JP5890330B2 - Duplex stainless steel and duplex stainless steel pipe - Google Patents
Duplex stainless steel and duplex stainless steel pipe Download PDFInfo
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- JP5890330B2 JP5890330B2 JP2013004891A JP2013004891A JP5890330B2 JP 5890330 B2 JP5890330 B2 JP 5890330B2 JP 2013004891 A JP2013004891 A JP 2013004891A JP 2013004891 A JP2013004891 A JP 2013004891A JP 5890330 B2 JP5890330 B2 JP 5890330B2
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- 229910001039 duplex stainless steel Inorganic materials 0.000 title claims description 65
- 239000000463 material Substances 0.000 claims description 69
- 229910001566 austenite Inorganic materials 0.000 claims description 25
- 229910000859 α-Fe Inorganic materials 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 12
- 229910052758 niobium Inorganic materials 0.000 claims description 10
- 229910052719 titanium Inorganic materials 0.000 claims description 10
- 239000012535 impurity Substances 0.000 claims description 8
- 229910052720 vanadium Inorganic materials 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 238000005260 corrosion Methods 0.000 description 90
- 230000007797 corrosion Effects 0.000 description 90
- 229910000831 Steel Inorganic materials 0.000 description 44
- 239000010959 steel Substances 0.000 description 44
- 230000000694 effects Effects 0.000 description 18
- 229910052804 chromium Inorganic materials 0.000 description 13
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 12
- 229910052750 molybdenum Inorganic materials 0.000 description 12
- 229910052757 nitrogen Inorganic materials 0.000 description 12
- 229910001220 stainless steel Inorganic materials 0.000 description 12
- 239000010935 stainless steel Substances 0.000 description 11
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 10
- 238000004519 manufacturing process Methods 0.000 description 10
- 239000003518 caustics Substances 0.000 description 7
- 238000000034 method Methods 0.000 description 7
- 150000004767 nitrides Chemical class 0.000 description 7
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- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- 229910002092 carbon dioxide Inorganic materials 0.000 description 6
- 239000001569 carbon dioxide Substances 0.000 description 6
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- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 6
- 230000001965 increasing effect Effects 0.000 description 6
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- 238000012545 processing Methods 0.000 description 4
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- 229910052715 tantalum Inorganic materials 0.000 description 4
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
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- 229910000765 intermetallic Inorganic materials 0.000 description 3
- 229910052748 manganese Inorganic materials 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
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- FAPWRFPIFSIZLT-UHFFFAOYSA-M sodium chloride Inorganic materials [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
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- 229910052717 sulfur Inorganic materials 0.000 description 3
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- 239000007864 aqueous solution Substances 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000006378 damage Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
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- 229910052726 zirconium Inorganic materials 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
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- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical class Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 description 1
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- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- VLAPMBHFAWRUQP-UHFFFAOYSA-L molybdic acid Chemical compound O[Mo](O)(=O)=O VLAPMBHFAWRUQP-UHFFFAOYSA-L 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
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Description
本発明は、塩化物、硫化水素、炭酸ガス等の腐食性物質を含有する環境（以下、腐食環境と称することがある）において使用される二相ステンレス鋼材および二相ステンレス鋼管に関するものである。 The present invention relates to a duplex stainless steel material and a duplex stainless steel pipe used in an environment containing a corrosive substance such as chloride, hydrogen sulfide, carbon dioxide gas (hereinafter sometimes referred to as a corrosive environment).
ステンレス鋼材は、腐食環境において不働態皮膜と呼ばれるＣｒの酸化物を主体とする安定な表面皮膜を自然に形成し、耐食性を発現する材料である。特に、フェライト相とオーステナイト相からなる二相ステンレス鋼材は、強度特性がオーステナイト系ステンレス鋼やフェライト系ステンレス鋼に対して優れ、耐孔食性と耐応力腐食割れ性が良好である。このような特徴のため、二相ステンレス鋼材は、アンビリカル、海水淡水化プラント、ＬＮＧ気化器等の海水環境の構造材料をはじめとして、油井管や各種化学プラント等の腐食性が厳しい環境の構造材料として使用されている。 Stainless steel is a material that naturally forms a stable surface film mainly composed of a Cr oxide called a passive film in a corrosive environment and exhibits corrosion resistance. In particular, a duplex stainless steel material composed of a ferrite phase and an austenite phase is superior in strength characteristics to austenitic stainless steel and ferritic stainless steel, and has good pitting corrosion resistance and stress corrosion cracking resistance. Due to these characteristics, duplex stainless steel materials are used for structural materials in highly corrosive environments such as oil well pipes and various chemical plants, including structural materials for seawater environments such as umbilicals, seawater desalination plants, and LNG vaporizers. It is used as
しかしながら、使用環境に塩化物（塩化物イオン）等の腐食性物質が多量に含有される場合には、二相ステンレス鋼材中の介在物や不働態皮膜の欠陥等を起点として、二相ステンレス鋼材に局部腐食いわゆる孔食が発生する場合がある。また、二相ステンレス鋼材のすきま部分においては、すきま内部では塩化物イオン等の腐食性物質が濃縮してより厳しい腐食環境となり、さらにすきま外部と内部との間で酸素濃淡電池を形成して、すきま内部の局部腐食がより促進され、いわゆるすきま腐食が発生する場合がある。さらに、孔食やすきま腐食等の局部腐食は、応力腐食割れ（ＳＣＣ）の起点となる場合が多く、安全性の観点から耐食性、特に耐局部腐食特性のさらなる向上が求められている。 However, if the usage environment contains a large amount of corrosive substances such as chloride (chloride ions), the duplex stainless steel material starts from inclusions in the duplex stainless steel material or defects in the passive film. In some cases, so-called pitting corrosion may occur. In addition, in the gap portion of duplex stainless steel material, corrosive substances such as chloride ions are concentrated inside the gap, resulting in a more severe corrosive environment, and an oxygen concentration cell is formed between the outside and inside of the gap, Local corrosion inside the crevice is further promoted, and so-called crevice corrosion may occur. Furthermore, local corrosion such as pitting corrosion and crevice corrosion often becomes the starting point of stress corrosion cracking (SCC), and further improvement in corrosion resistance, particularly local corrosion resistance, is required from the viewpoint of safety.
特に、石油や天然ガスの掘削に用いられる油井管材料においては、近年、より深層の油井やガス井の開発が進められており、従来よりも高温で、かつ、硫化水素、炭酸ガス、塩化物等の腐食性物質を多量に含む環境に曝される場合が多くなっているため、従来よりもさらに優れた耐食性が要求されている。 In particular, in oil well pipe materials used for oil and natural gas drilling, development of deeper oil wells and gas wells has been progressing in recent years, and at higher temperatures than conventional ones, hydrogen sulfide, carbon dioxide, chlorides. Since there are many cases where it is exposed to an environment containing a large amount of corrosive substances such as the above, further superior corrosion resistance is required.
ステンレス鋼の耐孔食性は、Ｃｒ量（質量％）を［Ｃｒ］、Ｍｏ量（質量％）を［Ｍｏ］、Ｗ量（質量％）を［Ｗ］、Ｎ量（質量％）を［Ｎ］とした際、［Ｃｒ］＋３．３［Ｍｏ］＋１６［Ｎ］で計算される孔食指数ＰＲＥ（Pitting Resistance Equivalent）や、Ｗを含む場合は［Ｃ］＋３．３（［Ｍｏ］＋０．５［Ｗ］）＋１６［Ｎ］で計算されるＰＲＥＷで表され、Ｃｒ、Ｍｏ、Ｎの含有量を多くすれば優れた耐孔食性が得られることが知られている。通常の二相ステンレス鋼ではＰＲＥ（またはＰＲＥＷ）を３５以上となるように、さらにスーパー二相ステンレス鋼では４０以上になるようにＣｒ、Ｍｏ、Ｎ、Ｗ添加量が調整されている。また、Ｃｒ、Ｍｏ、Ｎの含有量の増加は、耐すきま腐食性の向上にも寄与することが知られている。 The pitting corrosion resistance of stainless steel is as follows: Cr amount (% by mass) is [Cr], Mo amount (% by mass) is [Mo], W amount (% by mass) is [W], and N amount (% by mass) is [N]. ], A pitting corrosion index PRE (Pitting Resistance Equivalent) calculated by [Cr] +3.3 [Mo] +16 [N], or [C] +3.3 ([Mo] +0. 5 [W]) + 16 [N]. It is known that if the content of Cr, Mo, N is increased, excellent pitting corrosion resistance can be obtained. The addition amounts of Cr, Mo, N, and W are adjusted so that PRE (or PREW) is 35 or more in normal duplex stainless steel, and 40 or more in super duplex stainless steel. Further, it is known that an increase in the content of Cr, Mo, and N contributes to an improvement in crevice corrosion resistance.
例えば、特許文献１には、Ｃｒ、Ｍｏ、Ｎ、Ｗの含有量の制御によりＰＲＥＷが４０以上である耐食性に優れる二相ステンレス鋼が開示されている。また、特許文献２には、Ｃｒ、Ｍｏ、Ｗ、Ｎの含有量の制御に加え、ＢやＴａの含有量を制御し、耐食性および熱間加工性に優れる二相ステンレス鋼が開示されている。特許文献３には、Ｃｒ、Ｍｏ、Ｗ、Ｎの含有量の制御に加え、Ｔｉ、Ｖ、Ｎｂ、Ｔａ、Ｚｒ、Ｂ等の含有量を制御し、耐食性および熱間加工性に優れる二相ステンレス鋼が開示されている。 For example, Patent Document 1 discloses a duplex stainless steel excellent in corrosion resistance having a PREW of 40 or more by controlling the contents of Cr, Mo, N, and W. Patent Document 2 discloses a duplex stainless steel that controls the contents of B and Ta in addition to controlling the contents of Cr, Mo, W, and N, and is excellent in corrosion resistance and hot workability. . In Patent Document 3, in addition to controlling the contents of Cr, Mo, W, and N, the contents of Ti, V, Nb, Ta, Zr, and B are controlled, and two phases that are excellent in corrosion resistance and hot workability Stainless steel is disclosed.
二相ステンレス鋼材は、強度特性に優れる反面、圧延や引抜等の加工が通常のステンレス鋼材よりも難しい場合が多い。また硫化水素や炭酸ガス、塩化物イオンを含む厳しい腐食環境で二相ステンレス鋼材を適用するには、耐食性の向上が必要である。しかしながらＣｒ、Ｍｏ、Ｎ、およびＷの含有量の調整だけでは耐食性の改善が不十分な場合がある。さらに耐食性向上目的で添加するＣｒ、Ｍｏの増加によりσ相析出が助長されるため、靱性や加工性を劣化させる懸念がある。 The duplex stainless steel material is excellent in strength characteristics, but on the other hand, processing such as rolling and drawing is often more difficult than ordinary stainless steel material. Further, in order to apply the duplex stainless steel material in a severe corrosive environment containing hydrogen sulfide, carbon dioxide gas, and chloride ions, it is necessary to improve the corrosion resistance. However, the improvement of corrosion resistance may be insufficient only by adjusting the contents of Cr, Mo, N, and W. Furthermore, since sigma phase precipitation is promoted by an increase in Cr and Mo added for the purpose of improving corrosion resistance, there is a concern that toughness and workability are deteriorated.
そして、特許文献１では、鋼材の耐食性（耐孔食性）を８０℃、２０％−ＮａＣｌ中での孔食電位で評価しているが、ＰＲＥＷ＝４２程度では約３００ｍＶ程度であり、昨今求められる厳しい腐食環境においては、必ずしも十分な耐食性を確保できるとは言えない。 And in patent document 1, although the corrosion resistance (pitting corrosion resistance) of steel materials is evaluated by the pitting corrosion potential in 80 degreeC and 20% -NaCl, when PREW = 42, it is about 300 mV and is calculated | required these days. In a severe corrosive environment, it cannot always be said that sufficient corrosion resistance can be secured.
また、特許文献２では、鋼中にＢを添加しているが、Ｂは鋼中のＮと結合してＢＮを生成することで、耐食性に寄与するＮ濃度を低下させてしまうおそれがある。また、特許文献２では、Ｗ添加量が５〜１０質量％と高く、コスト上昇を招いて経済的に不利である。 Moreover, in patent document 2, although B is added in steel, there exists a possibility that B may combine with N in steel and produces | generates BN, and may reduce N density | concentration which contributes to corrosion resistance. Moreover, in patent document 2, W addition amount is as high as 5-10 mass%, and raises cost, and is economically disadvantageous.
また、特許文献３では、鋼中にＮｂ、Ｔｉ、Ｚｒを添加しているが、これらの元素は鋼中のＮと結合して窒化物を生成することで、耐食性に寄与するＮ濃度を低下させてしまうおそれがある。また、生成した窒化物が粗大である場合、靱性を低下させてしまう。 In Patent Document 3, Nb, Ti, and Zr are added to the steel, but these elements combine with N in the steel to form nitrides, thereby reducing the N concentration that contributes to corrosion resistance. There is a risk of letting you. Moreover, when the produced | generated nitride is coarse, toughness will be reduced.
本発明は、このような状況に鑑みてなされたものであり、その課題は、塩化物、硫化水素、炭酸ガス等の腐食性物質を含有する環境において良好な耐食性を発現すると共に、良好な熱間加工性を発現する二相ステンレス鋼材、および、良好な耐食性を発現する二相ステンレス鋼管を提供することにある。 The present invention has been made in view of such a situation, and the problem is that it exhibits good corrosion resistance in an environment containing corrosive substances such as chloride, hydrogen sulfide, carbon dioxide gas, and has good heat resistance. An object of the present invention is to provide a duplex stainless steel material that exhibits inter-workability and a duplex stainless steel tube that exhibits good corrosion resistance.
前記のようにステンレス鋼材は、Ｃｒの酸化物を主体とする不働態皮膜により耐食性を発現する材料である。二相ステンレス鋼材は一般的にフェライト相とオーステナイト相から構成されているため、これら異相界面で不連続性を有しており、フェライト相とオーステナイト相との界面においては不働態皮膜が不安定になる傾向が強いため、塩化物イオンの不働態皮膜破壊作用を受けやすく、局部腐食が発生しやすくなる。本発明者らは、前記課題を解決するために製造面や諸特性を害さない範囲において、二相ステンレス鋼材の不働態皮膜の安定性および保護性を強化することに着目し、耐食性を向上させる技術検討を行った。 As described above, a stainless steel material is a material that exhibits corrosion resistance by a passive film mainly composed of Cr oxide. Since duplex stainless steel is generally composed of a ferrite phase and an austenite phase, it has discontinuities at the interface between these different phases, and the passive film becomes unstable at the interface between the ferrite phase and the austenite phase. Therefore, it tends to be affected by the passive film destruction action of chloride ions, and local corrosion tends to occur. In order to solve the above-mentioned problems, the inventors pay attention to enhancing the stability and protective property of the passive film of the duplex stainless steel material within a range that does not impair the manufacturing surface and various characteristics, and improve the corrosion resistance. Technical study was conducted.
前記のようにステンレス鋼材はＣｒの酸化物を主体とする不動態皮膜により耐食性を発現する材料であることから、本発明者らは鋼中のＣｒ実効濃度向上の観点から検討を行った。その結果、鋼中に不要なＣｒ系介在物が形成することで鋼中の実効Ｃｒ濃度が低下してしまうため、不要なＣｒ系介在物の析出を抑制する方法が有効であることを見出した。 As described above, since the stainless steel material is a material that exhibits corrosion resistance by a passive film mainly composed of Cr oxide, the present inventors have studied from the viewpoint of improving the effective Cr concentration in the steel. As a result, the formation of unnecessary Cr inclusions in the steel results in a decrease in the effective Cr concentration in the steel, and it has been found that a method for suppressing the precipitation of unnecessary Cr inclusions is effective. .
一般的にステンレス鋼材における介在物として炭化物や酸化物があげられるため、これら介在物の形成原因となる鋼中のＣやＯを他の元素で固定することが重要である。ここで、Ｏについては脱酸のために添加したＳｉやＡｌ、または、ＣａやＭｇによる固定が可能であるため、特に鋼中の不要なＣを固定する観点から検討を行った。さらに、前記のようにステンレス鋼材の耐孔食性はＮ量（[Ｎ]）を含む孔食指数ＰＲＥ（Ｗ）で表されることから、鋼中の実効Ｎ濃度も耐食性の向上に影響を与えるため、不要なＮ系介在物の析出を抑制する観点からも検討を行った。 Since carbides and oxides are generally included as inclusions in stainless steel materials, it is important to fix C and O in the steel that causes these inclusions to be formed by other elements. Here, O can be fixed with Si or Al added for deoxidation, or Ca or Mg, and therefore, examination was performed from the viewpoint of fixing unnecessary C in steel. Further, as described above, the pitting corrosion resistance of the stainless steel material is expressed by the pitting corrosion index PRE (W) including the N amount ([N]), so the effective N concentration in the steel also affects the improvement of the corrosion resistance. Therefore, examination was also performed from the viewpoint of suppressing the precipitation of unnecessary N-based inclusions.
そして、鋼中での不要なＣの固定能が高く、さらに耐食性の確保に必要なＮを固定しにくい元素としてＴａを適度に添加することで、鋼中のＣｒおよびＮの実効濃度を高めることができ、結果として不動態皮膜の安定性が高まり、耐食性が向上することを見出した。 And, the effective concentration of Cr and N in steel is increased by moderately adding Ta as an element that has a high ability to fix unnecessary C in steel and that is difficult to fix N necessary for ensuring corrosion resistance. As a result, it has been found that the stability of the passive film is increased and the corrosion resistance is improved.
本発明に係る二相ステンレス鋼材は、フェライト相とオーステナイト相とからなる二相ステンレス鋼材であって、前記二相ステンレス鋼材の成分組成は、Ｃ：０．１００％質量以下、Ｓｉ：０．１０〜２．００質量％、Ｍｎ：０．１０〜２．００質量％、Ｐ：０．０５０質量％以下、Ｓ：０．０１００質量％以下、Ａｌ：０．０１０〜０．０５０質量％、Ｎｉ：１．０〜１０．０質量％、Ｃｒ：２２．０〜２８．０質量％、Ｍｏ：２．０〜６．０質量％、Ｎ：０．２０〜０．５０質量％、Ｔａ：０．０１〜０．５０質量％であって、残部がＦｅおよび不可避的不純物からなることを特徴とする。 The duplex stainless steel material according to the present invention is a duplex stainless steel material composed of a ferrite phase and an austenite phase. The component composition of the duplex stainless steel material is C: 0.100% by mass or less, Si: 0.10 To 2.00% by mass, Mn: 0.10 to 2.00% by mass, P: 0.050% by mass or less, S: 0.0100% by mass or less, Al: 0.010 to 0.050% by mass, Ni : 1.0 to 10.0% by mass, Cr: 22.0 to 28.0% by mass, Mo: 2.0 to 6.0% by mass, N: 0.20 to 0.50% by mass, Ta: 0 0.01 to 0.50 mass%, with the balance being Fe and inevitable impurities.
前記のように、二相ステンレス鋼材は、所定量のＣ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｎｉ、Ｃｒ、Ｍｏ、Ｎ、Ｔａを含有することによって、耐食性が向上すると共に、熱間加工性の低下が抑制される。 As described above, the duplex stainless steel material contains a predetermined amount of C, Si, Mn, P, S, Al, Ni, Cr, Mo, N, and Ta, thereby improving corrosion resistance and hot working. The decline in sex is suppressed.
また、本発明に係る二相ステンレス鋼材は、前記成分組成が、さらにＣｏ：０．１０〜２．００質量％、Ｃｕ：０．１０〜２．００質量％、Ｖ：０．０１〜０．５０質量％、Ｔｉ：０．０１〜０．５０質量％、Ｎｂ：０．０１〜０．５０質量％よりなる群から選ばれる１種以上を含有することが好ましい。 In the duplex stainless steel material according to the present invention, the component composition further includes Co: 0.10 to 2.00% by mass, Cu: 0.10 to 2.00% by mass, and V: 0.01 to 0.00. It is preferable to contain 1 or more types chosen from the group which consists of 50 mass%, Ti: 0.01-0.50 mass%, Nb: 0.01-0.50 mass%.
前記のように、二相ステンレス鋼材は、所定量のＣｏ、Ｃｕ、Ｖ、Ｔｉ、Ｎｂよりなる群から選ばれる１種以上をさらに含有することによって、耐食性がさらに向上する。また、Ｃｏ、Ｃｕはオーステナイト相の安定化にも寄与し、Ｖ、Ｔｉ、Ｎｂは強度特性や熱間加工性の向上にも寄与する。 As described above, the duplex stainless steel material further improves corrosion resistance by further containing at least one selected from the group consisting of Co, Cu, V, Ti, and Nb in a predetermined amount. Further, Co and Cu contribute to stabilization of the austenite phase, and V, Ti and Nb contribute to improvement of strength characteristics and hot workability.
また、本発明に係る二相ステンレス鋼材は、前記成分組成が、さらにＭｇ：０．０００５〜０．０２００質量％、Ｃａ：０．０００５〜０．０２００質量％、の１種または２種を含有することが好ましい。 Further, the duplex stainless steel material according to the present invention further includes one or two of the above component compositions of Mg: 0.0005 to 0.0200 mass%, Ca: 0.0005 to 0.0200 mass%. It is preferable to do.
前記のように、二相ステンレス鋼材は、所定量のＭｇ、Ｃａの１種または２種をさらに含有することによって、局部腐食の起点となりやすい不動態皮膜欠損箇所となるような粗大なＭｎＳ等の介在物の生成が抑制され、耐局部腐食性が向上する。また、粗大なＭｎＳ等の介在物の生成が抑制されることで熱間加工性が向上する。 As described above, the duplex stainless steel material further contains a predetermined amount of Mg, Ca, or two kinds of coarse MnS or the like which becomes a passive film deficient portion that tends to start local corrosion. Formation of inclusions is suppressed and local corrosion resistance is improved. Moreover, hot workability improves by the production | generation of inclusions, such as coarse MnS, being suppressed.
さらに、本発明に係る二相ステンレス鋼管は、前記の二相ステンレス鋼材からなることを特徴とする。
前記のように、二相ステンレス鋼管は、鋼管を二相ステンレス鋼材で構成することによって、鋼管表面に形成される不働態皮膜の安定性が高まるため、局部腐食を大幅に抑制でき、耐食性が向上する。
Furthermore, the duplex stainless steel pipe according to the present invention is characterized by comprising the duplex stainless steel material described above.
As mentioned above, the duplex stainless steel pipe is made of a duplex stainless steel material, which increases the stability of the passive film formed on the surface of the steel pipe, so that local corrosion can be greatly suppressed and corrosion resistance is improved. To do.
本発明の二相ステンレス鋼材によれば、塩化物、硫化水素、炭酸ガス等の腐食性物質を含有する環境において良好な耐食性を発現すると共に、良好な熱間加工性を発現する。また、本発明の二相ステンレス鋼管によれば、塩化物、硫化水素、炭酸ガス等の腐食性物質を含有する環境において良好な耐食性を発現する。その結果、二相ステンレス鋼管は、アンビリカル、海水淡水化プラント、ＬＮＧ気化器等の海水環境の構造材料をはじめとして、油井管や各種化学プラント等の腐食性が厳しい環境の構造材料への使用が可能となる。 According to the duplex stainless steel material of the present invention, it exhibits good corrosion resistance and good hot workability in an environment containing corrosive substances such as chloride, hydrogen sulfide, and carbon dioxide. Moreover, according to the duplex stainless steel pipe of the present invention, good corrosion resistance is exhibited in an environment containing a corrosive substance such as chloride, hydrogen sulfide, carbon dioxide. As a result, duplex stainless steel pipes can be used not only for structural materials in seawater environments such as umbilicals, seawater desalination plants, and LNG vaporizers, but also for structural materials in highly corrosive environments such as oil well pipes and various chemical plants. It becomes possible.
＜二相ステンレス鋼材＞
本発明に係る二相ステンレス鋼材の実施形態について詳細に説明する。
本発明の二相ステンレス鋼材は、フェライト相とオーステナイト相とからなる二相ステンレス鋼材であって、前記二相ステンレス鋼材の成分組成は、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｎｉ、Ｃｒ、Ｍｏ、Ｎ、Ｔａを所定量含有し、残部がＦｅおよび不可避的不純物からなる。以下、各構成について説明する。
<Duplex stainless steel>
An embodiment of the duplex stainless steel material according to the present invention will be described in detail.
The duplex stainless steel material of the present invention is a duplex stainless steel material composed of a ferrite phase and an austenite phase, and the component composition of the duplex stainless steel material is C, Si, Mn, P, S, Al, Ni, Cr , Mo, N, and Ta are contained in a predetermined amount, with the balance being Fe and inevitable impurities. Each configuration will be described below.
（鋼材組織）
本発明の二相ステンレス鋼材は、フェライト相とオーステナイト相の二相からなるものである。フェライト相とオーステナイト相からなる二相ステンレス鋼材においては、ＣｒやＭｏ等のフェライト相安定化元素はフェライト相に濃縮し、ＮｉやＮ等のオーステナイト相安定化元素はオーステナイト相に濃縮する傾向にある。このとき、フェライト相のオーステナイト相に対する面積比が３０％未満または７０％を超える場合には、Ｃｒ、Ｍｏ、Ｎｉ、Ｎ等の耐食性に寄与する元素のフェライト相とオーステナイト相における濃度差異が大きくなりすぎて、フェライト相とオーステナイト相のいずれか耐食性に劣る側が選択腐食されて耐食性が劣化する傾向が大きくなる。したがって、フェライト相とオーステナイト相との面積比も最適化することが推奨され、フェライト相の面積比は、耐食性の観点から３０〜７０％が好ましく、４０〜６０％がさらに好ましい。このようなフェライト相とオーステナイト相の面積比は、フェライト相安定化元素とオーステナイト相安定化元素の含有量を調整することによって適正化することが可能である。
(Steel structure)
The duplex stainless steel material of the present invention is composed of two phases of a ferrite phase and an austenite phase. In a duplex stainless steel material composed of a ferrite phase and an austenite phase, ferrite phase stabilizing elements such as Cr and Mo tend to concentrate in the ferrite phase, and austenite phase stabilizing elements such as Ni and N tend to concentrate in the austenite phase. . At this time, when the area ratio of the ferrite phase to the austenite phase is less than 30% or more than 70%, the concentration difference between the ferrite phase and the austenite phase of elements contributing to the corrosion resistance such as Cr, Mo, Ni, and N becomes large. Too much, either the ferrite phase or the austenite phase, which is inferior in corrosion resistance, is selectively corroded, and the tendency of the corrosion resistance to deteriorate increases. Therefore, it is recommended that the area ratio between the ferrite phase and the austenite phase is also optimized, and the area ratio of the ferrite phase is preferably 30 to 70% and more preferably 40 to 60% from the viewpoint of corrosion resistance. Such an area ratio between the ferrite phase and the austenite phase can be optimized by adjusting the contents of the ferrite phase stabilizing element and the austenite phase stabilizing element.
また、本発明の二相ステンレス鋼材は、フェライト相とオーステナイト相以外にσ相やＣｒの炭窒化物等の異相も耐食性や機械特性等の諸特性を害さない程度に許容できる。フェライト相とオーステナイト相との面積の合計は、９５％以上とすることが好ましく、９７％以上とすることがさらに好ましい。 In addition, the duplex stainless steel material of the present invention can tolerate other phases such as the σ phase and Cr carbonitride in addition to the ferrite phase and austenite phase to such an extent that the corrosion resistance and mechanical properties are not impaired. The total area of the ferrite phase and the austenite phase is preferably 95% or more, and more preferably 97% or more.
二相ステンレス鋼材の成分組成の数値範囲の限定理由について説明する。
（Ｃ：０．１００質量％以下）
Ｃは、鋼材中でＣｒ等との炭化物を形成して耐食性および熱間加工性を低下させるため、有害な元素である。そのため、Ｃ含有量は０．１００質量％以下とする。なお、Ｃ含有量はできる限り少ない方が良いため、好ましくは０．０８０質量％以下、より好ましくは０．０６０質量％以下である。なお、Ｃは、鋼材中に含有されていない、すなわち、０質量％であっても良い。
The reason for limiting the numerical range of the component composition of the duplex stainless steel material will be described.
(C: 0.100 mass% or less)
C is a harmful element because it forms a carbide with Cr or the like in the steel material to lower the corrosion resistance and hot workability. Therefore, the C content is 0.100% by mass or less. In addition, since it is better that the C content is as small as possible, it is preferably 0.080% by mass or less, more preferably 0.060% by mass or less. Note that C may not be contained in the steel material, that is, 0% by mass.
（Ｓｉ：０．１０〜２．００質量％）
Ｓｉは、脱酸とフェライト相の安定化のために必要な元素である。このような効果を得るため、Ｓｉ含有量は０．１０質量％以上とする。しかし、過剰にＳｉを含有させると熱間加工性が劣化することから、Ｓｉ含有量は２．００質量％以下とする。Ｓｉ含有量の好ましい下限値は０．１５質量％であり、さらに好ましくは０．２０質量％である。また、Ｓｉ含有量の好ましい上限値は１．５０質量％であり、さらに好ましい上限値は１．００質量％である。
(Si: 0.10 to 2.00% by mass)
Si is an element necessary for deoxidation and stabilization of the ferrite phase. In order to acquire such an effect, Si content shall be 0.10 mass% or more. However, if Si is excessively contained, hot workability deteriorates, so the Si content is 2.00% by mass or less. The preferable lower limit of the Si content is 0.15% by mass, and more preferably 0.20% by mass. Moreover, the upper limit with preferable Si content is 1.50 mass%, and a more preferable upper limit is 1.00 mass%.
（Ｍｎ：０．１０〜２．００質量％）
Ｍｎは、Ｓｉと同様に脱酸効果があり、さらに強度確保のために必要な元素である。このような効果を得るため、Ｍｎ含有量は０．１０質量％以上とする。しかし、過剰にＭｎを含有させると粗大なＭｎＳを形成して耐食性および熱間加工性が劣化することから、Ｍｎ含有量は２．００質量％以下とする。Ｍｎ含有量の好ましい下限値は０．１５質量％であり、さらに好ましくは０．２０質量％である。また、Ｍｎ含有量の好ましい上限値は１．５０質量％であり、さらに好ましくは１．００質量％である。
(Mn: 0.10 to 2.00% by mass)
Mn has a deoxidizing effect like Si, and is an element necessary for ensuring strength. In order to acquire such an effect, Mn content shall be 0.10 mass% or more. However, if Mn is excessively contained, coarse MnS is formed and the corrosion resistance and hot workability deteriorate, so the Mn content is 2.00% by mass or less. The lower limit with preferable Mn content is 0.15 mass%, More preferably, it is 0.20 mass%. Moreover, the upper limit with preferable Mn content is 1.50 mass%, More preferably, it is 1.00 mass%.
（Ｐ：０．０５０質量％以下）
Ｐは、溶製時に混入する不純物であり、耐食性に有害な元素であり、また溶接性や加工性も劣化させる元素である。そのため、Ｐ含有量は０．０５０質量％以下とする。なお、Ｐ含有量はできる限り少ない方が良いため、好ましくは０．０４０質量％以下であり、さらに好ましくは０．０３０質量％以下である。また、Ｐは、鋼材中に含有されていない、すなわち、０質量％であって良いが、Ｐ含有量の過度の低減は、製造コストの上昇をもたらすので、Ｐ含有量の実操業上の下限値は０．０１０質量％である。
(P: 0.050 mass% or less)
P is an impurity mixed during melting, an element harmful to corrosion resistance, and an element that deteriorates weldability and workability. Therefore, the P content is 0.050 mass% or less. In addition, since it is better that the P content is as small as possible, it is preferably 0.040% by mass or less, and more preferably 0.030% by mass or less. Further, P may not be contained in the steel material, that is, it may be 0% by mass. However, excessive reduction of the P content causes an increase in production cost, so the lower limit of P content in actual operation. The value is 0.010% by mass.
（Ｓ：０．０１００質量％以下）
Ｓは、Ｐと同様に溶製時に混入する不純物であり、Ｍｎ等と結合して硫化物系介在物を形成して、耐食性や熱間加工性を劣化させる元素である。そのため、Ｓ含有量は０．０１００質量％以下とする。なお、Ｓ含有量はできる限り少ない方が良いため、好ましくは０．００３０質量％以下である。
(S: 0.0100 mass% or less)
S, like P, is an impurity mixed during melting, and is an element that combines with Mn or the like to form sulfide inclusions and degrades corrosion resistance and hot workability. Therefore, the S content is 0.0100% by mass or less. Since the S content is preferably as small as possible, it is preferably 0.0030% by mass or less.
（Ａｌ：０．０１０〜０．０５０質量％）
Ａｌは、Ｓｉ、Ｍｎと同様に脱酸の効果があり、溶製時の酸素量低減に必要な元素である。このような効果を得るため、Ａｌ含有量は０．０１０質量％以上とする。しかし、過剰にＡｌを含有させると酸化物系介在物を生成し耐孔食性に悪影響を及ぼすことから、Ａｌ含有量は０．０５０質量％以下とする。Ａｌ含有量の好ましい範囲は０．０１０〜０．０２０質量％である。
(Al: 0.010-0.050 mass%)
Al, like Si and Mn, has an effect of deoxidation, and is an element necessary for reducing the amount of oxygen during melting. In order to acquire such an effect, Al content shall be 0.010 mass% or more. However, if Al is excessively contained, oxide inclusions are generated and the pitting corrosion resistance is adversely affected. Therefore, the Al content is set to 0.050% by mass or less. A preferable range of the Al content is 0.010 to 0.020% by mass.
（Ｎｉ：１．０〜１０．０質量％）
Ｎｉは、耐食性向上に必要な元素であり、特に、塩化物環境における局部腐食抑制に効果が大きい。また、Ｎｉは、低温靱性を向上させるのにも有効であり、さらにオーステナイト相を安定化させるためにも必要な元素である。こうした効果を得るため、Ｎｉ含有量は１．０質量％以上とする。しかし、過剰にＮｉを含有させると、オーステナイト相が多くなりすぎて強度が低下すること、金属間化合物（σ相）が生成しやすくなり熱間加工性を劣化させることから、Ｎｉ含有量は１０．０質量％以下とする。Ｎｉ含有量の好ましい下限値は２．０質量％であり、さらに好ましくは３．０質量％である。また、Ｎｉ含有量の好ましい上限値は９．５質量％であり、さらに好ましくは９．０質量％である。
(Ni: 1.0-10.0 mass%)
Ni is an element necessary for improving corrosion resistance, and is particularly effective for suppressing local corrosion in a chloride environment. Ni is also an element that is effective for improving low-temperature toughness and is also necessary for stabilizing the austenite phase. In order to acquire such an effect, Ni content shall be 1.0 mass% or more. However, if Ni is excessively contained, the austenite phase is excessively increased and the strength is lowered, and an intermetallic compound (σ phase) is easily generated and hot workability is deteriorated. 0.0 mass% or less. The lower limit with preferable Ni content is 2.0 mass%, More preferably, it is 3.0 mass%. Moreover, the upper limit with preferable Ni content is 9.5 mass%, More preferably, it is 9.0 mass%.
（Ｃｒ：２２．０〜２８．０質量％）
Ｃｒは、不働態皮膜の主要成分であり、ステンレス鋼材の耐食性発現の基本元素である。また、Ｃｒは、フェライト相を安定化させる元素でもある。フェライト相とオーステナイト相の二相組織を維持して耐食性、強度を両立させるため、Ｃｒ含有量は２２．０質量％以上とする。しかし、過剰にＣｒを含有させると金属間化合物（σ相）が生成しやすくなり熱間加工性を劣化させることから、Ｃｒ含有量は２８．０質量％以下とする。Ｃｒ含有量の好ましい下限値は２３．０質量％であり、さらに好ましくは２４．０質量％である。また、Ｃｒ含有量の好ましい上限値は２７．５質量％であり、さらに好ましくは２７．０質量％である。
(Cr: 22.0-28.0 mass%)
Cr is a main component of the passive film, and is a basic element for developing the corrosion resistance of the stainless steel material. Cr is also an element that stabilizes the ferrite phase. In order to maintain the two-phase structure of the ferrite phase and the austenite phase to achieve both corrosion resistance and strength, the Cr content is set to 22.0% by mass or more. However, when Cr is excessively contained, an intermetallic compound (σ phase) is easily generated and hot workability is deteriorated, so the Cr content is set to 28.0% by mass or less. The lower limit with preferable Cr content is 23.0 mass%, More preferably, it is 24.0 mass%. Moreover, the upper limit with preferable Cr content is 27.5 mass%, More preferably, it is 27.0 mass%.
（Ｍｏ：２．０〜６．０質量％）
Ｍｏは、溶解時にモリブデン酸を生成して、インヒビター作用により耐局部腐食性を向上させる効果を発揮し、耐食性を向上させる元素である。また、Ｍｏは、フェライト相を安定化させる元素でもあり、鋼材の耐孔食性・耐割れ性を改善させる元素でもある。このような効果を得るため、Ｍｏ含有量は２．０質量％以上とする。しかし、過剰にＭｏを含有させるとσ相等の金属間化合物の生成を助長し、耐食性および熱間加工性を劣化させることから、Ｍｏ含有量は６．０質量％以下とする。Ｍｏ含有量の好ましい下限値は２．２質量％であり、さらに好ましくは２．５質量％である。また、Ｍｏ含有量の好ましい上限値は５．５質量％であり、さらに好ましくは５．０質量％である。
(Mo: 2.0 to 6.0 mass%)
Mo is an element that generates molybdic acid at the time of dissolution and exhibits an effect of improving local corrosion resistance by an inhibitor action, thereby improving the corrosion resistance. Mo is also an element that stabilizes the ferrite phase and is an element that improves the pitting corrosion resistance and crack resistance of the steel material. In order to acquire such an effect, Mo content shall be 2.0 mass% or more. However, if Mo is excessively contained, the formation of intermetallic compounds such as the σ phase is promoted, and the corrosion resistance and hot workability are deteriorated. Therefore, the Mo content is set to 6.0% by mass or less. The lower limit with preferable Mo content is 2.2 mass%, More preferably, it is 2.5 mass%. Moreover, the upper limit with preferable Mo content is 5.5 mass%, More preferably, it is 5.0 mass%.
（Ｎ：０．２０〜０．５０質量％）
Ｎは、強力なオーステナイト相を安定化させる元素であり、σ相の生成感受性を増加させずに耐食性を向上させる効果があり、さらに鋼材の高強度化にも有効な元素でもある。このような効果を得るため、Ｎ含有量は０．２０質量％以上とする。しかし、過剰にＮを含有させると窒化物が形成され靭性や耐食性が低下すると共に、熱間加工性を劣化させ、鍛造・圧延時に耳割れや表面欠陥を生じさせることから、Ｎ含有量は０．５０質量％以下とする。Ｎ含有量の好ましい下限値は０．２２質量％であり、さらに好ましくは０．２５質量％である。また、Ｎ含有量の好ましい上限値は０．４５質量％であり、さらに好ましくは０．４０質量％である。
(N: 0.20 to 0.50 mass%)
N is an element that stabilizes a strong austenite phase, has an effect of improving corrosion resistance without increasing the formation sensitivity of the σ phase, and is also an element effective for increasing the strength of a steel material. In order to acquire such an effect, N content shall be 0.20 mass% or more. However, if N is excessively contained, nitrides are formed and the toughness and corrosion resistance are deteriorated, and hot workability is deteriorated, and ear cracks and surface defects are generated during forging and rolling. Therefore, the N content is 0. .50% by mass or less. The lower limit with preferable N content is 0.22 mass%, More preferably, it is 0.25 mass%. Moreover, the upper limit with preferable N content is 0.45 mass%, More preferably, it is 0.40 mass%.
（Ｔａ：０．０１〜０．５０質量％）
Ｔａは、Ｃと結合することでＣｒ系炭化物の生成抑制、および靱性や耐食性の低下に影響を及ぼすσ相の析出抑制効果を有する元素であり、鋼材の実質的なＣｒ濃度向上に寄与する効果がある。このような効果を得るため、Ｔａ含有量は０．０１質量％以上とする。しかし、過剰なＴａ添加は鋼中のＮと結合することで窒化物として析出してしまい、靱性、熱間加工性を低下させてしまう。また、窒化物の析出によりＮの実効濃度が低減し、σ相の析出により耐食性を低下させてしまう。そのため、Ｔａ含有量は０．５０質量％以下とする。Ｔａ含有量の好ましい下限値は０．０２質量％であり、さらに好ましくは０．０３質量％である。また、Ｔａ含有量の好ましい上限値は０．３０質量％であり、さらに好ましくは０．２５質量％である。
(Ta: 0.01 to 0.50 mass%)
Ta is an element having the effect of suppressing the formation of Cr-based carbides by combining with C, and the effect of suppressing the precipitation of σ phase, which affects the deterioration of toughness and corrosion resistance, and contributes to the substantial improvement of Cr concentration in steel materials. There is. In order to acquire such an effect, Ta content shall be 0.01 mass% or more. However, excessive Ta addition results in precipitation as nitrides due to bonding with N in the steel, thereby reducing toughness and hot workability. Further, the effective concentration of N is reduced by the precipitation of nitride, and the corrosion resistance is lowered by the precipitation of the σ phase. Therefore, the Ta content is 0.50% by mass or less. A preferable lower limit of the Ta content is 0.02% by mass, and more preferably 0.03% by mass. Moreover, the upper limit with preferable Ta content is 0.30 mass%, More preferably, it is 0.25 mass%.
（不可避的不純物）
不可避的不純物は、二相ステンレス鋼材の諸特性を害さない程度に含有することができる。例えば、Ｏであれば、その含有量は０．１質量％以下であり、好ましくは０．０９質量％以下である。それによって、本発明の耐食性発現効果を極大化することができる。
(Inevitable impurities)
Inevitable impurities can be contained to the extent that they do not harm the properties of the duplex stainless steel material. For example, if it is O, the content is 0.1 mass% or less, Preferably it is 0.09 mass% or less. Thereby, the corrosion resistance manifesting effect of the present invention can be maximized.
また、本発明の二相ステンレス鋼材は、本発明の効果に悪影響を与えない範囲で、さらに他の元素を含有させても良い。例えば、本発明の二相ステンレス鋼材は、前記成分組成が、さらに所定量のＣｏ、Ｃｕ、Ｖ、Ｔｉ、Ｎｂよりなる群から１種以上を含有することが好ましい。 Further, the duplex stainless steel material of the present invention may further contain other elements as long as the effects of the present invention are not adversely affected. For example, in the duplex stainless steel material of the present invention, the component composition preferably further contains one or more kinds from a group consisting of a predetermined amount of Co, Cu, V, Ti, and Nb.
（Ｃｏ：０．１０〜２．００質量％、Ｃｕ：０．１０〜２．００質量％、Ｖ：０．０１〜０．５０質量％、Ｔｉ：０．０１〜０．５０質量％、Ｎｂ：０．０１〜０．５０質量％よりなる群から１種以上）
ＣｏおよびＣｕは、耐食性を向上、および、オーステナイト相を安定化させる元素である。このような効果を得るため、これらの元素の含有量は各々０．１０質量％以上とする。しかし、過剰にＣｏおよびＣｕを含有させると熱間加工性が劣化することから、これらの元素の含有量は各々２．００質量％以下とする。これらの元素の含有量の好ましい下限値は、０．２０質量％である。また、これらの元素の含有量の好ましい上限値は１．５０質量％である。
(Co: 0.10 to 2.00 mass%, Cu: 0.10 to 2.00 mass%, V: 0.01 to 0.50 mass%, Ti: 0.01 to 0.50 mass%, Nb : One or more from the group consisting of 0.01 to 0.50% by mass)
Co and Cu are elements that improve the corrosion resistance and stabilize the austenite phase. In order to obtain such effects, the content of these elements is 0.10% by mass or more. However, since hot workability deteriorates when Co and Cu are excessively contained, the content of these elements is 2.00% by mass or less. A preferable lower limit of the content of these elements is 0.20% by mass. Moreover, the preferable upper limit of content of these elements is 1.50 mass%.
Ｖ、ＴｉおよびＮｂは、耐食性を向上させ、強度特性や熱間加工性を向上させる元素である。このような効果を得るため、これらの元素の含有量は各々０．０１質量％以上とする。しかし、過剰にＶ、ＴｉおよびＮｂを含有させると、粗大な炭化物や窒化物を形成し靭性を劣化させることから、これらの元素の含有量は各々０．５０質量％以下とする。これらの元素の含有量の好ましい下限値は、０．０５質量％である。また、これらの元素の含有量の好ましい上限値は、０．４０質量％である。 V, Ti, and Nb are elements that improve corrosion resistance and improve strength characteristics and hot workability. In order to obtain such an effect, the content of these elements is 0.01% by mass or more. However, if V, Ti, and Nb are excessively contained, coarse carbides and nitrides are formed and the toughness is deteriorated. Therefore, the content of these elements is set to 0.50% by mass or less. A preferable lower limit of the content of these elements is 0.05% by mass. Moreover, the preferable upper limit of content of these elements is 0.40 mass%.
また、本発明の二相ステンレス鋼材は、前記成分組成が、さらに、所定量のＭｇ、Ｃａの１種または２種を含有することが好ましい。 Moreover, as for the duplex stainless steel material of this invention, it is preferable that the said component composition contains 1 type or 2 types of Mg and Ca of a predetermined amount further.
（Ｍｇ：０．０００５〜０．０２０質量％、Ｃａ：０．０００５〜０．０２０質量％の１種または２種）
ＭｇおよびＣａは、鋼中に不純物として含有されるＳあるいはＯと結合して、ＭｎＳやＡｌ２Ｏ３等の介在物の形成を抑制して、熱間加工性を向上させる効果がある。このような効果を得るため、これらの元素の含有量は各々０．０００５質量％以上とする。しかし、過剰にＭｇおよびＣａを含有させると、酸化物系介在物の増加を招き、これら介在物が孔食や割れの起点となるために耐食性および熱間加工性が劣化することから、これらの元素の含有量は各々０．０２０質量％以下とする。これらの元素の好ましい含有量は、０．００２〜０．０２０質量％である。
(Mg: 0.0005 to 0.020 mass%, Ca: 0.0005 to 0.020 mass%, one or two)
Mg and Ca are combined with S or O contained in the steel as impurities, and suppress the formation of inclusions such as MnS and Al 2 O 3 , thereby improving the hot workability. In order to obtain such an effect, the content of these elements is 0.0005% by mass or more. However, excessive inclusion of Mg and Ca leads to an increase in oxide inclusions, and these inclusions serve as starting points for pitting corrosion and cracking, so that corrosion resistance and hot workability deteriorate. The element content is 0.020% by mass or less. Preferable content of these elements is 0.002-0.020 mass%.
また、本発明に係る二相ステンレス鋼材は、前記成分組成が、Ｃｒ量を［Ｃｒ］、Ｍｏ量を［Ｍｏ］、Ｎ量を［Ｎ］とした際に、［Ｃｒ］＋３．３［Ｍｏ］＋１６［Ｎ］≧４０であることが好ましい。
［Ｃｒ］＋３．３［Ｍｏ］＋１６［Ｎ］は、鋼材の耐食性を表す指標として従来知られている耐孔食性指数（ＰＲＥ：Pitting Resistance Equivalent）である。ＰＲＥ≧４０とすることによって、組織中のＣｒ量、Ｍｏ量、Ｎ量のバランスが適切なものとなり、鋼材の耐食性および強度が向上する。
In addition, the duplex stainless steel material according to the present invention has a composition of [Cr] +3.3 [Mo] when the Cr content is [Cr], the Mo content is [Mo], and the N content is [N]. ] +16 [N] ≧ 40 is preferable.
[Cr] +3.3 [Mo] +16 [N] is a pitting corrosion resistance (PRE) that is conventionally known as an index representing the corrosion resistance of a steel material. By setting PRE ≧ 40, the balance of Cr content, Mo content, and N content in the structure becomes appropriate, and the corrosion resistance and strength of the steel material are improved.
（二相ステンレス鋼材の製造方法）
本発明の二相ステンレス鋼材は、通常のステンレス鋼材の量産に用いられている製造設備および製造方法によって製造することができる。例えば、転炉あるいは電気炉にて溶解した溶鋼に対して、ＡＯＤ法やＶＯＤ法等による精錬を行って成分調整した後、連続鋳造法や造塊法等の鋳造方法で鋼塊とする。得られた鋼塊を１０００℃〜１２００℃程度の温度域にて熱間加工を行い、次いで冷間加工を行って所望の寸法形状にすることができる。
(Method for producing duplex stainless steel)
The duplex stainless steel material of the present invention can be produced by a production facility and a production method used for mass production of ordinary stainless steel materials. For example, the molten steel melted in a converter or electric furnace is refined by an AOD method, a VOD method, or the like to adjust the components, and then formed into a steel ingot by a casting method such as a continuous casting method or an ingot-making method. The obtained steel ingot can be hot-worked in a temperature range of about 1000 ° C. to 1200 ° C., and then cold-worked to obtain a desired dimensional shape.
本発明においては、機械特性に有害な析出物をなくすため、必要に応じて固溶化熱処理を施して急冷することが好ましい。固溶化熱処理の温度は、１０００〜１１００℃が好ましく、保持時間は１０分から３０分が好ましく、急冷は１０℃／秒以上の冷却速度で冷却することが好ましい。また、必要に応じてスケール除去等の表面調整のための酸洗を行うことができる。 In the present invention, in order to eliminate precipitates detrimental to mechanical properties, it is preferable to quench by applying a solution heat treatment as necessary. The temperature of the solution heat treatment is preferably 1000 to 1100 ° C., the holding time is preferably 10 to 30 minutes, and the rapid cooling is preferably performed at a cooling rate of 10 ° C./second or more. Moreover, the pickling for surface adjustments, such as scale removal, can be performed as needed.
＜二相ステンレス鋼管＞
本発明に係る二相ステンレス鋼管の実施形態について説明する。
本発明の二相ステンレス鋼管は、前記二相ステンレス鋼材からなるもので、通常のステンレス鋼管の量産に用いられる製造設備および製造方法によって製造することができる。例えば、丸棒を素材とした押出製管やマンネスマン製管、板材を素材として成形後に継ぎ目を溶接する溶接製管等によって、所望の寸法にすることができる。また、二相ステンレス鋼管の寸法は、鋼管が使用されるアンビリカル、海水淡水化プラント、ＬＮＧ気化器、油井管、各種化学プラント等に応じて適宜設定することができる。
<Duplex stainless steel pipe>
An embodiment of a duplex stainless steel pipe according to the present invention will be described.
The duplex stainless steel pipe of the present invention is made of the duplex stainless steel material and can be produced by a production facility and a production method used for mass production of ordinary stainless steel pipes. For example, a desired size can be obtained by an extruded pipe made of a round bar, a Mannesmann pipe, a welded pipe made by welding a seam after forming a plate material. The dimensions of the duplex stainless steel pipe can be appropriately set according to the umbilical, the seawater desalination plant, the LNG vaporizer, the oil well pipe, various chemical plants, etc. in which the steel pipe is used.
本発明に係る二相ステンレス鋼材の実施例について、以下に説明する。
（試料の作製）
電極アーク加熱機能を備える溶鋼処理設備によって、表１に示す成分組成の鋼（鋼記号Ａ〜Ｚ）をそれぞれ溶製し、５０ｋｇの丸鋳型（本体：約φ１４０×３２０ｍｍ）を用いて鋳造した。凝固した鋼塊を１２００℃まで加熱し同温度で熱間鍛造を施し、その後切断し、１１００℃で３０分保持の固溶化熱処理を施し、水冷して６００×１２０×６０ｍｍの鍛鋼品（試料Ｎｏ．１〜２６）に仕上げた。
Examples of the duplex stainless steel material according to the present invention will be described below.
(Sample preparation)
Steels (steel symbols A to Z) having the composition shown in Table 1 were melted by a molten steel processing facility equipped with an electrode arc heating function, and cast using a 50 kg round mold (main body: about φ140 × 320 mm). The solidified steel ingot is heated to 1200 ° C., hot forged at the same temperature, then cut, subjected to a solution heat treatment held at 1100 ° C. for 30 minutes, water cooled, and a forged steel product of 600 × 120 × 60 mm (sample No. .1 to 26).
また、各鋼のＰＲＥ＝［Ｃｒ］＋３．３［Ｍｏ］＋１６［Ｎ］を算出し、その結果も表１に示す。さらに、仕上げた鍛鋼品を加工方向と平行な断面を埋込み、鏡面研磨し、シュウ酸水溶液中で電解エッチングを行った後、倍率１００倍で光学顕微鏡観察を行い、各鍛鋼品の組織を確認した。その結果、いずれの鍛鋼品もフェライト相とオーステナイト相の二相からなるものであった。 Moreover, PRE = [Cr] +3.3 [Mo] +16 [N] was calculated for each steel, and the results are also shown in Table 1. Furthermore, the finished forged steel product was embedded in a cross section parallel to the processing direction, mirror-polished, electrolytically etched in an oxalic acid aqueous solution, and then observed with an optical microscope at a magnification of 100 times to confirm the structure of each forged steel product. . As a result, each forged steel product was composed of two phases of a ferrite phase and an austenite phase.
（試料の採取）
次に、鍛鋼品から加工方向に平行に採取した試料（２０ｍｍ×３０ｍｍ×２ｍｍ）を用いて、以下に示す手順で耐孔食性および熱間加工性を評価した。
(Sample collection)
Next, pitting corrosion resistance and hot workability were evaluated by the following procedure using a sample (20 mm × 30 mm × 2 mm) collected from the forged steel product in parallel with the processing direction.
（耐孔食性の評価）
試料表面をＳｉＣ＃６００研磨紙で湿式研磨し、超音波洗浄した後５０℃の３０％硝酸に１時間浸漬し不働態化処理をした。次に、試料にスポット溶接で導線を取り付け、試験部（試験面積：１０ｍｍ×１０ｍｍ）を残してエポキシ樹脂で被覆した。その試料を８０℃に保持した２０％ＮａＣｌ水溶液中に１０分間浸漬した後、＋６００ｍＶ（ｖｓ．ＳＣＥ：飽和カロメル電極）で１分間保持し、レーザー顕微鏡にて試験部の最大孔食深さを測定した。そして、最大孔食深さが４０μｍを超えるものを耐孔食性が不良（×）、最大孔食深さが４０μｍ以下で２０μｍを超えるものを耐孔食性が良好（○）、最大孔食深さが２０μｍ以下のものを耐孔食性が優れている（◎）と評価した。その結果を表２に示す。
(Evaluation of pitting corrosion resistance)
The sample surface was wet-polished with SiC # 600 abrasive paper, subjected to ultrasonic cleaning, and then immersed in 30% nitric acid at 50 ° C. for 1 hour for passivation treatment. Next, a lead wire was attached to the sample by spot welding, and the test part (test area: 10 mm × 10 mm) was left and covered with an epoxy resin. The sample was immersed in a 20% NaCl aqueous solution maintained at 80 ° C. for 10 minutes, then held at +600 mV (vs. SCE: saturated calomel electrode) for 1 minute, and the maximum pitting depth of the test part was measured with a laser microscope. did. When the maximum pitting depth exceeds 40 μm, the pitting resistance is poor (×), when the maximum pitting depth is 40 μm or less and exceeds 20 μm, the pitting resistance is good (◯), and the maximum pitting depth. Of 20 μm or less were evaluated as having excellent pitting corrosion resistance (◎). The results are shown in Table 2.
（熱間加工性の評価）
鍛鋼品の表面を目視にて観察し、表面欠陥の有無を観察した。そして、割れが発生しているものを熱間加工性が不良（×）、表面欠陥が多発しているものを熱間加工性がやや不良（△）、表面欠陥がわずかなものを熱間加工性が良好（○）、表面欠陥がないものを熱間加工性が優れている（◎）と評価した。その結果を表２に示す。
(Evaluation of hot workability)
The surface of the forged steel product was visually observed to observe the presence or absence of surface defects. Also, hot workability is poor (×) when cracks occur, hot workability is slightly poor (△) when surface defects occur frequently, and hot work is performed when surface defects are slight. Good (◯) and no surface defects were evaluated as being excellent in hot workability (）). The results are shown in Table 2.
表２の結果から、本発明の要件を満たす鋼（鋼記号Ａ〜Ｒ）を用いて作製した試料Ｎｏ．1〜１８（実施例）は、良好または優れた耐孔食性を有すると共に、良好または優れた熱間加工性を有することが確認された。
これに対して、本発明の要件を満たさない鋼（鋼記号Ｓ〜Ｚ）を用いて作製した試料Ｎｏ．１９〜２６（比較例）は、以下の不具合を有していることが確認された。
From the results in Table 2, sample Nos. Produced using steels (steel symbols A to R) satisfying the requirements of the present invention. It was confirmed that 1 to 18 (Examples) had good or excellent pitting corrosion resistance and good or excellent hot workability.
On the other hand, Sample No. produced using steel (steel symbols S to Z) that does not satisfy the requirements of the present invention. It was confirmed that 19 to 26 (comparative example) had the following problems.
試料Ｎｏ．１９は、Ｔａが過剰であるため、粗大な窒化物が多量に形成され、熱間加工性が劣った。また、σ相も形成され、耐孔食性も劣った。試料Ｎｏ．２０は、Ｔａが添加されていないため、σ相が多く形成され、耐孔食性および熱間加工性が劣った。試料Ｎｏ．２１は、Ｍｎが過剰であるため、多数の介在物（ＭｎＳ）が析出され、耐孔食性および熱間加工性が劣った。試料Ｎｏ．２２は、Ｓが過剰であるため、粗大な硫化物が多量に形成され、耐孔食性および熱間加工性が劣った。試料Ｎｏ．２３は、Ｃｒが不足しているため、耐孔食性および熱間加工性が劣った。試料Ｎｏ．２４は、Ｎｉが不足しているため、耐孔食性および熱間加工性が劣った。試料Ｎｏ．２５はＣが過剰であるため炭化物が多く形成され、耐孔食性および熱間加工性が劣った。試料Ｎｏ．２６はＭｏが過剰であるためσ相が多く形成され、耐孔食性および熱間加工性が劣った。 Sample No. In No. 19, since Ta was excessive, a large amount of coarse nitride was formed, and the hot workability was poor. Also, a σ phase was formed, and the pitting corrosion resistance was poor. Sample No. In No. 20, Ta was not added, so many σ phases were formed, and the pitting corrosion resistance and hot workability were inferior. Sample No. In No. 21, since Mn was excessive, a large number of inclusions (MnS) were precipitated, resulting in poor pitting corrosion resistance and hot workability. Sample No. In No. 22, since S was excessive, a large amount of coarse sulfide was formed, and pitting corrosion resistance and hot workability were inferior. Sample No. No. 23 was inferior in pitting corrosion resistance and hot workability due to lack of Cr. Sample No. No. 24 was inferior in pitting corrosion resistance and hot workability due to lack of Ni. Sample No. No. 25 was excessive in C, so a large amount of carbides were formed, and the pitting corrosion resistance and hot workability were poor. Sample No. In No. 26, Mo was excessive, so a large amount of σ phase was formed, and the pitting corrosion resistance and hot workability were poor.
以上のように、本発明の二相ステンレス鋼材および二相ステンレス鋼管について説明したが、本発明は実施形態および実施例によって制限を受けるものではなく、本発明の趣旨に適合し得る範囲で適当に変更を加えて実施することも可能であり、それらはいずれも本発明の技術的範囲に包含されるものである。 As described above, the duplex stainless steel material and duplex stainless steel pipe of the present invention have been described. However, the present invention is not limited by the embodiments and examples, and is appropriately within a range that can meet the spirit of the present invention. It is also possible to carry out with modification, and they are all included in the technical scope of the present invention.
Claims (4)
Ｃ：０．１００％質量以下、
Ｓｉ：０．１０〜２．００質量％、
Ｍｎ：０．１０〜２．００質量％、
Ｐ：０．０５０質量％以下、
Ｓ：０．０１００質量％以下、
Ａｌ：０．０１０〜０．０５０質量％、
Ｎｉ：１．０〜１０．０質量％、
Ｃｒ：２２．０〜２８．０質量％、
Ｍｏ：２．０〜６．０質量％、
Ｎ：０．２０〜０．５０質量％、
Ｔａ：０．０１〜０．５０質量％であって、残部がＦｅおよび不可避的不純物からなることを特徴とする二相ステンレス鋼材。 It is a duplex stainless steel material composed of a ferrite phase and an austenite phase, and the component composition of the duplex stainless steel material is:
C: 0.100% mass or less,
Si: 0.10 to 2.00% by mass,
Mn: 0.10 to 2.00% by mass,
P: 0.050 mass% or less,
S: 0.0100 mass% or less,
Al: 0.010 to 0.050 mass%,
Ni: 1.0-10.0 mass%,
Cr: 22.0-28.0 mass%,
Mo: 2.0 to 6.0 mass%,
N: 0.20 to 0.50 mass%,
Ta: 0.01 to 0.50 mass%, with the balance being Fe and inevitable impurities, a duplex stainless steel material.
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| US14/759,018 US20150354038A1 (en) | 2013-01-15 | 2014-01-10 | Duplex stainless steel material and duplex stainless steel pipe |
| EP14741060.9A EP2947169A4 (en) | 2013-01-15 | 2014-01-10 | Duplex stainless steel material and duplex stainless steel pipe |
| PCT/JP2014/050363 WO2014112445A1 (en) | 2013-01-15 | 2014-01-10 | Duplex stainless steel material and duplex stainless steel pipe |
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