EP0320548B1 - Verfahren zur Herstellung rostfreien Duplexstahls und Bauteile aus rostfreiem Duplexstahl mit verbesserten mechanischen Eigenschaften - Google Patents

Verfahren zur Herstellung rostfreien Duplexstahls und Bauteile aus rostfreiem Duplexstahl mit verbesserten mechanischen Eigenschaften Download PDF

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EP0320548B1
EP0320548B1 EP19870311114 EP87311114A EP0320548B1 EP 0320548 B1 EP0320548 B1 EP 0320548B1 EP 19870311114 EP19870311114 EP 19870311114 EP 87311114 A EP87311114 A EP 87311114A EP 0320548 B1 EP0320548 B1 EP 0320548B1
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max
duplex stainless
stainless steel
nickel
composition
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EP0320548A1 (de
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Robin K. Churchill
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Esco Corp
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Esco Corp
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Priority to US06/864,333 priority Critical patent/US4715908A/en
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Priority to DE19873781160 priority patent/DE3781160T2/de
Priority to EP19870311114 priority patent/EP0320548B1/de
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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
    • C22C38/001—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
    • C22C38/18—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

Definitions

  • This invention relates to a method of making a high strength duplex stainless steel and a product of this alloy in either cast or wrought form.
  • the material of this invention displays superior toughness, weldability and cracking resistance in H2S bearing environments compared to other duplex stainless steels of similar strength level.
  • duplex stainless steels of the prior art have had a number of drawbacks.
  • Cast grades generally exhibited only moderate impact toughness at room temperature, and suffered marked losses in toughness as temperatures decreased.
  • Duplex grades were also susceptible to serious embrittlement in the heat affected zones (HAZs) of welds. They also exhibited poor resistance to cracking in the sour (H2S-bearing) environments often encountered in oil industry applications. These deficiencies have been major factors inhibiting even wider application of these materials.
  • duplex stainless steels are designed to have a microstructure consisting of about 50% ferrite and 50% austenite. It is this microstructure which is responsible for the high strength and good corrosion resistance of these materials.
  • the desired ferrite:austenite ratio was obtained only by controlling the composition. This prevented alloy designers from using other techniques for improving the toughness of the ferrite phase which would lead to improved toughness of the total alloy.
  • the current invention involves the realization that the ferrite-austenite ratio can be adjusted not only by varying the composition, but also by varying the solution treatment temperature.
  • a duplex stainless steel having the following composition Carbon 0.001 to 0.08 Wt. % Manganese 0.001 to 2.00 Wt. % Silicon 0.001 to 1.50 Wt. % Chromium 20.00 to 27.50 Wt. % Nickel 8.00 to 11.00 Wt. % Molybdenum 3.00 to 4.50 Wt. % Sulfur 0.0001 to 0.050 Wt. % Phosphorus 0.0001 to 0.050 Wt. % Nitrogen 0.10 to 0.30 Wt. % Iron Balance is produced.
  • composition is balanced such that: where: Creq ⁇ 1.5(%Cr+%Si+%Mo) Nieq ⁇ %Ni+0.3(%Mn)+%Cu+22(%C)+5%N Products of this material are then solution treated by heating to a temperature in the range of 1107°C-1274°C (2050°F-2350°F) and then cooling rapidly as with a water quench.
  • the desired yield strength is developed by solution treating at a temperature selected according to the following approximate relationship: Where:
  • Patent No. 4,032,367 overlap those of the inventive alloy. Certain compositions of this material combined with certain solution treatment temperatures probably would give a good combination of strength and toughness. However, Patent 4,032,367 does not recognize the relationships between Creq: Nieq ratio, solution treatment temperature and mechanical properties necessary to accomplish this. Obtaining a good combination of strength and toughness with the information given in Patent 4,032,367 would simply be a matter of chance.
  • Other patents such as 4,500,351 and 4,055,448 disclose preferred Creq:Nieq relationships, but they differ from those of this invention and are not directly tied to mechanical properties or heat treatment.
  • the inventive material Compared to high strength duplex stainless steels of the prior art, the inventive material exhibits considerably greater impact toughness values, particularly at low temperatures. It also exhibits considerably greater impact toughness values in the HAZs of welds. Furthermore, the inventive material exhibits improved resistance to cracking when tested in a simulated sour gas environment according to NACE (National Association of Corrosion Engineers) Test Method TM-01-77.
  • NACE National Association of Corrosion Engineers
  • This invention is based on the realization that the ferrite contents (strength levels) of high strength duplex stainless steels can be effectively varied not only by adjusting composition, but also by selective use of solution treatment temperature.
  • higher solution treatment temperatures than those which have been commonly used for high strength duplex stainless steels, it is possible to obtain the desired ferrite contents (strength levels) using alloy compositions with higher nickel contents for a given content of Cr+Mo+Si. This results in higher nickel contents in the ferrite. Consequently, improvements in low temperature toughness, the toughness of HAZs and resistance to sulfide stress cracking are realized.
  • a heat of duplex stainless steel is produced to the following composition: Carbon 0.001 to 0.08 Wt. % Manganese 0.001 to 2.00 Wt. % Silicon 0.001 to 1.50 Wt. % Chromium 20.00 to 27.50 Wt. % Nickel 8.00 to 11.00 Wt. % Molybdenum 3.00 to 4.50 Wt. % Sulfur 0.0001 to 0.050 Wt. % Phosphorus 0.0001 to 0.050 Wt. % Nitrogen 0.10 to 0.30 Wt. % Iron Balance The composition is balanced such that: where: Creq ⁇ 1.5(%Cr+%Si+%Mo) Nieq ⁇ %Ni+0.3(%Mn)+%Cu+22(%C)+5%N
  • a product of this material (cast or wrought) is then solution treated by heating to a temperature in the range of 1107°C-1274°C (2050°F-2350°F), followed by rapid cooling (as with a water quench) to prevent formation of deleterious precipitates in the microstructure.
  • the specific composition and solution treatment temperature is selected so as to provide the desired combination of yield strength, impact toughness and corrosion resistance.
  • FIG. 2 shows a computer-drawn representation of the relationship between chromium equivalent: Nickel equivalent ratio, test temperature and impact toughness for cast material given a 1190°C (2200°F) solution treatment.
  • the experimental data used to develop this diagram are presented in Table II. Inspection of the diagram clearly shows that by maintaining low Creq:Nieq ratios, higher impact toughnesses can be realized.
  • the superior impact toughness of cast material of the inventive alloy can be appreciated when it is compared to the toughness of other cast duplex stainless steels having similar strength. Two such materials are Alloy 2205 and Ferralium Alloy 255*.
  • the impact toughness of these alloys and the inventive alloy are compared in Fig.3. It can be easily seen that the inventive alloy possesses considerably greater impact toughness, particularly at low temperatures. At -87.5°C (-100°F) the lowest impact toughness value of the inventive alloy was about 121.5J (90 ft. lbs)**. The best value of the other two alloys at -87.5°C (-100°F) was below 54J (40 ft. lbs).
  • the inventive alloy also shows superior weldability. While high strength duplex stainless steels of the prior art are known to suffer severe embrittlement in the HAZs of welds, this invention produces material which is far more resistant to the problem. In order to illustrate this, test welds were made in cast material from four heats of the inventive alloy, four heats of Ferralium Alloy 255 and one heat of Alloy 2205. Prior to welding, the inventive alloy material had been solution treated at 1190°C (2200°F), while the other materials had been solution treated at 1107°C (2050°F).
  • the HAZ impact toughness results are presented in graphical form in Fig.4. While the inventive material did show some loss of toughness (see Table II), the HAZs of the other alloys were seriously degraded in toughness.
  • the inventive alloy had HAZ impact toughness values above 67.5J (50 ft. lbs) at -87.5°C (-100°F) while the other two alloys gave values less than 27J (20 ft.lbs) at the same temperatures.
  • the corrosion resistance of the inventive alloy is similar to that of high strength duplex stainless steels of the prior art. For chloride-containing environments, this has been established electrochemically. Specimens of the inventive alloy and other duplex stainless steels have been subjected to rapid scan potentio-dynamic tests in a deaerated solution of water plus 5% sodium chloride plus 0.01M hydrochloric acid. The results of this comparison testing are presented in graph form in FIG. 5. Clearly, the test results of the inventive alloy are at least as good as those of any of the other alloys examined. It is appreciated that electrochemical corrosion resistance data are highly dependent upon technique and the specific test method. However, the tests performed were consistent so as to obtain data that were as comparable as possible.
  • the material of this invention has superior resistance to cracking in sour (H2S-bearing) environments.
  • H2S-bearing sour
  • NACE Standard TM-01-77 This test involves stressing tensile specimens of the material being studied in a solution simulating conditions in sour oil wells.
  • the solution consists of water, sodium chloride and acetic acid through which hydrogen sulfide and carbon dioxide gases are bubbled.
  • Specimens are stressed to various percentages of their yield strengths in order to determine the highest stress level at which fracture does not occur. The higher this stress level, the better the material's cracking resistance.
  • compositions can be utilized. These are shown in Table IV. For example, when superior corrosion resistance in chloride-containing environments is desired, composition "C” is advantageously employed. If maximum toughness is desired, composition “A” is preferred. Composition “A” is also preferred for thick-section parts since it is more resistant to formation of deleterious precipitates. Composition “B” offers a combination of improved corrosion resistance compared to Composition “A”, but with improved toughness with respect to Composition “C”. For further clarification, consider the following examples:
  • composition "A" would be selected.
  • a heat of the inventive alloy would be produced and solution treated at a temperature selected to give the desired yield strength level.

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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)
  • Heat Treatment Of Articles (AREA)

Claims (6)

  1. Rostfreier Duplex-Stahl mit Austenit-Ausbildungen in einer Ferrit-Matrix entstanden durch Erwärmen auf eine Temperatur im Bereich von 1107 °C - 1274 °C (2050 °F -  2350 °F) und danach schnellem Abkühlen, wobei der genannte Stahl besteht aus Kohlenstoff 0,001 bis 0,08 Gew.-% Mangan 0,001 bis 2,00 Gew.-% Silicium 0,001 bis 1,50 Gew.-% Chrom 20,00 bis 27,50 Gew.-% Nickel 8,00 bis 11,00 Gew.-% Molybdän 3,00 bis 4,50 Gew.-% Schwefel 0,0001 bis 0,050 Gew.-% Phosphor 0,0001 bis 0,050 Gew.-% Stickstoff 0,10 bis 0,30 Gew.-% Eisen Rest
    und normalen Verunreinigungen, so daß:
    Figure imgb0023
     wobei:

    Creq ≡ 1,5(%Cr + %Si + %Mo)
    Figure imgb0024
    Nieq ≡ %Ni + 0,3(%Mn) + %Cu + 22(%C) + 5%N
    Figure imgb0025

    und in der gegossenen Form größere Schlagzähigkeitswerte aufweist als Ferralium Alloy 255 und SAF 2205, wobei die Schlagzähigkeit bei V-Kerbprüfungen nach Charpy bei -87,5 °C (-100 °F) über 101,25 J (75 ft.lbs) liegt, wenn von Kielblöcken nach ASTM E23-82 geprüft wird, die Schlagzähigkeit in wärmebelasteten Zonen (HAZ) bei -87,5 °C (-100 °F) über ungefähr 67,5 J (50 ft.lbs) liegt und eine Streckgrenze von mindestens 448,2 MPa (65 KSI) aufweist.
  2. Rostfreier Duplex-Stahl nach Anspruch 1, dadurch gekennzeichnet, daß er enthält: Kohlenstoff 0,07 Gew.-% MAX Mangan 2,00 Gew.-% MAX Silicium 1,50 Gew.-% MAX Chrom 20,50 - 22,50 Gew.-% Nickel 8,00 - 9,50 Gew.-% Molybdän 3,00 - 4,00 Gew.-% Stickstoff 0,10 - 0,25 Gew.-% Schwefel 0,025 Gew.-% MAX Phosphor 0,04 Gew.-% MAX
  3. Rostfreier Duplex-Stahl nach Anspruch 1, dadurch gekennzeichnet, daß er enthält: Kohlenstoff 0,07 Gew.-% MAX Mangan 2,00 Gew.-% MAX Silicium 1,50 Gew.-% MAX Chrom 22,50 - 24,00 Gew.-% Nickel 8,50 - 10,00 Gew.-% Molybdän 3,00 - 4,00 Gew.-% Stickstoff 0,15 - 0,25 Gew.-% Schwefel 0,025 Gew.-% MAX Phosphor 0,04 Gew.-% MAX
  4. Rostfreier Duplex-Stahl nach Anspruch 1, dadurch gekennzeichnet, daß er enthält: Kohlenstoff 0,07 Gew.-% MAX Mangan 2,00 Gew.-% MAX Silicium 1,50 Gew.-% MAX Chrom 23,50 - 26,00 Gew.-% Nickel 9,00 - 10,50 Gew.-% Molybdän 3,00 - 4,00 Gew.-% Stickstoff 0,15 - 0,25 Gew.-% Schwefel 0,025 Gew.-% MAX Phosphor 0,04 Gew.-% MAX
  5. Verfahren zur Herstellung eines rostfreien Duplex-Stahls gekennzeichnet durch Herstellung einer Charge von rostfreiem Duplex-Stahl mit einer Zusammensetzung wie in einem der Ansprüche 1 bis 4 dargestellt und Lösungsglühen durch Erwärmen auf eine Temperatur im Bereich von 1107 °C - 1274 °C (2050 °F - 2350 °F).
  6. Verfahren nach Anspruch 5, gekennzeichnet durch schnelles Abkühlen nach dem Lösungsglühen.
EP19870311114 1985-11-26 1987-12-17 Verfahren zur Herstellung rostfreien Duplexstahls und Bauteile aus rostfreiem Duplexstahl mit verbesserten mechanischen Eigenschaften Expired EP0320548B1 (de)

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Application Number Priority Date Filing Date Title
US06/864,333 US4715908A (en) 1985-11-26 1986-05-19 Duplex stainless steel product with improved mechanical properties
DE19873781160 DE3781160T2 (de) 1987-12-17 1987-12-17 Verfahren zur herstellung rostfreien duplexstahls und bauteile aus rostfreiem duplexstahl mit verbesserten mechanischen eigenschaften.
EP19870311114 EP0320548B1 (de) 1987-12-17 1987-12-17 Verfahren zur Herstellung rostfreien Duplexstahls und Bauteile aus rostfreiem Duplexstahl mit verbesserten mechanischen Eigenschaften

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EP19870311114 EP0320548B1 (de) 1987-12-17 1987-12-17 Verfahren zur Herstellung rostfreien Duplexstahls und Bauteile aus rostfreiem Duplexstahl mit verbesserten mechanischen Eigenschaften

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AT397515B (de) * 1990-05-03 1994-04-25 Boehler Edelstahl Hochfeste korrosionsbeständige duplex-legierung
US5411545A (en) * 1994-03-14 1995-05-02 Medtronic, Inc. Medical electrical lead
CN114346142B (zh) * 2022-01-18 2023-07-14 山西太钢不锈钢股份有限公司 一种提高s32750超级双相不锈钢圆钢低温冲击韧性的锻造方法

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GB1307401A (en) * 1970-03-18 1973-02-21 Nippon Kokan Kk Austenitic heat resisting stainless steel
US4405389A (en) * 1982-10-21 1983-09-20 Ingersoll-Rand Company Austenitic stainless steel casting alloy for corrosive applications
US4500351A (en) * 1984-02-27 1985-02-19 Amax Inc. Cast duplex stainless steel
SE453838B (sv) * 1985-09-05 1988-03-07 Santrade Ltd Hogkvevehaltigt ferrit-austenitiskt rostfritt stal

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