Classifications

• • 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
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/053—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 30% but less than 40%
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S376/00—Induced nuclear reactions: processes, systems, and elements
  • Y10S376/90—Particular material or material shapes for fission reactors

Definitions

• the present invention relates to nickel-chromium and nickel-chromium-iron base alloys and, more particularly, to minimizing and/or overcoming the vexatious problem of stress-corrosion cracking of such alloys when exposed to a high purity water environment.
• the temperature of the high purity water is normally above room temperature and is commonly over 300 F., e.g. about 450 F. or 500 F. to about 660 F. and it is at such temperatures, particularly at the higher temperatures, where the occurrence of intergranular stress-corrosion attack is most likely.
• crevices in combination with aerated, high temperature, high purity water exert a most pronounced subversive influence in producing stress-corrosion cracking and other forms of corrosion. Whether the crevice by nature be a flaw, crack, sharp indentation or other such surface defect is rather inconsequential. The unfortunate fact remains that it is exceedingly difiicult, if not impossible, to avoid or prevent the occurence thereof. If the alloy is incapable of resisting stress-corrosion attack, there is also at least the likelihood of greater crevice buildup of corroded product.
• nickel-chromium and nickel-chromium-iron alloys wherein the amounts of chromium and/or iron are specially controlled or correlated alford markedly enhanced resistance to intergranular stress-corrosion attack when such alloy are brought into intimate contact with aerated high purity water at a temperature above about 300 F., e.g., 450 F. to about 660 F., notwithstanding the fact that the surface of such alloys contains a surface defect, such as a crevice.
• stress-corrosion cracking of nickel-chromium and nickel-chromiurn-iron alloys to be brought into contact with aerated high purity water, the temperature of the water being from above about 300 F. to about 660 F., e.g., 450 F. or 500 F.
• alloys of the following composition (based on weight percent): about 14% to about 35% chromium, up to about 50% iron, with the proviso that when the iron is present in an amount above about 0.5 the chromium is at least 20%, at least one element selected from the group consisting of aluminum and titanium, the aluminum being present in an amount up to 0.5%, e.g., about 0.01% to 0.4%, and the titanium being present in an amount up to about 0.5%, e.g., about 0.01% to 0.4%, up to about 1% silicon, e.g., about 0.05% to 0.5% silicon, up to about 0.15% carbon, e.g., up to 0.1% carbon, and the balance essentially nickel.
• alloys of the following composition based on weight percent: about 14% to about 35% chromium, up to about 50% iron, with the proviso that when the iron is present in an amount above about 0.5 the chromium is at least 20%, at least one element selected from the group consisting of aluminum and titanium, the aluminum
• chromium e.g., above 20%
• the theoretical explanation for this phenomenon is not completely understood, particularly when viewed in the light of the conventional amounts of chromium, e.g., 14% to 16%, widely used in nickel-chromium-iron alloys of the substantially non-age hardening type.
• the amount of chromium contemplated herein can be less than 20% provided the iron content of the alloys is less than about 0.5 e.g., less than 0.35% iron. Low iron contents also favorably contribute to resisting intergranular stress-corrosion cracking.
• the benefit conferred by either high chromium or low iron or both can be further increased by maintaining the carbon content below about 0.05 e.g., below 0.03%.
• alloy compositions falling within the following ranges be employed: about 20% to about 30% chromium, up to about 10% iron, with the proviso that when the iron content is above about 0.35%, the chromium is at least 22%, at least one element selected from the group consisting of aluminum and titanium, the aluminum being from about 0.03% to 0.2% and the titanium being from about 0.03% to 0.3%, silicon in an amount up to about 0.35%, up to about 0.05% carbon and preferably not more than 0.03% carbon, the balance being essentially nickel.
• both aluminum and titanium be present in a total amount of at least 0.2%.
• the chromium content is advantageously at least 23% or 24% regardless of the iron content.
• alloys of the type under consideration are commonly, as is Well known to those skilled in the art, produced and/or sold in the so-called annealed condition. That is to say, the alloys are generally subjected to an anneal heat treatment within the temperature range of 1500 F. to 2100 F., usually about 1600 F. to 1900 F., and thereafter cooled as by quenching. Intergranular stress-corrosion cracking can occur in this condition but this is only one aspect of the situation, albeit an important one. Frequently, such alloys are sensitized or used in applications whereby they become sensitized.
• alloys contemplated herein are often welded to form a welded structure; however, as a result of the welding operation, the alloys pass through (upon cooling) a sensitizing temperature range of below about 1500 F., to 800 F., e.g., about 1450 F. to 850 F. While an alloy might manifest good resistance to intergranular stress-corrosion cracking in the annealed condition, it may very well show cracking in the sensitized condition. This fact is illustrated herein and, thus, consideration should be given to both conditions (annealed and sensitized).
• alloy test specimens were prepared having compositions given in Table 1, Alloys A through I being outside the invention and Alloys Nos. 1 through 6 being within the scope thereof:
• the alloys of Table I were prepared using vacuum melting techniques and using materials of relatively high purity. After removing surface defects from the cast ingots, the alloys were heated to about 2200 F. and forged to flats (1 inch by 3.5 inches by 10 inches). After reheating to 2150 F., the flats were hot rolled to a thickness of about 0.2 inch. Subsequent to conventional processing, including cold rolling to provide specimens about 0.12 inch thick, the alloys were subjected to various treatments. Three different treatments were employed,
• This alloy contained three specimens (strips) of each alloy composition were 20.5% chromium. Broadly, this alloy is within the scope prepared, one being subjected to the solution anneal treatof the present invention although as indicated hereinment, the second being subjected to the sensitizing treatbefore, it is much preferred to use a chromium content ment and the third to the thermomechanical treatment of at least 23%. Alloy No. 4, which was quite similar to (often referred to as a stabilizing treatment). Alloy No.
• This test solution was ticularly the propagation of the cracking, it is quite adplaced in the autoclave and a head spaced having addivantageous to use a chromium content of not less than tional air was maintained.
• the test specimens were im- 24% and an iron content of not more than 0.35%. mersed in the solution and the autoclave sealed and It has also been found, and it is an additional feature brought to a test temperature of about 600 F. to 660 F. of the instant invention, that substantial amounts of ele- The autoclaves were opened about every two weeks and ments such as molybdenum can be tolerated provided the specimens inspected for cracks, whereafter the tests the chromium content is not less than 20%.
• Alloy G containing 1.7% W cracked in a relatively short period in the stabilized condition (3rd Treatment) Alloy No. 8 containing 7.7% molybdenum exhibited a much greater resistance to cracking and this is deemed attributable to the higher chromium content.
• alloys containing a relatively high amount of chromium, to wit, at least 20% chromium, together with low carbon contents, i.e., below 0.03% also exhibit improved resistance to intergranular stresscorrosion cracking. This is illustrated by Alloy No. 9.
• the present invention provides nickel-chromium and nickel-chromium-iron alloys highly resistant to intergranular stress-corrosion cracking when in contact with pressurized, aerated water at a temperature of above about 300 F. to about 660 F, notwithstanding that the surface of the alloys be characterized by a crevice or some such similar surface defect.
• the invention is also applicable in minimizing intergranular stress-corrosion cracking in aerated high purity water at surface areas which do not contain obvious crevices.
• Pressure vessels, heat exchangers, steam generation surfaces, tubing, etc. are illustrative of the type of articles which can be fabricated from the alloys of the invention.
• the present invention should not be confused with nickelchromium and nickel-chromium-iron alloys of the age hardening type and which contain substantial amounts of precipitation hardening ingredients such as aluminum and titanium.
• the alloys of the present invention are, as a practical matter, of the non-age hardening type.
• a process for minimizing intergranular stress-corromolybdenum 7 sion cracking of metal articles when in contact with aerated high purity water at a temperature of about 300 F. to about 660 P. which comprises flowing high purity Water past and in contact with such a metal article, the article being formed from an alloy containing at least 23% and up to 35% chromium, up to 25% iron, at least one element selected from the group consisting of up to 0.5% aluminum and up to 0.5 titanium, the sum of aluminum and titanium being at least about 0.2%, up to 1% silicon, up to 0.15% carbon, and the balance essentially nickel.
• the metal article is formed from an alloy which contains up to about 10% iron, 0.01% to 0.4% aluminum, 0.01% to 0.4% titanium, 0.05% to 0.5% silicon and up to 0.1% carbon.
• a nickel-chromium alloy characterized by improved resistance to intergranular stress-corrosion cracking particularly when in contact with aerated high purity water at a temperature of about 300 F. to 660 F., said alloy consisting essentially of about 24% to 35% chromium, up to 10% iron, at least one element selected from the group consisting of up to 0.5% aluminum and up to 0.5 titanium, the sum of aluminum and titanium being at least about 0.2%, up to 1% silicon, up to 0.15% carbon, and the balance essentially nickel.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Powder Metallurgy (AREA)
• Heat Treatment Of Steel (AREA)
• Conductive Materials (AREA)
• Heat Treatment Of Articles (AREA)

Applications Claiming Priority (1)

Publications (1)

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Cited By (4)

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• 1965
  • 1965-05-26 US US459110A patent/US3574604A/en not_active Expired - Lifetime
• 1966
  • 1966-05-18 GB GB22170/66A patent/GB1114996A/en not_active Expired
  • 1966-05-20 AT AT476566A patent/AT268700B/de active
  • 1966-05-23 NO NO163117A patent/NO116608B/no unknown
  • 1966-05-24 DE DE1533281A patent/DE1533281C3/de not_active Expired
  • 1966-05-25 LU LU51187A patent/LU51187A1/xx unknown
  • 1966-05-25 ES ES0327142A patent/ES327142A1/es not_active Expired
  • 1966-05-26 SE SE07214/66A patent/SE326564B/xx unknown
  • 1966-05-26 NL NL6607287A patent/NL6607287A/xx unknown
  • 1966-05-26 CH CH765666A patent/CH461816A/fr unknown
  • 1966-05-26 JP JP41033288A patent/JPS4942573B1/ja active Pending
  • 1966-05-26 BE BE681643D patent/BE681643A/xx unknown

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