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
• • 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
  • C22C19/058—Alloys based on nickel or cobalt based on nickel with chromium without Mo and W

Definitions

• the subject invention is directed to a high nickel-chromium-iron alloy, and more particularly to a Ni-Cr-Fe alloy of special chemistry and micro-structure such that it is capable of affording a desired combination of properties at elevated temperature upwards of 2000°F (1143°C) under oxidizing condition.
• rollers have been produced from electric-arc furnace melted, argon-oxygen decarburized (AOD) refined ingots.
• AOD argon-oxygen decarburized
• the composition used differed somewhat from the above, a typical composition being approximately 0.03%C, 0.3% Si, 0.3% Mn, 22.5% Cr, 0.4% Ti, 0.02% Nb, 1.27% Al, 60.8% Ni, 0.08% Co, 0.29% Mo. 0.015% N, less than 0.001% O2,and balance essentially iron.
• At 2050°F (1121°C) rollers lasted some 12 months and at times longer. However, at 2130°F (1165°C) such rollers manifested failure in 2 months or less.
• the alloy contemplated herein contains about 19 to 28% chromium, about 55 to 65% nickel, about 0.75 to 2% aluminum, about 0.2 to 1% titanium, up to about 1% each of silicon, molybdenum, manganese, and niobium, up to 0.1% carbon, from about 0.035% or 0.04% to 0.08% or 0.1% nitrogen, up to 0.01% boron and the balance essentially iron.
• a preferred alloy contains 21 to 25% Cr, 58 to 63% Ni, 1 to 2% Al, 0.3 to 0.7% Ti, 0.1 to 0.6% Si, 0.1 to 0.8% Mo, up to 0.6% Mn, up to 0.4% Nb, 0.02 to 0.1%C, 0.04 to 0.08% N, with iron being the balance.
• Nickel contributes to workability and fabricability as well as imparting strength and other benefits.
• Aluminum and chromium confer oxidation resistance but if present to the excess lend to undesirable microstructural phases such as sigma. Little is gained with chromium levels much above 28% or aluminum levels exceeding 2%.
• a level of about 0.1 to 0.5% Cr23C6 aids strength to about 2057°F (1125°C). This is particularly true if one or both of silicon and molybdenum are present to stabilize the carbide phase. In this regard the presence of 0.1 to 0.6% silicon and/or 0.1 to 0.8% molybdenum is advantageous.
• Titanium acts as a malleabilizer as well as serving to form the grain boundary pinning phase, TiN.
• Niobium will further stabilize the nitride phase and from 0.05 to 0.4% is beneficial.
• Manganese is preferably held to low levels, preferably not about 0.6%, since higher percentages detract from oxidation resistance. Up to 0.006% boron may be present to aid malleability. Calcium and/or magnesium in amounts, say up to 0.05 or 0.1%, are useful for deoxidation and malleabilization.
• Iron comprises essentially the balance of the alloy composition. This allows for the use of standard ferroalloys in melting thus reducing cost. As to other constituents, sulfur and phosphorus should be maintained at low levels, e.g., up to 0.015% sulphur and up to 0.02 or 0.03 phosphorus . Copper can be present.
• the alloy is electric-arc furnace melted, AOD refined and electroslag remelted (ESR) for (a) uniform distribution of the nitrides (b) better nitrogen content control, and (c) to maximize yield.
• ESR electroslag remelted
• the nitrogen can be added to the AOD refined melt by means of a nitrogen blow just prior to pouring the ingot to be ESR melted.
• the alloy is, as a practical matter, non age-hardenable or substantially non age-­hardenable, and is comprised essentially of a stable austenitic matrix virtually free of detrimental quantities of subversive phases. For example, upon heating for prolonged periods, say 300 hours, at tem­peratures circa 1100°F (593°C) to 1400°F(700°C) metallographic analysis did not reveal the presence of the sigma phase.
• Alloys A through C are low nitrogen compositions with varying carbon content. Although increasing carbon content progressively inhibited grain growth, it was ineffective in controlling gain size for long periods of time above about 1100°C (2010°F).
• the increasing nitrogen levels of Alloys 1 and 2 resulted in several beneficial attributes in alloys of the invention.
• the uniform dispersion of nitride resulted in stabilization of the grain size and longer stress rupture lives at elevated temperature.
• the oxidation resistance of alloys within the invention was also improved (surprisingly) as measured by the reduction of the denuded zone beneath the surface scale.
• the nitrogen level of Alloy D was also beneficial in comparison with A, B and C but it is deemed that Alloy D would not perform as well as Alloys 1 and 2 over prolonged periods as is indicated by the data in Table II.
• Alloys A and B were fabricated into 26.9 mm diameter (1.06 in) x 2438.4mm (96 in.) rollers using 2.0 mm (0.08 in.) gauge sheets and then field tested in an actual furnace operating at 1165°C (2130°F). Both alloys failed by stress rupture in a short time. Alloy C was hot worked into a solid bar 26.9 mm (1.06 in.) diameter and placed in field operation for 6 days. The average grain size was 12 mils. after exposure with grains as large as 60 mils. The stress rupture life of an alloy similar to alloy A at 1177°C (2150°F) and 6.89 MPa (1 Ksi) was 308 hours.
• Alloys 1 and 2 were fabricated similarly and exposed to the same thermal conditions as alloys A through C. (Alloys D, 1 and 2 are intermediate carbon content compositions with increasing nitrogen levels). The beneficial effect of increasing nitrogen content on grain size stability is demonstrated by the data in Table II. Rollers were fabricated from Alloy 2 (and also D) as described for Alloys A and B and are currently in field service without incident. Alloy 1 was fabricated into a solid roller as described for Alloy C. This alloy (1) was tested in field service at 1165°C (2130°F) for 8 days and then metallographically evaluated for grain size. The grain size was 12 mils after exposure and 2 mils prior to exposure.
• electric-arc furnace melting, AOD refining with a nitrogen blow, followed by ESR remelting of the alloy is the preferred manufacture route over air induction furnace melting of the ingots because of improved yield to final product and because of the better dispersion of the nitrides.
• An additional and unexpected benefit of the nitrogen additions is a marked reduction of the depth of the denuded zone (depletion of chromium and aluminum contents) as the nitrogen content is increased.
• Table III shows the depth of the denuded zone for alloys C, D and 2. This dramatic increase in resistance to alloy depletion in the base alloy is attributed to the effect of nitrogen on grain size retention and concomitantly on oxide scale density and tenacity.
• the subject invention provide nickel chromium alloys which afford a combination of desirable metallurgical properties including (1) good oxidation resistance at elevated temperatures (2) high stress-rupture lives at such temperatures, and (3) a relatively stable microstructure.
• the alloys are characterized by (4) a substantially uniform distribution of titanium nitrides (TiN) throughout the grains and grain boundaries.
• TiN titanium nitrides
• the nitrides are stable in the microstructure up to near the melting point provided at least 0.04% nitrogen is present. A nitrogen level down to 0.035% might be satisfactory in certain instances.
• the grain size not exceed about 15 mils, preferably being not more than 12 mils, the size of the grains being uniform outwardly to the alloy surface.
• the alloy of the present invention has been described in connection with the behavior of rollers in furnaces for frit production, the alloy is also deemed useful for heating elements, ignition tubes, radiant tubes, combustor components, burners, heat exchangers, furnace fixtures, mufflers, belts, etc.
• the metal and ceramic process industries, chemical manufactures and the petroleum and petrochemical processing industries are illustrative of industries in which the alloy of the invention is deemed particularly useful.

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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 Articles (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Heat Treatments In General, Especially Conveying And Cooling (AREA)
• Powder Metallurgy (AREA)

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Citations (3)

• 1987
  • 1987-06-29 CA CA000540806A patent/CA1304608C/en not_active Expired - Lifetime
  • 1987-06-30 EP EP87109408A patent/EP0251295B1/de not_active Expired - Lifetime
  • 1987-07-02 AU AU75056/87A patent/AU7505687A/en not_active Abandoned
  • 1987-07-02 KR KR1019870007029A patent/KR880001836A/ko not_active Application Discontinuation
  • 1987-07-02 BR BR8703367A patent/BR8703367A/pt unknown
  • 1987-07-03 JP JP62166780A patent/JPS6326321A/ja active Pending

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