JPH0285351A - Manufacture of vacuum vessel - Google Patents

Abstract

PURPOSE:To manufacture a vacuum vessel excellent in released gas characteristic by applying surface oxidation to a stainless steel having a specific composition consisting of C, Si, Mn, Cr, Ni, N, and Fe and then assembling the above steel into a vacuum vessel. CONSTITUTION:A stainless steel having a composition consisting of, by weight, <=0.08% C, <=2.0% Si, 2.0-15.0% Mn, 15-23% Cr, 7-20% Ni, 0.05-0.35% N, and the balance Fe with inevitable impurities is subjected to surface oxidation. As the above surface oxidation, it is suitable to carry out heating in an oxidizing atmosphere, e.g., in the air at about 200-500 deg.C for about 5-50hr. By the above oxidation treatment, an oxide film of about 300-1000Angstrom is formed. Then, the stainless steel is assembled into a vacuum vessel. By this method, the vacuum vessel reduced in the amount of gas released in a high vacuum state can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing vacuum containers such as vacuum chambers and piping.

[Conventional technology]

Traditionally, 5O3304 has been used as a material for vacuum containers.
18Cr-8Ni stainless steel X (such as 5US304L)
JISG 4304 etc.) are mainly used, and the surface is G
It is generally used after being subjected to BB (glass bead blasting) treatment and electrolytic polishing treatment.

The above stainless steel material releases a small amount of gas, has excellent corrosion resistance, workability, and weldability, and is almost satisfactory as a material for a vacuum container, and a vacuum on the order of 10-'Pa can be obtained relatively easily.

[Problem to be solved by the invention]

However, for example, MBE (Molecular, Beam, Epitaxy) equipment requires a vacuum on the order of 10-'Pa in terms of the quality of the crystal grown, but recent vacuum needs have become more sophisticated. In order to meet this requirement, it is essential in the design and production of vacuum equipment that the amount of gas released from the material for the vacuum container be as small as possible. The present invention aims to provide a stainless steel material with excellent gas release characteristics suitable for high vacuum containers, piping, etc.

[Means and effects for solving the problem] In view of the above circumstances, the present inventors have conducted various studies in order to obtain a metal material that emits an extremely small amount of gas (and also has excellent corrosion resistance, workability, and weldability). As a result, we found that stainless steel containing a large amount of Mn and N met this purpose.
Although a patent application has already been filed (Japanese Patent Application No. J1162-157893), as a result of further detailed study, it was confirmed that surface oxidation treatment of the stainless steel described above further reduces the amount of gas released from the same material.

Surface oxidation is usually 200 to 500 in air at atmospheric pressure.
by heating for 5 to 50 hours at a temperature of °C,
The atmosphere is not limited to air, but may be any other oxidizing atmosphere.

The composition range of the stainless steel targeted by the present invention is, in terms of weight ratio, C0.08% or less, Si2.0% or less, Mn2,0 to
15.0%, Cr15-23%, Nt7-20%, NO
, 05-0.35%, the remainder being substantially Fe.

The reason for limiting the range of each component is as follows.

CTC is an austenite stabilizing element, but if it is too large, Cr carbide will precipitate during welding, impairing corrosion resistance, so the upper limit was set at 0.08%.

S i: S i is necessary for deoxidation during steel manufacturing,
Although it works effectively for oxidation resistance, it is a strong ferrite-forming element, and if it exceeds 2.0%, it impairs workability, so the upper limit was set at 2.0%.

Mn: Mn is effective as an austenite stabilizing element and at the same time significantly reduces the amount of gas released into vacuum. The lower limit of 2.0% was determined based on these gas release characteristics; if it is lower than this, there will be little effect, and if it exceeds 15.0%, the ductility will decrease and workability will be impaired, so the upper limit is set at 15.0%. did.

Cr: Cr is a basic component of stainless steel and requires a minimum of 15% for good corrosion resistance.

On the other hand, if it exceeds 23%, the workability deteriorates, so the upper limit is set at 23%.
%.

Ni: Ni is one of the basic components of austenitic stainless steel. Although it is an effective element for workability and corrosion resistance, it requires a lower limit of 7% or more. In addition, if it exceeds 20%, the improvement effect rate is small and it is expensive, so the upper limit is set to 20%.
%.

NUN is a strong austenite stabilizing element and at the same time improves hot workability. 0.0 for improving hot workability
Requires addition of 5% or more. On the other hand, if it is too high, deformation resistance increases and manufacturability is impaired, so the upper limit was set at 0.35%.

In addition to the present invention, stainless steels containing large amounts of Mn and N exist, such as 5tlS 201 (Mn5.5~
7.5%, N≦0.25%), but the composition range is different from that of the present invention, and these existing alloys
The active addition of n and H is solely for the purpose of stabilizing the austenite phase as a substitute for Ni, and together with creating a surface oxidation state, it is possible to reduce the amount of released gas, which was first revealed by the present inventors. There was no knowledge whatsoever regarding the effect of suppressing emission gas characteristics. Furthermore, since these existing alloys are Ni-saving types, they have a drawback in corrosion resistance (
S (Ni content of Is 201 is 3.5-5.5%). There is XM19 in the ASTM standard as an exceptionally high Ni content, but it contains Nb and V, and Nb and V are Ti.
Similarly, increasing the amount of hydrogen in the alloy significantly increases the amount of gas released in the high vacuum region, making it unsuitable as a material for vacuum applications.

The reason why surface-oxidized high-Mn stainless steel exhibits an effect on gas emission characteristics is unknown, but as a result of examining the surface oxide film using Auger electron spectroscopy (AES), we found that the comparative example shown in the example below 1, 5US304L is an oxide mainly composed of iron and chromium, whereas the present invention 2.3 and 4
In stainless steel, the oxides were mainly iron, chromium, and manganese. Regarding the thickness of the oxide film, all four types are 500 ~
No correlation was found with the amount of gas released in the 700-person sample. In high vacuum regions, particularly in ultra-high vacuum regions, the main component of residual gas in vacuum is hydrogen gas. This is mainly because hydrogen in the stainless steel, which is the constituent material of the vacuum vessel, is released from the surface in contact with the vacuum side, but in high Mn stainless steel, Mn
It is thought that the surface oxide film containing hydrogen slows down the diffusion of hydrogen and suppresses its release into the vacuum.

Stainless steel kept in the atmosphere has a thin oxide film such as a passive film on its surface, no matter how metallic it gives off. Approximately 30 to 50 coatings are present on the stainless steel surface polished with SiC #600. 200-5 in the atmosphere
When the oxidation treatment is carried out at a temperature of 0.000C for 5 to 50 hours, a film of about 300 to 1000 layers is formed.

For films with the same composition and structure, the larger the film thickness, the greater the ability to suppress hydrogen diffusion, but when the film thickness significantly exceeds 1,000 ml, a crank occurs within the film, and the ability to suppress hydrogen diffusion begins to decrease. .

〔Example〕

The gas emission characteristics of stainless steel manufactured by the manufacturing method of the present invention and SOS 304L as a comparative example are shown below.

A plate-shaped sample was cut out from the material subjected to vacuum melting, hot rolling, and solution treatment, and after polishing with #600 SiC paper and degreasing with acetone, each sample was subjected to the treatments shown in Table 1 and used in the test. The sample surface area was set to be equal to or larger than the sample chamber surface area, and the released gas was measured using the orifice method.

This test involved evacuation at room temperature for 24 hours, and after baking at 250° C. for 24 hours, evacuation at room temperature for 24 hours.

Table 1 shows the components of the sample material. The test results are shown in Table 2.

Table 2 From the results, it is clear that the stainless steel prepared by the manufacturing method of the present invention has a smaller amount of released gas and extremely excellent released gas characteristics than the comparative example SO3304L.

〔Effect of the invention〕

As shown in the examples, the present invention provides a stainless steel material with excellent gas release properties suitable for use in high vacuum containers, piping, etc., including equipment requiring ultra-high vacuum. It facilitates the design and production of vacuum equipment, making it possible to use pumps with a small pumping capacity even in equipment used in medium- and high-vacuum areas, and its industrial value is extremely large.

Claims (2)

[Claims] (1) C: 0.08% or less, Si: 2.0% or less, Mn
:2.0~15.0%, Cr:15~23%, Ni:7
20%, N: 0.05 to 0.35%, and the remainder is Fe and inevitable impurities. A method for manufacturing a vacuum container, which comprises surface oxidizing stainless steel and then assembling the stainless steel into a vacuum container. (2) C: 0.08% or less, Si: 2.0% or less, Mn
:2.0~15.0%, Cr:15~23%, Ni:7
~20%, N: 0.05~0.35%, and the remainder is Fe and unavoidable impurities. Production method.