JPH01316439A - Stainless steel for extreme high vacuum apparatus - Google Patents

Abstract

PURPOSE:To obtain the title stainless steel contg. extremely few deposits as well as nonmetallic inclusions and in which the drastical reduction of the gas to be released from a steel is permitted by regulating the compositional limit value of Ni, Cr, etc. CONSTITUTION:A stainless steel contg., by weight, <=0.010% P, <=0.010% S, <=0.4% Si, <=0.4% Mn, <=0.010% Al, <=0.005% O, <=0.008% C and <=0.015% N; where <=0.090% 10XC+N is regulated, contg. 9-35% Ni, 15-26% Cr, and the balance Fe with inevitable impurities is prepd. If required, one or more kinds among <=3% Mo, <=3% Cu and <=0.02% Sn are furthermore added to the above compsn. In this way, at the time of forming a vacuum apparatus by the use of the above stainless steel, the speed of the gas to be released from the steel can drastically be reduced because of extremely few nonmetallic inclusions and deposits, by which the capacity of the vacuum apparatus can exceedingly be improved.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is applicable to ultra-high vacuum (P < 10 Pa) to extremely high vacuum (P < 10 Pa) Concerning stainless steel for piping, valves, valves, tees, elbows, bellows, containers, etc. that make up the equipment.

[Conventional technology]

SUS 316L% SUS is used for piping, Harz valves, tees, elbows, bellows, containers, etc. that make up the vacuum equipment in manufacturing equipment used in the production of semiconductors such as VLSIs, and scientific equipment such as electron microscopes and particle accelerators. Stainless steel such as 304 or non-ferrous metal such as aluminum is used.

For example, in VLSI manufacturing technology, SUS 31 is used for super IJ gas supply piping connected to ultra-high vacuum equipment with improved corrosion resistance and ion bombardment resistance on the reaction chamber surface.
6L stainless steel is used. In order to minimize the gas released from the gas supply system and the inside of the reaction chamber,
By electrolytically polishing the surface of the gas-contact area, it is finished to a mirror surface with no process-altered layer. Recently, SUS 316L stainless steel, which has been vacuum melted twice, is used in order to reduce the amount of occluded gas itself in the material.

[Problem that the invention seeks to solve]

□ The structural materials used in conventional ultra-high vacuum equipment are:
Made of stainless steel and aluminum alloy. Vacuum equipment related to various advanced technologies such as semiconductor manufacturing equipment and nuclear fusion equipment,
Its performance is greatly affected by the type, amount, and rate of gas released from this structural material. Therefore, much research has been conducted on the outgassing of materials. As a result, in the case of hydrogen, which is the main gas released in the ultra-high vacuum region, the solubility in the material is several orders of magnitude lower in aluminum than in stainless steel.

■ Hydrogen in the same bath in stainless steel can be removed to some extent by baking at high temperatures. ■ Aluminum has a small amount of solid solution of hydrogen, but since the recrystallization temperature is low at 250 to 35 Q'C for alloys, high temperatures are required. I found out that I couldn't do Bakizog.

From these research results, the materials currently used in vacuum equipment are as follows: ■ To control surface adsorption, the surfaces in contact with gas are electrolytically polished, and after pre-baking at a high temperature of 0400℃ or higher, ◎ Stainless steel is used by performing surface treatment such as oxidation film treatment on the surface of the gas contacting part.

However, depending on the shape of the device, high-temperature prebaking may be difficult, and it is also difficult to perform surface treatment uniformly over the entire gas contact area, so it is not always possible to satisfy the best conditions.

Furthermore, operations such as prebaking and surface treatment require special equipment, which increases costs and takes time.

[Means for solving problems]

Gas release from stainless steel that makes up ultra-high vacuum equipment,
As a result of repeated studies on hydrogen, which is a particular problem, it was found that it is deeply related to nonmetallic inclusions and even precipitates inside the material.

That is, as schematically shown in FIG. 2, the nonmetallic inclusions (1) scattered on the surface of the gas-contacted part are removed by surface treatment such as electrolytic polishing. This becomes a fine pinhole (2) and becomes a stagnation area for adsorbed gas.

(2) Since the non-metallic inclusions (1) inside the material trap hydrogen atoms (3), the hydrogen concentration around the non-metallic inclusions (1) is high and the diffusion is fast. Therefore, even if the total hydrogen level in the material is lowered by repeating vacuum melting twice, hydrogen will collect locally, so the solid solubility will not actually decrease. The amount released when added also does not decrease.

Micro precipitates such as carbon and nitrogen (
When 4) occurs, it acts as a place where hydrogen atoms (3) are trapped, causing gas release similar to the above.

Based on these facts, the present invention significantly reduces and finely disperses non-metallic inclusions and precipitates in steel, resulting in extremely low gas emissions from inside the material and
In the present invention, we have developed a stainless steel for ultra-high vacuum equipment that also has excellent corrosion resistance.

That is, the first invention of the present application provides a stainless steel for extremely high vacuum equipment, which has extremely few nonmetallic inclusions (1) and precipitates, and therefore has an extremely low gas release rate, as shown in FIG. .

In addition, the second invention of the present invention provides a stainless steel for extremely high vacuum equipment, which has very few nonmetallic inclusions and precipitates, which results in an extremely low gas release rate, and which also has a high degree of corrosion resistance.

The configuration of the present invention will be explained in detail below.

Nonmetallic inclusions in steel are involved in gas release in the following ways. That is, l) It falls off due to electrolytic polishing and becomes a pinhole.

2) Hydrogen atoms are trapped around nonmetallic inclusions, and even if the apparent solid solubility of hydrogen is low, local hydrogen stagnation is formed and diffusion is rapid.

In order to control non-metallic inclusions from such points, the present invention has specified the composition. That is, p, s, and o in the steel should be as low as possible, and Si.

By minimizing Mn, the total number of inclusions is also reduced. Furthermore, regarding 0, it is impossible to reduce the content in steel to zero, so Sl.

By reducing Mn and Al, Cr and Fe-based oxides were created and finely dispersed. As a result, even if inclusions exist, it is possible to eliminate inclusions with a size of 5 μm or more in the final product size of the device, and to limit the amount of trapped hydrogen atoms.

Furthermore, by reducing C and N, the precipitation of carbides and nitrides at grain boundaries, etc. is prevented, thereby limiting the trapping of hydrogen atoms by the precipitates.

Furthermore, in the second invention, each element of MO, Cu, and Sn is
Corrosion resistance is improved by containing a species or two or more species.

Next, the reasons for limiting the composition of the steel of the present invention will be explained.

Ni: Ni has the effect of stabilizing the austenite structure and is an important element. This Ni content is 9wt.
If it is less than 1, the amount of δ-F'e increases and hot workability is inhibited. On the other hand, adding an excessive amount of Ni to the amount of Cr described below is disadvantageous in terms of economic efficiency, so 35wt4 is the upper limit for the amount of Ni added. Therefore, the amount of Ni is 9 to 35 wt
Let's do it.

Cr: Cr is an essential element for improving corrosion resistance. If the content is less than 15wt1, the effect of addition cannot be obtained sufficiently, but if it is added in excess of 26wt1, it becomes an obstacle in obtaining an austenate single phase. Therefore, the amount of Cr is set to 15 to 26 wt%.

Si, Mn: Both Si and Mn are deoxidizing elements, but they conversely deteriorate the cleanliness of steel. In the present invention, inclusions are reduced and finely dispersed by regulating both Si and Mn to 0.4 wt % or less.

p, s: Both p and s act as impurities and degrade cleanliness, so it is preferable that they be as low as possible. For this reason, each content was regulated to 0.010 wt % or less.

Since 0:0 remains in the steel as nonmetallic inclusions during solidification and impairs cleanliness, it is preferably as low as possible. For this reason, it is regulated to 0.005 wt or less.

Al: Al is effective as a deoxidizing element, but adding more than necessary increases the shape of inclusions.

Therefore, o, oi Owt is restricted to 1 or less.

C, N: Both C and N are effective elements for increasing strength,
Cr precipitates mainly at grain boundaries as Cr carbon(nitride) through stress relief heat treatment, high-temperature prebaking, or in the weld heat affected zone. Therefore, C and N are o and o o s, respectively.
wt%, regulated to 0.015wt% or less, but even if each individually is below this value, if C and N are contained at 0.090wt% or more in 10×C1N, Cr carbonitrides become grains. precipitates in the field. Therefore, C and N are C: 0.008w
t% or less, N: 0.015wt or less, inhibition, 10
×C-)-N: Regulated to 0.090 wt% or less.

MO=MO required in the second invention is the most effective element for stabilizing passivation, improving corrosion resistance, and improving oxidation resistance and pitting corrosion resistance. However, if it is added in an amount exceeding 3 wt %, processability will be inhibited and the amount of Ni will need to be increased, so it is added within a range of 3 wt % or less.

Cu, Sn: Cu also required in the second invention
Although Cu and Sn are effective for corrosion resistance, even if they are added in excess of 3wt% for Cu and o or ozwt% for Sn, an effect commensurate with the amount added cannot be expected, and for this reason, Cu is Below, Sn is 0.02wt%
Add in the following ranges.

The stainless steel for ultra-high vacuum equipment of the present invention is normally melted in a vacuum induction furnace (VIM), but it can also be melted twice by melting in a vacuum induction furnace and then remelting in a vacuum arc furnace (VAR). be exposed.

〔Example〕

Specific examples of the present invention will be described below.

After melting steel with the composition shown in Table 1 below in a vacuum induction furnace,
It was then remelted in a vacuum arc furnace.

Then, it was made into a billet by agglomeration and blooming, and was made into a pipe by hot extrusion. Thereafter, the tube was cold-rolled and cold-drawn to form a thin tube with an outer diameter of 9.53 m and a wall thickness of 1.0 m, subjected to solution treatment, and finally the inner surface was electrolytically polished. This allowed us to evaluate the materials used as the piping that constitutes the vacuum device.

Of course, similar evaluations can be obtained for vacuum device components such as valves, valves, tees, elbows, bellows, and containers. The evaluation methods were inclusion evaluation, precipitate evaluation, and gas release characteristics evaluation. Among these, inclusion evaluation is
In addition to the commonly performed JIS GO555R steel microscopic examination method for non-metallic inclusions, we actually counted spherical inclusions and linear inclusions per ton of size over an area of 10 x 2 using a 400x microscope. The counting method was used to average the number of samples per 1×2. In addition, the precipitate evaluation is
After heating at 400° C. for 24 hr, a thin film was cut out, and the presence or absence of precipitation of grain boundary carbonitrides was examined using a transmission electron microscope. Furthermore, to evaluate the gas release characteristics, which is the most important characteristic, a 4 m test tube was pre-baked (the inside of the tube was heated for 10 minutes).
%rr and heated at 400°C for 24 hours), purge with ultra-high purity He gas to remove N! .

This was done by measuring the partial pressures of co, , and H over time. The results are shown in Tables 2 and 3 below.

According to this, the steel of the present invention clearly has fewer inclusions than the comparative steel, and there are no coarse inclusions. Precipitates at grain boundaries are also not observed in the steel of the present invention. Therefore, the gas released from the steel of the present invention decreased at a much faster rate than the comparative steel, and exhibited excellent performance.

〔Effect of the invention〕

If a vacuum device is constructed using the above-mentioned stainless steel for ultra-high vacuum equipment of the present invention, the amount of gas released from the steel can be extremely reduced because there are extremely few nonmetallic inclusions and precipitates. This makes it possible to significantly improve the performance of vacuum equipment. In addition to these advantages, the pre-baking conditions can be relaxed, which reduces manufacturing costs and improves the performance of parts with shapes that restrict baking, making it possible to improve the overall vacuum system. Performance can be expected to improve.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram schematically showing the state of nonmetallic inclusions and precipitates inside the stainless steel of the present invention, and Fig. 2 is a schematic diagram showing the state of nonmetallic inclusions and precipitates inside the conventional stainless steel. FIG. In the figure, (1) is a nonmetallic inclusion, (2) is a pinhole, (
3) indicates a hydrogen atom, and (4) indicates an inclusion. Patent applicant Nippon Kokan Co., Ltd. Inventor Toyama Mima Yu Minami Benma
Mountain 1) Kaikai Takeshi
Hiroshi Takizawa Homa
Sadahiko Murase Patent Attorney Masatoshi Yoshihara Masatoshi Tomabechi Figure 2 Figure 1

Claims (1)

[Claims] 1. P: 0.010wt% or less, S: 0.010wt%
Below, Si: 0.4wt% or less, Mn: 0.4wt% or less, Al: 0.010wt% or less, O: 0.005wt%
% or less, C: 0.008wt% or less, N: 0.015w
Stainless steel for extremely high vacuum equipment, containing 10×C+N: 0.090 wt% or less, Ni: 9 to 35 wt%, Cr: 15 to 26 wt%, and the balance being Fe and inevitable impurities. 2, P: 0.010wt% or less, S: 0.010wt%
Below, Si: 0.4wt% or less, Mn: 0.4wt% or less, Al: 0.010wt% or less, O: 0.005wt%
5 or less, C: 0.008wt% or less, N: 0.015w
t% or less, but contains 10×C+N: 0.090wt% or less, Ni: 9 to 35wt%, Cr: 15 to 26wt%, further Mo: 3wt% or less, Cu: 3wt% or less,
Stainless steel for ultra-high vacuum equipment, containing one or more Sn: 0.02 wt% or less, and the balance being Fe and unavoidable impurities.