JPH0673507A - Austenitic stainless steel pipe for high purity gas piping - Google Patents

Abstract

PURPOSE:To obtain an austenitic stainless steel pipe for high purity gas piping, having corrosion resistance to corrosive gases by specifying the contents of Cr, Ni, and Mo as essential alloy components and also specifying the roughness in the internal surface. CONSTITUTION:In the austenitic stainless steel pipe for high purity gas piping, the contents of Cr, Ni, and Mo as essential alloy components in the steel are controlled, by weight, to 15.0-30.0%, 15.0-30.0%, and 4.0-8.0%, respectively, and 0.05-0.25% N is further incorporated, if necessary, and also the maximum roughness in the internal surface is regulated to <3mum. By this method, the occurrence of corrosion in the pipe, particularly corrosion in a weld heat-affected zone, in the case in which the outside air gas containing trace amounts of moisture is mixed into corrosive gases, can effectively be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic stainless steel pipe used for high purity gas pipe such as semiconductor manufacturing equipment.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing, the degree of integration has increased in recent years, and, for example, a device called VLSI requires a fine processing technique with a line width of 1 μm or less. In such a VLSI manufacturing process, a minute amount of dust or a minute amount of impurity gas adheres to and is adsorbed on the Si wafer as a material to cause a circuit failure, which greatly affects the product quality and yield. Therefore, it is necessary that the reaction gas and the carrier gas used have high purity, that is, the amount of fine particles and impurity gas in the gas is small. Accordingly, in the gas pipe used for supplying the gas, it is required that the emission of fine particles and the emission of gas from the inner surface of the pipe be as small as possible.

Conventionally, a seamless austenitic stainless steel pipe made of SUS316L steel has been frequently used for high-purity pipes used in such semiconductor manufacturing processes, and the inner surface of the pipe is attached with impurities such as fine particles and water. And in order to reduce adsorption, by cold working, bright annealing, polishing, or a combination thereof, for example,
In the case of cold working + bright annealing, the inner surface has a maximum roughness of less than 3 μm, and those subjected to polishing treatment such as abrasive grain polishing, electrolytic polishing, and chemical polishing have a maximum roughness of less than 1 μm. Then, in the gas flowing through the gas pipe, Ar and N ₂ for carrier or purging,
In addition, silanes called special material gas as reaction gas,
Hydrogen chloride, chlorine, etc. are used.

Inert gases such as Ar and N ₂ do not have any adverse effect on SUS316L steel which is a piping material. However, most of the special material gases used as the reaction gas are unstable, react with a small amount of water vapor, and corrode SUS316L steel. Therefore, when using SUS316L steel for the reaction gas pipe, the water vapor in the pipe must be kept as low as possible, and dry high-purity inert gas should be kept sealed inside the pipe except when in use. Is common.

[0005]

However, since the reaction gas is supplied from the gas container to each device, it is possible to prevent outside air containing moisture, though a small amount, from entering the pipe when the gas container is replaced. It is unavoidable that the reaction of the reaction gas with the reaction gas may corrode the inner surface of the SUS316L steel pipe, even if it is the inner surface. Research to suppress this corrosion by improving the oxide film on the inner surface of the pipe is relatively advanced (Japanese Patent Laid-Open No. 1-198463, Kobe Steel Technical Report / vol.
39 No. 4 (1989) P57-60). However, according to the investigation by the present inventors, this corrosion preferentially occurs in the welded joint portion of the piping system, particularly in the heat affected zone away from the melting boundary, and the corrosion prevention measures considering the weld heat affected zone are the main. As far as the inventors know, it does not exist. Therefore, at present, there is a concern about gas contamination due to corrosion of the heat affected zone.

An object of the present invention is to provide an austenitic stainless steel pipe for high purity gas pipe which can prevent pipe corrosion when outside air gas containing a trace amount of moisture is mixed with corrosive gas.

[0007]

In order to clarify the corrosion behavior when a corrosive gas is passed through a high-purity gas pipe made of SUS316L steel, the inventors of the present invention, chlorine, which is one of the corrosive gas. The following corrosion test was conducted using gas.
Chlorine gas containing 100 ppm of water was added to the test pipe made of SUS316L steel inner surface electropolished steel pipe at 0.5 MPa.
It was sealed, and water in the pipe was condensed by cooling it with liquid nitrogen, and then the pipe was opened to the atmosphere to observe the corrosion state of the inner surface of the pipe. As a result, no corrosion occurred in the test pipe except for the welded portion (butt TIG welded portion), but the surface of the welded portion, particularly the heat-affected zone, corroded and rusted. From these test results, the present inventors confirmed the importance of corrosion countermeasures in terms of steel composition, and repeated the corrosion test using austenitic stainless steel pipes of various compositions in order to find out the countermeasures. As a result, Cr, Ni, Mo and N in the steel, especially Mo, are effective in preventing corrosion of the weld thermal expansion part.
It was found that even in the severe corrosion test described above, the corrosion of the weld heat affected zone can be prevented.

The present invention has been made on the basis of such knowledge, and Cr, Ni and Mo, which are the main alloying components in steel, are contained in the following weight% and, if necessary, 0.05 to 0.2.
The gist is an austenitic stainless steel pipe for high-purity gas piping, which contains 5% by weight of N and has a maximum roughness of an inner surface of less than 3 μm. Cr: 15.0 to 30.0% by weight Ni: 15.0 to 30.0% by weight Mo: 4.0 to 8.0% by weight

[0009]

The action and the reason for limitation of the steel components in the austenitic stainless steel pipe for high purity gas pipe of the present invention will be described below.

Cr: 15 to 30 wt% Cr is an element for improving corrosion resistance, and the higher the content, the greater the effect. In order to prevent corrosion of the welded portion, Cr of 15% by weight or more is necessary. However, when the content exceeds 30% by weight, an intermetallic compound or the like precipitates during heat treatment or hot working to cause embrittlement, which makes it difficult to process the steel pipe, and also increases the toughness of the welded portion. to degrade. Therefore, the content of Cr is set to 15 to 30% by weight.

Ni: 15 to 30 wt% Ni is an element effective in improving the corrosion resistance, and is essential in that the steel structure has an austenite single phase. When the steel structure is not an austenite single phase, the corrosion resistance and toughness of the welded part are significantly reduced. If the Ni content is less than 15% by weight, the austenite single phase does not occur, while if it exceeds 30% by weight, the hot workability is remarkably reduced and the economical efficiency is impaired. Therefore, the content of Ni is 15 to
It was set to 30% by weight.

Mo: 4-8 wt% Mo is the most important element in improving the corrosion resistance in the heat affected zone of the welded joint. This Mo is less than 4% by weight at most in general austenitic stainless steel pipes for high-purity gas piping, and only 2 to 3% by weight is contained in SUS316L steel that is most frequently used.
Although the content of o can secure the corrosion resistance to an inert gas or an inert gas mixed with water vapor, oxygen, etc., it cannot secure the corrosion resistance to a corrosive gas such as chlorine gas, especially the welding heat affected zone. In the steel pipe of the present invention,
In order to ensure excellent corrosion resistance that the weld heat affected zone is not corroded by corrosive gas such as chlorine gas, Mo is 4
Weight% or more is required. Further, the higher the content of Mo, the more the corrosion resistance is improved. However, if the content of Mo exceeds 8% by weight, precipitation of intermetallic compounds easily occurs,
Deterioration of hot workability and deterioration of toughness of the welded part become remarkable. Therefore, the content of Mo is set to 4 to 8% by weight.
The high Mo content steel of the present invention does not deteriorate in properties other than corrosion resistance, that is, hot workability and toughness, as compared with the conventional low Mo content steel represented by SUS316L.

N: 0.05 to 0.25% by weight N is effective for forming an austenite single-phase structure like Ni, and is also effective for improving corrosion resistance like Cr and Mo. In the steel pipe of the present invention, this N is 0.05 if necessary.
Up to 0.25% by weight. N content is 0.05% by weight
If less than 0.25% by weight, the effect of N addition cannot be obtained, while 0.25% by weight
If it is contained in excess, the workability in hot workability deteriorates and it becomes difficult to manufacture steel pipes.

Elements other than Cr, Ni, Mo and N include elements usually used in austenitic stainless steel. If necessary, S, Pb, Se,
Machinability improving components such as Te and Sn, Ca, Ce, Mg,
B, REM and other processability improving components, and even trace amounts of Ti, N
b, Zr and other C stabilizing components are selectively contained. Regarding the corrosion resistance, there are five components of Cr, Ni, Mo and N, but W, Cu and the like may be added for further improvement. Moreover, in order to prevent dust generation from the inner surface of the pipe due to non-metallic inclusions in the steel, which is a problem in stainless steel pipes for high-purity gas piping, it is necessary to reduce Si, Mn, Al, O, S forming the inclusions as much as possible. Good. The simple actions and desired contents of these elements are described below.

Si, Mn, Al These elements are used as deoxidizers during the refining of steel,
It is effective in reducing oxide inclusions in steel, and may usually contain Si and Mn in an amount of 2.0% by weight or less and Al in an amount of 0.2% by weight or less.

P, S These elements are impurity elements and deteriorate the workability and corrosion resistance, so it is desirable to reduce them as much as possible. Normally, P is 0.03% by weight or less, and S is 0.0.
It is preferably 1% by weight or less.

C C causes precipitation of Cr carbide due to welding and improper heat treatment, and deteriorates corrosion resistance and toughness. Therefore, the C content should be as low as possible, preferably not more than 0.08% by weight, and more preferably 0.0.
It is preferable to be 3% by weight or less.

Pb, Se, Te, Sn (S) These elements are contained in the steel pipe of the present invention when machinability is required to process the steel pipe into a pipe part having a desired shape.
You may add in order to improve the cuttability. The content of S is 0.01 wt% or less for the above-mentioned reason, and 1.0 wt% or less for other elements, 1 type or 2 types.
It may contain more than one species.

Ca, Ce, Mg, B, REM These elements are added singly or in combination for the purpose of improving hot workability in the case of producing the steel pipe of the present invention, particularly the seamless steel pipe. The content may be 0.03% by weight or less. If the total content exceeds 0.03% by weight, the workability and corrosion resistance will be deteriorated.

Ti, Nb, Zr These elements are strong carbide-forming elements, and have the effect of stabilizing C and suppressing / preventing precipitation of Cr carbide, thus improving corrosion resistance and toughness. The total content of one kind or two or more kinds may be 1.0 wt% or less. As a result, even when the steel pipe of the present invention is used after being subjected to heat treatment at 500 to 800 ° C., Cr carbide precipitation can be effectively suppressed / prevented, and as a result, deterioration of corrosion resistance and toughness is reliably prevented. can do.

W, Cu These elements improve the corrosion resistance, and may contain one kind or two kinds or more in a total content of 2.0% by weight or less. If it is contained in an amount of more than 2.0% by weight, workability will be significantly deteriorated.

Next, the tube inner surface roughness, which is another constituent factor of the present invention, will be described.

Also in the steel pipe of the present invention, the maximum roughness of the inner surface of the pipe is set to less than 3 μm in order to prevent minute dust from remaining on the inner surface of the pipe and to ensure the cleanliness required for a high-purity gas pipe. This is either cold working, bright annealing, polishing,
Alternatively, it can be realized by a combination thereof. Specific examples of the cold working method include cold rolling and cold drawing. Cold rolling is preferable from the viewpoint of smoothing the inner surface of the pipe. Bright annealing and polishing are performed to further smooth the inner surface after cold working. Examples of the polishing method include mechanical polishing, electrolytic polishing, chemical polishing, and complex polishing including a combination thereof. Specific examples of the combination of smoothing the inner surface of the pipe include cold rolling + cold drawing + bright annealing + electrolytic polishing, and cold drawing + electrolytic polishing.

It is to be noted that, as the raw pipe, a seamless steel pipe having no welded portion is preferable, but in the present invention, since the corrosion resistance of the welded portion is enhanced by improving the steel composition, a steel pipe having a seam such as an electric resistance welded steel pipe is provided. But it's okay.

[0025]

EXAMPLES Examples of the present invention will be described below.

40 mm outer diameter having the chemical composition shown in Table 1.
× Hot-rolled seamless austenitic stainless steel pipe with a wall thickness of 3 mm is used as a raw pipe, and this is cold-rolled and cold-drawn to obtain a steel pipe with an outer diameter of 6.35 mm × wall thickness of 1 mm. Then, the inner surface of the tube was smoothed by electrolytic polishing. Table 1 also shows the maximum roughness of the inner surface of the pipe after smoothing. No. 8 is N
o.2 The inner surface smoothness of the steel pipe is reduced.

After these steel pipes were butt-welded under the conditions shown in Table 2, the corrosion resistance of the welded portion was investigated. Corrosion resistance is
The presence or absence of corrosion in the above-mentioned corrosion test using chlorine gas is 50
It was evaluated by observing with a double optical microscope. The corrosion test process is shown in Table 3 and the test results are shown in Table 4. ◯ indicates that no corrosion was observed at all, Δ indicates that slight corrosion was observed, and × indicates that the surface was covered with rust and severe corrosion was observed.

As shown in Table 4, N which is the steel pipe of the present invention
In Nos. 1 to 4, no corrosion was observed not only in the base metal but also in the welded part. In contrast, in Comparative Example No. 5 in which the inner surface was extremely smooth, no corrosion occurred in the base metal, but severe corrosion occurred in the weld because the Mo content was low. In addition, in No. 8 in which the smoothness of the inner surface is poor even though it contains a sufficient amount of Mo, severe corrosion occurs in both the base metal and the welded portion, and the smoothness of the inner surface satisfies the corrosion resistance. It turns out that this is one of the essential constituents.

Further, the same test was carried out on the TIG welded steel pipe, but no corrosion was observed on all welded parts including the pipe welded part.

Other than chlorine, examples of the corrosive gas for which the steel pipe of the present invention is effective include chlorosilanes, boron halides, and phosphorus halides.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

As is apparent from the above description, the austenitic stainless steel pipe for high purity gas pipe of the present invention uses corrosive gas, and the outside air is mixed into the gas due to conversion of the gas container. Even if it is unavoidable, it is possible to prevent corrosion of all the welded parts including the base metal and the heat affected zone. Therefore, the purity of the supply gas is prevented from lowering, and the high-purity gas is effectively supplied.

Front page continued (72) Inventor Hideaki Sachi, 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) In-house Masahiro 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Inventor Takenobu Matsuo 2-3-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Electron Ltd. (72) Inventor Go Wakabayashi 2-3-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Electron Co., Ltd. (72) Inventor Shuji Moriya 2-3-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Tokyo Electron Co., Ltd. (72) Inventor Yoshinobu Ando 1-14-1 Kawana, Fujisawa-shi, Kanagawa Sumikin Stainless Steel Pipe Shonan Factory Co., Ltd.

Claims (2)

[Claims] 1. A main alloying component in steel, Cr, N
Austenite-stainless steel pipe for high-purity gas pipe, characterized in that i and Mo are contained in the following weight% and the maximum roughness of the inner surface is less than 3 μm. Cr: 15.0 to 30.0% by weight Ni: 15.0 to 30.0% by weight Mo: 4.0 to 8.0% by weight 2. Cr and N, which are the main alloying components in steel,
i and Mo are contained in the following weight%, and 0.05 to
Contains 0.25% by weight of N and maximum inner surface roughness of 3 μm
Austenite / stainless steel pipe for high-purity gas pipe characterized by being less than. Cr: 15.0 to 30.0% by weight Ni: 15.0 to 30.0% by weight Mo: 4.0 to 8.0% by weight