JPH06322490A - Stainless steel for high purity gas excellent in workability and machinability - Google Patents

Abstract

PURPOSE:To provide stainless steel for high purity gas excellent in workability and machinability. CONSTITUTION:This stainless steel for high purity gas excellent in workability and machinability is, one having a compsn. contg. 10 to 25% Ni, 15 to 30% Cr, 2 to 7% Mo and 0.10 to 0.30% N and in which the content of C in impurities is regulated to <=0.03%, Si to <=0.5%, Mn to <=0.5%, P to <=0.01% S to <=0.003%, O to <=0.005%, Ti to <=0.02% and Al to less than (0.01/N(%)) and Ni-bal. value given by the following formula is regulated to O to <3: Ni-bal. = Nieq. -1. lCreq. +8.2; where Nieq.=Ni(%)+0.5Mn(%)+30(C(%)+N(%)) and Creq.=Cr(%)+1.5Si(%)+Mo(%). The steel may furthermore be incorporated with 0.20 to 0.80% Cu. This steel combines excellent particle generating properties (cleanliness), corrosion resistance, hot and cold workability and machinability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to stainless steel for high-purity gas used in semiconductor manufacturing processes and the like.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing, high integration has progressed in recent years, and in the manufacture of devices called VLSI,
It is necessary to process a fine pattern of 1 μm or less.
In such a VLSI manufacturing process, since minute dust and trace impurity gas adheres to and is adsorbed on the wiring pattern and causes a circuit failure, both the reaction gas and the carrier gas used are of high purity, that is, gas. It is necessary that the amount of fine particles and impurity gas in the inside is small. Therefore, in high-purity gas pipes and members, fine particles (particles) as contaminants emitted from the inner surface of the pipes and members.
And it is required that the amount of gas is as small as possible.

Further, as a semiconductor manufacturing gas, nitrogen,
In addition to an inert gas such as argon, a corrosive gas such as chlorine or chlorosilanes is also used. Therefore, a member in contact with such a corrosive gas is naturally required to have high corrosion resistance.

Conventionally, such members as semiconductor manufacturing gas pipes and joints have been smoothed to have an inner surface roughness Rmax of 1 μm or less in order to reduce adhesion and adsorption of dust and water. . Electropolishing is applied as a method for smoothing the inner surface, followed by washing with high-purity water and drying with high-purity gas to obtain a product.

Austenitic stainless steels, especially SUS316L, are generally the main materials for materials such as gas pipes and joints for semiconductor production. Seamless steel pipes are used for pipes and bar steel is used for members such as joints. "Cutting" or "hot forging + cutting" finish products are used respectively.

Other than the standard steels mentioned above, JP-A-63-161145
In order to reduce the generation of particles from the inner surface of the tube as described above, Japanese Patent Laid-Open Publication No. Mn, Si, Al, O (oxygen)
Disclosed is a steel pipe for a clean room in which the content of non-metallic inclusions is reduced by controlling the content of such substances.

[0007]

As an effective measure for reducing the generation of particles, which is indispensable for the performance of stainless steel pipes for high-purity gas pipes, etc., smoothing of the inner surface of the pipes and further Japanese Patent Laid-Open No. 63-161145 have been described. There is a reduction in non-metallic inclusions as shown. As the performance of the stainless steel pipe for piping, in addition to the above-mentioned particle generation characteristics and corrosion resistance, weldability and gas release characteristics are important. Welding joints, valves, flowmeters, and other piping components are indispensable for gas piping systems.
Since these pipe parts also require high cleanliness for high-purity gas, they are manufactured from stainless steel in which generation of particles is reduced, similar to the material of steel pipes.

Manufacture of piping parts is mainly carried out by using bar steel as a raw material and machining using a lathe, a drill, etc. Therefore, machinability is also a particularly important performance for the stainless steel as the raw material. In conventional free-cutting stainless steels for general use, P, S, Se, Pb, Bi, etc. are added and machinability is given by the non-metallic inclusions or precipitates formed by these elements in the stainless steel structure. To do. However, in the case of stainless steel for high-purity gas, these inclusions and the like have to be reduced as much as possible in view of the above-mentioned required performance, so that the machinability is extremely poor and the machining of piping parts is difficult. .

Therefore, in manufacturing the above-mentioned piping parts, it is important to reduce the degree of cutting as much as possible, and it is desirable to introduce hot or cold forging. However, comparing hot forging and cold forging, cold forging is more comprehensively evaluated in terms of reduction of cutting man-hours, dimensional accuracy, surface quality and material yield, work cost, etc. The development of stainless steel materials for high-purity gas that can be introduced with the "forging + cutting" method is highly anticipated.

Further, in order to manufacture a steel bar or a steel pipe which is a raw material, naturally, it is necessary to use stainless steel having good hot workability.

The present invention has been made to solve the above problems, and an object of the present invention is to have low particle generation characteristics (cleanability) and corrosion resistance, which are essential as stainless steel for high-purity gas. An object of the present invention is to provide a stainless steel having both excellent hot workability or hot and cold workability and machinability.

[0012]

The summary of the present invention is as follows.
The stainless steel for high-purity gas has excellent workability and machinability of (1) and (2).

(1)% by weight, Ni: 10 to 25%, Cr: 15 to 30
%, Mo: 2 to 7% and N: 0.10 to 0.30%, the balance consisting of Fe and unavoidable impurities, and C in the impurities.
0.03% or less, Si 0.5% or less, Mn 0.5% or less, P 0.
01% or less, S is 0.003% or less, O (oxygen) is 0.005% or less, Ti is 0.02% or less, Al is less than [0.01 / N (%)], and the Ni-bal. Value given by the following formula is 0 or more, 3
High-purity gas stainless steel with excellent workability and machinability, which is characterized by being less than

Ni-bal. = Ni eq.-1.1Cr eq. + 8.2 ..... However, Ni eq. = Ni (%) + 0.5Mn (%) + 30 [C (%) +
N (%)] Cr eq. = Cr (%) + 1.5Si (%) + Mo (%) (2) In addition to the chemical composition described in (1) above, Cu: 0.2
A stainless steel for high-purity gas containing 0 to 0.80%, which is excellent in workability and machinability according to the above (1).

In order to solve the above-mentioned problems, the present inventors have used stainless steels having various chemical compositions, and have a particle generation characteristic which is a typical performance as a pipe for high purity gas, and a material steel. The hot and cold workability and machinability, which represent the performance, were investigated. As a result, it was found that the following are effective in improving hot workability, cold workability and machinability without deteriorating particle generation characteristics.

In order to improve the particle generation characteristics, the content of the impurity element is suppressed below a certain value.

In order to improve the machinability, N is contained in an appropriate amount, and the Al content that easily forms a nitride with N is adjusted (in the case of austenitic stainless steel, N is included).
Is known as a solid solution strengthening element for compensating for the strength reduction of low C steel, but the machinability improving effect has not been studied so far. ).

Cu is contained in an appropriate amount in order to improve the workability during cold forging.

In order to improve hot workability, Ni-ba
l. Adjust the value within a certain range.

[0020]

The reason for defining the chemical composition of the stainless steel of the present invention as described above will be described. Hereinafter,% means% by weight.

Ni, Cr, Mo: Ni, Cr and Mo are all important elements for the corrosion resistance and structural adjustment of steel. In order to maintain the structure as austenitic stainless steel and higher corrosion resistance, Ni is 10 to 25%, Cr is 15 to 30%, and Mo is
Was 2 to 7%. Outside of these ranges, the desired corrosion resistance and metallic structure cannot be obtained.

Cu: Cu is an important alloying element that improves cold workability, which is one of the objects of the present invention, and is contained if necessary. That is, Cu has the function of stabilizing the austenite phase and reducing the work hardening rate. Furthermore, it is an element that also has an effect of improving machinability. If the Cu content is less than 0.20%, good cold workability and machinability cannot be obtained. On the other hand, when it exceeds 0.80%, embrittlement becomes remarkable due to the solid solution action of Cu and the hot workability is deteriorated, which makes it difficult to manufacture steel pipes and steel bars. Therefore, when Cu is contained, the content range is 0.20 to 0.80%.

N: N is an important alloying element that improves machinability, which is one of the objects of the present invention. It is considered that the machinability is improved because, in the case of drill drilling, the increase in N makes chips more likely to break during cutting and is easily discharged out of the hole during drilling.

When the N content is less than 0.10%, the above effects are small and good machinability cannot be obtained. On the other hand, 0.30%
If it exceeds, hot workability deteriorates, and it becomes difficult to manufacture steel pipes and steel bars. Therefore, the N content range is 0.10 to
It was set to 0.30%.

C: Since C deteriorates the corrosion resistance due to the precipitation of Cr carbide, its content is preferably low. In consideration of the use of the steel of the present invention for strong corrosive gas, 0.03
% Or less.

Si, Mn: Si, Mn have a deoxidizing effect and are effective elements for highly cleaning stainless steel. However, Si, Mn
In both cases, it is easy to combine with O and S in the steel to form non-metallic inclusions, and it is desirable that the content of both of them is low in the high-purity gas stainless steel. Therefore, the contents of Si and Mn are both set to 0.5% or less.

P, S: If the content of P exceeds 0.01% and the content of S exceeds 0.003%, both are harmful to corrosion resistance and hot workability. Especially when S is very small
It produces MnS and is extremely harmful to corrosion resistance. Therefore, P
Content was 0.01% or less, and S content was 0.003% or less.

Al: Al also has a deoxidizing effect like Si and Mn,
In addition, it is an element that easily forms nonmetallic inclusions. Also, N
In the above range, if excessive Al is present, Al
Nitride is generated, the cleanliness of the steel is deteriorated, and the particle generation characteristics are deteriorated.

Whether or not Al nitrides are formed can be predicted from the contents of N and Al. The present inventors systematically investigated the relationship of the precipitation of nitrides, and found that if the relationship of the contents of N and Al is maintained at [N (%) × Al (%)] of less than 0.01, the result is high. N
It was found that Al-nitride did not precipitate even in the contained stainless steel. Therefore, the Al content is set to less than [0.01 / N (%)].

O: O (oxygen) is an element that forms non-metallic inclusions along with S, and it is necessary to reduce it as much as possible. As a range that does not adversely affect the corrosion resistance, the O content is 0.0
It was less than 05%.

Ti: Ti is an element that easily forms a nitride, and even a trace amount is harmful in the above high N content range. Therefore, the Ti content is set to 0.02% or less.

Ni-bal. Value: When the Ni-bal. Value is less than 0, only an unstable austenite structure containing a ferrite phase can be obtained, and mechanical properties and corrosion resistance are deteriorated. On the other hand, when it is 3 or more, the hot workability is deteriorated, and although there is no problem in the production of small-scale steel ingots in the laboratory, in commercial-scale mass production, cracking occurs during hot forging and hot rolling of steel ingots. Is likely to occur. Therefore, the Ni-bal. Value calculated from the alloy element content of the steel of the present invention was set to 0 or more and less than 3.

In the steel of the present invention, if W is contained in an amount of 3% or less, corrosion resistance is improved, and if B, Ca, or a rare earth element is contained in an amount of 0.01% or less, hot workability is improved.

[0034]

[Example] A stainless steel having the chemical composition shown in Tables 1 and 2 was melted, and a plate material having a wall thickness of 10 mm, an outer diameter of 6.4 mm, and a wall thickness of 1 m
m, 4 m long seamless steel pipe and 20 mm outer diameter steel bar were formed by hot working and then subjected to 1100 ° C → water cooling solution treatment,
The plate material was subjected to a machinability test and a hardness measurement test after hot working, the tube material to a particle generation characteristic test, and the steel bar to a cold workability test.

[0035]

[Table 1]

[0036]

[Table 2]

The inner surface of the steel pipe has an Rmax by electrolytic polishing.
After smoothing to 0.7 μm, it was washed with high-purity water and dried at 80 ° C. by passing 99.999% Ar gas. For particle generation characteristics, using the device shown in Fig. 1, after hitting the electrolytic polishing tube with a plastic hammer, measure the number of particles generated at 0.1 μm or more through high-purity nitrogen gas, and measure the number of times that particle generation disappears. It was evaluated by.

For the machinability, by preparing two of the above plate materials and performing a drilling test with the tools and the drilling conditions shown in Table 3, each plate material can be drilled with one new drill. The number of holes and the chip properties were evaluated.

[0039]

[Table 3]

Hot workability is as follows: 800-1200 ° C, thickness 30 mm,
A material having a width of 80 mm was rolled to a thickness of 5 mm, and the presence or absence of cracks at the edges of the plate was evaluated.

The cold workability is 6 mm in outer diameter from the above steel bar,
A 11.5 mm long test piece was cut out and the cracking limit strain (logarithmic strain) during cold upset processing was measured using the sample: 12 case.
It evaluated by the relative value set to 100.

Tables 4 and 5 summarize the evaluation results of hot workability, cold workability, particle generation characteristics and machinability.

[0043]

[Table 4]

[0044]

[Table 5]

As can be seen from Table 4, the stainless steel having the chemical composition within the range defined by the present invention had good hot workability and excellent particle generation characteristics and machinability.

As can be seen from Table 5, the stainless steel having the chemical composition within the range defined by the present invention has good hot workability and cold workability, and exhibits excellent particle generation characteristics and machinability. It was

[0047]

INDUSTRIAL APPLICABILITY The steel of the present invention is a stainless steel which has low particle generation characteristics (cleanability), corrosion resistance, excellent hot and cold workability and machinability, which are indispensable for high-purity gas. If this steel is used as a raw material steel, high-purity gas pipe members such as joints can also be manufactured from a steel bar by "cold working + cutting" finish.

[Brief description of drawings]

FIG. 1 is a schematic view schematically showing an apparatus for evaluating particle generation characteristics on the inner surface of a steel pipe.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoji Yamaguchi Sumitomo Metal Industry Co., Ltd. Kokura Steel Works, No. 1, Konomi-cho, Kokurakita-ku, Kitakyushu

Claims (2)

[Claims] 1. By weight%, Ni: 10 to 25%, Cr: 15 to 30%,
Mo: 2 to 7% and N: 0.10 to 0.30%, the balance is
Consists of Fe and inevitable impurities, and C in the impurities is 0.03
% Or less, Si 0.5% or less, Mn 0.5% or less, P 0.01%
Below, S is 0.003% or less, O (oxygen) is 0.005% or less,
If Ti is 0.02% or less and Al is less than [0.01 / N (%)],
And, the Ni-bal. Value given by the following formula is 0 or more and less than 3, high-purity gas stainless steel excellent in workability and machinability. Ni-bal. = Ni eq.-1.1Cr eq. +8.2 ..... However, Ni eq. = Ni (%) + 0.5Mn (%) + 30 [C (%) +
N (%)] Cr eq. = Cr (%) + 1.5Si (%) + Mo (%) 2. By weight, Ni: 10-25%, Cr: 15-30%,
Mo: 2 to 7%, Cu: 0.20 to 0.80% and N: 0.10 to 0.30
%, The balance consists of Fe and unavoidable impurities,
Impurity C is 0.03% or less, Si is 0.5% or less, Mn is 0.5
% Or less, P 0.01% or less, S 0.003% or less, O (oxygen
) Is 0.005% or less, Ti is 0.02% or less, and Al is [0.01
/ N (%)] and given by the following formula: Ni-bal.
A stainless steel for high-purity gas having excellent workability and machinability, which is characterized by a value of 0 or more and less than 3. Ni-bal. = Ni eq.-1.1Cr eq. +8.2 ..... However, Ni eq. = Ni (%) + 0.5Mn (%) + 30 [C (%) +
N (%)] Cr eq. = Cr (%) + 1.5Si (%) + Mo (%)