WO2018025942A1 - Austenitic stainless steel - Google Patents
Austenitic stainless steel Download PDFInfo
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- WO2018025942A1 WO2018025942A1 PCT/JP2017/028146 JP2017028146W WO2018025942A1 WO 2018025942 A1 WO2018025942 A1 WO 2018025942A1 JP 2017028146 W JP2017028146 W JP 2017028146W WO 2018025942 A1 WO2018025942 A1 WO 2018025942A1
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Definitions
- the present invention relates to an austenitic stainless steel, and particularly to an austenitic stainless steel excellent in acid resistance.
- So-called “fossil fuels” such as petroleum and coal used as boiler fuel for thermal power generation or industrial use contain sulfur (S). For this reason, when fossil fuel burns, sulfur oxides (SO x ) are generated in the exhaust gas. When the temperature of the exhaust gas decreases, SO x reacts with moisture in the gas to become sulfuric acid, and condensation occurs on the surface of the low-temperature member that is below the dew point temperature, thereby causing sulfuric acid dew point corrosion.
- the exhaust gas temperature is maintained at a high temperature of 150 ° C. or higher so that sulfuric acid does not dew on the surface of the member.
- low alloy steel When the exhaust gas temperature is not maintained at 150 ° C. or higher, sulfuric acid having a high concentration of about 80% is condensed on the surface of the member in the temperature range of about 140 ° C. In such an environment, so-called “low alloy steel” has been used as steel for various members. This is because the low alloy steel has higher corrosion resistance than the general-purpose stainless steel against the high temperature and high concentration sulfuric acid as described above.
- Non-Patent Document 1 the amount of sulfuric acid that condenses in the region where the temperature is lowered by 20 to 60 ° C. below the dew point of sulfuric acid is the largest, so that corrosion due to sulfuric acid increases. For this reason, when the exhaust gas temperature is not maintained at 150 ° C. or higher, it is generally an area where the most corrosion resistance is required at a temperature in the vicinity of 100 ° C., where the concentration of sulfuric acid is about 70%. However, in this region, not only general-purpose stainless steel but also low alloy steel cannot be used due to the large amount of corrosion.
- Patent Document 1 discloses a sulfuric acid dew-point corrosion stainless steel excellent in hot workability. Is disclosed.
- Patent Document 2 discloses an austenitic stainless steel having excellent resistance to sulfuric acid corrosion and excellent workability.
- the stainless steel described in Patent Document 1 is intended to stabilize the austenite structure and ensure corrosion resistance by containing 0.05% by weight or more of N (nitrogen).
- N nitrogen
- the sulfuric acid corrosion resistance of the austenitic stainless steel to which Cu, Cr, and Mo are added in combination decreases.
- the N content is 0.05% by weight or more, if the Cu content is increased in order to increase the resistance to sulfuric acid corrosion, the hot workability in the temperature range below 1000 ° C. is significantly reduced. There is a problem of becoming.
- the austenitic stainless steel described in Patent Document 2 has excellent sulfuric acid corrosion resistance and workability. However, there is still room for improvement regarding the resistance to sulfuric acid corrosion.
- An object of the present invention is to solve the above problems and to provide an austenitic stainless steel having excellent acid resistance in an environment where high concentration sulfuric acid is condensed.
- an environment in which high-concentration sulfuric acid condenses means an environment in which sulfuric acid having a concentration of 40 to 70% is condensed at a temperature of 50 to 100 ° C.
- the present invention has been made to solve the above-mentioned problems, and the gist thereof is the following austenitic stainless steel.
- An austenitic stainless steel comprising a base material and a film formed on at least a part of the surface of the base material,
- the chemical composition of the base material is mass%, C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.040% or less, S: 0.010% or less, O: 0.020% or less, N: less than 0.050%, Ni: 12.0-27.0%, Cr: 15.0% or more and less than 20.0%, Cu: more than 3.5% and 8.0% or less, Mo: more than 2.0% and 5.0% or less, Co: 0.05% or less, Sn: 0.05% or less, V: 0 to 0.5% Nb: 0 to 1.0%, Ti: 0 to 0.5%, W: 0 to 5.0% Zr: 0 to 1.0%, Al: 0 to 0.5%, Ca: 0 to 0.01%, B: 0 to 0.01% REM: 0 to 0.01%, Balance: Fe and impurities,
- the chemical composition of the base material is mass%, V: 0.01 to 0.5% Nb: 0.02 to 1.0%, Ti: 0.01 to 0.5%, W: 0.1-5.0% Zr: 0.02 to 1.0%, Al: 0.01 to 0.5%, Ca: 0.0005 to 0.01%, B: 0.0005 to 0.01%, and REM: 0.0005 to 0.01%, Containing one or more selected from The austenitic stainless steel according to (1) above.
- an austenitic stainless steel having excellent acid resistance can be obtained in an environment where high concentration sulfuric acid is condensed.
- the composition of the film formed on the base material surface that comes into contact with a high concentration of sulfuric acid is important.
- the acid resistance can be greatly improved.
- an oxide film mainly composed of Fe is formed on the surface, and then an acid treatment is performed to preferentially dissolve the Fe component. It has been found that Ni, Cu and Mo can be concentrated.
- An austenitic stainless steel according to the present invention includes a base material and a film formed on at least a part of the surface of the base material. Each of the base material and the coating will be described in detail below.
- C 0.05% or less C is an element having an effect of increasing strength. However, it combines with Cr to form Cr carbide at the grain boundary, thereby reducing the intergranular corrosion resistance. Therefore, the C content is 0.05% or less. In addition, when it is necessary to raise intensity
- Si 1.0% or less Si is an element having a deoxidizing action. However, if its content exceeds 1.0%, it reduces the hot workability, and coupled with the increase in Cu content, it becomes extremely difficult to process the product on an industrial scale. Therefore, the Si content is 1.0% or less.
- the Si content is preferably 0.6% or less. Since Si does not necessarily need to be contained, a lower limit is not particularly provided. However, in order to obtain the above effect, the Si content is preferably 0.05% or more.
- the Al content is extremely low for the purpose of improving hot workability, it is preferable that 0.1% or more of Si is contained to sufficiently perform the deoxidation action.
- Mn 2.0% or less Mn has the effect of fixing S to improve hot workability and stabilize the austenite phase. However, even if Mn is contained in an amount exceeding 2.0%, the effect is saturated and the cost is increased. Therefore, the Mn content is set to 2.0% or less.
- the Mn content is preferably 1.5% or less. Since it is not always necessary to contain Mn, a lower limit is not particularly provided. However, in order to obtain the above effect, the Mn content is preferably 0.1% or more.
- P 0.040% or less
- the content is preferably as low as possible.
- the corrosion resistance is significantly deteriorated in an environment in which a high concentration of sulfuric acid is condensed. Therefore, the P content is 0.040% or less.
- S 0.010% or less S is contained as an impurity in steel and deteriorates hot workability. Therefore, the content is preferably as low as possible. In particular, when the S content exceeds 0.010%, the hot workability is significantly deteriorated. Therefore, the S content is set to 0.010% or less.
- O 0.020% or less O is contained in the steel as an impurity and reduces hot workability and ductility. Therefore, the content is preferably as low as possible. In particular, when the O content exceeds 0.020%, the hot workability and ductility are significantly reduced, so the O content is set to 0.020% or less.
- N Less than 0.050% N has heretofore been actively added for the purpose of stabilizing the austenite structure or increasing the resistance to local corrosion such as pitting corrosion or crevice corrosion.
- N content is 0.050% or more
- Cu exceeds 3.5%
- Mo exceeds 2.0%
- the corrosion resistance of the austenitic stainless steel containing less than% Cr is lowered.
- the hot workability is reduced when the N content is 0.050% or more. .
- the N content is set to less than 0.050%.
- the N content is preferably as low as possible and is preferably 0.045% or less.
- Ni 12.0-27.0%
- Ni has the effect of stabilizing the austenite phase and also has the effect of enhancing the corrosion resistance in an environment where high concentration of sulfuric acid is condensed.
- it is necessary to contain Ni in an amount of 12.0% or more.
- the effect is saturated even if it contains exceeding 27.0%.
- Ni is an expensive element, the cost is extremely high and the economy is lacking. Therefore, the Ni content is 12.0 to 27.0%.
- Cr 15.0% or more and less than 20.0% Cr is an element effective for ensuring the corrosion resistance of austenitic stainless steel.
- N is regulated to the above-described content
- a high concentration Good corrosion resistance can be ensured in an environment where sulfuric acid condenses.
- Cr is excessively contained, even in the case of austenitic stainless steel in which the N content is reduced and Cu and Mo are added in combination, the corrosion resistance in the environment described above deteriorates, and the workability is further improved. Also occurs.
- the Cr content when the Cr content is 20.0% or more, the corrosion resistance of the austenitic stainless steel in the environment is significantly deteriorated.
- the Cr content by making the Cr content less than 20.0%, the hot workability of the austenitic stainless steel combined with Cu and Mo can be improved, and product processing on an industrial scale can be facilitated. It becomes possible. Therefore, the Cr content is 15.0% or more and less than 20.0%.
- Cu More than 3.5% and not more than 8.0% Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment.
- Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment.
- Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment.
- Mo more than 2.0% to 5.0% or less Mo is an element effective for ensuring the corrosion resistance of austenitic stainless steel.
- Mo is an element effective for ensuring the corrosion resistance of austenitic stainless steel.
- Mo is contained together with the above-mentioned amounts of Cr and Cu, good corrosion resistance is imparted to austenitic stainless steel having the above-mentioned content in an environment where high-concentration sulfuric acid is condensed. can do.
- Mo when Mo is excessively contained, the hot workability is lowered.
- the Mo content exceeds 5.0%, the hot workability is significantly deteriorated even if N is contained as described above. Therefore, the Mo content is more than 2.0% and not more than 5.0%.
- Co 0.05% or less
- Co is an element contained in steel as an impurity. Co is an effective element for increasing the toughness of steel, but it is an expensive element and therefore does not need to be actively added. Therefore, the Co content is 0.05% or less.
- Sn 0.05% or less Since Sn is contained as an impurity in steel and deteriorates hot workability, its content is preferably as low as possible. In particular, when the Sn content exceeds 0.05%, the hot workability is significantly deteriorated. Therefore, the Sn content is 0.05% or less.
- V 0.5% or less
- V has an effect of fixing C and enhancing corrosion resistance, particularly intergranular corrosion resistance, and may be contained as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the V content is 0.5% or less. In order to acquire said effect, it is preferable that V content shall be 0.01% or more.
- Nb 0 to 1.0%
- Nb has the effect of fixing C and improving the corrosion resistance, particularly intergranular corrosion resistance, so it may be contained if necessary.
- its content exceeds 1.0%, even when N is made the above-mentioned content, a nitride is formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Nb content is 1.0% or less.
- the Nb content is preferably 0.02% or more.
- Ti 0 to 0.5% Ti, like Nb, has the effect of fixing C and improving corrosion resistance, particularly intergranular corrosion resistance. Therefore, Ti may be included as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Ti content is 0.5% or less. In order to acquire said effect, it is preferable that Ti content shall be 0.01% or more.
- W 0-5.0% W has an effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and may be contained as necessary. However, if the content exceeds 5.0%, the above effect is saturated and the cost is increased. Therefore, the W content is 5.0% or less. In order to acquire said effect, it is preferable that W content shall be 0.1% or more.
- Zr 0 to 1.0%
- Zr has the effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and thus may be contained as necessary. However, if the content exceeds 1.0%, the above effect is saturated and the cost is increased. Therefore, the Zr content is 1.0% or less. In order to acquire said effect, it is preferable that Zr content shall be 0.02% or more.
- Al 0 to 0.5% Since Al has a deoxidizing action, Al may be contained when the Si content is extremely low. However, when the content exceeds 0.5%, hot workability is deteriorated even in the austenitic stainless steel in which N is the above content. Therefore, the Al content is 0.5% or less.
- the lower limit of the Al content is not particularly defined and may be in the range of impurities. However, in order to keep the Si content extremely low, it is preferable that the Si content is positively added to contain 0.02% or more to sufficiently perform the deoxidation action. Even when 0.05% or more of Si is contained, the Al content is preferably set to 0.01% or more in order to sufficiently exhibit the deoxidation effect.
- Ca 0 to 0.01% Since Ca has an effect of combining with S and suppressing a decrease in hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the Ca content is 0.01% or less. In order to obtain the above effect, the Ca content is preferably 0.0005% or more, and more preferably 0.001% or more.
- B 0 to 0.01% Since B has an effect of improving hot workability, B may be contained as necessary. However, excessive addition of B promotes the precipitation of Cr—B compounds at the grain boundaries, leading to deterioration of corrosion resistance. In particular, when the B content exceeds 0.01%, the corrosion resistance is remarkably deteriorated. Therefore, the B content is 0.01% or less. In order to obtain the above effect, the B content is preferably 0.0005% or more, and more preferably 0.001% or more.
- REM 0 to 0.01% Since REM (rare earth element) has an effect of improving hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the REM content is 0.01% or less. In order to acquire said effect, it is preferable that REM content shall be 0.0005% or more.
- REM refers to a total of 17 elements of Sc, Y, and lanthanoid
- the content of REM refers to the total content of these elements.
- the balance is Fe and impurities.
- impurities are components that are mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when steel is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.
- membrane is formed in at least one part of the surface which a base material has. And it becomes possible to improve acid resistance significantly by raising the total content of Cr, Ni, Cu and Mo relative to Fe in the film.
- the maximum Cr depth at which the Cr concentration is maximum exists in the film, and the chemical composition at the maximum Cr depth needs to satisfy the following formula (i).
- the maximum Cr depth there is no restriction
- each element symbol in the above formula represents the content (at%) of each element on the steel surface.
- the coating according to the present invention generally has a structure including a surface layer layer in which Cr is relatively concentrated and a base material layer in which Ni or the like is relatively concentrated. That is, a minimum Cr depth at which the Cr concentration is minimum exists on the base material side from the above maximum Cr depth.
- the chemical composition at the maximum Cr depth preferably satisfies the following formula (ii), and the chemical composition at the minimum Cr depth preferably satisfies the following formula (iii).
- each element symbol in the above formula represents the content (at%) of each element.
- the thickness of the film is not particularly limited, but is preferably in the range of 2 to 10 nm, for example. If the thickness of the film is less than 2 nm, the sulfuric acid corrosion resistance may not be sufficiently obtained. On the other hand, if the thickness of the film exceeds 10 nm, the film composition may be uneven and the film may be easily peeled off.
- the chemical composition of the film is measured by depth analysis using X-ray photoelectric spectroscopy (XPS). From the depth analysis described above, the concentration profile of each element is derived as a ratio (at%) to the components excluding O, C, and N. Then, by specifying the maximum Cr depth and the minimum Cr depth, the concentration of each element at the depth is obtained, and the above formulas (i) to (iii) are calculated from these values.
- XPS X-ray photoelectric spectroscopy
- the thickness of the film is determined from the O (oxygen) concentration profile. Specifically, the position at which the concentration is 1/3 of the maximum concentration of O is determined as the boundary between the film and the base material, and the length from the film surface to the above boundary is defined as the thickness of the film. . It is desirable to measure the composition and thickness of the film at a plurality of locations and adopt the average value.
- ⁇ Heat treatment process> The steel material is first subjected to heat treatment for 60 to 600 seconds in a temperature range of 1060 to 1140 ° C. Thereby, an oxide film mainly composed of Fe is formed on the surface of the steel material. If the heat treatment temperature is less than 1060 ° C., the formation of the Fe oxide film becomes insufficient. On the other hand, when the heat treatment temperature exceeds 1140 ° C., the crystal grains of the base material become coarse and Fe diffusion is reduced, so that the Fe oxide film becomes non-uniform and the film is more easily peeled off. As a result, in any of the above cases, the concentration of Cr, Ni, Cu and Mo is less likely to occur.
- the steel material is subjected to acid treatment following the heat treatment.
- the acid treatment step it is possible to concentrate Cr, Ni, Cu and Mo on the steel surface by preferentially dissolving the Fe component.
- it is preferably immersed in hydrofluoric acid at 30 to 50 ° C., 5 to 8% by volume HNO 3 , and 5 to 8% by volume HF for 1 to 5 hours.
- the chemical composition and thickness of the coating formed on the surface of each steel pipe were measured by depth analysis using XPS. Specifically, the concentration profile of each element is derived as a ratio (at%) to the components excluding O, C and N, and after specifying the maximum Cr depth and the minimum Cr depth, each element at the depth is determined. The concentration of was determined. Then, the above formulas (i) to (iii) were calculated from these values. In this example, test no. In the examples other than 18, the maximum Cr depth exists in the outermost layer of the coating, and in all the examples, the minimum Cr depth exists on the base material side from the maximum Cr depth.
- the thickness of the film was determined from the O (oxygen) concentration profile. Specifically, the position where the concentration is 1/3 of the maximum concentration of O is determined as the boundary between the coating and the base material, and the length from the coating surface to the above-described boundary is defined as the thickness of the coating. .
- a corrosion test was carried out in a sulfuric acid environment.
- the corrosion test was performed by immersing each steel pipe in a solution having a temperature of 100 ° C. and a sulfuric acid concentration of 70%. And the corrosion weight loss after being immersed for 8 hours was measured, and the corrosion rate per unit area was computed.
- the corrosion rate is 1.00 g / (m 2 ⁇ h) or less, it is determined that the sulfuric acid corrosion resistance is excellent.
- the test No. 1 which satisfied the provisions of the present invention and concentrated Cr, Ni, Cu and Mo in the film.
- the corrosion rate was 1.00 g / (m 2 ⁇ h) or less, which was excellent in sulfuric acid corrosion resistance.
- the austenitic stainless steel which has the outstanding acid resistance in the environment where a high concentration sulfuric acid condenses is obtained. Therefore, the austenitic stainless steel according to the present invention is used in heat exchangers, flues and chimneys used in thermal power generation or industrial boilers, exhaust gas desulfurization equipment members used in various industries, or sulfuric acid environments. It can be applied to various members such as structural members used in equipment.
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Abstract
An austenitic stainless steel which comprises a base material and a coating film that is formed on at least a part of the surface of the base material, and wherein: the chemical composition of the base material contains, in mass%, 0.05% or less of C, 1.0% or less of Si, 2.0% or less of Mn, 0.040% or less of P, 0.010% or less of S, 0.020% or less of O, less than 0.050% of N, 12.0-27.0% of Ni, 15.0% or more but less than 20.0% of Cr, more than 3.5% but 8.0% or less of Cu, more than 2.0% but 5.0% or less of Mo, 0.05% or less of Co, 0.05% or less of Sn, 0-0.5% of V, 0-1.0% of Nb, 0-0.5% of Ti, 0-5.0% of W, 0-1.0% of Zr, 0-0.5% of Al, 0-0.01% of Ca, 0-0.01% of B and 0-0.01% of REM, with the balance made up of Fe and impurities; and the chemical composition of the coating film at the maximum Cr depth satisfies, in at%, (Cr + Ni + Cu + Mo)/Fe ≥ 1.0.
Description
本発明は、オーステナイト系ステンレス鋼に係り、特に耐酸性に優れたオーステナイト系ステンレス鋼に関する。
The present invention relates to an austenitic stainless steel, and particularly to an austenitic stainless steel excellent in acid resistance.
火力発電用または産業用のボイラ燃料として使用される石油および石炭といった所謂「化石燃料」には、硫黄（Ｓ）が含まれている。このため、化石燃料が燃焼すると排ガス中に硫黄酸化物（ＳＯｘ）が生成する。排ガスの温度が低下すると、ＳＯｘはガス中の水分と反応して硫酸となり、露点温度以下にある低温の部材表面で結露し、これによって硫酸露点腐食が生ずる。
So-called “fossil fuels” such as petroleum and coal used as boiler fuel for thermal power generation or industrial use contain sulfur (S). For this reason, when fossil fuel burns, sulfur oxides (SO x ) are generated in the exhaust gas. When the temperature of the exhaust gas decreases, SO x reacts with moisture in the gas to become sulfuric acid, and condensation occurs on the surface of the low-temperature member that is below the dew point temperature, thereby causing sulfuric acid dew point corrosion.
同様に、各種産業で使用される排煙脱硫装置においても、ＳＯｘを含むガスが流れる場合、その温度が低下すると硫酸露点腐食が生じてしまう。以下本明細書においては、簡単のためにＳＯｘを含むガスを排ガスと記して説明する。
Similarly, in a flue gas desulfurization apparatus used in various industries, when a gas containing SO x flows, sulfuric acid dew point corrosion occurs when the temperature decreases. Hereinafter, in the present specification, for simplicity, a gas containing SO x will be described as exhaust gas.
上記の現象が生ずるため、排ガス系に使用される熱交換器などにおいては、部材表面で硫酸が露を結ばないように排ガス温度を１５０℃以上の高い温度に保持していた。
Since the above phenomenon occurs, in a heat exchanger used for an exhaust gas system, the exhaust gas temperature is maintained at a high temperature of 150 ° C. or higher so that sulfuric acid does not dew on the surface of the member.
ところが、近年のエネルギー需要の増大およびエネルギー有効利用の観点から、熱エネルギーをできるだけ有効に回収するため、例えば、熱交換器からの排ガス温度を硫酸の露点以下まで低くする動きがあり、硫酸に対して抵抗性を有する材料が求められるようになった。
However, from the viewpoint of increasing energy demand in recent years and effective use of energy, in order to recover thermal energy as effectively as possible, for example, there is a movement to lower the exhaust gas temperature from the heat exchanger to below the dew point of sulfuric acid. Therefore, a material having resistance has been demanded.
排ガス温度を１５０℃以上に保持しない場合、一般的な組成の排ガスからは１４０℃程度の温度域で、８０％程度の高濃度の硫酸が部材表面で結露する。このような環境においては、所謂「低合金鋼」が各種部材用鋼として用いられてきた。これは、前記のような高温高濃度の硫酸に対しては、汎用のステンレス鋼よりも低合金鋼の方が耐食性が高いためである。
When the exhaust gas temperature is not maintained at 150 ° C. or higher, sulfuric acid having a high concentration of about 80% is condensed on the surface of the member in the temperature range of about 140 ° C. In such an environment, so-called “low alloy steel” has been used as steel for various members. This is because the low alloy steel has higher corrosion resistance than the general-purpose stainless steel against the high temperature and high concentration sulfuric acid as described above.
一方、非特許文献１に記載されているように、硫酸の露点よりも２０～６０℃温度が下がった領域で結露する硫酸の量が最も多くなるため、硫酸による腐食が大きくなる。このため、排ガス温度を１５０℃以上に保持しない場合には、一般に、１００℃近傍の温度において最も耐食性を要求される領域となり、ここでは硫酸の濃度は約７０％となる。しかし、この領域では汎用のステンレス鋼はもちろん、低合金鋼でも腐食量が大きく使用できない。
On the other hand, as described in Non-Patent Document 1, the amount of sulfuric acid that condenses in the region where the temperature is lowered by 20 to 60 ° C. below the dew point of sulfuric acid is the largest, so that corrosion due to sulfuric acid increases. For this reason, when the exhaust gas temperature is not maintained at 150 ° C. or higher, it is generally an area where the most corrosion resistance is required at a temperature in the vicinity of 100 ° C., where the concentration of sulfuric acid is about 70%. However, in this region, not only general-purpose stainless steel but also low alloy steel cannot be used due to the large amount of corrosion.
これまで、硫酸環境中にある部材に対しては、特定の耐食材料を用いればよいことが提案されており、例えば、特許文献１には、熱間加工性に優れた耐硫酸露点腐食ステンレス鋼が開示されている。
Up to now, it has been proposed that a specific corrosion-resistant material should be used for a member in a sulfuric acid environment. For example, Patent Document 1 discloses a sulfuric acid dew-point corrosion stainless steel excellent in hot workability. Is disclosed.
また、特許文献２には、硫酸腐食に対して優れた抵抗性を有するとともに加工性にも優れたオーステナイト系ステンレス鋼が開示されている。
Further, Patent Document 2 discloses an austenitic stainless steel having excellent resistance to sulfuric acid corrosion and excellent workability.
特許文献１に記載のステンレス鋼は、０．０５重量％以上のＮ（窒素）を含有させてオーステナイト組織の安定化および耐食性の確保を図ろうとするものである。しかしながら、Ｎを０．０５重量％以上含有させた場合には、Ｃｕ、ＣｒおよびＭｏを複合添加したオーステナイト系ステンレス鋼の耐硫酸腐食性が却って低下してしまう。さらに、Ｎ含有量が０．０５重量％以上の場合には、耐硫酸腐食性を高めるためにＣｕ含有量を増やしていくと、１０００℃を下回る温度域での熱間加工性の低下が著しくなるという問題がある。
The stainless steel described in Patent Document 1 is intended to stabilize the austenite structure and ensure corrosion resistance by containing 0.05% by weight or more of N (nitrogen). However, when N is contained in an amount of 0.05% by weight or more, the sulfuric acid corrosion resistance of the austenitic stainless steel to which Cu, Cr, and Mo are added in combination decreases. Furthermore, when the N content is 0.05% by weight or more, if the Cu content is increased in order to increase the resistance to sulfuric acid corrosion, the hot workability in the temperature range below 1000 ° C. is significantly reduced. There is a problem of becoming.
また、特許文献２に記載のオーステナイト系ステンレス鋼は、優れた耐硫酸腐食性と加工性とを有するものである。しかし、耐硫酸腐食性に関しては、さらに改善の余地が残されている。
The austenitic stainless steel described in Patent Document 2 has excellent sulfuric acid corrosion resistance and workability. However, there is still room for improvement regarding the resistance to sulfuric acid corrosion.
本発明は上記の問題を解決し、高濃度の硫酸が凝結する環境において、優れた耐酸性を有するオーステナイト系ステンレス鋼を提供することを目的とする。
An object of the present invention is to solve the above problems and to provide an austenitic stainless steel having excellent acid resistance in an environment where high concentration sulfuric acid is condensed.
なお、以下の記載において、「高濃度の硫酸が凝結する環境」とは、５０～１００℃の温度で４０～７０％の濃度の硫酸が結露する環境を意味するものとする。
In the following description, “an environment in which high-concentration sulfuric acid condenses” means an environment in which sulfuric acid having a concentration of 40 to 70% is condensed at a temperature of 50 to 100 ° C.
本発明は、上記の課題を解決するためになされたものであり、下記のオーステナイト系ステンレス鋼を要旨とする。
The present invention has been made to solve the above-mentioned problems, and the gist thereof is the following austenitic stainless steel.
（１）母材と、前記母材が有する表面の少なくとも一部に形成された皮膜とを備えたオーステナイト系ステンレス鋼であって、
前記母材の化学組成が、質量％で、
Ｃ：０．０５％以下、
Ｓｉ：１．０％以下、
Ｍｎ：２．０％以下、
Ｐ：０．０４０％以下、
Ｓ：０．０１０％以下、
Ｏ：０．０２０％以下、
Ｎ：０．０５０％未満、
Ｎｉ：１２．０～２７．０％、
Ｃｒ：１５．０％以上２０．０％未満、
Ｃｕ：３．５％を超えて８．０％以下、
Ｍｏ：２．０％を超えて５．０％以下、
Ｃｏ：０．０５％以下、
Ｓｎ：０．０５％以下、
Ｖ：０～０．５％、
Ｎｂ：０～１．０％、
Ｔｉ：０～０．５％、
Ｗ：０～５．０％、
Ｚｒ：０～１．０％、
Ａｌ：０～０．５％、
Ｃａ：０～０．０１％、
Ｂ：０～０．０１％、
ＲＥＭ：０～０．０１％、
残部：Ｆｅおよび不純物であり、
前記皮膜のＣｒ濃度が最大となる最大Ｃｒ深さにおける化学組成が下記式（ｉ）を満足する、
オーステナイト系ステンレス鋼。
（Ｃｒ＋Ｎｉ＋Ｃｕ＋Ｍｏ）／Ｆｅ≧１．０ ・・・（ｉ）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。 (1) An austenitic stainless steel comprising a base material and a film formed on at least a part of the surface of the base material,
The chemical composition of the base material is mass%,
C: 0.05% or less,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.040% or less,
S: 0.010% or less,
O: 0.020% or less,
N: less than 0.050%,
Ni: 12.0-27.0%,
Cr: 15.0% or more and less than 20.0%,
Cu: more than 3.5% and 8.0% or less,
Mo: more than 2.0% and 5.0% or less,
Co: 0.05% or less,
Sn: 0.05% or less,
V: 0 to 0.5%
Nb: 0 to 1.0%,
Ti: 0 to 0.5%,
W: 0 to 5.0%
Zr: 0 to 1.0%,
Al: 0 to 0.5%,
Ca: 0 to 0.01%,
B: 0 to 0.01%
REM: 0 to 0.01%,
Balance: Fe and impurities,
The chemical composition at the maximum Cr depth at which the Cr concentration of the film is maximum satisfies the following formula (i):
Austenitic stainless steel.
(Cr + Ni + Cu + Mo) /Fe≧1.0 (i)
However, each element symbol in the above formula represents the content (at%) of each element.
前記母材の化学組成が、質量％で、
Ｃ：０．０５％以下、
Ｓｉ：１．０％以下、
Ｍｎ：２．０％以下、
Ｐ：０．０４０％以下、
Ｓ：０．０１０％以下、
Ｏ：０．０２０％以下、
Ｎ：０．０５０％未満、
Ｎｉ：１２．０～２７．０％、
Ｃｒ：１５．０％以上２０．０％未満、
Ｃｕ：３．５％を超えて８．０％以下、
Ｍｏ：２．０％を超えて５．０％以下、
Ｃｏ：０．０５％以下、
Ｓｎ：０．０５％以下、
Ｖ：０～０．５％、
Ｎｂ：０～１．０％、
Ｔｉ：０～０．５％、
Ｗ：０～５．０％、
Ｚｒ：０～１．０％、
Ａｌ：０～０．５％、
Ｃａ：０～０．０１％、
Ｂ：０～０．０１％、
ＲＥＭ：０～０．０１％、
残部：Ｆｅおよび不純物であり、
前記皮膜のＣｒ濃度が最大となる最大Ｃｒ深さにおける化学組成が下記式（ｉ）を満足する、
オーステナイト系ステンレス鋼。
（Ｃｒ＋Ｎｉ＋Ｃｕ＋Ｍｏ）／Ｆｅ≧１．０ ・・・（ｉ）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。 (1) An austenitic stainless steel comprising a base material and a film formed on at least a part of the surface of the base material,
The chemical composition of the base material is mass%,
C: 0.05% or less,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.040% or less,
S: 0.010% or less,
O: 0.020% or less,
N: less than 0.050%,
Ni: 12.0-27.0%,
Cr: 15.0% or more and less than 20.0%,
Cu: more than 3.5% and 8.0% or less,
Mo: more than 2.0% and 5.0% or less,
Co: 0.05% or less,
Sn: 0.05% or less,
V: 0 to 0.5%
Nb: 0 to 1.0%,
Ti: 0 to 0.5%,
W: 0 to 5.0%
Zr: 0 to 1.0%,
Al: 0 to 0.5%,
Ca: 0 to 0.01%,
B: 0 to 0.01%
REM: 0 to 0.01%,
Balance: Fe and impurities,
The chemical composition at the maximum Cr depth at which the Cr concentration of the film is maximum satisfies the following formula (i):
Austenitic stainless steel.
(Cr + Ni + Cu + Mo) /Fe≧1.0 (i)
However, each element symbol in the above formula represents the content (at%) of each element.
（２）前記母材の化学組成が、質量％で、
Ｖ：０．０１～０．５％、
Ｎｂ：０．０２～１．０％、
Ｔｉ：０．０１～０．５％、
Ｗ：０．１～５．０％、
Ｚｒ：０．０２～１．０％、
Ａｌ：０．０１～０．５％、
Ｃａ：０．０００５～０．０１％、
Ｂ：０．０００５～０．０１％、および、
ＲＥＭ：０．０００５～０．０１％、
から選択される１種以上を含有する、
上記（１）に記載のオーステナイト系ステンレス鋼。 (2) The chemical composition of the base material is mass%,
V: 0.01 to 0.5%
Nb: 0.02 to 1.0%,
Ti: 0.01 to 0.5%,
W: 0.1-5.0%
Zr: 0.02 to 1.0%,
Al: 0.01 to 0.5%,
Ca: 0.0005 to 0.01%,
B: 0.0005 to 0.01%, and
REM: 0.0005 to 0.01%,
Containing one or more selected from
The austenitic stainless steel according to (1) above.
Ｖ：０．０１～０．５％、
Ｎｂ：０．０２～１．０％、
Ｔｉ：０．０１～０．５％、
Ｗ：０．１～５．０％、
Ｚｒ：０．０２～１．０％、
Ａｌ：０．０１～０．５％、
Ｃａ：０．０００５～０．０１％、
Ｂ：０．０００５～０．０１％、および、
ＲＥＭ：０．０００５～０．０１％、
から選択される１種以上を含有する、
上記（１）に記載のオーステナイト系ステンレス鋼。 (2) The chemical composition of the base material is mass%,
V: 0.01 to 0.5%
Nb: 0.02 to 1.0%,
Ti: 0.01 to 0.5%,
W: 0.1-5.0%
Zr: 0.02 to 1.0%,
Al: 0.01 to 0.5%,
Ca: 0.0005 to 0.01%,
B: 0.0005 to 0.01%, and
REM: 0.0005 to 0.01%,
Containing one or more selected from
The austenitic stainless steel according to (1) above.
（３）前記皮膜のＣｒ濃度が最小となる最小Ｃｒ深さが、前記最大Ｃｒ深さより前記母材側に存在し、
前記最大Ｃｒ深さにおける化学組成が下記式（ii）を満足し、かつ、前記最小Ｃｒ深さにおける化学組成が下記式（iii）を満足する、
上記（１）または（２）に記載のオーステナイト系ステンレス鋼。
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）≧１．０ ・・・（ii）
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）＜１．０ ・・・（iii）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。 (3) The minimum Cr depth at which the Cr concentration of the coating is minimum exists on the base material side from the maximum Cr depth,
The chemical composition at the maximum Cr depth satisfies the following formula (ii), and the chemical composition at the minimum Cr depth satisfies the following formula (iii).
The austenitic stainless steel according to (1) or (2) above.
Cr / (Ni + Cu + Mo) ≧ 1.0 (ii)
Cr / (Ni + Cu + Mo) <1.0 (iii)
However, each element symbol in the above formula represents the content (at%) of each element.
前記最大Ｃｒ深さにおける化学組成が下記式（ii）を満足し、かつ、前記最小Ｃｒ深さにおける化学組成が下記式（iii）を満足する、
上記（１）または（２）に記載のオーステナイト系ステンレス鋼。
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）≧１．０ ・・・（ii）
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）＜１．０ ・・・（iii）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。 (3) The minimum Cr depth at which the Cr concentration of the coating is minimum exists on the base material side from the maximum Cr depth,
The chemical composition at the maximum Cr depth satisfies the following formula (ii), and the chemical composition at the minimum Cr depth satisfies the following formula (iii).
The austenitic stainless steel according to (1) or (2) above.
Cr / (Ni + Cu + Mo) ≧ 1.0 (ii)
Cr / (Ni + Cu + Mo) <1.0 (iii)
However, each element symbol in the above formula represents the content (at%) of each element.
本発明によれば、高濃度の硫酸が凝結する環境において、優れた耐酸性を有するオーステナイト系ステンレス鋼が得られる。
According to the present invention, an austenitic stainless steel having excellent acid resistance can be obtained in an environment where high concentration sulfuric acid is condensed.
本発明者らは、特許文献２に記載のオーステナイト系ステンレス鋼をベースとして、耐硫酸腐食性をさらに向上させる方法について鋭意検討を重ねた結果、以下の知見を得た。
As a result of intensive studies on a method for further improving the sulfuric acid corrosion resistance based on the austenitic stainless steel described in Patent Document 2, the present inventors have obtained the following knowledge.
耐硫酸腐食性を向上させる上では、高濃度の硫酸と接触する、母材表面に形成される皮膜の組成が重要となる。皮膜中においてＣｒ、Ｎｉ、ＣｕおよびＭｏの合計含有量をＦｅに対して相対的に高めることによって、耐酸性を大幅に向上させることが可能になる。
In order to improve the sulfuric acid corrosion resistance, the composition of the film formed on the base material surface that comes into contact with a high concentration of sulfuric acid is important. By increasing the total content of Cr, Ni, Cu and Mo relative to Fe in the film, the acid resistance can be greatly improved.
また、鋼に対して所定の条件で熱処理を施すことで表面にＦｅを主体とする酸化皮膜を形成させた後、酸処理を施してＦｅ成分を優先的に溶解させることによって、皮膜中にＣｒ、Ｎｉ、ＣｕおよびＭｏを濃化させることが可能になることを見出した。
In addition, after heat treatment is performed on steel under a predetermined condition, an oxide film mainly composed of Fe is formed on the surface, and then an acid treatment is performed to preferentially dissolve the Fe component. It has been found that Ni, Cu and Mo can be concentrated.
本発明は上記の知見に基づいてなされたものである。以下、本発明の各要件について詳しく説明する。
The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.
１．構成
本発明に係るオーステナイト系ステンレス鋼は、母材と、当該母材が有する表面の少なくとも一部に形成された皮膜とを備える。母材および皮膜のそれぞれについて、以下に詳しく説明する。 1. Configuration An austenitic stainless steel according to the present invention includes a base material and a film formed on at least a part of the surface of the base material. Each of the base material and the coating will be described in detail below.
本発明に係るオーステナイト系ステンレス鋼は、母材と、当該母材が有する表面の少なくとも一部に形成された皮膜とを備える。母材および皮膜のそれぞれについて、以下に詳しく説明する。 1. Configuration An austenitic stainless steel according to the present invention includes a base material and a film formed on at least a part of the surface of the base material. Each of the base material and the coating will be described in detail below.
２．母材について
母材の化学組成について、詳しく説明する。各元素の限定理由は下記のとおりである。なお、以下の説明において含有量についての「％」は、「質量％」を意味する。 2. About the base material The chemical composition of the base material will be described in detail. The reasons for limiting each element are as follows. In the following description, “%” for the content means “% by mass”.
母材の化学組成について、詳しく説明する。各元素の限定理由は下記のとおりである。なお、以下の説明において含有量についての「％」は、「質量％」を意味する。 2. About the base material The chemical composition of the base material will be described in detail. The reasons for limiting each element are as follows. In the following description, “%” for the content means “% by mass”.
Ｃ：０．０５％以下
Ｃは、強度を高める作用を有する元素である。しかし、Ｃｒと結合して粒界にＣｒ炭化物を形成し、耐粒界腐食性を低下させてしまう。したがって、Ｃ含有量は０．０５％以下とする。なお、強度を高める必要がある場合には０．０３％を超えて含有させるのが好ましい。一方、耐食性の確保が優先される場合には、Ｃ含有量は低い方がよく、０．０３％以下とすることが好ましい。下限は特に設ける必要はないが、上記の効果を得るためには、Ｃ含有量は０．０１％以上とすることが好ましい。 C: 0.05% or less C is an element having an effect of increasing strength. However, it combines with Cr to form Cr carbide at the grain boundary, thereby reducing the intergranular corrosion resistance. Therefore, the C content is 0.05% or less. In addition, when it is necessary to raise intensity | strength, it is preferable to make it contain exceeding 0.03%. On the other hand, when priority is given to ensuring corrosion resistance, the C content is preferably low, and is preferably 0.03% or less. The lower limit is not particularly required, but in order to obtain the above effect, the C content is preferably 0.01% or more.
Ｃは、強度を高める作用を有する元素である。しかし、Ｃｒと結合して粒界にＣｒ炭化物を形成し、耐粒界腐食性を低下させてしまう。したがって、Ｃ含有量は０．０５％以下とする。なお、強度を高める必要がある場合には０．０３％を超えて含有させるのが好ましい。一方、耐食性の確保が優先される場合には、Ｃ含有量は低い方がよく、０．０３％以下とすることが好ましい。下限は特に設ける必要はないが、上記の効果を得るためには、Ｃ含有量は０．０１％以上とすることが好ましい。 C: 0.05% or less C is an element having an effect of increasing strength. However, it combines with Cr to form Cr carbide at the grain boundary, thereby reducing the intergranular corrosion resistance. Therefore, the C content is 0.05% or less. In addition, when it is necessary to raise intensity | strength, it is preferable to make it contain exceeding 0.03%. On the other hand, when priority is given to ensuring corrosion resistance, the C content is preferably low, and is preferably 0.03% or less. The lower limit is not particularly required, but in order to obtain the above effect, the C content is preferably 0.01% or more.
Ｓｉ：１．０％以下
Ｓｉは、脱酸作用を有する元素である。しかし、その含有量が１．０％を超えると熱間加工性の低下を助長し、Ｃｕ含有量の増加と相俟って、工業的規模での製品への加工が極めて難しくなる。したがって、Ｓｉ含有量は１．０％以下とする。Ｓｉ含有量は０．６％以下であるのが好ましい。Ｓｉは必ずしも含有させる必要がないため下限は特に設けないが、上記の効果を得るためには、Ｓｉ含有量は０．０５％以上とすることが好ましい。また、熱間加工性を高める目的からＡｌ含有量を極めて低くした場合には、０．１％以上のＳｉを含有させて脱酸作用を充分に行わせることが好ましい。 Si: 1.0% or less Si is an element having a deoxidizing action. However, if its content exceeds 1.0%, it reduces the hot workability, and coupled with the increase in Cu content, it becomes extremely difficult to process the product on an industrial scale. Therefore, the Si content is 1.0% or less. The Si content is preferably 0.6% or less. Since Si does not necessarily need to be contained, a lower limit is not particularly provided. However, in order to obtain the above effect, the Si content is preferably 0.05% or more. In addition, when the Al content is extremely low for the purpose of improving hot workability, it is preferable that 0.1% or more of Si is contained to sufficiently perform the deoxidation action.
Ｓｉは、脱酸作用を有する元素である。しかし、その含有量が１．０％を超えると熱間加工性の低下を助長し、Ｃｕ含有量の増加と相俟って、工業的規模での製品への加工が極めて難しくなる。したがって、Ｓｉ含有量は１．０％以下とする。Ｓｉ含有量は０．６％以下であるのが好ましい。Ｓｉは必ずしも含有させる必要がないため下限は特に設けないが、上記の効果を得るためには、Ｓｉ含有量は０．０５％以上とすることが好ましい。また、熱間加工性を高める目的からＡｌ含有量を極めて低くした場合には、０．１％以上のＳｉを含有させて脱酸作用を充分に行わせることが好ましい。 Si: 1.0% or less Si is an element having a deoxidizing action. However, if its content exceeds 1.0%, it reduces the hot workability, and coupled with the increase in Cu content, it becomes extremely difficult to process the product on an industrial scale. Therefore, the Si content is 1.0% or less. The Si content is preferably 0.6% or less. Since Si does not necessarily need to be contained, a lower limit is not particularly provided. However, in order to obtain the above effect, the Si content is preferably 0.05% or more. In addition, when the Al content is extremely low for the purpose of improving hot workability, it is preferable that 0.1% or more of Si is contained to sufficiently perform the deoxidation action.
Ｍｎ：２．０％以下
Ｍｎは、Ｓを固定して熱間加工性を高めるとともに、オーステナイト相を安定化させる作用を有する。しかし、２．０％を超える量のＭｎを含有させてもその効果は飽和し、コストが嵩むばかりである。したがって、Ｍｎ含有量を２．０％以下とする。Ｍｎ含有量は１．５％以下であるのが好ましい。Ｍｎは必ずしも含有させる必要がないため下限は特に設けないが、上記の効果を得るためには、Ｍｎ含有量は０．１％以上とすることが好ましい。 Mn: 2.0% or less Mn has the effect of fixing S to improve hot workability and stabilize the austenite phase. However, even if Mn is contained in an amount exceeding 2.0%, the effect is saturated and the cost is increased. Therefore, the Mn content is set to 2.0% or less. The Mn content is preferably 1.5% or less. Since it is not always necessary to contain Mn, a lower limit is not particularly provided. However, in order to obtain the above effect, the Mn content is preferably 0.1% or more.
Ｍｎは、Ｓを固定して熱間加工性を高めるとともに、オーステナイト相を安定化させる作用を有する。しかし、２．０％を超える量のＭｎを含有させてもその効果は飽和し、コストが嵩むばかりである。したがって、Ｍｎ含有量を２．０％以下とする。Ｍｎ含有量は１．５％以下であるのが好ましい。Ｍｎは必ずしも含有させる必要がないため下限は特に設けないが、上記の効果を得るためには、Ｍｎ含有量は０．１％以上とすることが好ましい。 Mn: 2.0% or less Mn has the effect of fixing S to improve hot workability and stabilize the austenite phase. However, even if Mn is contained in an amount exceeding 2.0%, the effect is saturated and the cost is increased. Therefore, the Mn content is set to 2.0% or less. The Mn content is preferably 1.5% or less. Since it is not always necessary to contain Mn, a lower limit is not particularly provided. However, in order to obtain the above effect, the Mn content is preferably 0.1% or more.
Ｐ：０．０４０％以下
Ｐは、不純物として鋼中に含まれ、熱間加工性および耐食性を劣化させるため、その含有量はできるだけ低い方がよい。特に、Ｐ含有量が０．０４０％を超えると、高濃度の硫酸が凝結する環境における耐食性の劣化が著しい。したがって、Ｐ含有量は０．０４０％以下とする。 P: 0.040% or less P is contained in steel as an impurity and deteriorates hot workability and corrosion resistance. Therefore, the content is preferably as low as possible. In particular, when the P content exceeds 0.040%, the corrosion resistance is significantly deteriorated in an environment in which a high concentration of sulfuric acid is condensed. Therefore, the P content is 0.040% or less.
Ｐは、不純物として鋼中に含まれ、熱間加工性および耐食性を劣化させるため、その含有量はできるだけ低い方がよい。特に、Ｐ含有量が０．０４０％を超えると、高濃度の硫酸が凝結する環境における耐食性の劣化が著しい。したがって、Ｐ含有量は０．０４０％以下とする。 P: 0.040% or less P is contained in steel as an impurity and deteriorates hot workability and corrosion resistance. Therefore, the content is preferably as low as possible. In particular, when the P content exceeds 0.040%, the corrosion resistance is significantly deteriorated in an environment in which a high concentration of sulfuric acid is condensed. Therefore, the P content is 0.040% or less.
Ｓ：０．０１０％以下
Ｓは、不純物として鋼中に含まれ、熱間加工性を劣化させるため、その含有量はできるだけ低い方がよい。特に、Ｓ含有量が０．０１０％を超えると、熱間加工性の著しい劣化を招く。したがって、Ｓ含有量は０．０１０％以下とした。 S: 0.010% or less S is contained as an impurity in steel and deteriorates hot workability. Therefore, the content is preferably as low as possible. In particular, when the S content exceeds 0.010%, the hot workability is significantly deteriorated. Therefore, the S content is set to 0.010% or less.
Ｓは、不純物として鋼中に含まれ、熱間加工性を劣化させるため、その含有量はできるだけ低い方がよい。特に、Ｓ含有量が０．０１０％を超えると、熱間加工性の著しい劣化を招く。したがって、Ｓ含有量は０．０１０％以下とした。 S: 0.010% or less S is contained as an impurity in steel and deteriorates hot workability. Therefore, the content is preferably as low as possible. In particular, when the S content exceeds 0.010%, the hot workability is significantly deteriorated. Therefore, the S content is set to 0.010% or less.
Ｏ：０．０２０％以下
Ｏは不純物として鋼中に含まれ、熱間加工性および延性を低下させるため、その含有量はできるだけ低い方がよい。特に、Ｏ含有量が０．０２０％を超えると、熱間加工性および延性の低下が著しいため、Ｏ含有量は０．０２０％以下とする。 O: 0.020% or less O is contained in the steel as an impurity and reduces hot workability and ductility. Therefore, the content is preferably as low as possible. In particular, when the O content exceeds 0.020%, the hot workability and ductility are significantly reduced, so the O content is set to 0.020% or less.
Ｏは不純物として鋼中に含まれ、熱間加工性および延性を低下させるため、その含有量はできるだけ低い方がよい。特に、Ｏ含有量が０．０２０％を超えると、熱間加工性および延性の低下が著しいため、Ｏ含有量は０．０２０％以下とする。 O: 0.020% or less O is contained in the steel as an impurity and reduces hot workability and ductility. Therefore, the content is preferably as low as possible. In particular, when the O content exceeds 0.020%, the hot workability and ductility are significantly reduced, so the O content is set to 0.020% or less.
Ｎ：０．０５０％未満
Ｎは、従来、Ｎはオーステナイト組織の安定化の目的、または、孔食もしくは隙間腐食などの局部腐食に対する抵抗性を高める目的から積極的に添加されてきた。しかし、高濃度の硫酸が凝結する環境においては、Ｎの含有量が０．０５０％以上になると、３．５％を超えるＣｕ、２．０％を超えるＭｏおよび１５．０％以上２０．０％未満のＣｒを含有させたオーステナイト系ステンレス鋼の耐食性が却って低下してしまう。さらに、ＣｕおよびＭｏの含有量の上限をそれぞれ８．０％および５．０％にした場合であっても、Ｎの含有量が０．０５０％以上になると熱間加工性が低下してしまう。高濃度の硫酸が凝結する環境における耐食性と熱間加工性とをオーステナイト系ステンレス鋼に付与させるため、Ｎ含有量は０．０５０％未満とする。なお、Ｎ含有量は低ければ低いほどよく、０．０４５％以下であるのが好ましい。 N: Less than 0.050% N has heretofore been actively added for the purpose of stabilizing the austenite structure or increasing the resistance to local corrosion such as pitting corrosion or crevice corrosion. However, in an environment where high-concentration sulfuric acid condenses, when the N content is 0.050% or more, Cu exceeds 3.5%, Mo exceeds 2.0%, and 15.0% or more 20.0%. On the contrary, the corrosion resistance of the austenitic stainless steel containing less than% Cr is lowered. Further, even when the upper limit of Cu and Mo contents is 8.0% and 5.0%, respectively, the hot workability is reduced when the N content is 0.050% or more. . In order to provide the austenitic stainless steel with corrosion resistance and hot workability in an environment where high-concentration sulfuric acid is condensed, the N content is set to less than 0.050%. The N content is preferably as low as possible and is preferably 0.045% or less.
Ｎは、従来、Ｎはオーステナイト組織の安定化の目的、または、孔食もしくは隙間腐食などの局部腐食に対する抵抗性を高める目的から積極的に添加されてきた。しかし、高濃度の硫酸が凝結する環境においては、Ｎの含有量が０．０５０％以上になると、３．５％を超えるＣｕ、２．０％を超えるＭｏおよび１５．０％以上２０．０％未満のＣｒを含有させたオーステナイト系ステンレス鋼の耐食性が却って低下してしまう。さらに、ＣｕおよびＭｏの含有量の上限をそれぞれ８．０％および５．０％にした場合であっても、Ｎの含有量が０．０５０％以上になると熱間加工性が低下してしまう。高濃度の硫酸が凝結する環境における耐食性と熱間加工性とをオーステナイト系ステンレス鋼に付与させるため、Ｎ含有量は０．０５０％未満とする。なお、Ｎ含有量は低ければ低いほどよく、０．０４５％以下であるのが好ましい。 N: Less than 0.050% N has heretofore been actively added for the purpose of stabilizing the austenite structure or increasing the resistance to local corrosion such as pitting corrosion or crevice corrosion. However, in an environment where high-concentration sulfuric acid condenses, when the N content is 0.050% or more, Cu exceeds 3.5%, Mo exceeds 2.0%, and 15.0% or more 20.0%. On the contrary, the corrosion resistance of the austenitic stainless steel containing less than% Cr is lowered. Further, even when the upper limit of Cu and Mo contents is 8.0% and 5.0%, respectively, the hot workability is reduced when the N content is 0.050% or more. . In order to provide the austenitic stainless steel with corrosion resistance and hot workability in an environment where high-concentration sulfuric acid is condensed, the N content is set to less than 0.050%. The N content is preferably as low as possible and is preferably 0.045% or less.
Ｎｉ：１２．０～２７．０％
Ｎｉは、オーステナイト相を安定化させる作用を有するとともに、高濃度の硫酸が凝結する環境中での耐食性を高める作用もある。こうした効果を充分確保するためには、１２．０％以上の量のＮｉを含有させる必要がある。しかし、２７．０％を超えて含有させてもその効果は飽和する。さらに、Ｎｉは高価な元素であるため、コストが極めて高くなって経済性に欠ける。したがって、Ｎｉ含有量は１２．０～２７．０％とする。なお、高濃度の硫酸が凝結する環境中で充分な耐食性を確保するためには、１５．０％を超える量のＮｉを含有させることが好ましく、２０．０％を超える量のＮｉを含有させることがより好ましい。 Ni: 12.0-27.0%
Ni has the effect of stabilizing the austenite phase and also has the effect of enhancing the corrosion resistance in an environment where high concentration of sulfuric acid is condensed. In order to sufficiently secure such an effect, it is necessary to contain Ni in an amount of 12.0% or more. However, the effect is saturated even if it contains exceeding 27.0%. Furthermore, since Ni is an expensive element, the cost is extremely high and the economy is lacking. Therefore, the Ni content is 12.0 to 27.0%. In order to ensure sufficient corrosion resistance in an environment where high-concentration sulfuric acid condenses, it is preferable to contain Ni in an amount exceeding 15.0%, and Ni in an amount exceeding 20.0%. It is more preferable.
Ｎｉは、オーステナイト相を安定化させる作用を有するとともに、高濃度の硫酸が凝結する環境中での耐食性を高める作用もある。こうした効果を充分確保するためには、１２．０％以上の量のＮｉを含有させる必要がある。しかし、２７．０％を超えて含有させてもその効果は飽和する。さらに、Ｎｉは高価な元素であるため、コストが極めて高くなって経済性に欠ける。したがって、Ｎｉ含有量は１２．０～２７．０％とする。なお、高濃度の硫酸が凝結する環境中で充分な耐食性を確保するためには、１５．０％を超える量のＮｉを含有させることが好ましく、２０．０％を超える量のＮｉを含有させることがより好ましい。 Ni: 12.0-27.0%
Ni has the effect of stabilizing the austenite phase and also has the effect of enhancing the corrosion resistance in an environment where high concentration of sulfuric acid is condensed. In order to sufficiently secure such an effect, it is necessary to contain Ni in an amount of 12.0% or more. However, the effect is saturated even if it contains exceeding 27.0%. Furthermore, since Ni is an expensive element, the cost is extremely high and the economy is lacking. Therefore, the Ni content is 12.0 to 27.0%. In order to ensure sufficient corrosion resistance in an environment where high-concentration sulfuric acid condenses, it is preferable to contain Ni in an amount exceeding 15.0%, and Ni in an amount exceeding 20.0%. It is more preferable.
Ｃｒ：１５．０％以上２０．０％未満
Ｃｒはオーステナイト系ステンレス鋼の耐食性を確保するのに有効な元素である。特に、Ｎを上述の含有量に規制したオーステナイト系ステンレス鋼において、１５．０％以上のＣｒ、好ましくは１６．０％以上のＣｒを後述する量のＣｕおよびＭｏとともに含有させると、高濃度の硫酸が凝結する環境で良好な耐食性を確保することができる。しかし、Ｃｒを過剰に含有させると、Ｎ含有量を低くし、ＣｕとＭｏとを複合添加したオーステナイト系ステンレス鋼の場合であっても、前記の環境中における耐食性が却って劣化し、さらに加工性の低下も生じる。特に、Ｃｒ含有量が２０．０％以上となると前記環境中におけるオーステナイト系ステンレス鋼の耐食性劣化が著しくなる。また、Ｃｒ含有量を２０．０％未満とすることによって、ＣｕとＭｏとを複合添加したオーステナイト系ステンレス鋼の熱間加工性を高めて、工業的規模での製品加工を容易にすることが可能になる。したがって、Ｃｒ含有量は１５．０％以上２０．０％未満とする。 Cr: 15.0% or more and less than 20.0% Cr is an element effective for ensuring the corrosion resistance of austenitic stainless steel. In particular, in the austenitic stainless steel in which N is regulated to the above-described content, when 15.0% or more of Cr, preferably 16.0% or more of Cr is contained together with the amounts of Cu and Mo described below, a high concentration Good corrosion resistance can be ensured in an environment where sulfuric acid condenses. However, when Cr is excessively contained, even in the case of austenitic stainless steel in which the N content is reduced and Cu and Mo are added in combination, the corrosion resistance in the environment described above deteriorates, and the workability is further improved. Also occurs. In particular, when the Cr content is 20.0% or more, the corrosion resistance of the austenitic stainless steel in the environment is significantly deteriorated. In addition, by making the Cr content less than 20.0%, the hot workability of the austenitic stainless steel combined with Cu and Mo can be improved, and product processing on an industrial scale can be facilitated. It becomes possible. Therefore, the Cr content is 15.0% or more and less than 20.0%.
Ｃｒはオーステナイト系ステンレス鋼の耐食性を確保するのに有効な元素である。特に、Ｎを上述の含有量に規制したオーステナイト系ステンレス鋼において、１５．０％以上のＣｒ、好ましくは１６．０％以上のＣｒを後述する量のＣｕおよびＭｏとともに含有させると、高濃度の硫酸が凝結する環境で良好な耐食性を確保することができる。しかし、Ｃｒを過剰に含有させると、Ｎ含有量を低くし、ＣｕとＭｏとを複合添加したオーステナイト系ステンレス鋼の場合であっても、前記の環境中における耐食性が却って劣化し、さらに加工性の低下も生じる。特に、Ｃｒ含有量が２０．０％以上となると前記環境中におけるオーステナイト系ステンレス鋼の耐食性劣化が著しくなる。また、Ｃｒ含有量を２０．０％未満とすることによって、ＣｕとＭｏとを複合添加したオーステナイト系ステンレス鋼の熱間加工性を高めて、工業的規模での製品加工を容易にすることが可能になる。したがって、Ｃｒ含有量は１５．０％以上２０．０％未満とする。 Cr: 15.0% or more and less than 20.0% Cr is an element effective for ensuring the corrosion resistance of austenitic stainless steel. In particular, in the austenitic stainless steel in which N is regulated to the above-described content, when 15.0% or more of Cr, preferably 16.0% or more of Cr is contained together with the amounts of Cu and Mo described below, a high concentration Good corrosion resistance can be ensured in an environment where sulfuric acid condenses. However, when Cr is excessively contained, even in the case of austenitic stainless steel in which the N content is reduced and Cu and Mo are added in combination, the corrosion resistance in the environment described above deteriorates, and the workability is further improved. Also occurs. In particular, when the Cr content is 20.0% or more, the corrosion resistance of the austenitic stainless steel in the environment is significantly deteriorated. In addition, by making the Cr content less than 20.0%, the hot workability of the austenitic stainless steel combined with Cu and Mo can be improved, and product processing on an industrial scale can be facilitated. It becomes possible. Therefore, the Cr content is 15.0% or more and less than 20.0%.
Ｃｕ：３．５％を超えて８．０％以下
Ｃｕは、硫酸環境中での耐食性を確保するのに必須の元素である。３．５％を超えるＣｕを前述の量のＣｒおよび後述する量のＭｏとともに含有させることで、高濃度の硫酸が凝結する環境において、Ｎを上述の含有量にしたオーステナイト系ステンレス鋼に良好な耐食性を付与することができる。ＣｕおよびＭｏと複合添加するＣｕの含有量が多いほど耐食性向上効果が大きいので、Ｃｕ含有量は４．０％を超える量とすることが好ましい。なお、Ｃｕ含有量を増やすことにより前記環境中での耐食性は向上するが熱間加工性が低下し、特に、Ｃｕ含有量が８．０％を超えると、Ｎを上述の含有量にしても熱間加工性の著しい劣化を生ずる。したがって、Ｃｕ含有量は３．５％を超えて８．０％以下とする。 Cu: More than 3.5% and not more than 8.0% Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment. By including Cu in excess of 3.5% together with the above-mentioned amount of Cr and the amount of Mo described later, in an environment where high-concentration sulfuric acid condenses, it is good for an austenitic stainless steel with the above-mentioned content. Corrosion resistance can be imparted. The greater the content of Cu added in combination with Cu and Mo, the greater the effect of improving corrosion resistance. Therefore, the Cu content is preferably set to an amount exceeding 4.0%. In addition, although corrosion resistance in the said environment improves by increasing Cu content, although hot workability falls, especially when Cu content exceeds 8.0%, N is made into said content. This causes a significant deterioration in hot workability. Therefore, the Cu content is more than 3.5% and not more than 8.0%.
Ｃｕは、硫酸環境中での耐食性を確保するのに必須の元素である。３．５％を超えるＣｕを前述の量のＣｒおよび後述する量のＭｏとともに含有させることで、高濃度の硫酸が凝結する環境において、Ｎを上述の含有量にしたオーステナイト系ステンレス鋼に良好な耐食性を付与することができる。ＣｕおよびＭｏと複合添加するＣｕの含有量が多いほど耐食性向上効果が大きいので、Ｃｕ含有量は４．０％を超える量とすることが好ましい。なお、Ｃｕ含有量を増やすことにより前記環境中での耐食性は向上するが熱間加工性が低下し、特に、Ｃｕ含有量が８．０％を超えると、Ｎを上述の含有量にしても熱間加工性の著しい劣化を生ずる。したがって、Ｃｕ含有量は３．５％を超えて８．０％以下とする。 Cu: More than 3.5% and not more than 8.0% Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment. By including Cu in excess of 3.5% together with the above-mentioned amount of Cr and the amount of Mo described later, in an environment where high-concentration sulfuric acid condenses, it is good for an austenitic stainless steel with the above-mentioned content. Corrosion resistance can be imparted. The greater the content of Cu added in combination with Cu and Mo, the greater the effect of improving corrosion resistance. Therefore, the Cu content is preferably set to an amount exceeding 4.0%. In addition, although corrosion resistance in the said environment improves by increasing Cu content, although hot workability falls, especially when Cu content exceeds 8.0%, N is made into said content. This causes a significant deterioration in hot workability. Therefore, the Cu content is more than 3.5% and not more than 8.0%.
Ｍｏ：２．０％を超えて５．０％以下
Ｍｏは、オーステナイト系ステンレス鋼の耐食性を確保するのに有効な元素である。２．０％を超える量のＭｏを前述した量のＣｒおよびＣｕとともに含有させると、高濃度の硫酸が凝結する環境において、Ｎを上述の含有量にしたオーステナイト系ステンレス鋼に良好な耐食性を付与することができる。しかし、Ｍｏを過剰に含有させると熱間加工性が低下し、特に、Ｍｏ含有量が５．０％を超えると、Ｎを上述の含有量にしても熱間加工性の著しい劣化を生ずる。したがって、Ｍｏ含有量は２．０％を超えて５．０％以下とする。なお、高濃度の硫酸が凝結する環境中で充分な耐食性を確保するためには、３．０％を超える量のＭｏを含有させることが好ましい。 Mo: more than 2.0% to 5.0% or less Mo is an element effective for ensuring the corrosion resistance of austenitic stainless steel. When more than 2.0% of Mo is contained together with the above-mentioned amounts of Cr and Cu, good corrosion resistance is imparted to austenitic stainless steel having the above-mentioned content in an environment where high-concentration sulfuric acid is condensed. can do. However, when Mo is excessively contained, the hot workability is lowered. In particular, when the Mo content exceeds 5.0%, the hot workability is significantly deteriorated even if N is contained as described above. Therefore, the Mo content is more than 2.0% and not more than 5.0%. In order to ensure sufficient corrosion resistance in an environment where high-concentration sulfuric acid is condensed, it is preferable to contain Mo in an amount exceeding 3.0%.
Ｍｏは、オーステナイト系ステンレス鋼の耐食性を確保するのに有効な元素である。２．０％を超える量のＭｏを前述した量のＣｒおよびＣｕとともに含有させると、高濃度の硫酸が凝結する環境において、Ｎを上述の含有量にしたオーステナイト系ステンレス鋼に良好な耐食性を付与することができる。しかし、Ｍｏを過剰に含有させると熱間加工性が低下し、特に、Ｍｏ含有量が５．０％を超えると、Ｎを上述の含有量にしても熱間加工性の著しい劣化を生ずる。したがって、Ｍｏ含有量は２．０％を超えて５．０％以下とする。なお、高濃度の硫酸が凝結する環境中で充分な耐食性を確保するためには、３．０％を超える量のＭｏを含有させることが好ましい。 Mo: more than 2.0% to 5.0% or less Mo is an element effective for ensuring the corrosion resistance of austenitic stainless steel. When more than 2.0% of Mo is contained together with the above-mentioned amounts of Cr and Cu, good corrosion resistance is imparted to austenitic stainless steel having the above-mentioned content in an environment where high-concentration sulfuric acid is condensed. can do. However, when Mo is excessively contained, the hot workability is lowered. In particular, when the Mo content exceeds 5.0%, the hot workability is significantly deteriorated even if N is contained as described above. Therefore, the Mo content is more than 2.0% and not more than 5.0%. In order to ensure sufficient corrosion resistance in an environment where high-concentration sulfuric acid is condensed, it is preferable to contain Mo in an amount exceeding 3.0%.
Ｃｏ：０．０５％以下
Ｃｏは、不純物として鋼中に含まれる元素である。Ｃｏは、鋼の靱性を高めるために有効な元素であるが、高価な元素であるため、積極的に添加する必要はない。したがって、Ｃｏ含有量は０．０５％以下とする。 Co: 0.05% or less Co is an element contained in steel as an impurity. Co is an effective element for increasing the toughness of steel, but it is an expensive element and therefore does not need to be actively added. Therefore, the Co content is 0.05% or less.
Ｃｏは、不純物として鋼中に含まれる元素である。Ｃｏは、鋼の靱性を高めるために有効な元素であるが、高価な元素であるため、積極的に添加する必要はない。したがって、Ｃｏ含有量は０．０５％以下とする。 Co: 0.05% or less Co is an element contained in steel as an impurity. Co is an effective element for increasing the toughness of steel, but it is an expensive element and therefore does not need to be actively added. Therefore, the Co content is 0.05% or less.
Ｓｎ：０．０５％以下
Ｓｎは、不純物として鋼中に含まれ、熱間加工性を劣化させるため、その含有量はできるだけ低い方がよい。特に、Ｓｎ含有量が０．０５％を超えると、熱間加工性の著しい劣化を招く。したがって、Ｓｎ含有量は０．０５％以下とする。 Sn: 0.05% or less Since Sn is contained as an impurity in steel and deteriorates hot workability, its content is preferably as low as possible. In particular, when the Sn content exceeds 0.05%, the hot workability is significantly deteriorated. Therefore, the Sn content is 0.05% or less.
Ｓｎは、不純物として鋼中に含まれ、熱間加工性を劣化させるため、その含有量はできるだけ低い方がよい。特に、Ｓｎ含有量が０．０５％を超えると、熱間加工性の著しい劣化を招く。したがって、Ｓｎ含有量は０．０５％以下とする。 Sn: 0.05% or less Since Sn is contained as an impurity in steel and deteriorates hot workability, its content is preferably as low as possible. In particular, when the Sn content exceeds 0.05%, the hot workability is significantly deteriorated. Therefore, the Sn content is 0.05% or less.
Ｖ：０．５％以下
Ｖは、Ｃを固定して耐食性、なかでも耐粒界腐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．５％を超えると、Ｎを上述の含有量にした場合でも窒化物が生成して却って耐食性が低下し、さらに、熱間加工性の劣化も招く。したがって、Ｖ含有量は０．５％以下とする。上記の効果を得るためには、Ｖ含有量は０．０１％以上とすることが好ましい。 V: 0.5% or less V has an effect of fixing C and enhancing corrosion resistance, particularly intergranular corrosion resistance, and may be contained as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the V content is 0.5% or less. In order to acquire said effect, it is preferable that V content shall be 0.01% or more.
Ｖは、Ｃを固定して耐食性、なかでも耐粒界腐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．５％を超えると、Ｎを上述の含有量にした場合でも窒化物が生成して却って耐食性が低下し、さらに、熱間加工性の劣化も招く。したがって、Ｖ含有量は０．５％以下とする。上記の効果を得るためには、Ｖ含有量は０．０１％以上とすることが好ましい。 V: 0.5% or less V has an effect of fixing C and enhancing corrosion resistance, particularly intergranular corrosion resistance, and may be contained as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the V content is 0.5% or less. In order to acquire said effect, it is preferable that V content shall be 0.01% or more.
Ｎｂ：０～１．０％
Ｎｂは、Ｃを固定して耐食性、なかでも耐粒界腐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が１．０％を超えると、Ｎを上述の含有量にした場合でも窒化物が生成して却って耐食性が低下し、さらに、熱間加工性の劣化も招く。したがって、Ｎｂ含有量は１．０％以下とする。上記の効果を得るためには、Ｎｂ含有量は０．０２％以上とすることが好ましい。 Nb: 0 to 1.0%
Nb has the effect of fixing C and improving the corrosion resistance, particularly intergranular corrosion resistance, so it may be contained if necessary. However, if its content exceeds 1.0%, even when N is made the above-mentioned content, a nitride is formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Nb content is 1.0% or less. In order to obtain the above effect, the Nb content is preferably 0.02% or more.
Ｎｂは、Ｃを固定して耐食性、なかでも耐粒界腐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が１．０％を超えると、Ｎを上述の含有量にした場合でも窒化物が生成して却って耐食性が低下し、さらに、熱間加工性の劣化も招く。したがって、Ｎｂ含有量は１．０％以下とする。上記の効果を得るためには、Ｎｂ含有量は０．０２％以上とすることが好ましい。 Nb: 0 to 1.0%
Nb has the effect of fixing C and improving the corrosion resistance, particularly intergranular corrosion resistance, so it may be contained if necessary. However, if its content exceeds 1.0%, even when N is made the above-mentioned content, a nitride is formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Nb content is 1.0% or less. In order to obtain the above effect, the Nb content is preferably 0.02% or more.
Ｔｉ：０～０．５％
Ｔｉは、Ｎｂと同様にＣを固定して耐食性、なかでも耐粒界腐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．５％を超えると、Ｎを上述の含有量にした場合でも窒化物が生成して却って耐食性が低下し、さらに、熱間加工性の劣化も招く。したがって、Ｔｉ含有量は０．５％以下とする。上記の効果を得るためには、Ｔｉ含有量は０．０１％以上とすることが好ましい。 Ti: 0 to 0.5%
Ti, like Nb, has the effect of fixing C and improving corrosion resistance, particularly intergranular corrosion resistance. Therefore, Ti may be included as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Ti content is 0.5% or less. In order to acquire said effect, it is preferable that Ti content shall be 0.01% or more.
Ｔｉは、Ｎｂと同様にＣを固定して耐食性、なかでも耐粒界腐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．５％を超えると、Ｎを上述の含有量にした場合でも窒化物が生成して却って耐食性が低下し、さらに、熱間加工性の劣化も招く。したがって、Ｔｉ含有量は０．５％以下とする。上記の効果を得るためには、Ｔｉ含有量は０．０１％以上とすることが好ましい。 Ti: 0 to 0.5%
Ti, like Nb, has the effect of fixing C and improving corrosion resistance, particularly intergranular corrosion resistance. Therefore, Ti may be included as necessary. However, if its content exceeds 0.5%, even when N is made the above-mentioned content, nitrides are formed, and on the contrary, corrosion resistance is lowered, and further hot workability is deteriorated. Therefore, the Ti content is 0.5% or less. In order to acquire said effect, it is preferable that Ti content shall be 0.01% or more.
Ｗ：０～５．０％
Ｗは、高濃度の硫酸が凝結する環境における耐食性を高める作用があるため、必要に応じて含有させてもよい。しかし、その含有量が５．０％を超えると、上記の効果は飽和し、コストが嵩むばかりである。したがって、Ｗ含有量は５．０％以下とする。上記の効果を得るためには、Ｗ含有量は０．１％以上とすることが好ましい。 W: 0-5.0%
W has an effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and may be contained as necessary. However, if the content exceeds 5.0%, the above effect is saturated and the cost is increased. Therefore, the W content is 5.0% or less. In order to acquire said effect, it is preferable that W content shall be 0.1% or more.
Ｗは、高濃度の硫酸が凝結する環境における耐食性を高める作用があるため、必要に応じて含有させてもよい。しかし、その含有量が５．０％を超えると、上記の効果は飽和し、コストが嵩むばかりである。したがって、Ｗ含有量は５．０％以下とする。上記の効果を得るためには、Ｗ含有量は０．１％以上とすることが好ましい。 W: 0-5.0%
W has an effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and may be contained as necessary. However, if the content exceeds 5.0%, the above effect is saturated and the cost is increased. Therefore, the W content is 5.0% or less. In order to acquire said effect, it is preferable that W content shall be 0.1% or more.
Ｚｒ：０～１．０％
Ｚｒは、高濃度の硫酸が凝結する環境における耐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が１．０％を超えると、上記の効果は飽和し、コストが嵩むばかりである。したがって、Ｚｒ含有量は１．０％以下とする。上記の効果を得るためには、Ｚｒ含有量は０．０２％以上とすることが好ましい。 Zr: 0 to 1.0%
Zr has the effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and thus may be contained as necessary. However, if the content exceeds 1.0%, the above effect is saturated and the cost is increased. Therefore, the Zr content is 1.0% or less. In order to acquire said effect, it is preferable that Zr content shall be 0.02% or more.
Ｚｒは、高濃度の硫酸が凝結する環境における耐食性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が１．０％を超えると、上記の効果は飽和し、コストが嵩むばかりである。したがって、Ｚｒ含有量は１．０％以下とする。上記の効果を得るためには、Ｚｒ含有量は０．０２％以上とすることが好ましい。 Zr: 0 to 1.0%
Zr has the effect of enhancing the corrosion resistance in an environment where high-concentration sulfuric acid condenses, and thus may be contained as necessary. However, if the content exceeds 1.0%, the above effect is saturated and the cost is increased. Therefore, the Zr content is 1.0% or less. In order to acquire said effect, it is preferable that Zr content shall be 0.02% or more.
Ａｌ：０～０．５％
Ａｌは、脱酸作用を有するため、Ｓｉ含有量を極めて低く抑える場合には、含有させてもよい。しかし、その含有量が０．５％を超えると、Ｎを上述の含有量にしたオーステナイト系ステンレス鋼であっても熱間加工性が低下してしまう。したがって、Ａｌ含有量は０．５％以下とする。Ａｌ含有量の下限は特に規定せず、不純物の範囲であってもよい。但し、Ｓｉ含有量を極めて低く抑える場合には、積極的に添加して０．０２％以上を含有させ、脱酸作用を充分に行わせることが好ましい。なお、０．０５％以上のＳｉを含有させた場合でも、脱酸作用を充分に発揮させるためには、Ａｌ含有量を０．０１％以上とすることが好ましい。 Al: 0 to 0.5%
Since Al has a deoxidizing action, Al may be contained when the Si content is extremely low. However, when the content exceeds 0.5%, hot workability is deteriorated even in the austenitic stainless steel in which N is the above content. Therefore, the Al content is 0.5% or less. The lower limit of the Al content is not particularly defined and may be in the range of impurities. However, in order to keep the Si content extremely low, it is preferable that the Si content is positively added to contain 0.02% or more to sufficiently perform the deoxidation action. Even when 0.05% or more of Si is contained, the Al content is preferably set to 0.01% or more in order to sufficiently exhibit the deoxidation effect.
Ａｌは、脱酸作用を有するため、Ｓｉ含有量を極めて低く抑える場合には、含有させてもよい。しかし、その含有量が０．５％を超えると、Ｎを上述の含有量にしたオーステナイト系ステンレス鋼であっても熱間加工性が低下してしまう。したがって、Ａｌ含有量は０．５％以下とする。Ａｌ含有量の下限は特に規定せず、不純物の範囲であってもよい。但し、Ｓｉ含有量を極めて低く抑える場合には、積極的に添加して０．０２％以上を含有させ、脱酸作用を充分に行わせることが好ましい。なお、０．０５％以上のＳｉを含有させた場合でも、脱酸作用を充分に発揮させるためには、Ａｌ含有量を０．０１％以上とすることが好ましい。 Al: 0 to 0.5%
Since Al has a deoxidizing action, Al may be contained when the Si content is extremely low. However, when the content exceeds 0.5%, hot workability is deteriorated even in the austenitic stainless steel in which N is the above content. Therefore, the Al content is 0.5% or less. The lower limit of the Al content is not particularly defined and may be in the range of impurities. However, in order to keep the Si content extremely low, it is preferable that the Si content is positively added to contain 0.02% or more to sufficiently perform the deoxidation action. Even when 0.05% or more of Si is contained, the Al content is preferably set to 0.01% or more in order to sufficiently exhibit the deoxidation effect.
Ｃａ：０～０．０１％
Ｃａは、Ｓと結合して熱間加工性の低下を抑える効果を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．０１％を超えると、鋼の清浄度が低下して、熱間での製造時に疵が発生する原因となる。したがって、Ｃａ含有量は０．０１％以下とする。上記の効果を得るためには、Ｃａ含有量は０．０００５％以上とすることが好ましく、０．００１％以上とすることがより好ましい。 Ca: 0 to 0.01%
Since Ca has an effect of combining with S and suppressing a decrease in hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the Ca content is 0.01% or less. In order to obtain the above effect, the Ca content is preferably 0.0005% or more, and more preferably 0.001% or more.
Ｃａは、Ｓと結合して熱間加工性の低下を抑える効果を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．０１％を超えると、鋼の清浄度が低下して、熱間での製造時に疵が発生する原因となる。したがって、Ｃａ含有量は０．０１％以下とする。上記の効果を得るためには、Ｃａ含有量は０．０００５％以上とすることが好ましく、０．００１％以上とすることがより好ましい。 Ca: 0 to 0.01%
Since Ca has an effect of combining with S and suppressing a decrease in hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the Ca content is 0.01% or less. In order to obtain the above effect, the Ca content is preferably 0.0005% or more, and more preferably 0.001% or more.
Ｂ：０～０．０１％
Ｂは、熱間加工性を改善する効果を有するため、必要に応じて含有させてもよい。しかし、Ｂの過剰な添加は粒界でのＣｒ－Ｂ化合物の析出を促し、耐食性の劣化を招く。特に、Ｂの含有量が０．０１％を超えると著しい耐食性の劣化をきたす。したがって、Ｂ含有量は０．０１％以下とする。上記の効果を得るためには、Ｂ含有量は０．０００５％以上とすることが好ましく、０．００１％以上とすることがより好ましい。 B: 0 to 0.01%
Since B has an effect of improving hot workability, B may be contained as necessary. However, excessive addition of B promotes the precipitation of Cr—B compounds at the grain boundaries, leading to deterioration of corrosion resistance. In particular, when the B content exceeds 0.01%, the corrosion resistance is remarkably deteriorated. Therefore, the B content is 0.01% or less. In order to obtain the above effect, the B content is preferably 0.0005% or more, and more preferably 0.001% or more.
Ｂは、熱間加工性を改善する効果を有するため、必要に応じて含有させてもよい。しかし、Ｂの過剰な添加は粒界でのＣｒ－Ｂ化合物の析出を促し、耐食性の劣化を招く。特に、Ｂの含有量が０．０１％を超えると著しい耐食性の劣化をきたす。したがって、Ｂ含有量は０．０１％以下とする。上記の効果を得るためには、Ｂ含有量は０．０００５％以上とすることが好ましく、０．００１％以上とすることがより好ましい。 B: 0 to 0.01%
Since B has an effect of improving hot workability, B may be contained as necessary. However, excessive addition of B promotes the precipitation of Cr—B compounds at the grain boundaries, leading to deterioration of corrosion resistance. In particular, when the B content exceeds 0.01%, the corrosion resistance is remarkably deteriorated. Therefore, the B content is 0.01% or less. In order to obtain the above effect, the B content is preferably 0.0005% or more, and more preferably 0.001% or more.
ＲＥＭ：０～０．０１％
ＲＥＭ（希土類元素）は、熱間加工性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．０１％を超えると、鋼の清浄度が低下して、熱間での製造時に疵が発生する原因となる。したがって、ＲＥＭ含有量は０．０１％以下とする。上記の効果を得るためには、ＲＥＭ含有量は０．０００５％以上とすることが好ましい。 REM: 0 to 0.01%
Since REM (rare earth element) has an effect of improving hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the REM content is 0.01% or less. In order to acquire said effect, it is preferable that REM content shall be 0.0005% or more.
ＲＥＭ（希土類元素）は、熱間加工性を高める作用を有するため、必要に応じて含有させてもよい。しかし、その含有量が０．０１％を超えると、鋼の清浄度が低下して、熱間での製造時に疵が発生する原因となる。したがって、ＲＥＭ含有量は０．０１％以下とする。上記の効果を得るためには、ＲＥＭ含有量は０．０００５％以上とすることが好ましい。 REM: 0 to 0.01%
Since REM (rare earth element) has an effect of improving hot workability, it may be contained as necessary. However, if its content exceeds 0.01%, the cleanliness of the steel is lowered, which causes wrinkles during hot production. Therefore, the REM content is 0.01% or less. In order to acquire said effect, it is preferable that REM content shall be 0.0005% or more.
ここで、ＲＥＭとは、Ｓｃ、Ｙおよびランタノイドの合計１７元素を指し、ＲＥＭの含有量は、これらの元素の合計含有量を指す。
Here, REM refers to a total of 17 elements of Sc, Y, and lanthanoid, and the content of REM refers to the total content of these elements.
本発明のオーステナイト系ステンレス鋼の母材の化学組成において、残部はＦｅおよび不純物である。ここで「不純物」とは、鋼を工業的に製造する際に、鉱石、スクラップ等の原料、製造工程の種々の要因によって混入する成分であって、本発明に悪影響を与えない範囲で許容されるものを意味する。
In the chemical composition of the base material of the austenitic stainless steel of the present invention, the balance is Fe and impurities. Here, “impurities” are components that are mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when steel is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.
３．皮膜について
上述のように、母材が有する表面の少なくとも一部には、皮膜が形成されている。そして、皮膜中においてＣｒ、Ｎｉ、ＣｕおよびＭｏの合計含有量をＦｅに対して相対的に高めることによって、耐酸性を大幅に向上させることが可能になる。 3. About a film | membrane As mentioned above, the film | membrane is formed in at least one part of the surface which a base material has. And it becomes possible to improve acid resistance significantly by raising the total content of Cr, Ni, Cu and Mo relative to Fe in the film.
上述のように、母材が有する表面の少なくとも一部には、皮膜が形成されている。そして、皮膜中においてＣｒ、Ｎｉ、ＣｕおよびＭｏの合計含有量をＦｅに対して相対的に高めることによって、耐酸性を大幅に向上させることが可能になる。 3. About a film | membrane As mentioned above, the film | membrane is formed in at least one part of the surface which a base material has. And it becomes possible to improve acid resistance significantly by raising the total content of Cr, Ni, Cu and Mo relative to Fe in the film.
具体的には、皮膜中には、Ｃｒ濃度が最大となる最大Ｃｒ深さが存在し、当該最大Ｃｒ深さにおける化学組成が下記式（ｉ）を満足する必要がある。なお、最大Ｃｒ深さの位置については特に制限はなく、皮膜の最表層に存在していてもよい。
（Ｃｒ＋Ｎｉ＋Ｃｕ＋Ｍｏ）／Ｆｅ≧１．０ ・・・（ｉ）
但し、上記式中の各元素記号は、鋼表面における各元素の含有量（ａｔ％）を表す。 Specifically, the maximum Cr depth at which the Cr concentration is maximum exists in the film, and the chemical composition at the maximum Cr depth needs to satisfy the following formula (i). In addition, there is no restriction | limiting in particular about the position of the maximum Cr depth, You may exist in the outermost layer of a membrane | film | coat.
(Cr + Ni + Cu + Mo) /Fe≧1.0 (i)
However, each element symbol in the above formula represents the content (at%) of each element on the steel surface.
（Ｃｒ＋Ｎｉ＋Ｃｕ＋Ｍｏ）／Ｆｅ≧１．０ ・・・（ｉ）
但し、上記式中の各元素記号は、鋼表面における各元素の含有量（ａｔ％）を表す。 Specifically, the maximum Cr depth at which the Cr concentration is maximum exists in the film, and the chemical composition at the maximum Cr depth needs to satisfy the following formula (i). In addition, there is no restriction | limiting in particular about the position of the maximum Cr depth, You may exist in the outermost layer of a membrane | film | coat.
(Cr + Ni + Cu + Mo) /Fe≧1.0 (i)
However, each element symbol in the above formula represents the content (at%) of each element on the steel surface.
また、本発明に係る皮膜は、概してＣｒが相対的に濃化した表層側の層とＮｉ等が相対的に濃化した母材側の層とを含む構造となっている。すなわち、上記の最大Ｃｒ深さより母材側には、Ｃｒ濃度が最小となる最小Ｃｒ深さが存在することとなる。
Further, the coating according to the present invention generally has a structure including a surface layer layer in which Cr is relatively concentrated and a base material layer in which Ni or the like is relatively concentrated. That is, a minimum Cr depth at which the Cr concentration is minimum exists on the base material side from the above maximum Cr depth.
そして、最大Ｃｒ深さにおける化学組成は、下記式（ii）を満足することが好ましく、最小Ｃｒ深さにおける化学組成は、下記式（iii）を満足することが好ましい。
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）≧１．０ ・・・（ii）
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）＜１．０ ・・・（iii）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。 The chemical composition at the maximum Cr depth preferably satisfies the following formula (ii), and the chemical composition at the minimum Cr depth preferably satisfies the following formula (iii).
Cr / (Ni + Cu + Mo) ≧ 1.0 (ii)
Cr / (Ni + Cu + Mo) <1.0 (iii)
However, each element symbol in the above formula represents the content (at%) of each element.
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）≧１．０ ・・・（ii）
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）＜１．０ ・・・（iii）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。 The chemical composition at the maximum Cr depth preferably satisfies the following formula (ii), and the chemical composition at the minimum Cr depth preferably satisfies the following formula (iii).
Cr / (Ni + Cu + Mo) ≧ 1.0 (ii)
Cr / (Ni + Cu + Mo) <1.0 (iii)
However, each element symbol in the above formula represents the content (at%) of each element.
皮膜の厚さについては特に制限は設けないが、例えば、２～１０ｎｍの範囲であることが好ましい。皮膜の厚さが２ｎｍ未満では、耐硫酸腐食性が十分に得られないおそれがある。一方、皮膜の厚さが１０ｎｍを超えると、皮膜組成の不均一および皮膜の剥離が生じやすくなるおそれがあるためである。
The thickness of the film is not particularly limited, but is preferably in the range of 2 to 10 nm, for example. If the thickness of the film is less than 2 nm, the sulfuric acid corrosion resistance may not be sufficiently obtained. On the other hand, if the thickness of the film exceeds 10 nm, the film composition may be uneven and the film may be easily peeled off.
なお、本発明において、皮膜の化学組成は、Ｘ線光電分光法（ＸＰＳ）を用いた深さ分析により測定するものとする。上記の深さ分析により、各元素の濃度プロファイルをＯ、ＣおよびＮを除く成分に占める割合（ａｔ％）として導出する。そして、最大Ｃｒ深さおよび最小Ｃｒ深さを特定することで、当該深さにおける各元素の濃度を求め、それらの値から上記式（ｉ）～（iii）を算出する。
In the present invention, the chemical composition of the film is measured by depth analysis using X-ray photoelectric spectroscopy (XPS). From the depth analysis described above, the concentration profile of each element is derived as a ratio (at%) to the components excluding O, C, and N. Then, by specifying the maximum Cr depth and the minimum Cr depth, the concentration of each element at the depth is obtained, and the above formulas (i) to (iii) are calculated from these values.
また、皮膜の厚さは、Ｏ（酸素）の濃度プロファイルから求めることとする。具体的には、Ｏの最大濃度の１／３の濃度となる位置を、皮膜と母材との境界部と判断し、皮膜表面から上記の境界部までの長さを、皮膜の厚さとする。皮膜の組成および厚さの測定は、複数カ所で行い、その平均値を採用することが望ましい。
Also, the thickness of the film is determined from the O (oxygen) concentration profile. Specifically, the position at which the concentration is 1/3 of the maximum concentration of O is determined as the boundary between the film and the base material, and the length from the film surface to the above boundary is defined as the thickness of the film. . It is desirable to measure the composition and thickness of the film at a plurality of locations and adopt the average value.
４．製造方法
本発明に係るオーステナイト系ステンレス鋼の製造条件について特に制限はないが、例えば、上述の化学組成を有する鋼素材に対して、以下に示す条件で熱処理および酸処理を施すことにより、製造することができる。 4). Manufacturing method Although there is no restriction | limiting in particular about the manufacturing conditions of the austenitic stainless steel which concerns on this invention, For example, it manufactures by performing the heat processing and acid treatment on the conditions shown below with respect to the steel raw material which has the above-mentioned chemical composition. be able to.
本発明に係るオーステナイト系ステンレス鋼の製造条件について特に制限はないが、例えば、上述の化学組成を有する鋼素材に対して、以下に示す条件で熱処理および酸処理を施すことにより、製造することができる。 4). Manufacturing method Although there is no restriction | limiting in particular about the manufacturing conditions of the austenitic stainless steel which concerns on this invention, For example, it manufactures by performing the heat processing and acid treatment on the conditions shown below with respect to the steel raw material which has the above-mentioned chemical composition. be able to.
＜熱処理工程＞
上記鋼素材に対して、まず１０６０～１１４０℃の温度範囲に６０～６００ｓ保持する熱処理を施す。これにより、鋼素材表面にＦｅを主体とする酸化皮膜を形成させる。熱処理温度が１０６０℃未満ではＦｅ酸化皮膜の形成が不十分となる。一方、熱処理温度が１１４０℃を超えると母材の結晶粒が粗大になり、Ｆｅの拡散が少なくなるため、Ｆｅ酸化皮膜が不均一になり、さらに皮膜剥離が生じやすくなる。その結果、上記のいずれの場合においても、Ｃｒ、Ｎｉ、ＣｕおよびＭｏの濃化が生じにくくなる。 <Heat treatment process>
The steel material is first subjected to heat treatment for 60 to 600 seconds in a temperature range of 1060 to 1140 ° C. Thereby, an oxide film mainly composed of Fe is formed on the surface of the steel material. If the heat treatment temperature is less than 1060 ° C., the formation of the Fe oxide film becomes insufficient. On the other hand, when the heat treatment temperature exceeds 1140 ° C., the crystal grains of the base material become coarse and Fe diffusion is reduced, so that the Fe oxide film becomes non-uniform and the film is more easily peeled off. As a result, in any of the above cases, the concentration of Cr, Ni, Cu and Mo is less likely to occur.
上記鋼素材に対して、まず１０６０～１１４０℃の温度範囲に６０～６００ｓ保持する熱処理を施す。これにより、鋼素材表面にＦｅを主体とする酸化皮膜を形成させる。熱処理温度が１０６０℃未満ではＦｅ酸化皮膜の形成が不十分となる。一方、熱処理温度が１１４０℃を超えると母材の結晶粒が粗大になり、Ｆｅの拡散が少なくなるため、Ｆｅ酸化皮膜が不均一になり、さらに皮膜剥離が生じやすくなる。その結果、上記のいずれの場合においても、Ｃｒ、Ｎｉ、ＣｕおよびＭｏの濃化が生じにくくなる。 <Heat treatment process>
The steel material is first subjected to heat treatment for 60 to 600 seconds in a temperature range of 1060 to 1140 ° C. Thereby, an oxide film mainly composed of Fe is formed on the surface of the steel material. If the heat treatment temperature is less than 1060 ° C., the formation of the Fe oxide film becomes insufficient. On the other hand, when the heat treatment temperature exceeds 1140 ° C., the crystal grains of the base material become coarse and Fe diffusion is reduced, so that the Fe oxide film becomes non-uniform and the film is more easily peeled off. As a result, in any of the above cases, the concentration of Cr, Ni, Cu and Mo is less likely to occur.
＜酸処理工程＞
上記鋼素材に対して、上記の熱処理に続いて、酸処理を施す。酸処理工程において、Ｆｅ成分を優先的に溶解させることで、鋼表面にＣｒ、Ｎｉ、ＣｕおよびＭｏを濃化させることが可能になる。Ｆｅ成分を優先的に溶解させるためには、３０～５０℃、５～８体積％ＨＮＯ３、５～８体積％ＨＦの弗硝酸中に１～５ｈ浸漬することが好ましい。 <Acid treatment process>
The steel material is subjected to acid treatment following the heat treatment. In the acid treatment step, it is possible to concentrate Cr, Ni, Cu and Mo on the steel surface by preferentially dissolving the Fe component. In order to preferentially dissolve the Fe component, it is preferably immersed in hydrofluoric acid at 30 to 50 ° C., 5 to 8% by volume HNO 3 , and 5 to 8% by volume HF for 1 to 5 hours.
上記鋼素材に対して、上記の熱処理に続いて、酸処理を施す。酸処理工程において、Ｆｅ成分を優先的に溶解させることで、鋼表面にＣｒ、Ｎｉ、ＣｕおよびＭｏを濃化させることが可能になる。Ｆｅ成分を優先的に溶解させるためには、３０～５０℃、５～８体積％ＨＮＯ３、５～８体積％ＨＦの弗硝酸中に１～５ｈ浸漬することが好ましい。 <Acid treatment process>
The steel material is subjected to acid treatment following the heat treatment. In the acid treatment step, it is possible to concentrate Cr, Ni, Cu and Mo on the steel surface by preferentially dissolving the Fe component. In order to preferentially dissolve the Fe component, it is preferably immersed in hydrofluoric acid at 30 to 50 ° C., 5 to 8% by volume HNO 3 , and 5 to 8% by volume HF for 1 to 5 hours.
以下、実施例によって本発明をより具体的に説明するが、本発明はこれらの実施例に限定されるものではない。
Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples.
表１に示す化学組成を有する鋼（鋼Ｎｏ．１～１１）を３．５ｔのＶＩＭ溶解炉を用いて溶製し、通常の方法で熱間鍛造、熱間押出および冷間引抜を行って、外径７５ｍｍ、肉厚３ｍｍの鋼管素材を作製した。その後、試験Ｎｏ．１～１７および１９～２８については、表２に示す条件において熱処理および酸処理を施し、オーステナイト系ステンレス鋼管とした。また、試験Ｎｏ．１８については、試験Ｎｏ．３と同じ条件で熱処理および酸処理を施した後、表面を研磨した。
Steels having the chemical compositions shown in Table 1 (steel Nos. 1 to 11) were melted using a 3.5 ton VIM melting furnace, and hot forging, hot extrusion, and cold drawing were performed by ordinary methods. A steel pipe material having an outer diameter of 75 mm and a wall thickness of 3 mm was produced. Thereafter, test no. For 1 to 17 and 19 to 28, heat treatment and acid treatment were performed under the conditions shown in Table 2 to obtain austenitic stainless steel pipes. In addition, Test No. For Test No. 18, test no. After performing heat treatment and acid treatment under the same conditions as in No. 3, the surface was polished.
次に、各鋼管表面に形成される皮膜の化学組成および厚さの測定を、ＸＰＳを用いた深さ分析により行った。具体的には、各元素の濃度プロファイルをＯ、ＣおよびＮを除く成分に占める割合（ａｔ％）として導出し、最大Ｃｒ深さおよび最小Ｃｒ深さを特定した後に、当該深さにおける各元素の濃度を求めた。そして、それらの値から上記式（ｉ）～（iii）を算出した。なお、本実施例においては、試験Ｎｏ．１８を除く例において、皮膜の最表層に最大Ｃｒ深さが存在しており、また、全ての例において、最小Ｃｒ深さが最大Ｃｒ深さより母材側に存在していた。
Next, the chemical composition and thickness of the coating formed on the surface of each steel pipe were measured by depth analysis using XPS. Specifically, the concentration profile of each element is derived as a ratio (at%) to the components excluding O, C and N, and after specifying the maximum Cr depth and the minimum Cr depth, each element at the depth is determined. The concentration of was determined. Then, the above formulas (i) to (iii) were calculated from these values. In this example, test no. In the examples other than 18, the maximum Cr depth exists in the outermost layer of the coating, and in all the examples, the minimum Cr depth exists on the base material side from the maximum Cr depth.
また、皮膜の厚さは、Ｏ（酸素）の濃度プロファイルから求めた。具体的には、Ｏの最大濃度の１／３の濃度となる位置を、皮膜と母材との境界部と判断し、皮膜表面から上記の境界部までの長さを、皮膜の厚さとした。
The thickness of the film was determined from the O (oxygen) concentration profile. Specifically, the position where the concentration is 1/3 of the maximum concentration of O is determined as the boundary between the coating and the base material, and the length from the coating surface to the above-described boundary is defined as the thickness of the coating. .
さらに、耐硫酸腐食性の評価を行うため、硫酸環境中での腐食試験を実施した。腐食試験は、温度が１００℃で硫酸濃度が７０％である溶液に各鋼管を浸漬することによって行った。そして８時間浸漬した後の腐食減量を測定し、単位面積当たりの腐食速度を算出した。本発明においては、上記腐食速度が１．００ｇ／（ｍ２・ｈ）以下となる場合に、耐硫酸腐食性に優れると判断することとした。
Furthermore, in order to evaluate sulfuric acid corrosion resistance, a corrosion test was carried out in a sulfuric acid environment. The corrosion test was performed by immersing each steel pipe in a solution having a temperature of 100 ° C. and a sulfuric acid concentration of 70%. And the corrosion weight loss after being immersed for 8 hours was measured, and the corrosion rate per unit area was computed. In the present invention, when the corrosion rate is 1.00 g / (m 2 · h) or less, it is determined that the sulfuric acid corrosion resistance is excellent.
それらの結果を表３に併せて示す。
The results are also shown in Table 3.
表３から分かるように、製造条件が不適切である試験Ｎｏ．１、２および１４～１７ならびに研磨肌の試験Ｎｏ．１８では、皮膜中にＣｒ、Ｎｉ、ＣｕおよびＭｏの濃化が生じないため、腐食速度が高く、耐硫酸腐食性が劣る結果となった。同様に、母材中のＣｕ含有量が本発明の規定から外れる試験Ｎｏ．２８では、Ｃｕによる耐酸性が得られないことに加えて、皮膜中のＣｒ、Ｎｉ、ＣｕおよびＭｏの濃化が不十分であったため、耐硫酸腐食性が劣る結果となった。
As can be seen from Table 3, test No. with inappropriate manufacturing conditions. 1, 2 and 14 to 17 and polishing skin test Nos. In No. 18, since concentration of Cr, Ni, Cu and Mo did not occur in the film, the corrosion rate was high and the sulfuric acid corrosion resistance was inferior. Similarly, the test No. in which the Cu content in the base material deviates from the definition of the present invention. In No. 28, acid resistance due to Cu was not obtained, and in addition, the concentration of Cr, Ni, Cu and Mo in the film was insufficient, resulting in poor sulfuric acid corrosion resistance.
これらに対して、本発明の規定を満足し、皮膜中にＣｒ、Ｎｉ、ＣｕおよびＭｏが濃化した試験Ｎｏ．３～１３および１９～２７では、腐食速度が１．００ｇ／（ｍ２・ｈ）以下となり、耐硫酸腐食性に優れる結果となった。
On the other hand, the test No. 1 which satisfied the provisions of the present invention and concentrated Cr, Ni, Cu and Mo in the film. For 3 to 13 and 19 to 27, the corrosion rate was 1.00 g / (m 2 · h) or less, which was excellent in sulfuric acid corrosion resistance.
本発明によれば、高濃度の硫酸が凝結する環境において、優れた耐酸性を有するオーステナイト系ステンレス鋼が得られる。したがって、本発明に係るオーステナイト系ステンレス鋼は、火力発電もしくは産業用ボイラで使用される熱交換器、煙道および煙突、ならびに各種産業で使用される排煙脱硫装置用部材または硫酸環境で使用される設備に用いられる構造部材など各種の部材に適用可能である。
ADVANTAGE OF THE INVENTION According to this invention, the austenitic stainless steel which has the outstanding acid resistance in the environment where a high concentration sulfuric acid condenses is obtained. Therefore, the austenitic stainless steel according to the present invention is used in heat exchangers, flues and chimneys used in thermal power generation or industrial boilers, exhaust gas desulfurization equipment members used in various industries, or sulfuric acid environments. It can be applied to various members such as structural members used in equipment.
ADVANTAGE OF THE INVENTION According to this invention, the austenitic stainless steel which has the outstanding acid resistance in the environment where a high concentration sulfuric acid condenses is obtained. Therefore, the austenitic stainless steel according to the present invention is used in heat exchangers, flues and chimneys used in thermal power generation or industrial boilers, exhaust gas desulfurization equipment members used in various industries, or sulfuric acid environments. It can be applied to various members such as structural members used in equipment.
Claims (3)
- 母材と、前記母材が有する表面の少なくとも一部に形成された皮膜とを備えたオーステナイト系ステンレス鋼であって、
前記母材の化学組成が、質量％で、
Ｃ：０．０５％以下、
Ｓｉ：１．０％以下、
Ｍｎ：２．０％以下、
Ｐ：０．０４０％以下、
Ｓ：０．０１０％以下、
Ｏ：０．０２０％以下、
Ｎ：０．０５０％未満、
Ｎｉ：１２．０～２７．０％、
Ｃｒ：１５．０％以上２０．０％未満、
Ｃｕ：３．５％を超えて８．０％以下、
Ｍｏ：２．０％を超えて５．０％以下、
Ｃｏ：０．０５％以下、
Ｓｎ：０．０５％以下、
Ｖ：０～０．５％、
Ｎｂ：０～１．０％、
Ｔｉ：０～０．５％、
Ｗ：０～５．０％、
Ｚｒ：０～１．０％、
Ａｌ：０～０．５％、
Ｃａ：０～０．０１％、
Ｂ：０～０．０１％、
ＲＥＭ：０～０．０１％、
残部：Ｆｅおよび不純物であり、
前記皮膜のＣｒ濃度が最大となる最大Ｃｒ深さにおける化学組成が下記式（ｉ）を満足する、
オーステナイト系ステンレス鋼。
（Ｃｒ＋Ｎｉ＋Ｃｕ＋Ｍｏ）／Ｆｅ≧１．０ ・・・（ｉ）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。 An austenitic stainless steel comprising a base material and a film formed on at least a part of the surface of the base material,
The chemical composition of the base material is mass%,
C: 0.05% or less,
Si: 1.0% or less,
Mn: 2.0% or less,
P: 0.040% or less,
S: 0.010% or less,
O: 0.020% or less,
N: less than 0.050%,
Ni: 12.0-27.0%,
Cr: 15.0% or more and less than 20.0%,
Cu: more than 3.5% and 8.0% or less,
Mo: more than 2.0% and 5.0% or less,
Co: 0.05% or less,
Sn: 0.05% or less,
V: 0 to 0.5%
Nb: 0 to 1.0%,
Ti: 0 to 0.5%,
W: 0 to 5.0%
Zr: 0 to 1.0%,
Al: 0 to 0.5%,
Ca: 0 to 0.01%,
B: 0 to 0.01%
REM: 0 to 0.01%,
Balance: Fe and impurities,
The chemical composition at the maximum Cr depth at which the Cr concentration of the film is maximum satisfies the following formula (i):
Austenitic stainless steel.
(Cr + Ni + Cu + Mo) /Fe≧1.0 (i)
However, each element symbol in the above formula represents the content (at%) of each element. - 前記母材の化学組成が、質量％で、
Ｖ：０．０１～０．５％、
Ｎｂ：０．０２～１．０％、
Ｔｉ：０．０１～０．５％、
Ｗ：０．１～５．０％、
Ｚｒ：０．０２～１．０％、
Ａｌ：０．０１～０．５％、
Ｃａ：０．０００５～０．０１％、
Ｂ：０．０００５～０．０１％、および、
ＲＥＭ：０．０００５～０．０１％、
から選択される１種以上を含有する、
請求項１に記載のオーステナイト系ステンレス鋼。 The chemical composition of the base material is mass%,
V: 0.01 to 0.5%
Nb: 0.02 to 1.0%,
Ti: 0.01 to 0.5%,
W: 0.1-5.0%
Zr: 0.02 to 1.0%,
Al: 0.01 to 0.5%,
Ca: 0.0005 to 0.01%,
B: 0.0005 to 0.01%, and
REM: 0.0005 to 0.01%,
Containing one or more selected from
The austenitic stainless steel according to claim 1. - 前記皮膜のＣｒ濃度が最小となる最小Ｃｒ深さが、前記最大Ｃｒ深さより前記母材側に存在し、
前記最大Ｃｒ深さにおける化学組成が下記式（ii）を満足し、かつ、前記最小Ｃｒ深さにおける化学組成が下記式（iii）を満足する、
請求項１または請求項２に記載のオーステナイト系ステンレス鋼。
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）≧１．０ ・・・（ii）
Ｃｒ／（Ｎｉ＋Ｃｕ＋Ｍｏ）＜１．０ ・・・（iii）
但し、上記式中の各元素記号は、各元素の含有量（ａｔ％）を表す。
The minimum Cr depth at which the Cr concentration of the film is minimum exists on the base material side from the maximum Cr depth,
The chemical composition at the maximum Cr depth satisfies the following formula (ii), and the chemical composition at the minimum Cr depth satisfies the following formula (iii).
The austenitic stainless steel according to claim 1 or 2.
Cr / (Ni + Cu + Mo) ≧ 1.0 (ii)
Cr / (Ni + Cu + Mo) <1.0 (iii)
However, each element symbol in the above formula represents the content (at%) of each element.
Priority Applications (6)
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| KR1020197005733A KR20190034286A (en) | 2016-08-03 | 2017-08-02 | Austenitic stainless steel |
| CA3032772A CA3032772A1 (en) | 2016-08-03 | 2017-08-02 | Austenitic stainless steel |
| JP2018531964A JP6724991B2 (en) | 2016-08-03 | 2017-08-02 | Austenitic stainless steel |
| CN201780048557.4A CN109563589B (en) | 2016-08-03 | 2017-08-02 | Austenitic stainless steel |
| EP17837044.1A EP3495526A4 (en) | 2016-08-03 | 2017-08-02 | Austenitic stainless steel |
| US16/322,228 US20190177808A1 (en) | 2016-08-03 | 2017-08-02 | Austenitic Stainless Steel |
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| US (1) | US20190177808A1 (en) |
| EP (1) | EP3495526A4 (en) |
| JP (1) | JP6724991B2 (en) |
| KR (1) | KR20190034286A (en) |
| CN (1) | CN109563589B (en) |
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| JP2003213379A (en) * | 2002-01-21 | 2003-07-30 | Sumitomo Metal Ind Ltd | Stainless steel having excellent corrosion resistance |
| CN109321822A (en) * | 2012-10-30 | 2019-02-12 | 株式会社神户制钢所 | Austenite stainless steel |
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2017
- 2017-08-02 WO PCT/JP2017/028146 patent/WO2018025942A1/en unknown
- 2017-08-02 CA CA3032772A patent/CA3032772A1/en not_active Abandoned
- 2017-08-02 KR KR1020197005733A patent/KR20190034286A/en not_active Application Discontinuation
- 2017-08-02 EP EP17837044.1A patent/EP3495526A4/en not_active Withdrawn
- 2017-08-02 CN CN201780048557.4A patent/CN109563589B/en active Active
- 2017-08-02 JP JP2018531964A patent/JP6724991B2/en active Active
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| EP3495526A1 (en) | 2019-06-12 |
| CA3032772A1 (en) | 2018-02-08 |
| JP6724991B2 (en) | 2020-07-15 |
| CN109563589A (en) | 2019-04-02 |
| US20190177808A1 (en) | 2019-06-13 |
| KR20190034286A (en) | 2019-04-01 |
| CN109563589B (en) | 2020-11-06 |
| JPWO2018025942A1 (en) | 2019-06-06 |
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