JPH08283917A - Austenitic stainless steel and welding material - Google Patents

Abstract

PURPOSE: To improve the ductility, toughness, and corrosion resistance of a piping member for semiconductor manufacturing process. CONSTITUTION: In the composition of an austenitic stainless steel used for piping member for semiconductor manufacturing process and a welding material for it, <=0.08% C, 8-16% Ni, and 16-22% Cr are incorporated and Si and Mn are excluded from constituents and further, if necessary, the allowable contents of Si and Mn, as impurities, are limited to <=0.1%. By this method, the ductility, toughness, and corrosion resistance of piping member for semiconductor manufacturing process can be improved, and deterioration in the purity of high-purity gas used for equipment can 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 used for piping or joints for ultra-high purity gas supply system or exhaust system for semiconductor manufacturing process or piping members such as tubes, and welding material thereof.

[0002]

2. Description of the Related Art Recent advances in semiconductor manufacturing technology have been remarkable. In the semiconductor manufacturing process, high-purity special gases are used, and the requirements for the purity of these gases are becoming stricter as the degree of integration of semiconductors increases. Then, the inner wall surfaces of the pipes and the pipe members such as joints and tubes that constitute the gas supply line of the semiconductor manufacturing apparatus are in direct contact with these special gases. Therefore, the piping material used in this field is required to be a material that does not release impurities such as gas contamination sources such as impurities, particles, and moisture during the supply of the special gas and has excellent corrosion resistance. Currently, as such a material, SUS30
Austenitic stainless steels such as 4, SUS304L, SUS316, and SUS316L are generally used.

[0003]

By the way, in the above-mentioned conventional materials, the upper limit of Si is 1% and the upper limit of Mn is 2%. However, as a result of diligent research, the present inventors have found that a σ phase is precipitated in the weld metal due to Si, which causes embrittlement and deterioration of corrosion resistance of the material, and also causes Mn generated from the molten portion at the time of welding. It was found that the corrosion resistance deteriorates due to the adhesion of metallic fume as the main component. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an austenitic stainless steel excellent in ductility and corrosion resistance, and a common metal welding material thereof.

[0004]

[Means for Solving the Problems] Means for achieving the above-mentioned object, that is, the first invention is C: 0.08% by weight.
% Or less, Ni: 8 to 16%, Cr: 16 to 22%, the balance being Fe and unavoidable impurities and being excellent in ductility and corrosion resistance, an austenitic stainless steel. The second invention, in addition to the components of the above-mentioned first invention, optionally comprises Mo: 2 to 3%, T by weight%.
i: 4 x (C%) to 0.6%, Nb: 8 x (C%) to 1
%, And the balance consists of Fe and unavoidable impurities, and is excellent in ductility and corrosion resistance, and is an austenitic stainless steel. A third invention is the same as the first or second invention, wherein the allowable content of Si and Mn as unavoidable impurities is 0.1% by weight.
% Is an austenitic stainless steel limited to below. A fourth invention is a common metal welding material having the same composition as the steels of the first to third inventions.

[0005]

[Function] Conventional SUS304 (L), SUS316
(L), SUS321, SUS347 are S in weight%
While i: 1.0% and Mn: 2% are positively added and contained, respectively, the steels and welding materials of the present invention do not contain Si and Mn, and their allowable contents as inevitable impurities. All of the amounts are characterized by being limited to 0.1% by weight or less. The reason for the limitation will be described below.

Si is a ferrite-forming element, and when contained in a large amount in the steel of the present invention, δ-ferrite is crystallized to cause deterioration of hot workability, ductility, corrosion resistance except stress corrosion resistance, and Si. Combines with oxygen in the steel to form non-metallic inclusions, which lowers the cleanliness of the steel and deteriorates the toughness. Therefore, in order to improve the toughness further than conventional steel, As an unavoidable impurity,
It is necessary to reduce the content as much as possible. Further, in the welding material, the components are adjusted so that 5 to 10% of δ ferrite is crystallized in the weld metal from the viewpoint of preventing hot cracking of the weld metal. In addition, in a part of the piping of the semiconductor manufacturing related apparatus, the gas heated to about 900 ° C. flows and the inner wall of the tube is heated to 600 ° C. or more. For example, δ ferrite having a high Si concentration is crystallized in the weld metal of the pipe material butt-welded with the conventional welding material for SUS316L containing about 0.5% Si. This welding metal is 60
It was found that δ-ferrite is transformed into a σ phase when exposed to a temperature of 0 ° C. or higher for a long time, resulting in a decrease in ductility and corrosion resistance due to σ-phase precipitation. Based on this finding, as a result of test examination of the correlation between the σ phase transformation of δ ferrite and the Si content,
It was confirmed that by reducing the Si content, the σ-phase transformation start time of δ ferrite shifts to a longer time side, and the σ-phase transformation is substantially suppressed. Therefore, it is necessary to add no Si to the welding material of the present invention as an unavoidable impurity and reduce its content as much as possible from the viewpoint of preventing reduction in ductility and corrosion resistance during use. However, considering the refining technology level in the current productive scale, the upper limit of the allowable content of Si as an unavoidable impurity is set to 0.1%.

When assembling pipes and joints by welding, metal fumes are generated from the molten portion during welding. This metal fume is mainly composed of Mn, which has the highest vapor pressure among the constituent components of stainless steel. This metal fume adheres to the vicinity of the weld and causes corrosion. Therefore, in order to obtain the complete corrosion resistance of the welded portion, it is necessary to reduce the amount of Mn fume generated during welding as much as possible, and for that purpose, the Mn content of the pipe material and the welding material must be reduced as much as possible. For the above reason, the stainless steel and the welding material of the present invention are characterized in that Mn is not added and the content thereof is reduced as an unavoidable impurity as much as possible. However, considering the refining technology level in the current productive scale, the upper limit of the allowable content of Mn as an unavoidable impurity is set to 0.1%.

C, Ni, Cr, Mo, Ti and N
The component range of b is JIS SUS304 (L), SUS3
16 (L), SUS321, and SUS347, and the reason for limiting the content range is omitted.

[0009]

EXAMPLE Austenitic stainless steel of the present invention having the composition shown in Table 1 and conventional stainless steel were melted in a vacuum induction heating furnace to prepare a 50 kg steel ingot. Half of this steel ingot was used as a rolled plate having a plate thickness of 5 mm, and the other half was drawn to obtain a welding material. Tensile test pieces and butt welding test materials were sampled from the solution-treated rolled plate. The results of the tensile test are shown in Table 2.

[0010]

[Table 1]

[0011]

[Table 2]

As apparent from Table 2, the material No. 1 to
No. 8 and the conventional material No. 9-No. Comparing Nos. 12 and 12, the tensile strengths are almost the same, but the elongation (ductility) of the material of the present invention is remarkably excellent. Next, the butt-welding test material was butt-welded by TIG welding using the common metal welding material produced by wire drawing in advance, and the Mn content of the metal fume adhering to the vicinity of the welded portion at the time of welding was quantified. The results are shown in Table 3, and the amount of Mn fume generated from the material of the present invention is 5
The amount of Mn fume is less than or equal to atomic% and less than 1/10 of the conventional material. Therefore, in the material of the present invention, it is considered that the corrosion near the welded portion due to the adhesion of Mn fume hardly occurs.

[0013]

[Table 3]

Subsequently, the weld metal was sampled from the above butt-welded material, and in all the test materials, δ ferrite was 5
It was confirmed that -10% crystallized. Then, this test material was heated and held at a temperature of 650 ° C., 700 ° C. or 750 ° C. In addition, this heating and holding was carried out by δ in the test material at each heating temperature.
It was performed until 5% of the ferrite was transformed into the σ phase. The results are shown in Table 4. The amount of δ ferrite in the as-welded weld metal and the weld metal after heating and holding was magnetically quantified using a ferrite meter, and the δ after heating and holding was measured.
The amount of transformation of ferrite into the σ phase was calculated by the following formula. Amount of transformation from δ ferrite to σ phase = δ ferrite amount in as-welded weld metal (%)
-Amount of δ-ferrite in weld metal after heating and holding (%) As is clear from Table 4, in the material of the present invention, it takes a long time for 5% of ferrite to transform into the σ phase, and the σ-phase transformation occurs. You can see that it is suppressed.

[0015]

[Table 4]

[0016]

As described above, the austenitic stainless steel of the present invention which does not contain Si and Mn has an improved ductility and M compared with the conventional ones containing Si and Mn.
Improvement of corrosion resistance by reducing n-fume is recognized. or,
The common metal welding material according to the present invention has the same property improving effect as that of the base metal, and also the welding metal produced during use due to the σ-phase precipitation suppressing action by reducing Si to the amount of impurities (0.1% or less). It is possible to prevent embrittlement and deterioration of corrosion resistance. Due to the above improvement, when the material of the present invention is used as a pipe member for semiconductor manufacturing process and a welding material thereof, there is an effect that the purity of the gas can be maintained at a high level without contaminating the high purity gas flowing in the pipe.

Claims (4)

[Claims] 1. C: 0.08% or less by weight%, Ni: 8
.About.16%, Cr: 16 to 22%, and the balance Fe and unavoidable impurities in the balance. 2. C: 0.08% or less by weight%, Ni: 8
.About.16%, Cr: 16 to 22%, and Mo:
2-3%, Ti: 4x (C%)-0.6%, Nb: 8x
(C%) to 1% of one or more kinds, and the balance is austenitic stainless steel consisting of iron and unavoidable impurities. 3. The austenitic stainless steel according to claim 1, wherein the allowable content of Si and Mn as unavoidable impurities is 0.1% or less by weight. 4. A welding material made of austenitic stainless steel having the composition according to claim 1.