US3762913A - Alloy and method of welding structures including this alloy - Google Patents

Alloy and method of welding structures including this alloy Download PDF

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Publication number
US3762913A
US3762913A US00611533A US3762913DA US3762913A US 3762913 A US3762913 A US 3762913A US 00611533 A US00611533 A US 00611533A US 3762913D A US3762913D A US 3762913DA US 3762913 A US3762913 A US 3762913A
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alloy
welds
weld
welding
tube
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US00611533A
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English (en)
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E Boyko
C Owens
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CBS Corp
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Westinghouse Electric Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
    • B23K35/3053—Fe as the principal constituent
    • B23K35/3066—Fe as the principal constituent with Ni as next major constituent

Definitions

  • ABSTRACT Also a method of welding iron-nickel-chromium alloy in which Ti and/or A1 are present to prevent cracks from forming.
  • This alloy has favorable high-temperature mechanical properties, particularly high tensile-stress resistance and high ductility at temperatures of l,l50 F., and it also has corrosion resistance at the same high temperatures to liquid sodium and steam.
  • Attempts have been made to use this alloy for cladding for fuel elements and for tube-to-plate or tube-to-tube sheet assemblies of heat exchangers. Such use requires that the cladding or assemblies be sealed by sound pressure-tight welds which must necessarily be crack-free. This requirement is particularly stringent as to assemblies in the light of the 20 or 30 year design life which is demanded of heat exchangers. The attempts have failed because it has not been possible to produce crack-free welds.
  • This invention arises from the discovery that the cracks in the welds are caused by the presence of chromiumcarbides, particularly massive molecules of Cr,,C, in the parts used and their formation, during the welding operation. These chromium carbides precipitate in-grain boundaries in the sheet and tubes used to make the structures and during the welding operation these carbides and others, produced under the heat of the welding arc, cause the cracks to form.
  • the formation of cracks is suppressed by including in the alloy adequate material having an affinity for carbon which may form carbides or nitrides dispersed throughout the matrix. An important such material is titanium; aluminum also serves as such material; and both Ti and Al may be used.
  • Another aspect of this invention is to maintain the carbon at a low magnitude.
  • an iron-nickelchromium alloy is provided in which the carbon is maintained at less than about 0.05 percent and the titanium is maintained at between eight and 10 times the carbon content.
  • the alloy according to this invention is herein called B-0 Alloy.
  • a recommended composition in accordance with this invention of this B-0 Alloy, with which are produced crack-free welded structures having high resistance to tensile stress and high ductility at high temperatures of about l,l50 F. and high corrosion resistance to steam and liquid sodium at these high temperatures, is as follows:
  • B-0 Alloy material for these structures should be solution annealed at 2l50F.
  • FIG. 1 is a view in longitudinal section of a fuel element in which the alloy according to this invention is included and which is made in the practice of the method of this invention;
  • FIG. 2 is a view in perspective of a tube-to'tube sheet assembly in which the alloy according to this invention is included and in the making of which the method of the invention is practiced;
  • FIGS. 3 constitutes a plan view and a view in side elevation of a typical sheet of a tube-to-tube sheet assembly as shown in FIG. 2 prepared for welding, and is included for the purpose of aiding those skilled in the art in practicing this invention and not with any intention of in any way limiting this invention;
  • FIG. 4 is a photomicrograph (at magnification 500K) of a specimen of the prior art iron-nickel-chromium alloy solution annealed at 2,100 F.;
  • FIG. 5 is a similar photomicrograph of a specimen of this alloy
  • FIG. 6 is an electron micrograph (at magnification 5,900X) of a specimen of this alloy.
  • FIG. 1 is another electron micrograph (at magnification 12,500X) of a specimen of this alloy
  • FIG. 8 is another electron micrograph (at magnification 23,000X) of a specimen of this alloy.
  • FIG. 9 is an electron diffraction pattern of a precipitate in this alloy.
  • FIG. 10 is a photornicrograph of a specimen of the weld zone of a fusion weld produced with the alloy from which FIGS. 1 through 9 were derived;
  • FIG. 10A is an electron micrograph (at magnification 1,500X) of a specimen of this weld zone
  • FIG. 11 is an electron micrograph (at magnification 23,000X) of a specimen of plate of another prior an alloy showing precipitate concentrated at grain boundaries;
  • FIG. 12 is a photomicrograph (at magnification 500X) of a specimen of bar stock of alloy according to this invention (B-0 Alloy);
  • FIGS. 13, 14 and 15 are electron micrographs (at magnifications 6,000X, 13,600X and 24,000X respectively) of this alloy
  • FIGS. 16 and 17 are electron micrographs (at magnifications 6,000X and 13,600X respectively) of a specimen of tubing of the iron-nickel-chromium alloy to which were welded lugs of the bar stock whose micrographs are shown in FIGS. 12 through 15 and the welds were found to be crack-free;
  • FIG. 18 is a photomicrograph (at magnification 500X) of a specimen of this tubing.
  • FIGS. 19 through 27 are photomicrographs (at magnification 50X) of welds produced in joining by TIG welding, with fillers of different compositions, parts of iron-nickel-chromium alloy at least one of which was composed of the alloy according to this invention (B-0 Alloy).
  • An element 51 includes fuel pellets 53 contained in cladding.
  • the cladding includes a shell 55 of 13-0 Alloy which is sealed by plugs 57 of 8-0 Alloy by circumferential welds 59. Insulating spacers 61 are interposed between the fuel pellets 53 and the plugs 57.
  • the fuel pellets 53 generate intense heat which is transferred to a heat exchange fluid (not shown), typically sodium, in which the fuel element 51 is immersed.
  • Thee cladding typically has a thickness of 0.010 inches to 0.015 inches.
  • the plugs are welded to the shell by fusion welding with a non-consumable electrode in a shield or atmosphere of inert gas (TIG welding) which may be argon or helium. Welding-grade pure gas is used (99.999 percent) purity.
  • TIG welding inert gas
  • Welding-grade pure gas is used (99.999 percent) purity.
  • FIG. 2 shows a tube-to-tube sheet assembly 71 including sheet 73 and tubes 75 welded pressure-tight into the sheet 73 by circumferential welds 77.
  • the sheet 73 is composed of 8-0 Alloy and may also be composed of AISI-304 stainless steel.
  • the tubes 75 are composed of 13-0 Alloy. Satisfactory welding is carried out by TIG fusion welding with the shoulder of a trepanned groove (81 FIG. 3) providing the filler material. For this welding, a groove 81 is trepanned around the hole 83 into which a tube 75 is to be sealed. Typical dimensions of a sheet 73 with the hole 83 and groove 81 are presented in FIG. 3.
  • High temperature corrosion resistant material and crack-free welds are necessary because the tubes 75 carry liquid sodium at a high temperature (1,l50 F.) and are typically immersed in highly corrosive steam at a high temperature.
  • the 3-0 Alloy meets these conditions and in addition has the necessary high tensile strength and ductility at high temperatures.
  • the specimens for study were TIG welds on flat-plate specimens without filler.
  • Metallographic examination revealed severe cracking in the weld zone occurring generally at weld puddle grain boundaries (FIG. 10).
  • a distinct segregated phase not identifiable by carbon extraction replication techniques was observed within each grain. It was noted that only one type of precipitate was present in the weld puddle metal, i.e., the dendritic structure, Cr, C.,, in an early stage of structure formation (FIG. 10A).
  • the Incoloy-800 alloy proved to be crack sensitive.
  • FIGS. 4 through 8 were then produced from specimens of the alloy annealed for 15 minutes at 1,800" F. and then for one hour at 2,100 F.
  • the micrographs, FIGS. 4 and 5 showed that carbides and nitrides of titanium were formed and that there were other massive carbides which seemed to be coextensive with the grain boundaries.
  • FIGS. 6, 7, and 8 are extraction replications, FIG.
  • FIG. 6 shows TiC and TiN and a chromium carbide precipitate.
  • FIG. 7 shows the precipitate in detail and
  • FIG. 8 shows that it it dendritic.
  • the dendritic precipitate was identified from its electron diffraction pattern as Cr C It was concluded that the crack sensitivity was caused by the chromium carbide and could be eliminated by suppressing the formation of this carbide. This object is accomplished according to this invention by providing an alloy with adequate titanium and/or aluminum to suppress the formation of chromium carbide.
  • EXAMPLE A This example covers a comparison of Incoloy-800 and B-0 Alloy. The following structures were used in this comparison:
  • FIG. 11 shows Ti(C,N) dispersed throughout the matrix.
  • FIGS. 12'' through 15 show Ti C,N pi'ecipitate diswelding the root pass across the 2 inch face and then filling the joint with filler wire.
  • EXAMPLE D A tube-to-tube sheet mock-up as shown in FIG. 2 was fabricated to illustrate weldability of B-0 Alloy. The
  • mock-up consisted of two tube sheets 73, 1 inch thick respectively of 304 stainless steel and B-0 Alloy. Tubes 75 of B-0 Alloy but with high-carbon content were welded to the tube sheets 73 byfusion welding and with filler wire addition.
  • An iron-nickel-chromium alloy having substantially the following composition in weight percent:

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  • Mechanical Engineering (AREA)
  • Arc Welding In General (AREA)
  • Butt Welding And Welding Of Specific Article (AREA)
US00611533A 1967-01-17 1967-01-17 Alloy and method of welding structures including this alloy Expired - Lifetime US3762913A (en)

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BE (1) BE709046A (US20090163788A1-20090625-C00002.png)
FR (1) FR1554063A (US20090163788A1-20090625-C00002.png)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3890143A (en) * 1972-04-14 1975-06-17 Nyby Bruk Ab Welded constructions of stainless steels
US4086107A (en) * 1974-05-22 1978-04-25 Nippon Steel Corporation Heat treatment process of high-carbon chromium-nickel heat-resistant stainless steels
US8961144B2 (en) 2011-06-30 2015-02-24 General Electric Company Turbine disk preform, welded turbine rotor made therewith and methods of making the same

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3890143A (en) * 1972-04-14 1975-06-17 Nyby Bruk Ab Welded constructions of stainless steels
US4086107A (en) * 1974-05-22 1978-04-25 Nippon Steel Corporation Heat treatment process of high-carbon chromium-nickel heat-resistant stainless steels
US8961144B2 (en) 2011-06-30 2015-02-24 General Electric Company Turbine disk preform, welded turbine rotor made therewith and methods of making the same

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BE709046A (US20090163788A1-20090625-C00002.png) 1968-07-08
FR1554063A (US20090163788A1-20090625-C00002.png) 1969-01-17

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