US3458366A - Wrought chromium base alloy - Google Patents

Wrought chromium base alloy Download PDF

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Publication number
US3458366A
US3458366A US491978A US3458366DA US3458366A US 3458366 A US3458366 A US 3458366A US 491978 A US491978 A US 491978A US 3458366D A US3458366D A US 3458366DA US 3458366 A US3458366 A US 3458366A
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alloy
zirconium
carbide
wrought
chromium
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US491978A
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Winston H Chang
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General Electric Co
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General Electric Co
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
    • C22C27/06—Alloys based on chromium

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  • This invention relates to chromium base alloys and, more particularly, to a wrought chromium base alloy of improved oxidation resistance and ductility.
  • a principal object of the present invention is to provide a wrought chromium base alloy of improved resistance to oxidation, nitriiication and scaling and of improved ductility.
  • Another object is to provide an improved 'wrought chromium base alloy moderately strengthened with a dispersion of carbides which at the same time enhance oxidation and nitrication resistance by inhibiting the formation of heavy scale and the penetration of oxygen and nitrogen into the structure of the alloy, the alloy having additional oxidation resistance as a result of the inclusion of yttrium and thorium ⁇ while maintaining good ductility.
  • Still another object of the invention is to provide such an improved chromium base alloy further strengthened with a solution strengthening element.
  • FIG. 1 is a graphical comparison of oxidation characteristics between cast and wrought alloy forms
  • FIG. 2 is a graphical comparison of the effect oxidation has on depth hardening between cast and wrought alloy forms
  • FIG. 3 is a graphical ⁇ comparison of air oxidation characteristics of one form of the alloy of this invention with a reported sheet alloy.
  • the alloy provided by the present invention is a wrought chromium base alloy strengthened by a zirconium carbide dispersion which has, in addition, a scavenging effect.
  • Such carbide dispersion which exists as a grain boundary network in the as-cast condition is controlled and made to be discontinuous in the wrought condition in order to inhibit the migration of oxygen and nitrogen along a carbide path or network normally susceptible to oxygen and nitrogen.
  • the discontinuous carbide phase in the wrought condition performs a triple function of acting both as a strengthening mechanism, as a scavenging agent by absorbing interstitials from the matrix and as an oxidation and nitrication inhibitor.
  • the alloy is improved further by the addition of a combination of yttrium and thorium retained in the alloy for additional oxidation resistance improvement.
  • a solution strengthening element such as molybdenum can be added to provide the alloy with the combination of dispersion and solution strengthening without significant effect on oxidation-nitrification resistance.
  • the wrought chromium base alloy of the present invention consists essentially of, by weight, 0.05-0.15% C; O.1-0.2% Y; 0.05-0.2% Th; an amount of zirconium from a minimum of 0.1% -
  • up to about 10% Mo can be added.
  • Working of titanium carbide-bearing chromium base alloys from cast to wrought form does not improve this condition.
  • Working of zirconium carbide-bearing alloys of this invention breaks up the grain boundary zirconium carbide network and distributes large, isolated masses of zirconium carbide throughout the alloy. This strengthens the alloy but requires any oxygen or nitrogen attempting to penetrate the alloy structure to pass through the more difticult-to-traverse chromium matrix.
  • Zirconium will rst enter into a solid solution with chromium up to the solubility of zirconium, which is less than about 0.1 weight percent Zr. Additional zirconium added then will combine with available carbon to form relatively large portions of zirconium carbide. Thereafter excess amounts of zirconium will form an intermetallic ZrCr2. In the absence of carbon, a precipitate of the ZrCrZ phase would form Iwith zirconium in excess of that in solid solution.
  • zirconium carbide When carbon is present with zirconium, zirconium carbide Will form preferentially in the grain boundaries, which are the last to solidify after casting of an alloy of this type, rather than in the grain matrix. Because the amounts of carbon required to dispersion strengthen the alloy are suiciently high, enough zirconium carbide precipitates on casting to from a continuous network along the grain boundaries. In addition to strengthening the al loy, zirconium carbide has the characteristic of accepting considerable amounts of oxygen and nitrogen. This scavenging characteristic is beneticial with regard to removing interstitials from the grain matrix.
  • the continuous carbide grain boundary network in the cast condition provides a ready oxidation path through the alloy in which the zirconium carbide first forms a Zr (C, O, N) compound which changes to ZrO2.
  • the alloy of the present invention is characterized by a discontinuous, isolated carbide str-ucture to inhibit oxygen and nitrogen penetrating actions while retaining the scavenging and strengthening characteristics.
  • zirconium is required to provide with carbon the combination of carbide dispersion strengthening and the formation of a discontinuous, isolated carbide structure to improve oxidation resistance while at the same time retaining ductility.
  • the minimum Zr required is the sum of Athe -amount of zirconium which -is soluble in chromium (up to abuot 0.1 weight percent) and the amount of zirconium required to combine with al-l of the carbon present preferentially to form zirconium carbide rather than chromium carbide.
  • the amount of carbon required to dispersion strengthen the alloy of the present invention is at least about ⁇ 0.05 weight percent. Less than 0.05% C does not form enough zirconium carbide to getter the interstitials. Thus there would be insuicient scavenging both during melting and during exposure in an oxidizing environment. However, more than about 0.15 weight percent carbon with sufficient zirconium forms excessive carbides and will not allow the creation of a discontinuous carbide structure. With insufficient zirconium, it forms the embrittling chromium carbide. Therefore the zirconium required in the alloy of the present invention at a minimum is about 0.1 weight percent +7.6 wt. percent carbon based on an atomic ratio consideration of 1 zirconium atom to 1 carbon atom.
  • Vit was recognized that although a small excess of zirconium can be tolerated allowing the formation of the intermetallic ZrCr2, the inclusion of more than about 3 weight percent zirconium allows the formation of amounts of ZrCr2 which will embrittle the alloy. Furthermore, long time oxidation resistance increases with increasing zirconium carbide up to the point where an oxidation path is created.
  • This control, according to the present invention, of the elements zirconium and carbon in a chromium base to provide an alloy of an improved combination of streng-th, oxidation resistance and ductility, particularly at 2200o F. and above, can be assisted further from an oxidation viewpoint by the inclusion of a combination of retained yttrium and thorium in the range of about 0.05-0.2 weight percent yttrium and about 0.05-0.2 weight percent thorium. Inclusion of amounts of each of these elements much below their respective lower limits provides insutiicient improvement in oxidation resistance. The addition of amounts greater than those speciiied cause the alloy to be brittle during reduction. Sometimes this condition is referred to as hot short.
  • the alloy of the presen-t invention in one fonm, can be formed by rst casting an alloy having a composition consisting essentially of, by weight, 0.050.l5% C; about ODS-0.2% Y; about ODS-0.2% Th, the above described minimum zirconium up to about 3%, up to about 10% Mo with the balance substantially chromium, and then reducing the cast structure to wrought form at a temperature between 2000-2500 F.
  • composition of alloys included in the study of, and which were melted in the evaluation of the presen-t invention are those shown in the following Table I.
  • the ingots were subsequently extruded to sheet bar at a temperature of 2400 F. without any diiculty a-t an extrusion ratio of Iabout 9 to 1. As was mentioned before, this temperature was selected to avoid cracking of the ingot during reduction and to avoid incipient melting.
  • the extrusion temperature of -about 2400 provided ease of processing while at the same :time avoiding excessive gr-ain growth.
  • the extruded bar was rolled to 0.05 sheets.
  • the first reduction was 50% in thickness at 2000 F. followed by finish rolling half of the material at 1800 F. and the other half at 1500 F. Both procedures yielded excellent sheets of 0.05" thick material.
  • a photomicrographic analysis of the grain structure after extrusion and rolling showed discontinuous isolated portions of ZrC and ZrCr2.
  • the grain boundary included about 92% ZrC and about 8% lZrCr2. After rolling, about 75% of the particles were ZrC and about 25% ZrCrz with the ZrC fragmented and discontinuous.
  • the preferential grain boundary precipitation in the as-cast condition is probably based on zirconiums low solubility in chromium and the fact that zirconium was segregated in the last solidifying massthe grainboundary-which formed the ZrC network upon complete solidiication. In the absence of carbon, the network would have been composed of Cr-ZrCr2.
  • Oxidation tests of 100 hour duration were conducted at temperatures of between 1600 and 22.00 F. For these tests, bar specimens of 0.22 x 0.35 X 0.5 for the rolled conditions were used. Specimen preparation consisted of grinding and polishing through 400 grit paper followed by water and alcohol rinsing. Specimens were placed in zirconia crucibles and oxidized continuously in a tubular furnace with natural air convection. The following Table II gives data for specimens in the cast condition in which the grain boundary carbide precipitate was continuous and in the wrought condition in which the zirconium car bide was discontinuous.
  • the effect of oxidation temperature on 100 hour weight gain of the alloy of Example 2 within the scope of the present invention is shown in FIG. l.
  • the upper curve represents the weight gain of a cast bar specimen whereas the lower band represents the range for extruded bar, extruded sheet and rolled sheet. It is interesting to note in FIG. 2 the significant effect of oxidation temperature on the hour depth of hardening of the alloy of Example 2.
  • the upper curve represents that for the as-cast condition whereas the lower curve is that for both the extruded bar and rolled sheet condition.
  • FIG. 3 That ligure compares air oxidation test data for a known sheet alloy, reported to be one of the best available based on chromium, with the sheet alloy form of Example 2.
  • the known alloy has a composition, by Weight, of 93.5% chromium, 0.5% titanium and 6% magnesium oxide. Both sheet alloys were at the same thickness of about 50 mils.
  • the solid lines in FIG. 3 show weight gain data and the broken line shows nitride thickness. The significant difference between the two alloys is easily recognized. No nitride line appears for the alloy of Example 2 because no nitride was found up to 2400 F. for 100 hours.
  • Example l has better oxidation resistance at lower temperatures than does the alloys of Examples 2 and 3, which are within the scope of the present invention the reverse becomes true at temperatures above about 2000 F. Furthermore, metallographic microstudies of the structure of the alloys of Examples l, 2 and 3, showed that because of the excess of carbon as compared with zirconium, there existed the carbide CrzgC which appears to have a significant embrittling effect on the alloy of Example 1. This is shown more particularly from the bend test data on sheet material shown in the following Table III.
  • the microstructure studies of the alloys of Examples 1, 2 and 3 show that after exposure for 100 hours at temperatures from 1600-2200 F., nitrilication of the alloys of Examples 1, 2 and 3 is effectively blocked with the presence of fragmented, discontinuous ZrC.
  • the weight gain data of Table II reflect nitrication inhibition which affects the alloy ductility.
  • the presence of the embrittle Cr23C6 has a significant eifect on ductility as shown by Table III. That alloy was so brittle as a result of the inclusion of the Cr23C6 carbide that it fractured without any deflection in the as-rolled condition and was significantly less ductile in the other conditions.
  • Example 1 had somewhat better oxidation resistance than does alloys 2 and 3 at lower temperatures, the existence of the chromium carbide resulting from the lack of further control of the elements zirconium and carbon results in an alloy having a significantly poorer combination of oxidation resistance and ductility.
  • LIZED CONDITIONl 0.05-0.l5% C (LUS-0.2% Y; UGS-0.2% Th; Zirconi- Ultma 02% yield um from a minimum of 0.1% +7.6 wt. percent C up Telll; Stfgh' Stfelggh: Elogftoht, to about 3% Zr; up to about 10% Mo with the bal- 'sm 'SM peice ance chromium and incidental impurities;

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)
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US491978A 1965-10-01 1965-10-01 Wrought chromium base alloy Expired - Lifetime US3458366A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4710425A (en) * 1985-12-17 1987-12-01 Gte Laboratories Inc. Abrasion resistant articles and composition utilizing a boron-doped refractory particle
EP1752551A1 (de) * 2004-04-30 2007-02-14 Japan Science and Technology Agency Auf feuerfestem metall basierendes legierungsmaterial mit hoher festigkeit und hoher rekristallisationstemperatur und herstellungsverfahren dafür

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3011889A (en) * 1959-09-25 1961-12-05 Gen Electric Oxidation resistant alloy
US3174853A (en) * 1962-03-15 1965-03-23 Gen Electric Chromium base alloys
US3227548A (en) * 1963-02-18 1966-01-04 Gen Electric Chromium base alloy
US3347667A (en) * 1964-05-21 1967-10-17 Gen Electric Chromium base alloy

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3011889A (en) * 1959-09-25 1961-12-05 Gen Electric Oxidation resistant alloy
US3174853A (en) * 1962-03-15 1965-03-23 Gen Electric Chromium base alloys
US3227548A (en) * 1963-02-18 1966-01-04 Gen Electric Chromium base alloy
US3347667A (en) * 1964-05-21 1967-10-17 Gen Electric Chromium base alloy

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4710425A (en) * 1985-12-17 1987-12-01 Gte Laboratories Inc. Abrasion resistant articles and composition utilizing a boron-doped refractory particle
EP1752551A1 (de) * 2004-04-30 2007-02-14 Japan Science and Technology Agency Auf feuerfestem metall basierendes legierungsmaterial mit hoher festigkeit und hoher rekristallisationstemperatur und herstellungsverfahren dafür
US20080017278A1 (en) * 2004-04-30 2008-01-24 Japan Science And Technology Agency High Melting Point Metal Based Alloy Material Lexhibiting High Strength and High Recrystallization Temperature and Method for Production Thereof
EP1752551A4 (de) * 2004-04-30 2010-09-15 Almt Corp Auf feuerfestem metall basierendes legierungsmaterial mit hoher festigkeit und hoher rekristallisationstemperatur und herstellungsverfahren dafür

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GB1106835A (en) 1968-03-20
NL6613946A (de) 1967-04-03

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