EP2476771B1 - Two-phase stainless steel - Google Patents

Two-phase stainless steel Download PDF

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Publication number
EP2476771B1
EP2476771B1 EP10815306.5A EP10815306A EP2476771B1 EP 2476771 B1 EP2476771 B1 EP 2476771B1 EP 10815306 A EP10815306 A EP 10815306A EP 2476771 B1 EP2476771 B1 EP 2476771B1
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EP
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duplex stainless
stainless steel
content
mass
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EP10815306.5A
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German (de)
English (en)
French (fr)
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EP2476771A4 (en
EP2476771A1 (en
Inventor
Hisashi Amaya
Hideki Takabe
Kazuhiro Ogawa
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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Priority to EP15156371.5A priority Critical patent/EP2902525B1/en
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Publication of EP2476771A4 publication Critical patent/EP2476771A4/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a ferrite-austenite duplex stainless steel excellent in stress corrosion cracking resistance, in particular to a duplex stainless steel suitable as a steel material for line pipes transporting petroleum, natural gas or the like.
  • duplex stainless steels composed of ferrite-austenite phases
  • Patent Document 1 describes a duplex stainless steel containing Cu in a content of 1 to 3% and improved in corrosion resistance in chloride and sulfide environments.
  • Patent Document 2 describes a duplex stainless steel in which the strength, toughness and seawater resistance are improved by appropriately regulating the contents of Cr, Ni, Cu, Mo, N and W and by controlling the area fraction of the ferrite phase to 40% through 70%.
  • EP 261 345 discloses a pitting resistant duplex stainless steel used in vessels retorts, piping and paper manufacturing industries.
  • the degradation of the corrosion resistance of the weld zone tends to occur during large heat input welding.
  • intermetallic compounds precipitate in the weld zone during large heat input welding, and hence embrittlement and degradation of the corrosion resistance tend to occur in the weld zone, and additionally, on the assumption of the transportation of petroleum or natural gas, insufficient is the stress corrosion cracking resistance in a chloride environment containing corrosive associated gases such as carbon dioxide gas and hydrogen sulfide.
  • the present invention has been performed for the purpose of solving the aforementioned problems, and an object of the present invention is to provide a duplex stainless steel excellent in the weldability during large heat input welding and excellent in the stress corrosion cracking resistance in the chloride environment containing corrosive associated gases.
  • the present inventors performed a series of various experiments and detailed studies for the purpose of actualizing in a duplex stainless steel the improvement of the weldability during large heat input welding and the improvement of the stress corrosion cracking resistance in the chloride environment. Consequently, the present inventors have obtained the following findings (a) to (f).
  • Figure 4 is a graph in which for duplex stainless steels having various chemical compositions, used in Examples described later, the content (mass%) of "Cr” is plotted on the X-axis and the content (mass%) of "7Mo + 3Cu” is plotted on the Y-axis.
  • the passivation film can be strengthened: 2.2Cr + 7Mo + 3Cu > 66 (1) wherein the symbols of elements in formula (1) respectively represent the contents (unit: mass%) of the elements in the steel.
  • the left hand side of formula (2) represents the driving force for the precipitation of the sigma phase; among the components constituting the duplex stainless steel, Cr, Mo and Ni are the elements to increase the driving force for the nucleation of the precipitation of the sigma phase; on the basis of various tests, it has been found that the degrees of contribution of Mo and Ni are 11 times and 10 times the degree of contribution of Cr, respectively.
  • the manifestation mechanism of the deterrent force against the precipitation of the sigma phase due to Cu and N is as follows.
  • the presence of a Cu atom or an N atom in the vicinity of each of the Ni atoms present in the crystal lattice suppresses the decrease of the interface energy in the ferrite/austenite phase interface, which is the site of the nucleation of the sigma phase; thus, the decrease amount of the free energy at the time of the precipitation reaction of the sigma phase is made small, and hence the driving force for the crystal nucleation can be made small to be associated with the aforementioned manifestation mechanism.
  • the present invention has been perfected on the basis of the aforementioned findings, and the gist of the present invention resides in the following items (1) to (4) regarding duplex stainless steel.
  • the duplex stainless steel according to the present invention is excellent in the weldability during large heat input welding and excellent in the stress corrosion cracking resistance in a chloride environment.
  • C is an element effective in stabilizing the austenite phase.
  • carbides tend to precipitate, and the corrosion resistance is degraded. Accordingly, the content of C is set at 0.03% or less.
  • Si is able to ensure the fluidity of the molten metal during welding, and hence is an element effective in preventing weld defects.
  • Si is required to be contained in a content of 0.2% or more.
  • the content of Si exceeds 1%, intermetallic compounds (such as the sigma phase) tend to be produced. Accordingly, the content of Si is set at 0.2 to 1%.
  • the content of Si is preferably 0.2 to 0.5%.
  • Mn is a component effective in improving the hot workability through the desulfurization and deoxidation effects during melting of the duplex stainless steel. Mn also has a function to increase the solubility of N. However, when the content of Mn exceeds 5.0%, the corrosion resistance is degraded. Accordingly, the content of Mn is set at 5.0% or less.
  • the content of P is set at 0.040% or less.
  • S is mixed in the steel as an impurity, and degrades the hot workability of the steel. Sulfides offer the origins of the occurrence of pitting and degrade the pitting resistance of the steel. For the purpose of avoiding these adverse effects, the content of S is set at 0.010% or less. The content of S is preferably 0.007% or less.
  • Al is a component effective as a deoxidizer of the steel.
  • the content of N in the steel is large, Al precipitates as AIN (aluminum nitride), and degrades the toughness and the corrosion resistance of the steel. Accordingly, the content of Al is set at 0.040% or less.
  • the content of Al as referred to in the present invention means the content of acid-soluble Al (what is called sol. Al).
  • Al is used as a deoxidizer in the duplex stainless steel according to the present invention, because the content of Si as a component effective deoxidizer is suppressed , and hence. However, when the duplex stainless steel is produced by vacuum melting, it is not necessary to contain Al.
  • Ni is a component effective in stabilizing austenite.
  • the content of Ni exceeds 8%, the resultant decrease of the amount of ferrite makes it difficult to ensure the fundamental properties of the duplex stainless steel and also facilitates the production of intermetallic compounds (such as the sigma phase).
  • the content of Ni is less than 4%, the amount of ferrite comes to be too large and thus the features of the duplex stainless steel are lost.
  • the solubility of N in ferrite is small, and hence due to the amount of ferrite becoming too large, nitrides precipitate and the corrosion resistance is degraded. Accordingly, the content of Ni is set at 4 to 8%.
  • Cr is a component effective in maintaining the corrosion resistance.
  • Cr is required to be contained in a content of 20% or more.
  • the content of Cr exceeds 28%, the precipitation of intermetallic compounds (such as the sigma phase) comes to be remarkable, and the degradation of the hot workability and the degradation of the weldability are caused. Accordingly, the content of Cr is set at 20 to 28%.
  • Mo is an element extremely effective in improving the SCC resistance.
  • Mo is required to be contained in a content of 0.5% or more.
  • the content of Mo exceeds 2.0%, the precipitation of intermetallic compounds is remarkably accelerated during large heat input welding, and the degradation of the hot workability and the degradation of the weldability are caused. Accordingly, the content of Mo is set at 0.5 to 2.0%.
  • the content of Mo is preferably 0.7 to 1.8% and more preferably 0.8 to 1.5%.
  • Cu is a component effective in strengthening the passivation film mainly composed of Cr in a chloride environment containing corrosive acidic gasses (such as carbon dioxide gas and hydrogen sulfide gas). Additionally, Cu precipitates in the matrix in an ultrafine manner during large heat input welding to become nucleation sites of intermetallic compounds (the sigma phase) so as to compete against the ferrite/austenite phase interface which is the proper nucleation site. Consequently, there occurs retardation of the sigma phase production, otherwise fast in growth, in the ferrite/austenite phase interface. For the purpose of obtaining these effects, Cu is required to be contained in a content exceeding 2.0%. On the other hand, when Cu is contained in a content exceeding 4.0%, the hot workability of the steel is impaired. Accordingly, the content of Cu is set to be more than 2.0% and 4.0% or less.
  • N is a powerful austenite former, and is effective in improving the thermal stability and the corrosion resistance of the duplex stainless steel.
  • the duplex stainless steel according to the present invention contains Cr and Mo, which are ferrite formers, in large amounts, and hence N is required to be contained in a content of 0.1% or more for the purpose of establishing an appropriate balance between ferrite and austenite.
  • the content of N exceeds 0.35%, the toughness and the corrosion resistance of the steel are degraded due to the occurrence of blow holes as weld defects, the nitride production caused by the thermal effects during welding or the like. Accordingly, the content of N is set at 0.1 to 0.35%.
  • the contents of Cr and Mo are regulated for the purpose of suppressing the precipitation of the intermetallic compounds. Accordingly, for the purpose of strengthening the passivation film mainly composed of Cr, Cu is required to be contained in an appropriate amount in addition to Mo.
  • the value of "2.2Cr + 7Mo + 3Cu" is 66 or less, a sufficient resistance against the stress corrosion cracking (SCC) in a chloride environment cannot be ensured as the case may be. Accordingly, the requirement of the above presented formula (1) is specified.
  • the duplex stainless steel according to the present invention has the aforementioned chemical composition, and the balance is composed of Fe and impurities.
  • the impurities as referred to herein mean the components which are mixed due to various factors in the production process including raw materials such as ores and scraps when the duplex stainless steel is industrially produced, and are tolerated within the range not adversely affecting the present invention.
  • the duplex stainless steel according to the present invention may contain, in addition to the aforementioned elements, one or more of the elements selected from at least one group of the following first to third groups.
  • V may be contained if necessary.
  • V is effective in improving the corrosion resistance (in particular, the corrosion resistance in an acidic environment) of the duplex stainless steel. More specifically, by containing V in combination with Mo and Cu, the crevice corrosion resistance can be improved. However, when the content of V exceeds 1.5%, there is an adverse possibility that the amount of ferrite is excessively increased, and the toughness and the corrosion resistance are degraded; accordingly, the content of V is set at 1.5% or less.
  • Second group One or more selected from among Ca: 0.02% or less, Mg: 0.02% or less and B: 0.02% or less
  • One or more selected from among Ca, Mg and B may be contained if necessary.
  • Each of Ca, Mg and B has an effect to fix S (sulfur) and O (oxygen) to improve the hot workability.
  • the content of S is regulated so as to be low, and hence the hot workability can be satisfactory even when Ca, Mg or B is not contained.
  • the content of each of these elements exceeds 0.02%, there is an adverse possibility that the amount of nonmetallic inclusions (such as the oxides and sulfides of Ca, Mg or B) is increased and such inclusions offer the origins of pitting and the degradation of the corrosion resistance occurs. Accordingly, when these elements are contained, the content of each of these elements is set at 0.02% or less. When two selected from among Ca, Mg and B are contained, the upper limit of the total content is 0.04%; and when three of Ca, Mg and B are contained, the upper limit of the total content is 0.06%.
  • Ca, Mg or B For the purpose of stably displaying the improvement effect of the hot workability due to Ca, Mg or B, it is preferable to contain Ca, Mg and B each alone or in total, in a content of "S(mass%) + (1/2) ⁇ O(mass%)" or more.
  • REM may be contained if necessary.
  • a rare earth metal also has an effect to fix S or O to enable further improvement of the hot workability of the duplex stainless steel.
  • the content of the rare earth metal exceeds 0.2%, there is an adverse possibility that the amount of nonmetallic inclusions (such as the oxides and sulfides of the rare earth metal) is increased and such inclusions offer the origins of pitting and the degradation of the corrosion resistance occurs. Accordingly, when the rare earth metal is contained, the content of the rare earth metal is set at 0.2% or less.
  • REM as referred to herein is a generic name of the 17 elements consisting of the 15 lanthanoid elements and Y and Sc, and one or more of these elements may be contained.
  • the content of REM means the total content of such elements.
  • the duplex stainless steel according to the present invention can be produced by the production equipment and the production method used for the usual commercial production.
  • an electric furnace for the melting of the duplex stainless steel, there can be used an electric furnace, an Ar-O 2 mixed gas bottom blowing decarburization furnace (AOD furnace), a vacuum decarburization furnace (VOD furnace) or the like.
  • AOD furnace Ar-O 2 mixed gas bottom blowing decarburization furnace
  • VOD furnace vacuum decarburization furnace
  • the molten steel obtained by melting may be cast into ingots, or may be cast into rod-like billets or the like by a continuous casting method.
  • duplex stainless steels (Present Inventions: Test Nos. 1 to 11, the Comparative: Test Nos. 12 to 25) having the chemical compositions shown in below-presented Table 1 were melted by using a vacuum furnace of 150 kg in capacity, and cast into ingots. Next, each of the ingots was heated to 1250°C, and forged into a 40-mm thick plate material.
  • each of the plate materials was again heated to 1250°C, and rolled so as to have a thickness of 15 mm by hot rolling (the working temperature: 1050°C or higher); then each of the plate materials after rolling was subjected to a solid solution heat treatment (a treatment of water cooling after being maintained in a soaked manner at 1070°C for 30 minutes) to prepare a test steel plate.
  • a solid solution heat treatment a treatment of water cooling after being maintained in a soaked manner at 1070°C for 30 minutes
  • Figure 1 shows a plate material 10 which is prepared by mechanical working.
  • (a) is a plan view and (b) is a front view.
  • FIG. 2 for each of the test steels, two pieces of the plate material 10 having a shape shown in Figure 1 were prepared and arranged so as for the groove faces to butt each other; then, a weld joint 20 was prepared by performing multilayer welding based on tungsten inert gas (TIG) welding from the one side of each of the plate materials.
  • Figure 2(a) is a plan view
  • Figure 2(b) is a front view of the weld joint 20.
  • TOG tungsten inert gas
  • FIG. 2(a) is a plan view
  • Figure 2(b) is a front view of the weld joint 20.
  • the welding material 30 of each of the weld joints 20 a welding material of 2 mm in outer diameter prepared from the Test No. 1 in Table 1 was used commonly for all the test steels. The welding was performed under the condition of the heat input amount of 30 kJ/cm, which was particularly highly efficient for a common welding working of stainless steel.
  • Figure 3 shows an oblique perspective view of a sampled specimen 40.
  • the upper surface is the rolled surface (the lower surface of the weld joint in Figurer 2).
  • the longitudinal direction of the specimen 40 is a direction perpendicular to the weld line.
  • Each of the specimens 40 was sampled in such a way that one of the two boundary lines between the welding material 30 and the plate material 10, on the surface (the rolled surface) of the concerned specimen 40, was to be located in the center of the surface of the concerned specimen 40.
  • a four-point bending test was performed.
  • a stress corresponding to the yield stress of the specimen was applied to the specimen in a NaCl aqueous solution (150°C) having a concentration of 25 mass% into which CO 2 at 3 MPa had been injected under pressure.
  • the test time of the four-point bending test was 720 hours.
  • Figure 4 is a graph showing the relation between "7Mo (mass%) + 3Cu (mass%)” and "Cr (mass%)" for the duplex stainless steels of Test Nos. 1, 4, 6, 13 and 20.
  • Table 2 no stress corrosion cracking occurred in the specimens prepared from the duplex stainless steels of Test Nos. 1, 4 and 6, whereas the stress corrosion cracking occurred in the specimens prepared from the duplex stainless steels of Test Nos. 13 and 20. Accordingly, as shown in Figure 4 , when a border line is drawn between the "7Mo (mass%) + 3Cu (mass%)" values of the duplex stainless steels of Test Nos.
  • the duplex stainless steels satisfying the requirements of the present invention can suppress the precipitation of the intermetallic compounds during large heat input welding, and each have an excellent stress corrosion cracking resistance in chloride environments.
  • duplex stainless steels according to the present invention are excellent in weldability during large heat input welding and excellent in the stress corrosion cracking resistance in chloride environments.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Arc Welding In General (AREA)
EP10815306.5A 2009-09-10 2010-09-01 Two-phase stainless steel Active EP2476771B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP15156371.5A EP2902525B1 (en) 2009-09-10 2010-09-01 Duplex stainless steel

Applications Claiming Priority (2)

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JP2009209160 2009-09-10
PCT/JP2010/064953 WO2011030709A1 (ja) 2009-09-10 2010-09-01 二相ステンレス鋼

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EP2476771A1 EP2476771A1 (en) 2012-07-18
EP2476771A4 EP2476771A4 (en) 2014-07-23
EP2476771B1 true EP2476771B1 (en) 2015-03-04

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US (1) US20120177529A1 (es)
EP (2) EP2902525B1 (es)
JP (1) JP4640536B1 (es)
CN (1) CN102482746B (es)
AU (1) AU2010293591B2 (es)
BR (1) BR112012005005B1 (es)
CA (1) CA2770378C (es)
IN (1) IN2012DN01250A (es)
MX (2) MX2012002870A (es)
WO (1) WO2011030709A1 (es)

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EP2677056B1 (en) * 2011-02-14 2016-05-18 Nippon Steel & Sumitomo Metal Corporation Duplex stainless steel
EP2677054B1 (en) * 2011-02-14 2020-03-25 Nippon Steel Corporation Duplex stainless steel plate or pipe, and process for production thereof
CN103781931B (zh) * 2011-09-06 2016-06-22 新日铁住金株式会社 双相不锈钢
ES2709028T3 (es) * 2012-03-30 2019-04-12 Nippon Steel & Sumitomo Metal Corp Proceso para la producción de junta soldada
CN103014549B (zh) * 2012-12-26 2015-11-18 振石集团东方特钢股份有限公司 一种高性能双相不锈钢及其加工方法
CN103602915B (zh) * 2013-11-22 2015-11-18 山东建筑大学 高碳高铬双相不锈钢
CN109072386A (zh) 2016-06-01 2018-12-21 新日铁住金株式会社 双相不锈钢和双相不锈钢的制造方法
JP6780426B2 (ja) * 2016-10-06 2020-11-04 日本製鉄株式会社 二相ステンレス鋼
JP6946737B2 (ja) * 2017-05-18 2021-10-06 日本製鉄株式会社 二相ステンレス鋼材及びその製造方法
CN107829029B (zh) * 2017-11-10 2020-02-07 洛阳双瑞特种装备有限公司 一种ZG022Cr22Ni5Mo3N材质双相不锈钢冶炼工艺方法
CN115584443A (zh) * 2021-07-05 2023-01-10 中国石油天然气集团有限公司 一种含铜抗菌双相不锈钢连续管及加工方法

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EP2677056B1 (en) * 2011-02-14 2016-05-18 Nippon Steel & Sumitomo Metal Corporation Duplex stainless steel

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MX352395B (es) 2017-11-22
EP2476771A4 (en) 2014-07-23
IN2012DN01250A (es) 2015-05-15
BR112012005005B1 (pt) 2023-01-24
CN102482746B (zh) 2016-06-22
AU2010293591A1 (en) 2012-03-01
CN102482746A (zh) 2012-05-30
EP2476771A1 (en) 2012-07-18
EP2902525A1 (en) 2015-08-05
CA2770378C (en) 2014-02-18
EP2902525B1 (en) 2016-05-11
JPWO2011030709A1 (ja) 2013-02-07
JP4640536B1 (ja) 2011-03-02
US20120177529A1 (en) 2012-07-12
WO2011030709A1 (ja) 2011-03-17
AU2010293591B2 (en) 2013-01-17
BR112012005005A2 (pt) 2016-05-03
CA2770378A1 (en) 2011-03-17
MX2012002870A (es) 2012-04-20

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