JP6724991B2 - Austenitic stainless steel - Google Patents
Austenitic stainless steel Download PDFInfo
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- JP6724991B2 JP6724991B2 JP2018531964A JP2018531964A JP6724991B2 JP 6724991 B2 JP6724991 B2 JP 6724991B2 JP 2018531964 A JP2018531964 A JP 2018531964A JP 2018531964 A JP2018531964 A JP 2018531964A JP 6724991 B2 JP6724991 B2 JP 6724991B2
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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 austenitic stainless steel, and more particularly to austenitic stainless steel having excellent 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。Sulfur (S) is contained in so-called "fossil fuels" such as oil and coal used as boiler fuels for thermal power generation or industrial use. Therefore, when the 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 the water content in the gas to form sulfuric acid, which condenses on the surface of the member having a low temperature below the dew point temperature, which causes 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 of the gas decreases. Hereinafter, in the present specification, a gas containing SO x will be described as an exhaust gas for the sake of simplicity.
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。 Because of the above phenomenon, in a heat exchanger used for an exhaust gas system, the exhaust gas temperature is kept at a high temperature of 150° C. or higher so that sulfuric acid does not condense 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 recent increase in energy demand and effective use of energy, in order to recover heat 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 come to be 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 from the exhaust gas having a general composition 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 20 to 60° C. lower than the dew point of sulfuric acid becomes the largest, so that the corrosion by sulfuric acid becomes large. Therefore, when the exhaust gas temperature is not maintained at 150° C. or higher, generally, the temperature is in the region where the highest corrosion resistance is required at a temperature near 100° C., and the concentration of sulfuric acid is about 70% here. However, in this region, not only general-purpose stainless steel but also low-alloy steel cannot be used due to its 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。 It has been proposed so far that a specific corrosion-resistant material may be used for a member in a sulfuric acid environment. For example, Patent Document 1 discloses a sulfuric acid dew-point corrosion-resistant 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 also 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 contains 0.05% by weight or more of N (nitrogen) in an attempt to stabilize the austenite structure and ensure corrosion resistance. 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 is rather deteriorated. Further, when the N content is 0.05% by weight or more, if the Cu content is increased in order to improve the sulfuric acid corrosion resistance, the hot workability in the temperature range lower than 1000° C. remarkably decreases. 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。 Further, the austenitic stainless steel described in Patent Document 2 has excellent sulfuric acid corrosion resistance and workability. However, there is still room for improvement in sulfuric acid corrosion resistance.
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 a high concentration of 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, the "environment in which high-concentration sulfuric acid condenses" means an environment in which 40-70% concentration of sulfuric acid condenses 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 in order to solve the above problems, and has as its gist the following austenitic stainless steels.
(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% by 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 to 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: 0-5.0%,
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 that maximizes the Cr concentration of the coating 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% by mass,
V: 0.01 to 0.5%,
Nb: 0.02-1.0%,
Ti: 0.01 to 0.5%,
W: 0.1-5.0%,
Zr: 0.02-1.0%,
Al: 0.01 to 0.5%,
Ca: 0.0005-0.01%,
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 metal side with respect to 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 in which a high concentration of 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。 The present inventors have earnestly studied a method for further improving sulfuric acid corrosion resistance based on the austenitic stainless steel described in Patent Document 2, and have obtained the following findings.
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 surface of the base material in contact with high concentration sulfuric acid is important. By increasing the total content of Cr, Ni, Cu and Mo in the film relative to Fe, it becomes possible to significantly improve the acid resistance.
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-treating the steel under predetermined conditions to form an oxide film mainly composed of Fe on the surface, acid treatment is performed to preferentially dissolve the Fe component, so that the Cr content in the film is increased. , Ni, Cu and Mo have been found to be able to 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 The 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 film 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. 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, “%” regarding the content means “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 action of increasing strength. However, they combine with Cr to form Cr carbides at the grain boundaries, which lowers the intergranular corrosion resistance. Therefore, the C content is 0.05% or less. When it is necessary to increase the strength, it is preferable that the content be more than 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 need not be set in particular, but in order to obtain the above effects, 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 effect. However, when its content exceeds 1.0%, it promotes the deterioration of hot workability, and in combination with the increase of Cu content, it becomes extremely difficult to process the product on an industrial scale. Therefore, the Si content is set to 1.0% or less. The Si content is preferably 0.6% or less. The lower limit is not particularly set because Si does not necessarily have to be contained, but in order to obtain the above effects, the Si content is preferably 0.05% or more. Further, when the Al content is made extremely low for the purpose of improving hot workability, it is preferable to add 0.1% or more of Si to sufficiently perform the deoxidizing 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 a function of fixing S to improve hot workability and stabilizing an 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 Mn does not necessarily have to be contained, the lower limit is not particularly set, but 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, its content is preferably as low as possible. In particular, when the P content exceeds 0.040%, the corrosion resistance is significantly deteriorated in the environment where 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 in the steel as an impurity and deteriorates the hot workability. Therefore, the S content is preferably as low as possible. In particular, if 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 deteriorates hot workability and ductility. Therefore, its content is preferably as low as possible. In particular, when the O content exceeds 0.020%, the hot workability and ductility are significantly deteriorated, 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 conventionally been positively added for the purpose of stabilizing the austenite structure or increasing the resistance to local corrosion such as pitting or crevice corrosion. However, in an environment where a high concentration of sulfuric acid condenses, when the N content is 0.050% or more, Cu exceeding 3.5%, Mo exceeding 2.0% and 15.0% or more 20.0 %, the corrosion resistance of the austenitic stainless steel containing less than Cr will rather decrease. Further, even when the upper limits of the Cu and Mo contents are 8.0% and 5.0%, respectively, the hot workability is deteriorated when the N content is 0.050% or more. .. The N content is set to less than 0.050% in order to impart corrosion resistance and hot workability in an environment in which a high concentration of sulfuric acid is condensed to the austenitic stainless steel. The lower the N content, the better, and it 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 to 27.0%
Ni has a function of stabilizing the austenite phase and also a function of enhancing corrosion resistance in an environment where a high concentration of sulfuric acid is condensed. In order to sufficiently secure such effects, it is necessary to contain Ni in an amount of 12.0% or more. However, the effect is saturated even if the content exceeds 27.0%. Furthermore, since Ni is an expensive element, the cost is extremely high and the economy is low. Therefore, the Ni content is set to 12.0 to 27.0%. In order to secure sufficient corrosion resistance in an environment where high-concentration sulfuric acid is condensed, it is preferable to contain Ni in an amount exceeding 15.0%, and Ni in an amount exceeding 20.0%. 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. Particularly, in the austenitic stainless steel in which N is regulated to the above content, if 15.0% or more of Cr, preferably 16.0% or more of Cr is contained together with the amounts of Cu and Mo described later, a high concentration is obtained. Good corrosion resistance can be ensured in an environment where sulfuric acid condenses. However, when Cr is excessively contained, the N content is lowered, and even in the case of the austenitic stainless steel in which Cu and Mo are added together, the corrosion resistance in the environment is rather deteriorated, and the workability is further deteriorated. Also decreases. In particular, when the Cr content is 20.0% or more, deterioration of corrosion resistance of the austenitic stainless steel in the environment becomes remarkable. Further, by setting the Cr content to be less than 20.0%, the hot workability of the austenitic stainless steel to which Cu and Mo are added in combination can be improved, and product processing on an industrial scale can be facilitated. It will be possible. Therefore, the Cr content is set to 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 8.0% or less Cu is an essential element for ensuring corrosion resistance in a sulfuric acid environment. By containing more than 3.5% Cu together with the above-mentioned amount of Cr and the amount of Mo described later, it is preferable for the austenitic stainless steel containing N in the above-mentioned amount in an environment where a high concentration of sulfuric acid is condensed. Corrosion resistance can be imparted. Since the greater the content of Cu to be added together with Cu and Mo, the greater the effect of improving corrosion resistance, the Cu content is preferably set to an amount exceeding 4.0%. It should be noted that by increasing the Cu content, the corrosion resistance in the environment is improved, but the hot workability is deteriorated. Particularly, when the Cu content exceeds 8.0%, N is set to the above content. Remarkably deteriorates 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% and 5.0% or less Mo is an element effective for ensuring the corrosion resistance of austenitic stainless steel. When Mo is contained in an amount exceeding 2.0% together with the amounts of Cr and Cu described above, good corrosion resistance is imparted to the austenitic stainless steel containing N in the above amount in an environment where high-concentration sulfuric acid is condensed. can do. However, when Mo is excessively contained, hot workability is deteriorated, and particularly when the Mo content exceeds 5.0%, the hot workability is remarkably deteriorated even when N is contained in the above range. Therefore, the Mo content is more than 2.0% and 5.0% or less. In order to secure 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 element effective for increasing the toughness of steel, but it is an expensive element, so it is not necessary to add it positively. 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 in steel as an impurity and deteriorates hot workability, its content is preferably as low as possible. In particular, if the Sn content exceeds 0.05%, the hot workability is significantly deteriorated. Therefore, the Sn content is set to 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 the effect of fixing C and increasing corrosion resistance, especially intergranular corrosion resistance, so V may be contained if necessary. However, when the content exceeds 0.5%, nitrides are generated even when the content of N is set to the above-mentioned amount, and the corrosion resistance is rather deteriorated, and further the hot workability is deteriorated. Therefore, the V content is 0.5% or less. In order to obtain the above effects, the V content is preferably 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 a function of fixing C and improving corrosion resistance, especially intergranular corrosion resistance, and thus may be contained if necessary. However, if the content exceeds 1.0%, even if the content of N is set to the above-mentioned content, a nitride is generated and the corrosion resistance is rather deteriorated, and further the hot workability is deteriorated. Therefore, the Nb content is 1.0% or less. In order to obtain the above effects, 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 increasing corrosion resistance, especially intergranular corrosion resistance, so Ti may be contained if necessary. However, when the content exceeds 0.5%, nitrides are generated even when the content of N is set to the above-mentioned amount, and the corrosion resistance is rather deteriorated, and further the hot workability is deteriorated. Therefore, the Ti content is 0.5% or less. In order to obtain the above effects, the Ti content is preferably 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 a function of enhancing the corrosion resistance in an environment in which a high concentration of sulfuric acid is condensed, so W may be contained if necessary. However, if the content exceeds 5.0%, the above effects are saturated, and the cost only increases. Therefore, the W content is 5.0% or less. In order to obtain the above effects, the W content is preferably 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 a function of enhancing the corrosion resistance in an environment in which a high concentration of sulfuric acid is condensed, and thus may be contained if necessary. However, if the content exceeds 1.0%, the above effects are saturated, and the cost only increases. Therefore, the Zr content is 1.0% or less. In order to obtain the above effects, the Zr content is preferably 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, it may be contained if the Si content is to be kept extremely low. However, if the content exceeds 0.5%, the hot workability deteriorates even with austenitic stainless steel containing N in the above content. Therefore, the Al content is 0.5% or less. The lower limit of the Al content is not particularly specified and may be in the range of impurities. However, in the case of suppressing the Si content to an extremely low level, it is preferable that the Si content is positively added to contain 0.02% or more to sufficiently perform the deoxidizing action. Even when Si is contained in an amount of 0.05% or more, the Al content is preferably 0.01% or more in order to sufficiently exert the deoxidizing 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%
Ca has an effect of suppressing deterioration of hot workability by combining with S, and thus may be contained if necessary. However, if its content exceeds 0.01%, the cleanliness of the steel decreases, causing defects during hot production. Therefore, the Ca content is 0.01% or less. In order to obtain the above effects, the Ca content is preferably 0.0005% or more, 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%
B has an effect of improving hot workability, and thus may be contained if necessary. However, excessive addition of B promotes precipitation of the Cr-B compound at the grain boundaries, leading to deterioration of corrosion resistance. In particular, if the B content exceeds 0.01%, the corrosion resistance is significantly deteriorated. Therefore, the B content is 0.01% or less. In order to obtain the above effects, the B content is preferably 0.0005% or more, 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%
REM (rare earth element) has a function of enhancing hot workability, and thus may be contained if necessary. However, if its content exceeds 0.01%, the cleanliness of the steel decreases, causing defects during hot production. Therefore, the REM content is 0.01% or less. In order to obtain the above effects, the REM content is preferably 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, the "impurity" is a component that is mixed in by raw materials such as ore and scrap when manufacturing steel industrially, and various factors in the manufacturing process, and is 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 the coating As described above, the coating is formed on at least a part of the surface of the base material. Then, by increasing the total content of Cr, Ni, Cu and Mo in the film relative to Fe, it becomes possible to significantly improve the acid resistance.
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 that maximizes the Cr concentration exists in the film, and the chemical composition at the maximum Cr depth must satisfy the following formula (i). The position of the maximum Cr depth is not particularly limited and may be present in the outermost layer of the film.
(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。 The coating according to the present invention generally has a structure including a layer on the surface layer side in which Cr is relatively concentrated and a layer on the base material side in which Ni or the like is relatively concentrated. That is, the minimum Cr depth that minimizes the Cr concentration exists on the base metal side with respect to 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.
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, sulfuric acid corrosion resistance may not be sufficiently obtained. On the other hand, if the thickness of the film exceeds 10 nm, the composition of the film may be non-uniform 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 to be measured by depth analysis using X-ray photoelectric spectroscopy (XPS). By the above depth analysis, 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 equations (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。 The thickness of the film is determined from the O (oxygen) concentration profile. Specifically, the position where the concentration of O is 1/3 of the maximum concentration is determined to be the boundary between the film and the base material, and the length from the film surface to the above boundary is the film thickness. .. It is desirable to measure the composition and thickness of the film at a plurality of points and use the average value thereof.
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 There is no particular limitation on the manufacturing conditions of the austenitic stainless steel according to the present invention, for example, by subjecting the steel material having the above-described chemical composition to heat treatment and acid treatment under the conditions shown below, it is manufactured. 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>
First, the steel material is subjected to a heat treatment of holding it in the temperature range of 1060 to 1140° C. for 60 to 600 seconds. As a result, an oxide film mainly containing Fe is formed on the surface of the steel material. If the heat treatment temperature is lower than 1060°C, the formation of the Fe oxide film will be 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 decreases, so that the Fe oxide film becomes non-uniform, and film peeling easily occurs. As a result, in any of the above cases, Cr, Ni, Cu, and Mo are less likely to be concentrated.
<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 step>
An acid treatment is applied to the steel material after the heat treatment. By preferentially dissolving the Fe component in the acid treatment step, it becomes possible to concentrate Cr, Ni, Cu and Mo on the steel surface. In order to preferentially dissolve the Fe component, it is preferable to immerse it in fluorinated nitric acid at 30 to 50° C., 5 to 8 volume% HNO 3 and 5 to 8 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, but 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 (steel Nos. 1 to 11) having the chemical compositions shown in Table 1 were melted using a 3.5t VIM melting furnace, and hot forged, hot extruded and cold drawn by a usual method. A steel pipe material having an outer diameter of 75 mm and a wall thickness of 3 mm was produced. After that, the test No. Regarding 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, the test No. For No. 18, test No. After 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 film 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, the maximum Cr depth and the minimum Cr depth are specified, and then each element at that depth is determined. Was determined. Then, the above formulas (i) to (iii) were calculated from those values. In this example, the test No. In all the examples except 18, the maximum Cr depth was present in the outermost surface layer of the film, and in all the examples, the minimum Cr depth was present on the base metal side with respect to 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 of O is 1/3 of the maximum concentration is determined to be the boundary between the film and the base material, and the length from the film surface to the above boundary is defined as the film thickness. ..
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 the sulfuric acid corrosion resistance, a corrosion test was carried out in a sulfuric acid environment. The corrosion test was carried out by immersing each steel pipe in a solution having a temperature of 100° C. and a sulfuric acid concentration of 70%. Then, the corrosion weight loss after immersion for 8 hours was measured, and the corrosion rate per unit area was calculated. In the present invention, it was decided that the sulfuric acid corrosion resistance was excellent when the corrosion rate was 1.00 g/(m 2 ·h) or less.
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, the test No. whose manufacturing conditions are inappropriate. Test Nos. 1 and 2 and 14 to 17 and polished skin. In No. 18, Cr, Ni, Cu and Mo were not concentrated in the film, so that 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 is out of the regulation of the present invention. In No. 28, the acid resistance due to Cu was not obtained, and the concentration of Cr, Ni, Cu and Mo in the film was insufficient, so the sulfuric acid corrosion resistance was inferior.
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, Test No. which satisfies the requirements of the present invention and in which Cr, Ni, Cu and Mo are concentrated in the coating film. In 3 to 13 and 19 to 27, the corrosion rate was 1.00 g/(m 2 ·h) or less, and the result 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。
According to the present invention, an austenitic stainless steel having excellent acid resistance can be obtained in an environment in which a high concentration of sulfuric acid is condensed. Therefore, the austenitic stainless steel according to the present invention is used in heat exchangers used in thermal power generation or industrial boilers, flues and chimneys, and flue 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)
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、
前記皮膜の厚さが2nm以上であり、
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。 A base material and an austenitic stainless steel having a coating formed on at least a part of the surface of the base material,
The chemical composition of the base material is% by 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 to 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: 0-5.0%,
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 thickness of the film is 2 nm or more,
The chemical composition at the maximum Cr depth that maximizes the Cr concentration of the coating 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.
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% by mass,
V: 0.01 to 0.5%,
Nb: 0.02-1.0%,
Ti: 0.01 to 0.5%,
W: 0.1-5.0%,
Zr: 0.02-1.0%,
Al: 0.01 to 0.5%,
Ca: 0.0005-0.01%,
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 that minimizes the Cr concentration of the coating is present on the base metal side with respect to 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.
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Publication number | Priority date | Publication date | Assignee | Title |
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US11634804B2 (en) | 2018-02-28 | 2023-04-25 | Nippon Steel Corporation | Austenitic stainless steel weld joint |
WO2023170935A1 (en) * | 2022-03-11 | 2023-09-14 | 日本製鉄株式会社 | Austenitic stainless steel material |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
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AU580758B2 (en) * | 1984-03-16 | 1989-02-02 | Inco Alloys International Inc. | High-strength alloy for industrial vessels |
JP2774709B2 (en) | 1991-05-22 | 1998-07-09 | 日本冶金工業 株式会社 | Sulfuric acid dew point corrosion resistant stainless steel with excellent hot workability |
JP3239763B2 (en) * | 1996-07-08 | 2001-12-17 | 住友金属工業株式会社 | Austenitic stainless steel with excellent resistance to sulfuric acid corrosion |
JP2002241900A (en) * | 1997-08-13 | 2002-08-28 | Sumitomo Metal Ind Ltd | Austenitic stainless steel having excellent sulfuric acid corrosion resistance and workability |
JPH11158584A (en) * | 1997-11-27 | 1999-06-15 | Sumitomo Metal Ind Ltd | Austenitic stainless steel excellent in sulfuric acid corrosion resistance |
JPH11189848A (en) * | 1997-12-25 | 1999-07-13 | Sumitomo Metal Ind Ltd | Austenitic stainless steel excellent in sulfuric acid corrosion resistance |
JP3294282B2 (en) | 1998-08-10 | 2002-06-24 | 住友金属工業株式会社 | Austenitic stainless steel with excellent sulfuric acid corrosion resistance and workability |
JP2001107196A (en) * | 1999-10-07 | 2001-04-17 | Sumitomo Metal Ind Ltd | Austenitic steel welded joint excellent in weld cracking resistance and sulfuric acid corrosion resistance and the welding material |
JP3454216B2 (en) * | 1999-12-24 | 2003-10-06 | 住友金属工業株式会社 | Austenitic stainless steel |
JP2002121655A (en) * | 2000-10-18 | 2002-04-26 | Nippon Steel Corp | Stainless steel for crude phosphoric acid having excellent corrosion resistance |
JP2003213379A (en) * | 2002-01-21 | 2003-07-30 | Sumitomo Metal Ind Ltd | Stainless steel having excellent corrosion resistance |
EP2915893A4 (en) * | 2012-10-30 | 2016-06-01 | Kobe Steel Ltd | Austenitic stainless steel |
-
2017
- 2017-08-02 EP EP17837044.1A patent/EP3495526A4/en not_active Withdrawn
- 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 CN CN201780048557.4A patent/CN109563589B/en active Active
- 2017-08-02 JP JP2018531964A patent/JP6724991B2/en active Active
- 2017-08-02 KR KR1020197005733A patent/KR20190034286A/en not_active Application Discontinuation
- 2017-08-02 US US16/322,228 patent/US20190177808A1/en not_active Abandoned
Also Published As
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CN109563589B (en) | 2020-11-06 |
CA3032772A1 (en) | 2018-02-08 |
WO2018025942A1 (en) | 2018-02-08 |
KR20190034286A (en) | 2019-04-01 |
EP3495526A1 (en) | 2019-06-12 |
US20190177808A1 (en) | 2019-06-13 |
EP3495526A4 (en) | 2020-01-08 |
CN109563589A (en) | 2019-04-02 |
JPWO2018025942A1 (en) | 2019-06-06 |
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