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
  • C22C19/007—Alloys based on nickel or cobalt with a light metal (alkali metal Li, Na, K, Rb, Cs; earth alkali metal Be, Mg, Ca, Sr, Ba, Al Ga, Ge, Ti) or B, Si, Zr, Hf, Sc, Y, lanthanides, actinides, as the next major constituent
• • 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

Definitions

• the present invention relates to corrosion-resistant alloys and more particularly to nickel-base alloys characterized by an improved combination of characteristics including ductility and resistance to corrosion by acid media.
• a passivating silicate film forms on the surfaces of these alloys.
• silicon content is increased, the resistance to corrosion is increased but the ductility is decreased. This loss of ductility results principally from the formation of brittle silicides, which occurs when the limit of solubility of silicon in nickel is exceeded.
• the beta phase, of composition Ni Si can also exist.
• the beta phase is, however, rarely present in binary alloys since it has now been found that, contrary to some previously published information, the beta phase is formed as a result of a peritectoid reaction (reaction between two solid phases to form a third solid phase) occurring at about 1040 C. It appears that during normal casting operations, the rate of cooling is sufiiciently rapid to suppress this peritectoid reaction and the structure observed is the metastable alpha-gamma eutectic.
• Another object of the invention is to provide a process for improving the strength and ductility of a corrosionresistant nickel alloy of special composition.
• the invention also contemplates providing a heat treated alloy characterized by a special microstructure and an improved combination of strength, ductility and corrosion resistance.
• the present invention contemplates a new nickel-silicon-titanium alloy possessing high corro- 3,3 l 1,47% Patented Mar. 28, 1967 sion resistance and good ductility and characterized by a microstructure comprising the beta phase Ni (Si, Ti).
• the alloy of the invention always contains at least about 1% and not more than 5% titanium and at least 7% silicon.
• the silicon content must be at least 7% since the corrosion resistance of similar alloys with less than 7% silicon is greatly inferior to that of alloys in accordance with the invention.
• the silicon content of the alloy of the invention is at least about 8% since when the silicon content is between 7% and 8% the corrosion resistance, though superior to that of binary alloys containing no beta phase, is not as good as that of alloys of the invention containing 8% or more silicon.
• the alloy of the invention can be a ternary alloy consisting essentially of nickel, silicon and titanium and it can also, in addition, contain any one or more of the elements copper, molybdenum and tungsten each in an amount not exceeding about 5% with the total of these elements not exceeding about 10%.
• the present invention is particularly directed to an alloy containing about 8% to about 11% silicon, titanium in an amount of at least 1% and not more than 5% and, advantageously, about 2% to about 3.5%, up to 10% of metal from the group consisting of copper, molybdenum and tungsten in amounts up to 5% each with balance essentially nickel. All alloy percentages set forth herein are by weight. With a silicon content of about 10%, a preferred titanium content in an alloy of the invention is about 2.5%. In order to achieve both ductility and corrosion resistance, the alloy of the invention should contain not more than about 12% silicon, i.e., have a silicon content of 7% to about 12%.
• the alloy tends to be brittle when the silicon content is more than 12% owing to the introduction of primary gamma phase at about 12% silicon. Consequently, it is especially advantageous that the silicon con tent be 7% to 11%.
• the silicon and titanium contents so that the sum of the silicon content plus one-half the titanium content is from about 9.5% to about 12.5% and it is even more advantageous that the silicon content plus one-half the titaniinn content be from about 11% to 12% with silicon from 7% to about 11%.
• Titanium in the alloy of the invention mitigates the inherent brittleness of high-silicon, e.g., 8% or 11% silicon, nickel alloys and enhances the ductility of the alloy of the invention. Addition of titanium raises the peritectoid temperature and with about 2% titanium or more the peritectoid reaction is eliminated and the beta phase forms directly from the liquid. Also, the presence of titanium in the passivating silicate surface film which forms on alloys of the invention enhances the corrosion resistance of articles made of the alloy of the invention.
• the microstructure of the alloy when in use must comprise a high amount of beta phase, i.e., at least about beta phase or, advantageously, about or more beta phase.
• the microstructure of the alloy can include the alpha or gamma phases, usually identifiable as the nickel-rich solid solution and the intermetallic compound Ni Si respectively, with titanium present in solution in the former and in solution in trace amounts in the latter.
• An alloy or article of the invention possesses an advantageous combination of strength, ductility and corrosion resistance when characterized by a microstructure containing at least about 90% beta phase, not more than about 10% alpha phase and/ or not more than about gamma phase.
• the corrosive attack of concentrated sulfuric acid appears to be of a different kind from that of dilute sulfuric acid, i.e., acid of less than 40% concentration.
• dilute sulfuric acid i.e., acid of less than 40% concentration.
• the alloy of the invention contains about 0.5% or more copper in addition to silicon and titanium, in aforedescribed amounts, with balance essentially nickel.
• Ductility of the alloy of the invention is decreased by increases in the copper content thereof and for obtaining a particularly good combination of ductility and corrosion resistance it is especially advantageous that all alloy in accordance with the invention contain about 1% to 2%, e.g., about 1%, copper. Good resistance to corrosive attack by concentrated sulfuric acid is obtained even when the alloy of the invention contains no copper.
• the alloy of the invention is referred to as being essentially nickel, it is to be understood that minor amounts of impurities and other elements which are not harmful to the useful characteristics, especially corrosion resistance and ductility, of the alloy can also be present.
• the alloy can contain up to 3% iron, 1% manganese and 1 0% cobalt.
• the total of impurities must not exceed an amount such that the sum is equal to unity.
• the alloy of the invention must not contain more than about 0.01% of sulfur and 0.1% in total of carbon and nitrogen, since greater amounts of these last mentioned elements are highly detrimental to the ductility and extrusion characteristics of the alloy.
• ingredients of the alloy are melted and cast by using conventional furnace and ladle apparatus.
• Articles of the alloy of the invention can be cast to the shape required or, in apductility with little change in corrosion resistance is obtained by heat treating at about 1050" C. for at least four hours.
• the total amount of alpha phase in the alloy is substantially unchanged by the heat treatment; the beneficial effect of the heat treatment on ductility is due at least in part to a change in morphology of the aipha phase in the alpha plus beta eutectic.
• the chemical compositions of fourteen examples of alloys in accordance with the present invention are set forth in Table I hereinafter. Alloys 1 through 14 were tested for resistance to corrosion in hot sulfuric acid of three different concentrations of aqueous solutions. The corrosion rates for the examples were determined and are set forth in Table I. In addition, Table I shows the corrosion rate of a 10% silicon, 3% copper, 87% nickel alloy (Alloy X) which differs from the alloy of the invention by not containing titanium as required by the invention. The corrosion rates set forth in Table I pertain to alloys in the as-cast or cast and heat-treated (1050 C. for 16 hours) condition, except for Alloys 8, 9, l0 and X which were tested in the as-extruded condition. There was found to be little difference between the corrosion resistance of each of the Alloys l7 and 11-14 in the as-cast condition and the same alloy in the cast and heat-treated condition.
• the alloy can be extruded.
• the alloy of the invention especially when the copper content thereof is not high, is characterized in the as-cast condition by superior ductility as compared to otherwise similar titanium-free alloys.
• the microstructure of the a loy in the as-cast condition is influenced by the cooling rate of the casting and will diifer somewhat according to the size and shape of the casting.
• Substantial enhancement of both the ductility and the ultimate tensile strength of the alloy of the invention are concomitantly achieved by heat treating the alloy for about four hours to about 24 hours at about 1000 C. to about 1100" C., the longer time being needed at the lower temperature and vice versa.
• a particularly good effect on The test results set forth in the foregoing table show superior corrosion-resistant characteristics of examples of the alloy of the invention, with titanium, as compared with the corrosion rate of Alloy X, without titanium. It is clearly evident in view of the test results set forth in Table I that titanium is highly necessary as an ingredient in the alloy of the invention in order to obtain good corrosion resistance.
• the examples having titanium contents in the advantageous range of 2% to 3.5% are characterized by advantageously low corrosion rates of less than 100 mgms./dm. /day (milligrams per square decirneter per day) in relatively high concentrations of acid such as 75% and sulfuric acid and that the examples containing copper in amounts up to 3% with titanium in the range 2% to 3.5 are characterized by advantageously low corrosion rates in dilute (25% concentration) boiling sulfuric acid and also in solutions of 75% and 90% sulfuric acid.
• nickel-silicon-titanium-copper alloys also have excellent resistance to corrosion by boiling sulfuric acid solutions of high concentrations greater than 65% and up to
• nickelsilicon-titanium-copper alloys without molybdenum do not have satisfactory resistance to corrosion by boiling sulfuric acid of intermediate concentrations, e.g., sulfuric acid solutions containing about 50% to about 65% acid by weight.
• Castings of the alloy of the invention are commonly used in the as-cast condition but can be heat treated to increase the ductility thereof by heat treatment comprising heating in the range of about 1000 C. to about 1100 C. for from about 4 to about 24 hours.
• the alloy of the invention is satisfactorily cooled from the heat treating temperature by air cooling.
• a specific example (Alloy 15) of an alloy in accordance with the invention contained about 9.3% silicon, about 2.8% titanium, about 3.1% copper, about 2.9% molybdenum, about 0.026% carbon, about 0.2% iron, less than 0.05% manganese, less than 0.06% aluminium and less than 0.01% chromium with the balance essentially nickel.
• Specimens of Alloy 15 exhibited good impact resistance by withstanding heavy blows of a hammer and thus were demonstrated to have impact resistant advantages over corrosion resistant iron-silicon alloys such as an iron-14.5% silicon alloy.
• Alloy 15 is an example of an especially advantageous alloy composition characterized by an excellent advantageously low corrosion rate not greater than about milligrams per square decimeter per day in boiling aqueous sulfuric acid at all concentrations up to 95%, which especially advantageous composition consists essentially of 9.2% to 10% silicon, 2.5% to 3% titanium, 2% to 3.5% copper, 2.5% to 3.5% molybdenum with balance essentially nickel.
• especially advantageous composition consists essentially of 9.2% to 10% silicon, 2.5% to 3% titanium, 2% to 3.5% copper, 2.5% to 3.5% molybdenum with balance essentially nickel.
• the amounts of copper and molybdenum in an alloy within the last stated composition be near the low end of the ranges for copper and molybdenum.
• Low corrosion rates of specimens of Alloy 15 in boiling sulfuric acid solutions are set forth in Table III. The specimens, which were in the as-cast condition, were suspended in the boiling acid for five periods of 24 hours each and the results set forth in Table III are averages of the corrosion rates during the last
• Alloy 16 of an alloy in accordance with the invention contained about 9.5% silicon, about 2.5% titanium, about 2.9% copper and about 3% molybdenum, with balance essentially nickel. Tests demonstrated that alloy 16 had low corrosion rates of 40 mgms./dm. day and mgms/dmF/day in boiling sulfuric acid solutions of 55% and 60% concentration, respectively. Also, Alloy 16 exhibited a high impact resistance (referred to herein as the energy absorbed in breaking an unnotched cylindrical bar about 2.25 inches long and about 0.45 inch in diameter) of 2.35 kilogram-meters (about 17 foot-pounds). The foregoing test results'pertaining to Alloy 16 were obtained on the alloy after heat treatment for 16 hours at 1050 C. and air-cooled.
• pact resistance For instance, a corrosion resistant ironsilicon alloy containing about 14.5% silicon is characterized by an unsatisfactory low impact resistance of 0.25 kg.-m. Impact test results set forth in Table IV show the alloy of the invention is characterized by satisfactory impact resistance that is clearly superior to the aforementioned low impact resistance of the iron-14.5% silicon alloy.
• the present invention is applicable to the production of tough corrosion-resistant articles which are preferably produced as castings or by extrusion or other methods, with or without heat treatment.
• Useful articles which can be made of the alloy of the invention include pipe fittings, parts for pumps, stirrers, valves, reaction vessels, storage tanks and transfer lines for use in association with corroslve media including sulfuric acid.
• the alloy of the invention is also useful for corrosion-resistant pipe, tubing, rod, bar, plate and flanges.
• An alloy consisting essentially of 7% to about 16% silicon, 1% to about 5% titanium, up to about 5% copper, up to about 5% molybdenum and up to about 5% tungsten with the proviso that the total of copper, molybdenum and tungsten does not exceed 10% of the alloy, up to 3% iron, up to 1% manganese and up to 10% cobalt provided that the sum of the relationship does not exceed 1% and the balance essentially nickel.
• An alloy as set forth in claim 1 containing not more than 11% silicon and wherein the silicon and titanium are in proportions in accordance with the relationship 5.
• An alloy as set forth in claim 1 containing about 10% silicon and about 3% titanium.
• An alloy as set forth in claim 1 containing about 10% silicon, about 2% titanium and about 3% copper.
• An alloy as set forth in claim 1 containing about 10% silicon, about 3% titanium and about 1% copper.
• An alloy as set forth in claim 1 containing about 10% silicon, about 3% titanium and about 3% molybdenum.
• An alloy as set forth in claim 1 containing about 10% silicon, about 3% titanium and about 3% tungsten.
• An alloy as set forth in claim 1 containing 9.2% to 10% silicon, 2.5% to 3% titanium, 2% to 3.5% copper and 2.5% to 3.5% molybdenum.
• microstructure comprising at least about 90% beta phase, not more than 10% alpha phase and not more than 5% gamma phase.
• a vesesl for use in containing boiling sulfuric acid made of an alloy consisting of at least 7% silicon and about 1% to about 5% titanium with the silicon and titanium in amounts proportioned in accordance with the relationship Si+0.5(% Ti) :95 to 11.5
• a vessel as set forth in claim 17 containing 9.2% to 10% silicon, 2.5% to 3% titanium, 2% to 3.5% copper and 2.5% to 3.5% molybdenum.
• a process for improving the tensile strength of a ni'ckelcilicon-titanium alloy comprising heating an alloy consisting of 7% to about 12% silicon, 1% to about 5% titanium, up to about 5% copper, up to about 5% molyb- 'denum and up to about 5% tungsten with the proviso that the total of copper, molybdenum and tungsten does not exceed 10% of the alloy, up to 3% iron, up to 1% manganese and up to 10% cobalt provided that the sum of the relationship does not exceed 1% and the balance essentially nickel at a temperature of 1000" C. to about 1100 C. for about 4 hours to about 24 hours.

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Cited By (4)

Citations (9)

• 1963
  • 1963-05-21 GB GB20204/63A patent/GB1018101A/en not_active Expired
• 1964
  • 1964-05-13 DE DEJ25826A patent/DE1232754B/de active Pending
  • 1964-05-19 DK DK249064AA patent/DK105499C/da active
  • 1964-05-20 ES ES0300039A patent/ES300039A1/es not_active Expired
  • 1964-05-21 NL NL6405637A patent/NL6405637A/xx unknown
  • 1964-05-21 CH CH660264A patent/CH433773A/fr unknown
  • 1964-05-21 SE SE6155/64A patent/SE307017B/xx unknown
  • 1964-05-21 BE BE648214D patent/BE648214A/xx unknown
• 1965
  • 1965-03-24 US US442495A patent/US3311470A/en not_active Expired - Lifetime

Patent Citations (9)

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