JPH11264010A - Production of high purity stainless steel resistant against ozone-containing water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve resistance against ozone-containing water by regulating C, total of Al and Si, single Al, Mn, Cr, Ni, P, S, O and N to specific contents, respectively, with a primary melting under vacuum and specifying the contents of Mn, O and N on and after secondary melting by using the method for a consumable electrode type dissolution. SOLUTION: In the primary melting, the composition of the molten steel is regulated to, by wt.%, <=0.020% C, 1.0-6.0% total of Al and Si or Al single, <=0.18% Mn, 12-30% Cr, 0-35% Ni, <=0.030% P, <=0.010% S, <=0.008% O and <=0.010% N. In the secondary melting, the composition is regulated to <=0.05% Mn, <=0.008% O and <=0.008% N. It is desirable to execute a heating treatment under weak oxidizing atmosphere of 10<-11> -10<-15> MPa gas partial pressure in the total of gaseous oxygen and steam or a nitric acid aqueous solution soaking treatment in 5-50 wt.% concn. or an anode electrolytic treatment for forming a coated film of alminium oxide at <=pH 1, etc., to the surface of a base material using the above cast slab as a blank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity stainless steel material useful as a piping member for ozone-containing water used in the production of semiconductors and pharmaceuticals, a component of a semiconductor production apparatus, and the like.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing, the degree of integration has been increasing in recent years. Therefore, in a device called a super LSI, a substrate such as a silicon wafer is
Processing of a fine wiring pattern having a width of 1 μm or less is required.

[0003] When minute dust adheres to such a fine wiring pattern or a minute amount of impurity gas adheres, a short circuit or the like of a circuit occurs and causes a circuit failure. Therefore, various measures have been taken to prevent such contamination when processing the substrate in the VLSI manufacturing process.

[0004] Processing of the substrate is performed in a clean room to prevent the substrate from being contaminated from the working environment. Of course, in order to ensure the cleanliness of the clean room, the indoor air must be clean,
The gas and water used therein must also be of high purity. For this reason, a high-purity gas containing a small amount of fine particles and impurity components and ultrapure water are used.

[0005] Stainless steel is used for piping and members used in such a semiconductor process.
Stainless steel materials that come into contact with high-purity gas or ultrapure water are usually treated to smooth the surface so that the surface area is as small as possible. In addition, since non-metallic inclusions in steel are the starting point of particle generation, ultra-clean stainless steel is used, which enhances deoxidation at the steelmaking stage and reduces oxides and other substances that cause non-metallic inclusions. Can be

In recent years, cleaning of a substrate such as a silicon wafer in a semiconductor manufacturing process or the like has been performed by using ultrapure water containing ozone.
(Hereinafter, ozone-containing water) has come to be used. However, in the case of cleaning with ozone-containing water, there is a problem in that the ozone-containing water is contaminated by piping and equipment used for supplying ozone-containing water. The contamination of ozone-containing water is caused by the corrosion of stainless steel used for piping and equipment by the ozone-containing water.
This is due to elution of metal ions such as Fe, Cr, and Ni. Stainless steel developed for ordinary ultrapure water and high-purity gas that does not contain ozone has almost good performance in preventing metal ion elution or dust generation in ultrapure water. However, since it was not developed in consideration of application to ozone-containing water, when it was used as a material for ozone-containing water, elution and dusting of metal ions occurred, and it was not practical.

[0007] Ultra-clean stainless steel is disclosed in
According to JP-A-90472, after melting by a vacuum induction melting method, a steel ingot is remelted by a vacuum arc melting method with or without a step of melting by a vacuum arc melting method or an electroslag melting method. , C: 0.0
06-0.020%, Si: 0.10% or less, Mn:
0.10 or less, Al: 0.03% or less, P: 0.030
% Of stainless steel is disclosed. However, the composition of this steel does not consider the corrosion resistance to ozone-containing water.

[0008] Stainless steel having an Al oxide film is
It is used as a high-temperature member exhibiting oxidation resistance. For example, in JP-A-6-271993, Si in steel,
An Al-containing austenitic stainless steel having an Al oxide film that is stable for a long time at a high temperature by optimizing the content of elements such as S, O, V, and Ti is disclosed. Austenitic stainless steel containing Al is poor in hot workability, and is disclosed in
No. 5348, Ca, rare earth elements and the like are added,
A with excellent hot workability by optimizing the content of S and O
An l-containing austenitic stainless steel is disclosed. Japanese Patent Application Laid-Open No. 7-62520 discloses a stainless steel member for a clean room, which has an oxide film mainly composed of Si. But,
Since these inventions do not consider the cleanliness of steel required for piping and equipment members used for supplying ozone-containing ultrapure water, if the steel comes into contact with ozone-containing water, it will have sufficient corrosion resistance. I can't say that I have

[0009]

An object of the present invention is to provide a pipe member for ozone-containing water, a constituent member of a semiconductor manufacturing apparatus, and the like, in which the amount of metal eluted in ozone-containing water is extremely small and nonmetallic inclusions are contained. Of slabs for producing high-purity stainless steel materials having a low content of gas components such as O and N and Mn, which are a cause of the occurrence, and having excellent hot workability, and an ozone-resistant water-based material using the slabs as a material. An object of the present invention is to provide a method for producing a high-purity stainless steel material.

[0010]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a method for producing an ozone-resistant aqueous high purity stainless steel slab as described in the following (1) and an ozone resistant aqueous high purity as described in the following (2) to (4). It is in the method of manufacturing stainless steel.

(1) By the first melting under vacuum, the weight%
C: 0.020% or less, Al and Si in total or Al alone 1.0 to 6.0%, Mn: 0.18% or less,
Cr: 12 to 30%, Ni: 0 to 35%, P: 0.03
0% or less, S: 0.010% or less, O (oxygen): 0.0
After adjusting the components to 08% or less and N: 0.010% or less,
By a secondary or subsequent dissolution method using a consumable electrode dissolution method, at least Mn of the above chemical components is 0.05% or less, and O
Is 0.008% or less and N is 0.008% or less.

(2) A base material made from the cast slab obtained by the production method of (1) is mixed with a weak acid having a partial pressure of a combined gas of oxygen gas and water vapor of not less than 10 ^-11 MPa and not more than 10 ^-5 MPa. A method in which an oxide film mainly composed of both Al oxide and Si oxide or Al oxide is formed on the surface of the base material by heating to 600 ° C. or more and 1200 ° C. or less in a oxidizing atmosphere.

(3) The base material made of the cast slab obtained by the production method of (1) is immersed in an aqueous solution of nitric acid having a concentration of 5% to 50% by weight so that the surface of the base material is , Al
A method of forming an oxide film mainly composed of both an oxide and a Si oxide or an Al oxide.

(4) The base material made of the cast slab obtained by the method (1) is subjected to anodic electrolysis in a solution having a pH of 1 or less, so that Al oxide and Si A method of forming an oxide film mainly containing both oxides or Al oxide.

The surface roughness of the oxide film formed by the above methods (1) to (4) is desirably smooth, and the center line maximum roughness (Rmax) is desirably less than 3 μm. In order to make the surface roughness of the oxide film less than 3 μm in Rmax, it is preferable that the surface roughness of the base material before the oxide film is formed be 2 μm or less in Rmax.

The present inventors have found that a stainless steel material provided with an oxide film mainly composed of an Al oxide and a Si oxide, particularly an Al oxide, has excellent ozone-containing water resistance. Further, in stainless steel containing a large amount of Al and Si, non-metallic inclusions such as nitrides and oxides are easily generated. The knowledge that the water content is further improved was obtained, and the above invention was completed.

[0017] The term "mainly composed of Al oxide or Si oxide" means that Al oxide or Al oxide is used for all the metal elements constituting the oxide film.
And Si in a total amount of 80 atomic% or more.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a cast slab of the present invention, primary melting under vacuum and vacuum arc melting (VA)
R) method, secondary and subsequent dissolving methods using a consumable electrode type dissolving method such as an electroslag dissolving (ESR) method.
In this secondary dissolution, Mn, O (oxygen) and N decrease, so that these elements which cause nonmetallic inclusions in steel can be reduced. However, since the amount of reduction is limited, the target value of the content of the product slab, Mn: 0.
It is preferable that the Mn after the first melting is 0.18% or less and the N is 0.010% or less with respect to 05% or less and N: 0.008% or less. Oxygen tends to decrease during the secondary melting, but from the viewpoint of ensuring high purity, the content of the product slab after the primary melting is the same as that of the product slab after the secondary melting.
It is desirably set to not more than 08%.

Hereinafter, the chemical composition of stainless steel, the method of manufacturing a cast slab, and the method of manufacturing a steel material excellent in water resistance to ozone by forming an oxide film on the surface, which are the object of the manufacturing method of the present invention, will be described. I do.

1. Chemical Composition The chemical composition described in the above (1) is substantially the same for the elements other than Mn and N after the primary dissolution and after the secondary dissolution. Hereinafter, the content of each element will be described. In addition,
The percentage display of the content of each element means% by weight.

C: C is used for the purpose of deoxidation, but in the case of the present invention, since Al having a deoxidizing effect is added, it is not necessary to contain C for the purpose of deoxidation. In order to prevent the precipitation of carbides, C is preferably as low as possible, and is set to 0.020% or less.

Al and Si: The stainless steel obtained by the method of the present invention has an oxide film formed by oxidizing Al and Si contained in the base material on the stainless steel surface of the base material, The oxide film exhibits ozone-containing water resistance. The total content of Al and Si is 1.
If the amount is less than 0%, the oxide film is not sufficiently formed, so that the stainless steel material cannot have sufficient ozone-containing water resistance. On the other hand, if the total content of Al and Si exceeds 6.0%, the toughness tends to decrease. Also,
In the case of an austenitic system, an intermetallic compound consisting of Ni and Al precipitates, so that the hot workability and toughness of the base material are reduced. Therefore, the total content of Al and Si is 1.0 to
6.0%. Preferably it is 2.0-4.0%.

The effect of improving the resistance to ozone-containing water is as follows:
l Since the oxide film is larger, the oxide in the film
It may be mainly composed of an oxide. In that case, Si may be not added. The Al content of Al alone is 1.0
To 6.0%, preferably 2.0 to 4.0%.

Mn: Mn forms a sulfide with S, and the sulfide remains as nonmetallic inclusions in the steel. Further, when the steel material is welded, the steel material may be preferentially concentrated on the surface of the welded portion, and may reduce the corrosion resistance of the steel material. Therefore, the Mn content of the product slab obtained by secondary and subsequent melting is 0.05%.
It was as follows. In order to reduce the Mn of this product slab to 0.05% or less, the Mn content after the first melting must be 0.18% or less.

Cr: Cr is an essential element for the base material. Cr is necessary for ensuring the corrosion resistance of stainless steel in an environment where a steel material is used. Further, by adding Cr, rust can be prevented from occurring in a neutral aqueous solution such as pure water and in an atmosphere of a clean room. In order to exert such an effect of Cr, it is necessary to contain 12% or more.

On the other hand, if the Cr content exceeds 30%,
The hot workability of the base material deteriorates. Further, when a stainless steel material is welded, an intermetallic compound containing Cr such as a sigma phase easily precipitates at a welded portion, so that toughness is reduced. Therefore, the content of Cr is set to 12 to 30%. Preferably, it is 18 to 25%.

When the base material is austenitic stainless steel containing 14 to 35% of Ni, the upper limit of the Cr content is set to 25% from the viewpoint of hot workability and toughness of the welded portion. preferable.

Ni: Ni has an effect of improving the corrosion resistance of the base material and is also an effective element for obtaining a stable austenite structure. In the stainless steel material of the present invention,
Ni is contained as required.

The base material may be any of ferrite, two-phase and austenite. However, a single phase such as a ferrite type and an austenite type has a feature that a more uniform oxide film is easily generated than a two phase type.

When the base material is a ferrite-based material, it is preferable to contain 0 to 5% of Ni in order to improve corrosion resistance. This is because when the Ni content exceeds 5%, the base material becomes a two-phase system, so that it is necessary to more accurately control the processing conditions when forming the oxide film.

When the base material is made of austenite,
Ni is 14% to obtain a stable austenite structure.
It is preferable to contain the above. On the other hand, when the content exceeds 35%, an intermetallic compound composed of Ni and Al precipitates, so that the hot workability and toughness of the base material decrease. Therefore, the Ni content is preferably 14 to 35%. The preferred content in the case of an austenitic system is 18 to 25%.

S: S forms sulfide which is a nonmetallic inclusion. If sulfide-based nonmetallic inclusions are present in the oxide film, the film will be defective, and the resistance to ozone-containing water will be reduced. In addition, the nonmetallic inclusions contribute to lowering the smoothness of the surface of the base material and also serve as a starting point of corrosion of the steel material.
Furthermore, this non-metallic inclusion becomes fine particles (dust) when the steel material is used as a pipe of a semiconductor manufacturing apparatus,
It causes contamination of a substrate such as a silicon wafer. As described above, it is better that S is as low as possible.
% Or less. Preferably it is 0.002% or less.

P: The lower the content, the better the weldability of the steel material. In particular, when the P content exceeds 0.03%, the weldability is remarkably reduced.
Preferably it is 0.02% or less.

N: In addition to forming Al nitride by combining with Al in steel, it easily combines with C, Cr, Ti, Nb, etc. to form carbonitride. These carbonitrides, like the sulfide-based nonmetallic inclusions, become defects in the oxide film and lower the resistance to ozone-containing water and generate fine particles. Therefore, the N content of the product slab is 0.0
08% or less. Preferably it is 0.005% or less. In order to obtain a product slab having an N content of 0.008% or less, the N content after the first melting needs to be 0.010% or less.

O (oxygen): O exists mainly as oxide-based nonmetallic inclusions in steel. The oxide-based nonmetallic inclusions, like the sulfide-based nonmetallic inclusions described above, become defects in the oxide film, reduce the ozone-containing water resistance, and cause the generation of fine particles. Since the lower the O content, the better, the O content of the product slab is 0.00
8% or less. Preferably, it is 0.005% or less. In order to set the O content of the product slab to such an amount, 1
The O content after the next dissolution is also 0.008% or less, preferably 0.005% or less.

The stainless steels to which the present invention is applied include Mo, Nb, Ti, B, and
Alloy elements such as La, Ce, W, and Cu may be added. These elements have almost no effect on the purity of steel.

2. The method of producing a cast slab The primary melting is preferably performed by a vacuum melting method capable of suppressing and increasing the rise of gas components such as oxygen and nitrogen which cause nonmetallic inclusions. Vacuum melting method (VIM method) and vacuum oxygen decarburization method (VOD method)
Is mentioned. However, in the case of VIM or VOD, there is a possibility that nonmetallic inclusions may be mixed in due to contact between molten steel and slag or refractory. While reducing these non-metallic inclusions, Mn, which causes non-metallic inclusions,
In order to reduce elements such as N and O, secondary and subsequent melting is required.

For the second melting and the third and subsequent melting, it is preferable to employ a consumable electrode type melting method such as a consumable electrode type vacuum arc melting method (VAR method) or an electroslag melting method (ESR method).

In the VAR method, an arc is generated between a steel ingot whose chemical composition has been adjusted by primary melting and a water-cooled copper crucible under a high vacuum as a consumable electrode, the electrode is melted by the heat, and the electrode is dropped. This is a method of laminating and solidifying molten steel. This method has the advantage of removing not only N and O but also Mn having a high vapor pressure when the molten steel is dropped. The deoxidized product coagulates and floats and is separated, and the segregation is suppressed by the effect of the water-cooled copper crucible, whereby the components are made uniform.

In the ESR method, a steel ingot whose chemical composition has been adjusted by primary melting is used as an electrode to supply electricity to the slag, the electrode is melted using the Joule heat of the molten slag, and the electrode material that has been properly lowered in the slag is removed. This is a method of laminating and solidifying in a water-cooled copper crucible. The atmosphere is sealed with an inert gas or evacuated, and lower oxides in the slag are reduced to prevent the formation of nonmetallic inclusions caused by Al and Si in the steel. These non-metallic inclusions can be absorbed therein.

When the content of Al is large as in the stainless steel to which the present invention is applied, segregation tends to occur during solidification, which may cause cracking during forging. Since the solidification of the slab in the case of the VAR method and the ESR method is one-way solidification from the crucible bottom upward, there is an advantage that segregation hardly occurs. Therefore, according to the production method of the present invention, a slab excellent in hot workability can be obtained even if the Al content is high.

The re-dissolution by the VAR method and the ESR method may be repeated a plurality of times.

3. Method for Forming Oxide Film Prior to forming the oxide film, first, the above product slab is processed into a shape suitable for the application by a hot rolling method or the like. By using this processed material as a base material and forming a film mainly composed of Al oxide and Si oxide or Al oxide on the surface thereof, a steel material excellent in ozone-containing water resistance is manufactured. In order to form this oxide film, A
It is necessary to select conditions for oxidizing l and Si or Al preferentially over other easily oxidizable alloy elements. The manufacturing method of the present invention in which oxidation of other alloying elements in steel is suppressed and Al and Si or Al are preferentially oxidized includes a high-temperature oxidation method and a wet oxidation method.

As described above, when a film mainly composed of Al oxide is formed, the Si content of the base material may be suppressed to a low value or may not be added.

Hereinafter, the two oxidation methods will be described.

(High-Temperature Oxidation Method) In order to preferentially oxidize Al and Si or Al in steel by the high-temperature oxidation method, oxygen and water vapor are separated in an atmosphere such as hydrogen gas, vacuum or an inert gas. It is preferable to heat to 600 to 1200 ° C. in a weakly oxidizing atmosphere containing 10 ^-11 to 10 ^-5 MPa in ^total pressure. Even when only one of oxygen and water vapor is used, the partial pressure may be 10 ^-11 to 10 ^-5 MPa.

The reason for the high-temperature oxidation is a weakly oxidizing atmosphere such as an inert gas containing 10 ^-11 to 10 ^-5 MPa of oxygen and water vapor as a sum of partial pressures, hydrogen or vacuum.

The sum of the partial pressures of oxygen and water vapor is 10 ^-11 MPa
If it is less than 1, Al and Si or Al are not sufficiently oxidized, so that an oxide film required for exhibiting the resistance to ozone-containing water is not formed. On the other hand, if the sum of the partial pressures of oxygen and water vapor exceeds 10 ^-5 MPa, elements other than Al and Si, such as Cr and Fe, are easily oxidized. For this reason, the ratio of Cr oxide, Fe oxide, and the like in the oxide film increases, and the ozone-resistant water resistance deteriorates. In addition, the smoothness of the surface tends to deteriorate, and a surface roughness of less than 3 μm in Rmax cannot be obtained. The preferred range of the sum of the partial pressures of oxygen and water vapor is 10 ⁻⁸ to 10 ⁻⁵ MPa.

When the heating temperature is lower than 600 ° C., A
l, Si is not sufficiently oxidized. On the other hand, when the heating temperature is 12
If the temperature exceeds 00 ° C., elements other than Al and Si, such as Cr and Fe, are also oxidized, so that the ratio of Cr oxide and Fe oxide in the oxide film increases. Further, the surface smoothness is also reduced. Therefore, when the heating temperature is lower than 600 ° C., the oxide film capable of imparting good ozone-containing water resistance to the steel material cannot be formed either when the heating temperature is higher than 1200 ° C. The heating temperature is preferably in the range of 850 to 1100 ° C.

The heating time is preferably from 5 minutes to 2 hours. Even when heating is performed under the above conditions, if the heating time is less than 5 minutes, it is difficult to sufficiently form an oxide film. On the other hand, when the heating time exceeds 2 hours, the productivity is reduced. The heating time is more preferably 5 minutes to 1 hour.

The above-mentioned high-temperature oxidation conditions can be applied to stainless steel having a chemical composition within the range specified in the present invention under the same conditions.

(Wet oxidation method) The wet oxidation method includes a dipping method and an anodic electrolysis method.

As a solution used for the immersion method, a nitric acid solution is suitable. In this case, the concentration of nitric acid in the solution is 5 to 5
The content is preferably 0% by weight. In the case of this concentration range, Al and Si in steel can be preferentially oxidized.

If the nitric acid concentration of the nitric acid solution is less than 5% by weight, elements such as Cr and Fe other than Al and Si are also easily oxidized. Therefore, the ratio of oxides of these elements in the oxide film increases. On the other hand, when the concentration of nitric acid exceeds 50% by weight, the steel material is corroded by nitric acid. Therefore, the smoothness of the surface is deteriorated, and the Rmax may be 3 μm or more.

The temperature of the nitric acid solution is preferably 20 to 90 ° C., and the treatment time is preferably 10 minutes to 5 hours. When the temperature of the nitric acid solution is lower than 20 ° C., the formation rate of the oxide film is low, and the oxidation treatment requires a long time. On the other hand, if the temperature of the solution is 9
When the temperature exceeds 0 ° C., the vapor of nitric acid is vigorously diffused from the nitric acid solution, so that the nitric acid concentration of the nitric acid solution decreases. Furthermore, the working environment is extremely poor. Note that the temperature of the nitric acid solution is more preferably set to 40 to 70 ° C.

When the immersion time in the nitric acid solution is less than 10 minutes, the oxide film is not sufficiently formed. On the other hand, when the immersion time in the nitric acid solution exceeds 5 hours, the productivity is reduced. The immersion time in the nitric acid solution is more preferably 30 minutes to 3 hours.

In the case of the anodic electrolysis method, it is preferable to perform anodic electrolysis in an acidic solution having a pH of 1 or less, such as a sulfuric acid aqueous solution having a concentration of 10% by weight.

The pH of the electrolyte used in the anodic electrolysis method is 1
If it exceeds, elements other than Al and Si, such as Cr and Fe, are also easily oxidized. Therefore, C in the oxide film
The ratio of r oxide, Fe oxide, and the like increases.

In the anodic electrolysis, it is preferable to control the potential so that the dissolution rate is constant even if the surface area of the electrode changes. This potential control can be performed, for example, by using a saturated calomel electrode (SCE) as a reference electrode and controlling the potential with respect to the reference electrode. In this case, the potential is 0.2 to 1.5 V (vs SCE), and the temperature of the electrolyte is 20 to
It is preferable that the treatment time is 90 ° C. and the treatment time is 10 minutes to 5 hours.

As described above, even if the electrolyte has a pH of 1 or less, if the potential with respect to SCE is less than 0.2 V,
Due to the low dissolution rate of Al and Si in steel, a sufficient oxide film may not be obtained in some cases. On the other hand, when the potential with respect to SCE exceeds 1.5 V, the oxide film becomes porous. Also, the ratio of Al oxide to Si oxide or Al oxide in the oxide film is reduced. Note that it is more preferable that the potential with respect to SCE be 0.4 to 1.0 V.

The temperature of the electrolyte is preferably 20 to 90 ° C.
When the temperature is lower than 20 ° C., an oxide film is not sufficiently formed. On the other hand, if the temperature exceeds 90 ° C., the vapor of the solvent such as sulfuric acid will be vigorously diffused from the electrolytic solution.
Decrease. Furthermore, the working environment is extremely poor. In addition, it is more preferable that the temperature of the electrolytic solution be 40 to 70 ° C.

The processing time of the anodic electrolysis is preferably 10 minutes to 5 hours. If the time is less than 10 minutes, the oxide film cannot be sufficiently formed. On the other hand, if it exceeds 5 hours, productivity will be reduced. The processing time of anodic electrolysis is 30 minutes to 3 minutes.
More preferably, it is time.

[0063]

EXAMPLES Example 1 The effect of secondary dissolution by a consumable electrode dissolution method was investigated. First, primary melting was performed by the VIM method and the VOD method, and stainless steel having the chemical composition shown in Table 1 was melted and cast into a 100 kg steel ingot.

Symbols AF are steel ingots by the VIM method.
C and E are austenitic and B, D and F are ferritic. Symbols G to L are steel ingots by the VOD method, G, I and K are austenitic, and H, J and L are ferritic. Of these ingots, E,
F, K and L are comparative examples in which any one of the chemical components deviates from the content after primary dissolution specified in the present invention.

[0065]

[Table 1]

From these steel ingots, an electrode material for secondary melting having a diameter of 75 mm and a length of 720 mm was prepared by machining. At the time of machining, a part of the steel ingot was left as a test material in order to investigate the ozone-resistant water resistance of the primary melting material. The conditions for the secondary dissolution of the above-described electrode material by the VAR method and the ESR method were the same as those in ordinary actual operation, such as the dissolution rate. The size of the slab after the secondary melting was about 180 mm in diameter and about 500 mm in length.

Table 2 shows the chemical composition of the slab after secondary melting. Hereinafter, the material after the first melting is referred to as a steel ingot, and the material after the second melting is referred to as a slab.

No. 1 to 8 are slabs of the present invention,
o. Nos. 1 and 2 are the VIM-VAR method. 3 and 4 are VIM
-ESR method, no. Nos. 5 and 6 are VOD-VAR method.
Reference numerals 7 and 8 are cast pieces obtained by the VOD-ESR method. No. 9
Nos. To 12 are comparative examples. 9 and 10 are VIM-VAR
Method, No. 11 and 12 are cast pieces by the VOD-ESR method. In the slabs of these comparative examples, Mn and N or the N content of the chemical components of the steel ingot after the first melting were out of the range specified in the present invention. Are also examples outside the range defined by the present invention.

[0069]

[Table 2]

Next, No. Slabs 1 to 12 and symbols A to L
A part of the steel ingot was subjected to hot rolling and cold rolling after hot forging to be processed into a sheet material having a thickness of 2 mm. Further, these plate members were subjected to a solution treatment in which the plate members were kept at 1050 ° C. for 30 minutes and then cooled with water. A test piece having a thickness of 1 mm, a width of 50 mm, and a length of 50 mm was sampled from the plate material after the solution treatment by machining, and the entire surface was buff-polished to obtain a mirror surface (Rmax).
To 0.3 to 0.5 μm). Thereafter, these test pieces, oxygen and the sum of the partial pressures of water vapor 10 ^- in a hydrogen gas atmosphere at 8 MPa, subjected to oxidation treatment to hold 90 minutes at 1100 ° C., to form an oxide film on the surface of the test piece Was.

The test piece after the oxidation treatment was examined for ozone-resistant water resistance by the following method. First, the specific resistance 17MΩc
In a state where the test piece is immersed in 50 ml of ultrapure water having a capacity of 2400 in a 40 ° C. oxygen atmosphere containing 110 g / m 3 of ozone.
Hold for a while. Next, the ozone-containing water was quantitatively analyzed by induction plasma ion mass spectrometry to determine the total amount of metal ions eluted into the ozone-containing water. Based on this result,
The apparent elution amount of metal ions per unit surface area including the end face of the test piece was calculated, and the ozone-resistant water resistance was evaluated based on the calculated elution amount of metal ions. Tables 1 and 2 also show the metal ion elution amount.

As shown in Table 1, the metal ion elution amount of a test piece made of a steel ingot after the first melting was 75.
The dose was slightly higher at 4 to 152.8 mg / m2. In particular, the symbols K and L whose Mn and N contents were out of the ranges specified in the present invention had considerably large amounts of elution.

On the other hand, as shown in Table 2, among the slabs after the secondary melting, slabs (Nos. 1 to 8) having a chemical composition within the range specified by the present invention were used as raw materials. For the test piece to perform, the metal ion elution amount is 26.2 to 34.3 mg.
/ M2, the amount of elution was smaller than that of a test piece made of a steel ingot after the first melting. Further, in Comparative Example No. Compared to the test pieces using cast pieces of Nos. 9 to 12, the amount of elution is remarkably small, and in the case of cast pieces manufactured by the method of the present invention, a steel material excellent in ozone-resistant water resistance can be obtained. Was confirmed.

It is considered that the reason is that since the gas components (N and O) and Mn in the steel are very small, there are few non-metallic inclusions serving as starting points of metal elution. Note that N in Comparative Example
o. 9 to 12, Mn and N content after secondary dissolution,
It was higher than the range specified in the present invention. Therefore, it is presumed that an oxide film effective for the ozone-containing aqueous solution was not formed, and the ozone-containing aqueous solution was inferior.

(Example 2) A method of forming an oxide film on the surface of a base material of a rolled material manufactured using the ozone-resistant aqueous high-purity stainless steel slab of the present invention as a material. investigated.

The test piece used was the sample No. of the present invention used in Example 1 above. No. 1 (VIM-VAR method, austenitic) and No. 1 of the present invention. 8 (VOD-ESR method, ferrite). These test pieces used in Example 1 were subjected to hot forging, hot rolling, solution treatment, machining, and mirror finish polishing.

These test pieces were oxidized by a high-temperature oxidation method and a wet oxidation method, and an oxide film was formed on the surface of the test piece as a base material. Table 3 shows the processing conditions related to the atmosphere of the high-temperature oxidation method. Comparative examples (d and e)
This is the case where the sum of the partial pressures of oxygen and water vapor deviates from the conditions specified in the present invention. Table 4 shows the processing conditions of the wet oxidation method. Of these conditions, i and j are comparative examples, and i
Is a nitric acid aqueous solution immersion method, and j is an anodic electrolysis method, in each case where the acid concentration is out of the conditions specified in the present invention. In addition, in the case of the oxidation treatment of h (example of the present invention) and j by the anodic oxidation method, the potential was controlled so that the dissolution rate was constant even if the surface area of the electrode was changed. That is, anodic electrolysis was performed using a saturated calomel electrode (SCE) as a reference electrode while controlling the potential of this electrode. In the case of the wet oxidation method, the treated test piece is washed with ultrapure water, and then 99.
It was dried with 999% by volume of argon gas.

With respect to the test piece after the oxide treatment, the kind of the oxide in the oxide film and the resistance to ozone-containing water were examined.

The type of the oxide was examined by a method of judging the presence of Al 2 O 3, SiO 2, etc. by examining the crystal structure of the compound contained in the film using laser Raman spectroscopy.

The resistance to ozone-containing water was examined in the same manner as in Example 1, and evaluated by the amount of metal eluted. Table 5
The results of these surveys are summarized below.

[0081]

[Table 3]

[0082]

[Table 4]

[0083]

[Table 5]

As is clear from Table 5, in the case of the present invention of Test Nos. 1 to 12 in which the oxidation treatment conditions satisfy the conditions specified in the present invention, the metal ion elution amount is 27.2 to 3
It was as low as 2.3 mg / m2, and it was confirmed that the ozone-containing aqueous solution was excellent.

On the other hand, in the case of Comparative Examples of Test Nos. 13 to 20 in which the oxidation treatment conditions deviated from the conditions specified in the present invention, the metal ion elution amount was 92.6 to 125.7 mg / m 2,
The number was about four times as large as that of the example of the present invention.

Table 5 shows the results of examination of the types of oxides in the coating, all of which were Al 2 O 3. Si
O2 was not detected because the Si content in the base material was as low as 0.011% in the base material A and 0.039% in the base material J.

[0087]

The cast slab obtained by the production method of the present invention has high purity with few nonmetallic inclusions in steel.
Since l segregation is small, it is excellent in hot workability. Further, the stainless steel in which an oxide film is formed on the surface of the base material processed using the cast slab by the method of the present invention is extremely excellent in resistance to ozone-containing water. Therefore, it exhibits excellent performance as a piping member for ozone-containing water used in the production of semiconductors and pharmaceuticals, as a component of a semiconductor production device, and the like.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C23C 8/14 C23C 8/14 8/18 8/18 22/50 22/50 C25D 11/02 C25D 11/02 // C22C 38/00 302 C22C 38/00 302Z 38/40 38/40

Claims (4)

[Claims] 1. A method for producing a cast for stainless steel having excellent water resistance to ozone by at least two times of primary melting and secondary melting. %, C: 0.020% or less, Al and Si
1.0 to 6.0% by total or Al alone, Mn:
0.18% or less, Cr: 12 to 30%, Ni: 0 to 35
%, P: 0.030% or less, S: 0.010% or less, O
(Oxygen): After adjusting the components to 0.008% or less and N: 0.010% or less, at least Mn of the above-mentioned chemical components is reduced to 0.
0% or less, O (oxygen) is 0.008% or less, and N is 0.1% or less.
A method for producing a cast slab for an ozone-resistant aqueous high-purity stainless steel material, characterized in that the content is 008% or less. 2. A method preform to the material of the slab obtained by the process according to claim 1, the gas combined oxygen gas and water vapor partial pressure of 10 or less ^-5 MPa or higher 10 ^-11 MPa By heating to 600 ° C. or more and 1200 ° C. or less in a weakly oxidizing atmosphere, Al oxide and S
A method for producing an ozone-resistant aqueous high-purity stainless steel material comprising forming an oxide film mainly composed of both i-oxides or Al oxides. 3. The surface of the base material by immersing the base material made from the slab obtained by the production method according to claim 1 in a nitric acid aqueous solution having a concentration of 5% to 50% by weight. A
A method for producing an ozone-resistant water-based high-purity stainless steel material, comprising forming an oxide film mainly composed of both an oxide and a silicon oxide or an aluminum oxide. 4. An aluminum oxide and a base material made of the slab obtained by the production method according to claim 1 are subjected to anodic electrolysis in a solution having a pH of 1 or less. Si
A method for producing an ozone-resistant aqueous high-purity stainless steel material comprising forming an oxide film mainly composed of both oxides or Al oxide.