EP0246092A2 - Durch Spannungskorrosion gegen Rissbildung beständige Legierungen - Google Patents

Durch Spannungskorrosion gegen Rissbildung beständige Legierungen Download PDF

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Publication number
EP0246092A2
EP0246092A2 EP87304275A EP87304275A EP0246092A2 EP 0246092 A2 EP0246092 A2 EP 0246092A2 EP 87304275 A EP87304275 A EP 87304275A EP 87304275 A EP87304275 A EP 87304275A EP 0246092 A2 EP0246092 A2 EP 0246092A2
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EP
European Patent Office
Prior art keywords
alloy
alloys
carbide
chromium
carbides
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP87304275A
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English (en)
French (fr)
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EP0246092A3 (de
Inventor
Raghaven Ayer
Henry Charles Hayworth
Michael Joseph Humphries
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ExxonMobil Technology and Engineering Co
Original Assignee
Exxon Research and Engineering Co
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Publication date
Application filed by Exxon Research and Engineering Co filed Critical Exxon Research and Engineering Co
Publication of EP0246092A2 publication Critical patent/EP0246092A2/de
Publication of EP0246092A3 publication Critical patent/EP0246092A3/de
Withdrawn legal-status Critical Current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
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/07—Alloys based on nickel or cobalt based on cobalt
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum

Definitions

  • the present invention relates to iron, nickel, and cobalt based alloys containing 12-50 wt.% Cr and 0.001 to 0.2 wt.% carbon, which alloys are substantially free of chromium carbides at equilibrium at temperatures from about 425°C - 750 0 C.
  • Sensitization is the term commonly used to describe precipitation of chromium, carbides at the grain boundaries of the alloy and the consequent depletion of chromium in the matrix adjacent to the grain boundaries. It is accepted in the art that the depletion of chromium from the matrix renders the alloy susceptible to intergranular corrosion and stress corrosion cracking.
  • niobium and titanium carbides are more stable than chromium carbides, at equilibrium, in their presence, there is still enough carbon left in the matrix at equilibrium to cause precipitation of chromium carbides at the grain boundaries at temperatures from about 425 0 C to 750°C.
  • iron, nickel, and cobalt based austenitic alloys containing from about 12-50 wt.% Cr, from about 0.001 - 0.2 wt.% C, and at least one carbide forming element whose carbide is more stable than chromium carbide, and which alloy, at equilibrium, generates a carbon concentration in solution which is insufficient to form chromium carbides at a temperature from about 425°C - 750 0 C.
  • the alloys are comprised of:
  • up to 3 wt.% Mn, up to 0.2 wt.% Al and up to 0.5% Si are present.
  • the alloys contain about 15-25 wt.% Cr, 70-80 wt.%. Ni, 0.001 - 0.2 wt.% C, and Hf in an amount from about 10(C+0+N) to about 30(C+O+N), where C, 0, and N are based on wt.%.
  • the Figure hereof are photomicrographs showing the microstructure of alloys A, B, D, and E of the examples, after exposure at 1040°C for one hour followed by exposure at 590°C for 1000 hours. These photomicrographs illustrate the preferential attack at the grain boundaries by the oxalic acid etch as evidenced by voids, or holes, at the grain boundaries. It can be observed in these photomicrographs that the grain boundaries of alloy E are not attacked by the oxalic acid etch, this is because of the absence of chromium carbides and, hence, absence of depletion of chromium at the grain boundaries of alloy E.
  • chromium carbides are detrimental to the intergranular corrosion and stress corrosion cracking resistance of austenitic alloys because they deplete the grain boundaries, and the regions neighboring the grain boundaries, of chromium.
  • the formation of chromium carbides is avoided by the addition of one or more carbide forming elements whose carbide is more stable than chromium carbide and which alloy, at equilibrium, has a carbon concentration, in the matrix, which is insufficient to form chromium carbides at a temperature from about 425°C to 750°C.
  • Preferred carbide forming elements suitable for use in the present invention are hafnium for iron, nickel, and cobalt based alloys, and tanatalum, for iron based alloys. Such carbide forming elements are present in an amount sufficient so that the concentration of carbon in the matrix is too low to cause precipitation of chromium carbides. This amount, generally based on weight percent, is equal to or greater than, about 10(C+0+N) but less than or equal to about 30(C+O+N), preferably about 15(C+O+N). For economical reasons it may be desirable to use lower cost Hf-Zr alloys as opposed to the more expensive elemental Hf.
  • Hf-Zr alloys are a by-product of the manufacturing process for producing Zr fuel rods in the nuclear industry and are available at a fraction of the cost of Hf. If Hf-Zr alloys are used in the practice of the present invention, they should be used such that no more than 0.75 wt.% Zr is present in the final alloy.
  • the use of such carbide forming elements in these amounts substantially eliminates the precipitation of chromium' carbides at the grain boundaries, thus resulting in a alloy having improved resistance to intergranular corrosion and stress corrosion cracking. Because the concentration of oxygen and nitrogen are usually much smaller with respect to carbon, the above criteria concerning the addition of hafnium and tantalum may be satisfied by considering the concentration of carbon alone.
  • the elements, and their concentrations, comprising the alloys of the present invention are important because their combination results in a class of alloys having unexpectedly good resistance to intergranular corrosion and stress corrosion cracking.
  • Chromium is important in the alloys of the present invention because it increases the overall corrosion resistance of the alloy. It will be noted though that increasing amounts of chromium leads to the formation of sigma, or other similar intermetallic phases.
  • the amount of chromium needed to provide corrosion resistance for the alloys of the present invention is at least about 12 wt.%, while a chromium content of up to about 50 wt.% may be needed in more severe corrosive environments and/or high temperatures.
  • Another preferred alloy is comprised of about 19 to 23 wt.% Cr, about 30 to 35 wt.% Ni, about 1.5 wt.% Mn, about 0.06 to 0.1 wt.% C, about 0.06 to 0.1 wt.% A l, up to about 0.5 wt.% Si, Hf in an amount of about 20(C+0+N), the balance being Fe.
  • More preferred alloys of the present invention are comprised of about -17 to 19 wt.% Cr, about 9 to 12 wt.% Ni, about 1.5 to 2.5 wt.% Mn, up to about 0.5 wt.% Si, less than about 0.08 wt.% C, Hf in an amount of about 20(C+O+N), the balance being Fe.
  • hafnium and/or tantalum in the iron based alloys and hafnium in the iron, nickel, and cobalt based alloys of the present invention results in the formation of stable hafnium and/or tantalum carbides.
  • the formation of hafnium and tantalum carbides decreases the carbon concentration of the matrix, thereby leaving the concentration of carbon too low for the precipitation of chromium carbides.
  • Other known carbide forming elements, such as niobium and titanium, in the alloys of the present invention were surprisingly found not to have the same beneficial effect as hafnium and tantalum.
  • niobium and titanium also deplete carbon from the matrix and result in the formation of stable niobium and titanium carbides, enough carbon still remains in the matrix, at equilibrium at a temperature of about 425°C to 750 P C, to result in formation of chromium carbides.
  • Hf is the preferred carbide forming element.
  • the alloys of the present invention may contain incidental impurities such as B, Sn, Pb, Zn, Bi, etc., each in an amount less than about 0.01 wt.%, as long as they do not render an adverse effect on the properties of the alloy.
  • the experimental alloys used herein were prepared from substantially pure-element raw materials. The individual elements were weighed to constitute about 50 lbs and melted in a vacuum induction furnace. Once the major alloying elements were molten, the molten metal was poured into a 2-1/2 inch diameter cast iron mold. The solidified casting was stripped from the mold, homogenized at 1200°C, and hot rolled at 1000 0 C to produce 1/2 inch thick plates.
  • Alloys A and B are commercially available alloy compositions with Alloy A containing Ti and Alloy B containing Nb and Ta. Alloy B is considered to be the best . commercially available conventional alloy in the industry to resist polythionic acid stress corrosion cracking. Alloys C, D and E are alloys of the present invention. These alloys contain Hf/C ratios ranging from 3.8 for alloy C, to 14.4 for alloy E. Although Alloys C , D, and E contain Ti, they all contain enough Hf, based on the amount of carbon, to prevent the formation of chromium carbides.
  • the data in Table II show that all of the alloys contained primary carbides (Ti, Nb, Ta, Hf-carbides) before aging, with the type and amount of carbide varying from alloy to alloy.
  • the commercial alloys A and B contain TiC and (Nb,Ta)C, respectively, while the alloys of the present invention contain T iC and HfC.
  • alloy A and alloy C form chromium carbides while alloy B and alloy D did not form any Cr carbides or any other precipitates.
  • Alloy E formed small amounts of Fe 2 (Hf,Ti) intermetallic precipitates both in the grains and at the grain boundaries. This was caused by the presence of titanium which is normally not required in the alloy.
  • Figure 1 shows the microstructure of the alloys after 1000 hrs. of aging.
  • the formation of the chromium carbides are seen as holes at the grain boundaries. These holes are the result of preferential attack of the chromium depleted regions around the carbides by a 10% oxalic acid etch used to reveal the structure of the alloys.
  • Alloys A, B, and D were etched for 15 seconds and alloy E for 45 seconds. Alloy E was etched for 45 seconds because after 15 seconds no sign of attack at .the grain boundaries was observed. Even after etching for 45 seconds, Alloy E showed no sign of grain boundary attack.
  • the absence of chromium carbides in alloy E is the result of Hf addition in sufficient quantities to tie up all or most of the carbon such that insufficient carbon is left to form detrimental chromium carbides during the aging treatment.
  • the reduced carbon level at equilibrium at a temperature of 425°C to 750°C is below that level at which chromium carbide can form.
  • the data show that precipitation of chromium carbide can be prevented by the addition of a sufficient quantity of a strongly carbide forming element which reduces the equilibrium concentration of dissolved carbon in the matrix to a level below that at which chromium carbide can form.

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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)
  • Catalysts (AREA)
  • Materials For Medical Uses (AREA)
EP87304275A 1986-05-15 1987-05-14 Durch Spannungskorrosion gegen Rissbildung beständige Legierungen Withdrawn EP0246092A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US86350886A 1986-05-15 1986-05-15
US863508 1986-05-15

Publications (2)

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EP0246092A2 true EP0246092A2 (de) 1987-11-19
EP0246092A3 EP0246092A3 (de) 1989-05-03

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EP87304275A Withdrawn EP0246092A3 (de) 1986-05-15 1987-05-14 Durch Spannungskorrosion gegen Rissbildung beständige Legierungen

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EP (1) EP0246092A3 (de)
JP (1) JPS6326336A (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0332460A1 (de) * 1988-03-11 1989-09-13 General Electric Company Austenitische rostfreie Stahllegierung
WO1998004757A1 (de) * 1996-07-25 1998-02-05 Schmidt + Clemens Gmbh & Co., Edelstahlwerk Kaiserau Austenitische nickel-chrom-stahllegierung
US6173702B1 (en) 1996-05-15 2001-01-16 Man B&W Diesel A/S Movable wall member in the form of an exhaust valve spindle or a piston in an internal combustion engine
GB2394960A (en) * 2002-11-04 2004-05-12 Doncasters Ltd Hafnium oxide dispersion hardened nickel-chromium-iron alloys
GB2394959A (en) * 2002-11-04 2004-05-12 Doncasters Ltd Hafnium particle dispersion hardened nickel-chromium-iron alloys
WO2015018017A1 (en) * 2013-08-08 2015-02-12 General Electric Company Precipitation-hardened stainless steel alloys

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5147602A (en) * 1991-05-20 1992-09-15 General Electric Company Corrosion resistant high chromium stainless steel alloy

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3366478A (en) * 1965-07-21 1968-01-30 Martin Marietta Corp Cobalt-base sheet alloy
US4764225A (en) * 1979-05-29 1988-08-16 Howmet Corporation Alloys for high temperature applications
GB2083499A (en) * 1980-09-05 1982-03-24 Firth Brown Ltd Austenitic steel
DE3121782C2 (de) * 1981-05-27 1986-05-07 Mannesmann AG, 4000 Düsseldorf Verwendung einer austenitischen Chrom-Nickel-Stahllegierung für Wärmetauscherkomponenten
JPS61130464A (ja) * 1984-11-30 1986-06-18 Nippon Steel Corp 高耐食性高強度ドリルカラ−用非磁性鋼

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0332460A1 (de) * 1988-03-11 1989-09-13 General Electric Company Austenitische rostfreie Stahllegierung
US6173702B1 (en) 1996-05-15 2001-01-16 Man B&W Diesel A/S Movable wall member in the form of an exhaust valve spindle or a piston in an internal combustion engine
WO1998004757A1 (de) * 1996-07-25 1998-02-05 Schmidt + Clemens Gmbh & Co., Edelstahlwerk Kaiserau Austenitische nickel-chrom-stahllegierung
US6409847B2 (en) 1996-07-25 2002-06-25 Schmidt & Clemens Gmbh & Co. Austenitic nickel-chromium steel alloys
GB2394960A (en) * 2002-11-04 2004-05-12 Doncasters Ltd Hafnium oxide dispersion hardened nickel-chromium-iron alloys
GB2394959A (en) * 2002-11-04 2004-05-12 Doncasters Ltd Hafnium particle dispersion hardened nickel-chromium-iron alloys
GB2394960B (en) * 2002-11-04 2007-04-25 Doncasters Ltd High temperature alloys
WO2015018017A1 (en) * 2013-08-08 2015-02-12 General Electric Company Precipitation-hardened stainless steel alloys

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Publication number Publication date
JPS6326336A (ja) 1988-02-03
EP0246092A3 (de) 1989-05-03

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