EP0780483B1 - Hochfester wärmebeständiger austenitischer Stahl mit verbesserter Schweissbarkeit - Google Patents

Hochfester wärmebeständiger austenitischer Stahl mit verbesserter Schweissbarkeit Download PDF

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Publication number
EP0780483B1
EP0780483B1 EP19960120536 EP96120536A EP0780483B1 EP 0780483 B1 EP0780483 B1 EP 0780483B1 EP 19960120536 EP19960120536 EP 19960120536 EP 96120536 A EP96120536 A EP 96120536A EP 0780483 B1 EP0780483 B1 EP 0780483B1
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EP
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Prior art keywords
amount
steels
strength
present
content
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EP19960120536
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English (en)
French (fr)
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EP0780483A1 (de
Inventor
Tetsuo c/o Nippon Steel Corporation Ishitsuka
Hiroyuki c/o Nippon Steel Corporation Mimura
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Nippon Steel Corp
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Nippon Steel Corp
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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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium

Definitions

  • the present invention relates to an austenitic heat-resisting steel having an excellent high-temperature strength, an improved weldability, and a high resistance to grain boundary corrosion and advantageously applicable to boilers used under severe service conditions.
  • An object of the present invention is to provide an austenitic heat-resisting steel having a good weldability and high-temperature strength.
  • a high-strength austenitic heat-resisting steel having improved weldability, consisting of:
  • a high-strength austenitic heat-resisting steel having improved weldability, consisting of:
  • the C amount must be reduced to as little as possible to prevent high-temperature cracking during welding or reduction in elongation. To ensure good weldability, the upper limit of the C content was determined based on the following experimental results.
  • Figure 1 shows a Varestraint test result indicating the weldability for steels (plots " ⁇ ") containing main components in amounts falling within the specified range of the present invention (Cr: 18%, Ni: 13%, W: 4%) except that the C content was varied, and a reference steel of JIS SUS310STB (plots " ⁇ ", corresponding to Comparative Steel Q in Examples to follow). It can be seen from Fig. 1 that the weldability is better than that of JIS SUS310STB when the C content is less than 0.05%. The upper limit of the C content was thus determined to be less than 0.05%.
  • Si is not only effective as a deoxidizer but also improves the oxidation resistance and the resistance to high-temperature corrosion. However, Si, when present in an excessive amount, reduces the creep rupture strength, the toughness and the weldability, and therefore, the Si content is limited to not more than 5%.
  • Mn is a deoxidizer and improves the weldability and the hot workability.
  • Mn when present in an excessive amount, causes degradation of the oxidation resistance, and therefore, the Mn content is limited to less than 2%.
  • Cr is essential for the oxidation resistance, resistance to steam oxidation, and resistance to high-temperature corrosion. To ensure properties comparable with or better than those of the conventional austenitic stainless steels, Cr must be present in an amount of not less than 15%. However, Cr, when present in an excessive amount, causes an increase in the Ni amount necessary to stabilize austenite and is not economical, and therefore, the Cr content is limited to not more than 20%.
  • Ni is essential for improving the stability of austenite and suppressing the formation of the ⁇ phase.
  • Ni In the steel according to the present invention, Ni must be present in an amount of 6% or more to stabilize austenite with respect to Cr and other ferrite formers present in the specified amounts.
  • the use of Ni in a large amount is not economical, and therefore, the Ni content is limited to not more than 15%.
  • Mo, W: Mo and W improve the high-temperature strength by solid solution strengthening or precipitation of the Laves phase and the effect is generally described as a function of the (Mo + W)% as shown in Fig. 2. It can be seen from Fig. 2 that, when the total amount of Mo and W is 2% or more, the creep rupture strength is sharply improved and the improvement is not substantially increased if the total amount of Mo and W is more than 10%.
  • the creep rupture strength substantially varies with the amounts of C and Nb.
  • the amounts of C and Nb are 0.025% or more and 0.25% or more, respectively, an improved creep rupture strength is obtained through a synergistic or combined effect of the W or W + Mo amount and the C + Nb amount.
  • the synergistic effect is not obtained when the W or W + Mo amount is less than 1.5%.
  • Mo and W when present in a total amount of more than 10%, also cause a problem in that the Laves phase and other intermetallic compounds coarsen and reduce the creep rupture strength.
  • W when Mo is added alone or not combined with W, the resistance to high-temperature corrosion is reduced with increase of the Mo amount as shown in Fig. 3.
  • W even when added alone or not combined with Mo, does not cause reduction in the resistance to high-temperature corrosion, and when combined with Mo, improves the resistance to high-temperature corrosion in comparison with that achieved when Mo alone is added. Therefore, W must be present in an amount of 1.5 to 10%. Mo may be present in combination with W but the Mo content must not be more than 2.0% because the resistance to high-temperature corrosion is sharply reduced when the Mo content is more than 2.0%, even when combined with W.
  • Nb sharply improves the long duration creep rupture strength by the formation of fine carbonitrides.
  • the Nb content must be 0.1% or more as can be seen from Fig. 4. The effect becomes more significant as the Nb amount is increased within a range in which Nb is completely dissolvable in a solid solution state. However, when the Nb amount is more than this range, undissolved carbides and nitrides are retained to reduce the creep rupture strength. Therefore, the Nb amount must not be more than 0.5%.
  • V forms fine nitrides and improves the long duration creep rupture strength. As shown in Fig. 5, this effect is obtained when the V amount is 0.05% or more and the improvement is reduced when the V amount is more than 1.5%. Therefore, the V amount is 0.05 to 1.5%.
  • P forms phosphides and improves the long duration creep rupture strength as shown in Fig. 6.
  • P when present in an excessive amount, sharply reduces not only the weldability but also the hot workability, and therefore, the P must not be present in an amount of more than 0.03%.
  • S segregates at crystal grain boundaries and reduces the hot workability and also facilitates the grain boundary embrittlement under the creep condition, and therefore, the S content is limited to not more than 0.005%.
  • N sharply improves the creep rupture strength by solid solution strengthening and the formation of nitrides. To compensate for the strength reduction because of the reduced C content for ensuring an improved weldability, N must be present in an amount of more than 0.15%. However, when N is present in an amount of more than 0.4%, the improvement in the long time creep rupture strength is not substantially increased but the toughness is reduced. Therefore, the N content is more than 0.15% and up to 0.4%.
  • Tables 1-1 and 2-1 summarize the chemical compositions and the properties of the steels tested. After being subjected to a solid solution heat treatment at 1250°C, the steels were subjected to a Varestraint test, a creep rupture test at 700, 750 and 800°C, and a high-temperature corrosion test at 650°C.
  • the Varestraint test was carried out using the GTAW welding method, under the conditions of a test piece thickness of 4 mm, a welding voltage of 10V, a welding current of 80A, a welding speed of 80 mm/min, and an applied strain of 4%.
  • the creep rupture data were standardized by the Larson-Miller method to estimate the creep rupture strength at 650°C for 100,000 hours.
  • the test results are summarized in Tables 1-2 and 2-2.
  • the steels A to Q in Tables 1-1 and 1-2 are the present inventive steels and the steels R to AI in Tables 2-1 and 2-2 are comparative steels.
  • Steels R and S correspond to JIS SUS347H and JIS SUS310S, respectively, which are commonly used in the conventional art.
  • the present inventive steels A to Q have a remarkably improved high-temperature strength and resistance to high-temperature corrosion in comparison with the comparative steel R or JIS SUS347H and an improved weldability in comparison with the comparative steel S or JIS SUS310S.
  • the comparative steels S to V have a poor weldability and exhibit a large total crack length in the Varestraint test.
  • the comparative steels X to Z contain W in amounts less than the present inventive range and the comparative steels AE, AF, AG contain Nb, V and N in amounts less than the present inventive ranges, respectively, so that all these comparative steels X to AG have a poor high-temperature strength.
  • the comparative steels AA to AD contain Mo in an amount more than the present inventive range and have an improved high-temperature strength but have a poor resistance to high-temperature corrosion.
  • inventive steel P and the comparative steels W and AH demonstrate the synergistic effect of the combined addition of W with C and Nb, in which the inventive steel P contains more than 0.025% C and more than 0.25% Nb and has an improved high-temperature strength even though the W content is near the lower limit of the specified range, whereas the comparative steel W contains less than 0.025% C and less than 0.25% Nb and has a poor high-temperature strength and the comparative steel AH contains W in an amount less than the lower limit of the specified range and has a poor high-temperature strength although C and Nb are present in amounts more than 0.025% and 0.25%, respectively.
  • the comparative steel AI contains an excessive amount of P and has an improved high-temperature strength but has a poor weldability.
  • the present invention provides a high-strength austenitic heat-resisting steel, having an improved weldability, which is inexpensive and commercially applicable.

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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)

Claims (2)

  1. Hochfester austenitischer wärmebeständiger Stahl mit verbesserter Schweißbarkeit, bestehend aus:
    C: weniger als 0,05 Gew.-%,
    Si: nicht mehr als 5 Gew.-%,
    Mn: weniger als 2 Gew.-%,
    P: nicht mehr als 0,03 Gew.-%,
    S: nicht mehr als 0,005 Gew.-%,
    Cr: 15 bis 20 Gew.-%,
    Ni: 6 bis 15 Gew.-%,
    W: 1,5 bis 10 Gew.-%,
    Nb: mehr als 0,1 bis zu 0,5 Gew.-%,
    V: 0,05 bis 1,5 Gew.-%,
    N: mehr als 0,15 bis zu 0,4 Gew.-%, wobei der Rest aus Fe und unvermeidlichen Verunreinigungen besteht.
  2. Hochfester austenitischer wärmebeständiger Stahl mit verbesserter Schweißbarkeit, bestehend aus:
    C: weniger als 0,05 Gew.-%,
    Si: nicht mehr als 5 Gew.-%,
    Mn: weniger als 2 Gew.-%,
    P: nicht mehr als 0,03 Gew.-%,
    S: nicht mehr als 0,005 Gew.-%,
    Cr: 15 bis 20 Gew.-%,
    Ni: 6 bis 15 Gew.-%,
    W: 1,5 bis 10 Gew.-%,
    Mo: nicht mehr als 2,0 Gew.-% und innerhalb des durch Mo + W ≤ 10 Gew.-% definierten Bereichs,
    Nb: mehr als 0,1 bis zu 0,5 Gew.-%,
    V: 0,05 bis 1,5 Gew.-%,
    N: mehr als 0,15 bis zu 0,4 Gew.-%, wobei der Rest aus Fe und unvermeidlichen Verunreinigungen besteht.
EP19960120536 1995-12-20 1996-12-19 Hochfester wärmebeständiger austenitischer Stahl mit verbesserter Schweissbarkeit Expired - Lifetime EP0780483B1 (de)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
JP332341/95 1995-12-20
JP33234195 1995-12-20
JP33234195 1995-12-20
JP13541296 1996-05-29
JP135412/96 1996-05-29
JP13541296A JP3388998B2 (ja) 1995-12-20 1996-05-29 溶接性に優れた高強度オーステナイト系耐熱鋼

Publications (2)

Publication Number Publication Date
EP0780483A1 EP0780483A1 (de) 1997-06-25
EP0780483B1 true EP0780483B1 (de) 2002-04-17

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EP19960120536 Expired - Lifetime EP0780483B1 (de) 1995-12-20 1996-12-19 Hochfester wärmebeständiger austenitischer Stahl mit verbesserter Schweissbarkeit

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EP (1) EP0780483B1 (de)
JP (1) JP3388998B2 (de)
DE (1) DE69620722T2 (de)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4523696B2 (ja) * 2000-04-18 2010-08-11 新日本製鐵株式会社 高温強度に優れたオーステナイト系耐熱鋼用ｔｉｇ溶接材料
DE10063117A1 (de) * 2000-12-18 2003-06-18 Alstom Switzerland Ltd Umwandlungskontrollierter Nitrid-ausscheidungshärtender Vergütungsstahl
JP3838216B2 (ja) * 2003-04-25 2006-10-25 住友金属工業株式会社 オーステナイト系ステンレス鋼
EP2730365B1 (de) * 2011-07-06 2018-08-08 Nippon Steel & Sumitomo Metal Corporation Schweissverbindung aus einem austenisierten stahl
JP5661001B2 (ja) * 2011-08-23 2015-01-28 山陽特殊製鋼株式会社 時効後靭性に優れた高強度オーステナイト系耐熱鋼
JP5794945B2 (ja) 2012-03-30 2015-10-14 新日鐵住金ステンレス株式会社 耐熱オーステナイト系ステンレス鋼板
US20170268085A1 (en) 2015-06-05 2017-09-21 Nippon Steel & Sumitomo Metal Corporation Austenitic stainless steel

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB617194A (en) * 1945-06-13 1949-02-02 Haynes Stellite Co Alloys for high temperature use
LU52783A1 (de) * 1966-01-13 1967-03-10
BE715586A (de) * 1967-06-07 1968-10-16 Ugine Kuhlmann
JPH0694583B2 (ja) * 1984-10-03 1994-11-24 株式会社東芝 耐熱オーステナイト鋳鋼

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JP3388998B2 (ja) 2003-03-24
JPH09228003A (ja) 1997-09-02
DE69620722T2 (de) 2002-12-05
DE69620722D1 (de) 2002-05-23
EP0780483A1 (de) 1997-06-25

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