating time of 5 minutes or more is sufficient for the deposition of boron nitride, but it is desirable to take into consideration the soaking state from the size and weight of the target steel material. The upper limit of the heating time is not particularly limited, but it is desirable to determine it from the viewpoint of energy consumption for heating and productivity.

[0032]

EXAMPLES Steel No. of the present invention having the composition of components shown in Table 1.
1-No. 7, comparative steel No. 8 to No. Melted 12,
Each 10 kg was used as a steel ingot. Next, this steel ingot is heated to 1250 ° C.
And then hot-rolled into a 12 mm thick plate, then 110
It was heated at 0 ° C. for 20 minutes and then cooled with water. 50 from this board
A plate material of × 120 × 4 mm was processed and provided for the accuracy of weldability. The welding method was non-filler TIG welding, welding of a bead-on-plate having a length of about 100 mm was performed under various welding conditions, and the presence or absence of welding defects was evaluated by an X-ray transmission test after welding (JIS Z3106). Also, from a 12 mm thick plate, 1
A small sample of 0 × 10 × 1 mm was sampled, the surface was buffed, further electrolytically polished, and subjected to a precipitation treatment in vacuum (10 ⁻⁶ Torr) at 850 ° C. for 1 hour. The surface of the deposited sample was analyzed by scanning Auger electron spectroscopy to measure the deposition area ratio of boron nitride.

Table 2 shows these results. As shown in Table 2, the invention steel No. 1-No. 7 and comparative steel No. 1
With 0 and 11, no HAZ cracks or blowholes were observed. However, the comparative steel No. In Nos. 10 and 11, the contents of B and N were smaller than the range of the present invention, respectively, and the deposition area ratio of deposited boron nitride was very small. On the other hand, the invention steel No. 1-No. 7 and comparative steel No. 8,
In the case of Comparative Steel Nos. 9 and 12, the precipitation area ratio of boron nitride was 90% or more. Since 8 and 12 were added in excess of the nitrogen range of the present invention, blowholes were confirmed in the weld,
No. In No. 9, since it was added over the range of B, hot cracking was observed in the heat affected zone (HAZ). On the other hand, the invention steel No. In Nos. 1 to 7, a precipitation area ratio of 90% or more was achieved, and welding without defects was possible in a wide range of welding heat input.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

According to the present invention, an austenitic stainless steel which is excellent in cleanliness both internally and in terms of its surface and also has excellent weldability, is used in semiconductor manufacturing equipment, physics and chemistry equipment, It is possible to provide excellent austenitic stainless steel as a material for equipment such as containers, flanges, valves and pipes used in a high vacuum or high purity gas atmosphere used for food equipment, medical equipment, particle accelerators and the like.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaichi Ishizawa, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (3)

[Claims] 1. An austenitic stainless steel having the following composition (the composition of the composition is wt%) excellent in cleanliness and weldability. C: 0.2% or less, Si: 1% or less, Mn: 2% or less, P: 0.025% or less, S: 0.004% or less, Sol.Al: 0.1% or less, Cr: 15-25% Ni: 6-30% , B: 0.003 to 0.015%, N: 0.08 to 0.12% Ca + Mg: 0.001 to 0.01%, and the balance Fe and unavoidable impurities. 2. An austenitic stainless steel excellent in cleanliness and weldability having the following component composition (the component composition is wt%). C: 0.2% or less, Si: 1% or less, Mn: 2% or less, P: 0.025% or less, S: 0.004% or less, Sol.Al: 0.1% or less, Cr: 15-25% Ni: 6-30% , B: 0.003 to 0.015%, N: 0.08 to 0.12% Mo + W: 3% or less, Ca + Mg: 0.001 to 0.1%, and the balance Fe and unavoidable impurities. 3. The following characteristics (component composition is wt%):
Austenitic stainless steel with excellent cleanliness and weldability. (A) An austenitic stainless steel having the chemical composition according to claim 1 or 2, wherein (b) boron nitride is deposited on the surface of the stainless steel in 90% or more of the surface.