US20100089501A1 - Martensitic Creep Resistant Steel Strengthened by Z-Phase - Google Patents

Martensitic Creep Resistant Steel Strengthened by Z-Phase Download PDF

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Publication number
US20100089501A1
US20100089501A1 US12/530,048 US53004808A US2010089501A1 US 20100089501 A1 US20100089501 A1 US 20100089501A1 US 53004808 A US53004808 A US 53004808A US 2010089501 A1 US2010089501 A1 US 2010089501A1
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Prior art keywords
phase
steel alloy
martensitic
steel
components
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US12/530,048
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English (en)
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Hilmar Danielsen
John Hald
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Danmarks Tekniskie Universitet
Orsted AS
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Dong Energy AS
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Assigned to DANMARKS TEKNISKE UNIVERSITET reassignment DANMARKS TEKNISKE UNIVERSITET ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: DANIELSEN, HILMAR
Assigned to DONG ENERGY A/S reassignment DONG ENERGY A/S ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HALD, JOHN
Publication of US20100089501A1 publication Critical patent/US20100089501A1/en
Abandoned legal-status Critical Current

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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
    • 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

Definitions

  • the present invention relates to martensitic or martensitic-ferritic steel alloys and in particular to creep resistant alloys to be used for high temperature components.
  • the invention further relates to manufacturing of such steels.
  • Tempered martensitic steel alloys offer the best combination of creep strength, oxidation resistance, thermal expansion coefficient and yield strength.
  • the martensitic steels contain minor amounts of elements like C, N, V, Nb which form precipitate particles such as M 23 C 6 carbides and MX (V,Nb)-carbonitrides. These precipitate particles provide high creep strength by particle strengthening, but during prolonged exposure to high temperature the M 23 C 6 carbides will coarsen and loose their particle strengthening effect. The coarsening rate of MX particles is low and they will remain fine and provide a major contribution to high long-term creep strength.
  • Z-phase nitride has since long been known from austenitic stainless steels where it may precipitate as very fine particles, which remain fine and contribute to high creep strength. However, in martensitic steels Z-phase was always found to grow to large average particle sizes.
  • a steel alloy comprising by wt % the following components: 9 to 15% Cr, 0.01-0.20% N, C in an amount less than 0.1%, one or more of: 0.01-0.5% V, 0.01-1% Nb, 0.01-2% Ta, and a balance being substantially iron and inevitable impurities, said steel alloy having a martensitic or martensitic-ferritic structure and comprising Z-phase (CrXN) particles, where X is one or more of the elements V, Nb, Ta, and where the Z-phase particles have an average size of less than 400 nm, such as less than 300 nm, such as less than 200 nm, such as less than 100 nm.
  • the present invention is based on the idea that the precipitation of Z-phase particles should be accelerated to obtain a large number of particles and thereby a small particle size.
  • the Z-phase particles may precipitate either during heat treatment as a part of the manufacturing or during service exposure. It may be advantageous e.g. with respect to quality control before use, if the particles precipitate already during the manufacturing of the steel.
  • the steel alloy may further comprise one or more of the following components: Co in an amount less than 8%, one or more of Mo and W in an amount less than 4%, one or more of Mn, Ni and Cu in an amount less than 3%, Si in an amount less than 2%, and B in an amount less than 0.04%.
  • a second aspect of the invention relates to a method of manufacturing a steel alloy as described above, said method comprising the steps of melting the components, molding the melt to form a material, subjecting the molded material to a solution temperature between 1000° C. and 1300° C., and subjecting the molded material to a tempering treatment at a temperature between 500° C. and 850° C.
  • the duration of the manufacturing steps depends on the size of the component being manufactured and on specific requirements for toughness and tensile strength. For thin tubes the holding times at solution and tempering temperatures may be in the order of 15 min, whereas for a massive 40 ton turbine casing the holding times may amount to several tens of hours.
  • a third aspect of the invention relates to a high temperature component comprising a steel alloy as described above.
  • high temperature component is meant a component that is designed to be exposed to temperatures above 500° C.
  • a fourth aspect of the invention relates to the use of a steel alloy as described above for high temperature components. It may typically be for components in power generation boilers or turbines, nuclear power generation facilities, jet engines, or components in chemical industry.
  • the first, second, third and fourth aspect of the present invention may each be combined with any of the other aspects.
  • FIG. 1 is an example of experimental results from creep tests on a prior art steel.
  • FIG. 2 shows precipitates in a steel alloy comprising MX and M 23 C 6 particles.
  • FIG. 3 shows precipitates in a steel alloy comprising M 23 C 6 and coarse Z-phase particles.
  • FIG. 4 shows precipitates in a steel alloy according to the present invention comprising fine Z-phase particles.
  • the figure shows the microstructure after exposure to 650° C. for 17,000 hours.
  • FIG. 5 shows very fine Z-phase particles in Steel 1 of table 1 after exposure to 650° C. for 3000 hours.
  • Components for use in power plants should be designed to operate at high temperatures and stresses for very long times, preferably more than 30 years. It is not practical to test new materials for so long, and therefore long-term properties are estimated by extrapolating results from shorter-term tests. Double logarithmic plots of test stress vs. rupture time normally show smooth curves, but many 11-12% Cr steels suffer a breakdown in long-term strength and the curves bend after several thousand hours of testing. An example of such bent curves is given in FIG. 1 , showing creep test results for a steel with 0.1% C, 11% Cr, 3% Co, 3% W, and minor contents of V, Nb and N.
  • the said studies of Z-phase in martensitic steels included the development of a thermodynamic model, which enables the prediction of the Z-phase thermodynamic stability and precipitation rate as a function of alloy composition.
  • the model predicts that increasing the Cr content accelerates Z-phase precipitation, and in order to retard Z-phase precipitation beyond normal operation times (30 years), the Cr content must be limited to 9%.
  • FIG. 4 shows fine Z-phase particles with an average size of 80 nm in the model alloy with 0.04% C; 12% Cr; 1% Mo, 1% Ni, 0.5% Co, 0.4% Nb and 0.07% N after 17,000 hours at 650° C.
  • the fine Z-phase particles will thus contribute to high long-term creep strength of the alloy, and it will be possible to combine high creep strength by Z-phase precipitation with high oxidation resistance from a 12% Cr content in the same alloy.
  • the martensitic or martensitic-ferritic microstructure is obtained by subjecting a molded steel alloy to a solution temperature where the microstructure consists of austenite or austenite and ⁇ -ferrite. This microstructure is best obtained at solution temperatures between 1000° C. and 1300° C.
  • the holding time at the solution temperature is determined according to the component size and may vary from a few minutes to several hours.
  • the austenitic part of the microstructure Upon cooling from the solution temperature, the austenitic part of the microstructure transforms into martensite, thus a martensitic or a martensitic-ferritic microstructure is formed.
  • the martensite formed after solution treatment is brittle.
  • the steel alloy should be subjected to a tempering treatment at a temperature of at least 500° C. If the tempering temperature exceeds 850° C., part of the microstructure may transform into austenite, which could result in low toughness. Holding time at the tempering temperature depends on the specific requirements for strength and toughness. For thin tubes it may be as low as 30 minutes, whereas large massive turbine forgings may require several tens of hours.
  • Steel 2 was subjected to a heat treatment consisting of solution treatment at 1100° C. for one hour and cooled by air followed by tempering at 650° C. for 24 hours.
  • This steel has a microstructure consisting of tempered martensite.
  • Target of steel 3 is to demonstrate the combined strengthening effect of high Tungsten and CrNbN Z-phase.
  • Target of steel 4 is to demonstrate the strengthening effect of CrTaN Z-phase.
  • Chromium is necessary to obtain high oxidation and corrosion resistance of the steel, thus an amount of at least 9% is necessary. Furthermore, it is a necessary component in order to obtain fine precipitation of Z-phase particles. However, too high amount of Chromium will result in the formation of excess amount of ⁇ -ferrite. Thus the maximum limit of Chromium is set to 15%.
  • Nitrogen enhances the hardenability of steels with low carbon content and contributes to the formation of a martensitic structure. Since Nitrogen is a necessary component of Z-phase, it is added in an amount of at least 0.01%. Too high amount of Nitrogen may result in the formation of porosities in the molded material, and thus the content is limited to a maximum of 0.20%.
  • Carbon in too high amount will result in the formation of M 23 C 6 carbides, which will consume Cr from the steel and delay Z-phase precipitation. Furthermore, it may form MX carbides rich in Nb or Ta and prevent the formation of Z-phase based on these elements. Thus the Carbon content is limited to a maximum of 0.1%.
  • Vanadium, Niobium and Tantalum are essential components to form the Z-phase in combination with Chromium and Nitrogen. Thus, one or more of these components should be added to the steel in amounts higher than 0.01%.
  • the maximum content of these components is balanced with the content of Nitrogen in order to avoid coarsening of the Z-phase. Thus, the maximum content of the components are set to 0.5% for Vanadium, 1% for Niobium and 2% for Tantalum.
  • Molybdenum and Tungsten are added to provide further solid solution hardening or particle strengthening by formation of inter-metallic Laves phase Fe 2 (Mo,W). Too high an amount of each component may result in the formation of an excess amount of ⁇ -ferrite and reduction of the toughness of the steel. Thus the content of Molybdenum or Tungsten is set to a maximum of 4%.
  • Manganese, Nickel, Cobalt or Copper are added in order to suppress the formation of excessive amounts of ⁇ -ferrite. Too high amounts of each element may result in limited ability to temper the alloys or reduced ductility. Thus, the maximum amount of Cobalt is set to 8%, and the maximum content of each of the components Manganese, Nickel or Copper is set to 3%.
  • Silicium is added to improve steelmaking and to enhance oxidation and corrosion resistance. However, too high an amount of Silicium may result in degradation of the toughness. Thus the maximum content of Silicium is set to 2%.
  • Boron may enhance hardenability of the steel and contributes to high creep strength through grain boundary strengthening. However, too high an amount may result in degradation of the toughness. Thus, the maximum limit of Boron is set to 0.04%.
  • Steel alloys according to the present invention are particularly advantageous for high temperature components in fossil fired steam power plants.
  • use in other fields of applications is also covered by the scope of the present invention.
  • Steel alloys according to the present invention are typically homogenous at a macroscopic level.
  • in-homogenous steel structures are also covered by the scope of the present invention.
  • Such in-homogeneities could e.g. be a variation in particle size across the thickness of a component.

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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)
US12/530,048 2007-03-05 2008-02-28 Martensitic Creep Resistant Steel Strengthened by Z-Phase Abandoned US20100089501A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US12/530,048 US20100089501A1 (en) 2007-03-05 2008-02-28 Martensitic Creep Resistant Steel Strengthened by Z-Phase

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US90517507P 2007-03-05 2007-03-05
EP07103496.1 2007-03-05
EP07103496 2007-03-05
PCT/DK2008/050049 WO2008106978A1 (fr) 2007-03-05 2008-02-28 Acier martensitique résistant au fluage renforcé par phase z
US12/530,048 US20100089501A1 (en) 2007-03-05 2008-02-28 Martensitic Creep Resistant Steel Strengthened by Z-Phase

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US20100089501A1 true US20100089501A1 (en) 2010-04-15

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US (1) US20100089501A1 (fr)
EP (1) EP2122001A1 (fr)
JP (1) JP2010520372A (fr)
CN (1) CN101668872B (fr)
WO (1) WO2008106978A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102018202351A1 (de) * 2018-02-15 2019-08-22 Siemens Aktiengesellschaft Wärmebehandlung für einen NiCrMoV-Stahl und martensitischer Stahl
DE102018217304A1 (de) * 2018-10-10 2020-04-16 Siemens Aktiengesellschaft Wärmebehandlung für einen NiCrMoV-Stahl und martensitischer Stahl

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102943209B (zh) * 2012-11-16 2014-07-02 中国科学院金属研究所 一种与Pb和Pb-Bi具有良好相容性的耐辐射马氏体耐热钢
KR102197204B1 (ko) * 2013-06-25 2021-01-04 테나리스 커넥션즈 비.브이. 고크롬 내열철강
DE102016206370A1 (de) * 2016-04-15 2017-10-19 Siemens Aktiengesellschaft Martensitischer Stahl mit verzögerter Z-Phase-Bildung und Bauteil
CN110106436B (zh) * 2019-03-18 2020-12-01 东北大学 一种耐高温耐蒸汽耐腐蚀锅炉用钢及其制备方法
KR102326684B1 (ko) * 2019-09-17 2021-11-17 주식회사 포스코 크리프 강도와 고온 연성이 우수한 크롬강판 및 그 제조방법

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4484956A (en) * 1983-02-23 1984-11-27 Sumitomo Metal Industries, Ltd. Process for producing heat-resistant ferritic stainless steel sheet
US5310431A (en) * 1992-10-07 1994-05-10 Robert F. Buck Creep resistant, precipitation-dispersion-strengthened, martensitic stainless steel and method thereof
US20040154706A1 (en) * 2003-02-07 2004-08-12 Buck Robert F. Fine-grained martensitic stainless steel and method thereof
US6921440B2 (en) * 1999-09-09 2005-07-26 Ugine Sa Niobium-stabilized 14% chromium ferritic steel, and use of same in the automobile sector

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4484956A (en) * 1983-02-23 1984-11-27 Sumitomo Metal Industries, Ltd. Process for producing heat-resistant ferritic stainless steel sheet
US5310431A (en) * 1992-10-07 1994-05-10 Robert F. Buck Creep resistant, precipitation-dispersion-strengthened, martensitic stainless steel and method thereof
US6921440B2 (en) * 1999-09-09 2005-07-26 Ugine Sa Niobium-stabilized 14% chromium ferritic steel, and use of same in the automobile sector
US20040154706A1 (en) * 2003-02-07 2004-08-12 Buck Robert F. Fine-grained martensitic stainless steel and method thereof
US6899773B2 (en) * 2003-02-07 2005-05-31 Advanced Steel Technology, Llc Fine-grained martensitic stainless steel and method thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102018202351A1 (de) * 2018-02-15 2019-08-22 Siemens Aktiengesellschaft Wärmebehandlung für einen NiCrMoV-Stahl und martensitischer Stahl
DE102018217304A1 (de) * 2018-10-10 2020-04-16 Siemens Aktiengesellschaft Wärmebehandlung für einen NiCrMoV-Stahl und martensitischer Stahl

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CN101668872A (zh) 2010-03-10
EP2122001A1 (fr) 2009-11-25
CN101668872B (zh) 2012-01-11
JP2010520372A (ja) 2010-06-10
WO2008106978A1 (fr) 2008-09-12

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