JP2020111783A - Stainless steel and stainless steel pipe having excellent rouge resistance, and pure steam route member - Google Patents

Abstract

To provide a stainless steel having excellent rouge resistance.SOLUTION: A stainless steel has a composition that comprises C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass% or less, Ni: 30 mass% or less, Cr: 16-35 mass%, Mo: 6.0 mass% or less, Cu: 0.8 mass% or less, N: 0.3 mass% or less with the balance being Fe and inevitable impurities, and meets the relationship of formula (1) (where each element symbol denotes the content of each element). In the stainless steel, a passive coating has a Cr concentration of 40 atom% or more. Cr+0.5Mo≥19 (1).SELECTED DRAWING: None

Description

The present invention relates to a stainless steel and a stainless steel tube having excellent rouge resistance, and a pure water vapor path member.

In fields such as pharmaceuticals, biotechnology, food, and cosmetics, various devices such as sterilizers, sterilizers, and disinfectants are processed using high-purity water vapor (hereinafter referred to as “pure steam”). .. Austenitic stainless steel is generally used for members contacting with pure water vapor in these devices and related equipment, but coloring called rouge may occur on the surface thereof.

Rouge is believed to be due to the deposition of iron-based metal oxides. Since this metal oxide may be mixed in a product to cause a foreign substance, or may be eluted into pure water vapor to deteriorate water quality, it is desired to suppress the generation of rouge.
As a conventional technique for suppressing the generation of rouge, a method has been proposed in which the surface of austenitic stainless steel is passivated and the Cr concentration in the passivation film is increased to 45 atom% or more (Patent Document 1).

JP, 11-29877, A

However, merely increasing the Cr concentration in the passive film as in the method of Patent Document 1 may not be able to sufficiently suppress the generation of rouge. Further, in the method of Patent Document 1, the steel type is limited to austenitic stainless steel, and it is not possible to improve the rouge resistance of various steel types. Here, the "rouge resistance" in the present specification means a property of suppressing the generation of rouge.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a stainless steel, a stainless steel pipe, and a pure water vapor passage member having excellent rouge resistance.

As a result of intensive studies to solve the above problems, the present inventors have found that the composition of stainless steel (especially the balance of Cr and Mo contents) and the Cr concentration in the passivation film show that they are resistant to rouge. They have found that they are closely related, and have completed the present invention.

That is, the present invention is C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass% or less. , Ni: 30% by mass or less, Cr: 16 to 35% by mass, Mo: 6.0% by mass or less, Cu: 0.8% by mass or less, N: 0.3% by mass or less, with the balance being Fe and unavoidable. And a passive impurity and has a composition satisfying the relationship of the following formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passivation film is 40 atomic% or more. It is a stainless steel with excellent rouge resistance.
Cr+0.5Mo≧19 (1)

Further, the present invention is C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass% or less. , Ni: 30% by mass or less, Cr: 16 to 35% by mass, Mo: 6.0% by mass or less, Cu: 0.8% by mass or less, N: 0.3% by mass or less, with the balance being Fe and unavoidable. And a passive impurity and has a composition satisfying the relationship of the following formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passivation film is 40 atomic% or more. It is a stainless steel pipe with excellent rouge resistance.
Cr+0.5Mo≧19 (1)

Further, the present invention is a pure water vapor passage member including the above stainless steel or the above stainless steel pipe.

According to the present invention, it is possible to provide a stainless steel, a stainless steel pipe, and a pure water vapor passage member having excellent rouge resistance.

It is a block diagram of the pure water supply system provided with a pure steam generator and a distilled water manufacturing device.

Hereinafter, preferred embodiments of the stainless steel, the stainless steel pipe, and the pure water vapor path member of the present invention will be described, but the present invention should not be construed as being limited thereto, and does not depart from the gist of the present invention. Various modifications and improvements can be made based on the knowledge of those skilled in the art. A plurality of constituent elements disclosed in each embodiment can form various inventions by an appropriate combination. For example, some components may be deleted from all the components shown in the embodiments, or components of different embodiments may be combined as appropriate.

(Stainless steel)
The stainless steel of this embodiment has C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass%. % Or less, Ni: 30% by mass or less, Cr: 16 to 35% by mass, Mo: 6.0% by mass or less, Cu: 0.8% by mass or less, N: 0.3% by mass or less, and the balance Fe. And inevitable impurities.
Moreover, the stainless steel of another embodiment further includes one or more selected from the group consisting of Nb: 0.8 mass% or less, Ti: 0.8 mass% or less, and Al: 0.5 mass% or less. be able to.
As used herein, the term “unavoidable impurities” means components such as O that are difficult to remove. This component is inevitably mixed in at the stage of melting the raw materials.

<C: 0.1 mass% or less>
C is an element that affects the workability and corrosion resistance of stainless steel, and particularly in a composition system containing a large amount of Cr and Mo, if the content of C is too large, it hardens and the workability deteriorates. Therefore, the upper limit of the C content is set to 0.1% by mass, preferably 0.09% by mass, and more preferably 0.08% by mass, from the viewpoint of workability. On the other hand, the lower limit of the C content is not particularly limited, but is preferably 0.001 mass% and more preferably 0.003 mass% from the viewpoint of corrosion resistance.

<Si: 1.0 mass% or less>
Si is an element that affects the workability of stainless steel, and if the content of Si is too large, the workability decreases. Therefore, the upper limit of the Si content is set to 1.0 mass%, preferably 0.9 mass%, and more preferably 0.8 mass% from the viewpoint of workability. On the other hand, the lower limit of the Si content is not particularly limited, but is preferably 0.01% by mass, more preferably 0.05% by mass, and further preferably 0.1% by mass.

<Mn: 2.0 mass% or less>
Mn is an element that affects the workability and corrosion resistance of stainless steel, and if the Mn content is too large, the workability and corrosion resistance decrease. Therefore, the upper limit of the Mn content is set to 2.0% by mass, preferably 1.9% by mass, and more preferably 1.8% by mass from the viewpoint of workability and corrosion resistance. On the other hand, the lower limit of the Mn content is not particularly limited, but is preferably 0.01% by mass, more preferably 0.05% by mass, and further preferably 0.1% by mass.

<P: 0.045 mass% or less>
P is an element that affects the workability and corrosion resistance of stainless steel, and if the content of P is too large, the workability and corrosion resistance decrease. Therefore, the upper limit of the P content is set to 0.045 mass%, preferably 0.035 mass% from the viewpoint of workability and corrosion resistance. On the other hand, the lower limit of the P content is not particularly limited, but is preferably 0.001 mass%, more preferably 0.005 mass%, and further preferably 0.01 mass%.

<S: 0.03 mass% or less>
S is an element that affects the workability and corrosion resistance of stainless steel, and if the content of S is too large, the workability and corrosion resistance decrease. Therefore, the upper limit of the S content is set to 0.03% by mass, preferably 0.02% by mass, and more preferably 0.015% by mass from the viewpoint of workability and corrosion resistance. On the other hand, the lower limit of the S content is not particularly limited, but is preferably 0.0001 mass%, more preferably 0.0005 mass%.

<Ni: 30% by mass or less>
Ni is an element that affects the elution resistance of stainless steel, and if the Ni content is too large, the elution resistance is reduced and rouge is likely to occur. Further, Ni is also a component necessary for forming an austenite phase when the stainless steel is austenitic. Therefore, the upper limit of the Ni content is set to 30% by mass, preferably 25% by mass, from the viewpoint of elution resistance and rouge resistance. On the other hand, the lower limit of the Ni content is not particularly limited, but is preferably 0.01% by mass, more preferably 0.02% by mass.

<Cr: 16 to 35 mass%>
Cr is an element that affects the workability, corrosion resistance and rouge resistance of stainless steel, and if the content of Cr is too low, the passive film is not sufficiently formed and corrosion resistance and rouge resistance are ensured. I can't. Therefore, the lower limit of the Cr content is set to 16% by mass, preferably 17% by mass, and more preferably 18% by mass. On the other hand, if the content of Cr is too large, the corrosion resistance and the rouge resistance are improved, but the workability is deteriorated. Therefore, the upper limit of the Cr content is set to 35% by mass, preferably 32% by mass, and more preferably 30% by mass from the viewpoint of workability.

<Mo: 6.0 mass% or less>
Mo is an element that affects the workability, corrosion resistance and rouge resistance of stainless steel. Mo is also an element having an action of regenerating the passive film when the passive film is damaged. However, if the content of Mo is too large, the workability decreases. Therefore, the upper limit of the Mo content is set to 6.0 mass%, preferably 5.8 mass% from the viewpoint of workability, corrosion resistance and rouge resistance. On the other hand, the lower limit of the Mo content is not particularly limited, but is preferably 0.01% by mass, more preferably 0.02% by mass, and further preferably 0.03% by mass.

<Cu: 0.8 mass% or less>
Cu is an element that affects the workability, elution resistance and rouge resistance of stainless steel, and if the Cu content is too high, the workability and elution resistance decrease and the rouge easily occurs. Therefore, the upper limit of the Cu content is set to 0.8% by mass, preferably 0.48% by mass, from the viewpoint of workability, elution resistance and rouge resistance. On the other hand, the lower limit of the Cu content is not particularly limited, but is preferably 0.005% by mass, more preferably 0.02% by mass, and further preferably 0.04% by mass.

<Nb and Ti: 0.8 mass% or less>
Nb and Ti are elements that affect the workability of stainless steel, and if the content of Nb and Ti is too large, the workability decreases. Therefore, the upper limit of the Nb and Ti contents is set to 0.8% by mass, preferably 0.6% by mass, and more preferably 0.4% by mass. On the other hand, the lower limit of the contents of Nb and Ti is not particularly limited, but is preferably 0.01% by mass, more preferably 0.05% by mass, and further preferably 0.1% by mass.

<Al: 0.5 mass% or less>
Al is an element that affects the workability of stainless steel, and if the content of Al is too large, the workability decreases. Therefore, the upper limit of the Al content is set to 0.5% by mass, preferably 0.3% by mass, and more preferably 0.2% by mass. On the other hand, the lower limit of the Al content is not particularly limited, but is preferably 0.01% by mass, more preferably 0.03% by mass, and further preferably 0.05% by mass.

<N: 0.3% by mass or less>
N is an element that affects the workability of stainless steel, and if the content of N is too large, it hardens and the workability decreases. Therefore, the upper limit of the N content is set to 0.3% by mass, preferably 0.25% by mass, from the viewpoint of workability. On the other hand, the lower limit of the N content is not particularly limited, but is preferably 0.001 mass%, more preferably 0.003 mass%, and further preferably 0.005 mass%.

Stainless steel may contain elements known in the art within a range that does not impair the effects of the present invention.

In order to improve rouge resistance in stainless steel, the balance of the contents of Cr and Mo is particularly important, and it is necessary to satisfy the relationship of the following formula (1).
Cr+0.5Mo≧19 (1)
In the above formula (1), each element symbol means the content of each element.
If the relationship of the above formula (1) is not satisfied, stainless steel having desired rouge resistance cannot be obtained.

The lower limit of Cr+0.5Mo in the above formula (1) is preferably 19.1, more preferably 19.2, and further preferably 19.3. With such a lower limit, the rouge resistance of stainless steel can be stably improved. On the other hand, the upper limit of Cr+0.5Mo is not particularly limited, but is preferably 38, more preferably 35, and further preferably 33.

Stainless steel has a passive film on its surface. Here, in the present specification, the "passivation film" means a chromium-rich oxide layer that improves the corrosion resistance (metal ion elution resistance) of stainless steel.
The Cr concentration in the passivation film is set to 40 atom% or more, preferably 45 atom% or more, and more preferably 50 atom% or more from the viewpoint of ensuring rouge resistance. On the other hand, the upper limit of the Cr concentration in the passivation film is not particularly limited, but is preferably 90 atom %, more preferably 80 atom %, further preferably 75 atom %.
Here, the Cr concentration in the passive film means that calculated by surface analysis of stainless steel using XPS (X-ray photoelectron spectroscopy).

The XPS measurement method is not particularly limited, but in this specification, the measurement was performed according to the following procedure.
First, a wide area photoelectron spectrum was measured for the outermost surface (passive state film) of stainless steel, and qualitative analysis was performed. After that, Ar ⁺ sputtering was performed in the depth direction from the surface, and the narrow-range photoelectron spectrum of the designated element (Si, Cr, Fe, Ni, Mo) was measured for each constant sputtering depth. The elemental composition ratio (atomic %) was calculated at each sputtering depth, and the Cr concentration in the passive film was obtained.

The XPS measurement conditions are not particularly limited, but in this specification, the following conditions were used.
Analytical device: Quantera SXM (fully automatic scanning X-ray photoelectron spectrometer) manufactured by Physical Electronics
X-ray source: Monochromatic Al Kα
Output: 44.8W
Beam diameter: 200 μmφ
Extraction angle: 45°
Sputtering conditions: Ar ⁺ energy 1 keV, sputter rate about 2.24 nm/min (SiO ₂ conversion)

The surface of the stainless steel preferably has an arithmetic average roughness Ra of 0.1 μm or less. When Ra is 0.1 μm or less, rouge tends to be less likely to occur.
Here, the term "arithmetic mean roughness Ra" as used herein means the value measured according to JIS B0601:2001.

The metal structure of stainless steel is not particularly limited, and may be any of ferrite type, austenite type, martensite type, and austenite/ferrite type.

The stainless steel having the above composition and the passive film can be manufactured according to a known method except that the slab having the above composition is used. Specifically, the slab having the above composition is hot-rolled, annealed and pickled, then cold-rolled, annealed and pickled repeatedly to a predetermined thickness, and then passivated. By carrying out, stainless steel can be manufactured. If necessary, the cold rolled steel sheet may be subjected to finishing such as mechanical polishing.
The passivation treatment is not particularly limited, but a treatment using an acidic solution may be performed. Specific examples of the passivation treatment include dipping treatment in an acidic solution, electrolytic polishing, and the like, but electrolytic polishing that can easily control the surface roughness of stainless steel is preferable.
The conditions of electrolytic polishing are not particularly limited, but for example, using a mixed solution containing phosphoric acid and sulfuric acid, a voltage of 3 to 15 V, a current density of 3 to 20 A/dm ² , a temperature of 40 to 60° C., and a time of 3 to 40 minutes. do it.

The stainless steel having the above composition and passivation film is excellent in rouge resistance, and thus is suitable for use in various members requiring rouge resistance. The member requiring rouge resistance is not particularly limited, but a pure steam path member, for example, a pure steam generator, or a sterilizer using pure steam, a member used in a sterilization device or a disinfection device, and the device concerned. Related equipment (for example, a sanitary pipe) etc. are mentioned. In the present specification, the “pure water vapor passage member” means a member that comes into contact with pure water vapor. Further, the “sanitary pipe” means a pipe that requires hygiene.

Here, as an example, a block diagram of a pure water supply system including a pure water vapor generator and a distilled water producing device is shown in FIG. As shown in FIG. 1, in this pure water supply system, a pure steam generator 1, a distilled water producing device 2, a tank 3, a pump 4, a heat exchanger 5, a valve 6, a meter 7, a sensor 8, a piping member 9 are provided. Also, the members used for the filter 10 may come into contact with pure water vapor. Therefore, in this pure water supply system, it is preferable to manufacture these members using the stainless steel of this embodiment.

(Stainless steel pipe)
The stainless steel pipe of the present embodiment has characteristics such as a composition and a passive film similar to those of the above stainless steel. Therefore, description of these features will be omitted.
The stainless steel pipe of the present embodiment can be manufactured by processing the above stainless steel into a tube. Specifically, a stainless steel pipe can be manufactured by bending stainless steel, welding both ends to each other, and then subjecting it to annealing, pickling, mechanical polishing and electrolytic polishing.
The stainless steel pipe of this embodiment is excellent in rouge resistance because it uses the above-mentioned stainless steel as a material.

(Pure water vapor path member)
The pure water vapor path member of the present embodiment includes the above stainless steel or the above stainless steel pipe. Since this pure water vapor passage member is excellent in rouge resistance, it is difficult for foreign substances (metal oxides) to be mixed in the product, and there is little risk that metal ions are eluted into pure water vapor to deteriorate water quality.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.
(Examples 1 to 9 and Comparative Examples 1 to 5)
A slab having the composition shown in Table 1 was hot-rolled, annealed, pickled, and repeatedly cold-rolled to manufacture a cold-rolled annealed sheet having a thickness of 1.0 mm. Next, the cold-rolled annealed plate was cut into a size of 30 mm×50 mm, then mechanically polished at #600, and then electrolytically polished in a mixed solution containing phosphoric acid and sulfuric acid to obtain stainless steel. The electropolishing was performed at a voltage of 3 to 15 V, a current density of 3 to 20 A/dm ² , a temperature of 40 to 60° C., and a time of 3 to 40 minutes.

For the stainless steels obtained in the above Examples and Comparative Examples, the Cr concentration in the passive film was measured according to the above method, and the arithmetic mean roughness was measured using a surface roughness profile measuring instrument (SURFCOM2900DX manufactured by Tokyo Seimitsu Co., Ltd.). Ra was measured. The results are shown in Table 2.
Next, the stainless steels obtained in the above Examples and Comparative Examples were placed inside a pipe connected to a pure water vapor generator, and the pressure was 2 kg/cm ² ·G and the temperature was about 120° C. in a pure water vapor environment. An exposure test was conducted for one year. For the stainless steel before and after the exposure test, the color tone L ^* , a ^*, and b ^* in the L ^* a ^* b ^* color space were measured using a spectrophotometer (CM-2600d manufactured by Konica Minolta), and the color difference ΔE ^* _ab =[(ΔL ^* ) ² +(Δa ^* ) ² +(Δb ^* ) ² ] ^1/2 was calculated. When the color difference ΔE ^* _ab is 10 or less, it can be evaluated that the generation of rouge could be suppressed (low coloring). The results are shown in Table 2.

As shown in Table 2, the stainless steels of Examples 1 to 9 in which the composition and the Cr concentration in the passivation film were within the predetermined ranges had a color difference ΔE ^* _ab of 10 or less, and the rouge was sufficiently generated. I was able to suppress it.
On the other hand, in the stainless steels of Comparative Examples 1 to 5 in which the composition and the Cr concentration in the passivation film are out of the predetermined ranges, the color difference ΔE ^* _ab becomes large, and the generation of rouge can be sufficiently suppressed. There wasn't.

As can be seen from the above results, it is possible to provide a stainless steel, a stainless steel pipe and a pure water vapor passage member having excellent rouge resistance.

1 Pure Water Vapor Generator 2 Distilled Water Production Device 3 Tank 4 Pump 5 Heat Exchanger 6 Valve 7 Instrument 8 Sensor 9 Piping Member 10 Filter

That is, the present invention is C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass% or less. , Ni: 30% by mass or less, Cr: 16 to 35% by mass, Mo: 6.0% by mass or less, Cu: 0.8% by mass or less, N: 0.3% by mass or less, with the balance being Fe and unavoidable. And a passive impurity and has a composition satisfying the relationship of the following formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passivation film is 40 atomic% or more. It is a stainless steel with excellent rouge resistance.
Cr+0.5Mo≧19 (1)
Moreover, this invention is C:0.1 mass% or less, Si:1.0 mass% or less, Mn:0.05-2.0 mass%, P:0.045 mass% or less, S:0.03. Mass% or less, Ni: 30 mass% or less, Cr: 16 to 35 mass%, Mo: 6.0 mass% or less, Cu: 0.8 mass% or less, N: 0.3 mass% or less, Nb: 0.8% by mass or less, Ti: 0.8% by mass or less, Al: 0.5% by mass or less, further containing at least one selected from the group, and the balance consisting of Fe and unavoidable impurities. It has a composition satisfying the relationship of the formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passivation film is 40 atomic% or more. Excellent stainless steel.

Further, the present invention is C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass% or less. , Ni: 30% by mass or less, Cr: 16 to 35% by mass, Mo: 6.0% by mass or less, Cu: 0.8% by mass or less, N: 0.3% by mass or less, with the balance being Fe and unavoidable. And a passive impurity and has a composition satisfying the relationship of the following formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passivation film is 40 atomic% or more. It is a stainless steel pipe with excellent rouge resistance.
Cr+0.5Mo≧19 (1)
Moreover, this invention is C:0.1 mass% or less, Si:1.0 mass% or less, Mn:0.05-2.0 mass%, P:0.045 mass% or less, S:0.03. Mass% or less, Ni: 30 mass% or less, Cr: 16 to 35 mass%, Mo: 6.0 mass% or less, Cu: 0.8 mass% or less, N: 0.3 mass% or less, Nb: 0.8% by mass or less, Ti: 0.8% by mass or less, Al: 0.5% by mass or less, further containing at least one selected from the group, and the balance consisting of Fe and unavoidable impurities. It has a composition satisfying the relationship of the formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passivation film is 40 atomic% or more. Excellent stainless steel pipe.

Claims (7)

C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass% or less, Ni: 30 mass% or less Hereinafter, Cr: 16 to 35 mass%, Mo: 6.0 mass% or less, Cu: 0.8 mass% or less, N: 0.3 mass% or less, and the balance consisting of Fe and inevitable impurities, Rouge resistance, which has a composition satisfying the relationship of the following formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passive film is 40 atomic% or more. Excellent stainless steel.
Cr+0.5Mo≧19 (1) The stainless steel according to claim 1, further comprising one or more selected from the group consisting of Nb: 0.8 mass% or less, Ti: 0.8 mass% or less, and Al: 0.5 mass% or less. The stainless steel according to claim 1 or 2, which is used for a pure water vapor passage member. C: 0.1 mass% or less, Si: 1.0 mass% or less, Mn: 2.0 mass% or less, P: 0.045 mass% or less, S: 0.03 mass% or less, Ni: 30 mass% or less Hereinafter, Cr: 16 to 35 mass%, Mo: 6.0 mass% or less, Cu: 0.8 mass% or less, N: 0.3 mass% or less, and the balance consisting of Fe and inevitable impurities, Rouge resistance, which has a composition satisfying the relationship of the following formula (1) (in the formula, each element symbol means the content of each element), and the Cr concentration in the passive film is 40 atomic% or more. Excellent stainless steel pipe.
Cr+0.5Mo≧19 (1) The stainless steel pipe according to claim 4, further comprising one or more selected from the group consisting of Nb: 0.8 mass% or less, Ti: 0.8 mass% or less, and Al: 0.5 mass% or less. A pure water vapor path member comprising the stainless steel according to any one of claims 1 to 3 or the stainless steel pipe according to claim 4 or 5. The pure water vapor path member according to claim 6, which is a sanitary pipe.

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