Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-08-11
2001-09-04
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C148S410000, C148S419000, C148S428000, C148S442000, C415S902000, C416S24100B, C420S447000, C420S448000, C420S449000, C420S450000, C420S454000, C420S580000, C420S588000, C428S637000
Reexamination Certificate
active
06284392
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improving the weldability of Ni-based superalloys so that they can be fabricated and repaired without extensive cracking, using conventional welding processes. These superalloys are used in turbine vanes and other structural components in combustion turbines and the like.
In many applications, Co based alloys are used, because of the difficulty in fabricating and repairing nickel based superalloys. But Co is costly and is considered a strategic material whose future supply may be uncertain and limited, so it is important to find weldable nickel-base superalloys that can replace cobalt-base superalloys.
2. Background Information
Cobalt or nickel based, so called high temperature “superalloys”, usually containing Cr, Al, Ti and Mo, among other component elements, are well known and have been used for years in making turbine blades and vanes for high performance gas turbines. At the higher operating stresses and temperatures for forthcoming gas turbines, Co base alloys either would not meet design requirements for creep strength, or would require additional cooling, with a corresponding cost of lower overall efficiency of the gas turbine system. Development of other alloys for use in applications now filled by Co base alloys is desirable for reasons of both cost and performance.
U.S. Pat. No. 4,039,330 (Shaw) teaches nickel base, Ni·Cr·Co superalloys having wt % compositional ranges of: Cr=22.4-24.0; Co=7.4-15.4; C=0.13-0.17; Mo=0.1-3.15; W=1.85-4.0; Nb=0.2-2.0; Ta=1.05-2.8-4.3; Al=1.39-2.19; Zr=0.09-0.22 and B=0.008-0.011, with the balance being Ni. Nickel base superalloys are, however, limited in their application in turbine vanes and the like because of low weldability. Weldability is an essential and critical material requirement impacting the ability to repair casting defects, fabrication of component assemblies requiring welding, and the repair of components damaged in service.
U.S. Pat. No. 3,898,109 (Shaw) teaches a high-strength, corrosion resistant superalloy that is currently in use in some gas turbines. It has wt % compositional ranges of: Cr=22.0-22.8; Co=18.5-19.5; C=0.13-0.17; Mo=0; W=1.8-2.2; Nb=0.9-1.1; Ta=1.3-1.5; Ti=3.6-3.8; Al=1.8-2.0; Zr=0.04-0.012, and B=0.004-0.012, with the balance being Ni. This superalloy is sold under the Trade Name “IN-939”. While this superalloy meets many of the demands of turbine vane applications, its utility is reduced by its limited weldability. There is a need, therefore, to optimize the weldability properties of nickel base superalloys for gas turbine applications, while avoiding detrimental effects on material strength, stability and other properties. Co-base superalloys have the advantage that they have relatively good weldability compared to Ni-base superalloys. This property is important to operators of land-based gas turbines because repair welds often have to be made to extend component service life. In addition, repair welds have to be made in the foundry on as-cast vanes and vane segments to meet quality requirements, and fabrication welds are needed for assembly of components.
U.S. Pat. No. 3,166,412 (Bieber) is an early teaching of cast nickel-based superalloys suitable for the production of gas turbine rotors. About 10 wt %-14 wt % Cr and at least 0.005 wt % B and 0.02 wt % Zr were thought important for strength and ductility while 5 wt %-7 wt % Al, 0.5 wt %-1.5 wt % Ti and 1 wt %-3 wt % (Columbium) Niobium-Nb were thought important as hardening and strengthening elements.
U.S. Pat. No. 5,480,283 (Doi et al.) teaches Ni based superalloys with high Co concentration having improved weldability, containing in wt %: Cr=15-25; Co=20-25; C=0.05-0.20; W=5-10; Ti=1.0-3.0; Al=1.0-3.0, with the balance being primarily Ni. B is not required, but if used can be present in the range of 0.001-0.03 wt %. Zr, in the range of 0-0.05 wt %, is mentioned only as adding to high temperature strength, as is B. Their Sample 6, which has improved creep rupture strength, contains 0.009 wt % B plus 0.03 wt % Zr. They equate good weldability to the proper combination of Al+Ti at less than 5.0 wt %.
FIG. 2
of that patent shows Al+Ti content vs length of weld cracks, with the best Samples being 2-5 and 13, none of which contain Zr. One of the worst Samples contained B=0.010 wt % and Zr=0.11 wt %—Sample 1. U.S. Pat. No. 5,330,711 (Snider) also teaches, generally, that good weldability depends on the inclusion of substantial amounts of Mo, a low Al/Ti ratio, and a low Al+Ti content to provide a low gamma prime volume fraction and a more ductile alloy, better able to accommodate stresses produced during the weld thermal cycle. Their best test Samples—as far as weldability goes were: B (prior art) and RS5. Those samples had B 0 wt %; Zr=0 wt %; Mo=3.1 wt % for Sample B and B=0.005 wt %; Zr=0.01 wt % and Mo=4.9 wt % for Sample RS5.
A patent directly related to turbine superalloys that are alloy repair weldable is EPA 0302302Al (Wood et al.), where the preferred compositional wt % range of the alloy was: Cr=22.2-22.8; Co=18.5-19.5; C=0.08-0.12; W=1.8-2.2; Nb=0.7-0.9; Ta=0.9-1.1; Ti=2.2-2.4; Al=1.1-1.3; Zr=0.005-0.02; and B=0.005-0.015, where Al+Ti=3.2-3.8 wt %, with the remainder essentially nickel. The combination of C+Zr were carefully balanced to increase castability and the content of Ti+Al+Ta+Nb was reduced to increase ductility.
U.S. Pat. No. 4,219,592 (Anderson et al.) relates to a fusion welding double surfacing process for crack prone superalloys used in gas turbine engines, where a first surface layer helps prevent such cracking. The crack resistant layer had a wt % composition of: Cr=14-22; Co=5-15; Mo=0-8; Ti=0.5-4; Al=0.7-3; Mn=0.5-3; Zr=0-0.1; and B=0-0.05 where Al+Ti is greater than 3 wt %, the balance being Ni. Weld crack resistance was attributed to substantial Mn inclusion.
While weldable Ni base superalloys are known, weldability is currently achieved by sacrificing the high temperature strength. There is a need for nickel base superalloys which can be welded by conventional technology without sacrificing castability, high temperature strength, stability and creep ductibility.
SUMMARY OF THE INVENTION
Therefore, it is a main object of this invention to provide such Ni base superalloys having even more improved weldability, without compromising other mechanical properties.
These and other objects of the invention are met by providing a high temperature resistant nickel base superalloy composition containing small amounts of both boron and zirconium which are effective in combination to provide increased weldability. Preferably, the range of boron in the composition is from 0.001 wt % to 0.005 wt. % and the range of zirconium is from 0.005 wt % to 0.05 wt %. The invention also resides in a high temperature resistant, nickel-base superalloy adapted for welding comprising the composition by weight percent: 20.0%-25% Cr; up to 19.5% Co; 3.4%-4.0% Ti; 1.6%-2.2% Al; 0.005%-0.05% Zr; 0.001%-0.005% B, with the balance substantially Ni.
Preferably Al+Ti is from 5.0%-6.2%. Preferably the high temperature resistant nickel-based creep resistant superalloy, which is adapted for welding, essentially consists of the composition by weight percent: 22.0%-23.0% Cr; up to 19.5% Co; 3.4%-4.0% Ti; 1.6%-2.2% Al; 1.6%-2.4% W; 1.2%-1.6% Ta; 0.8%-1.2% Nb; 0.005%-0.050% Zr; 0.001%-0.005% B; where Al+Ti is from 5.0%-6.2%; and Zr+B is from 0.005% to 0.06%, with the balance Ni.
These superalloys are repair weldable, ductile, capable of being cast in large cross sections, and require minimal heat treatment. The alloy preferably will have a Sigmajig transverse
Babu Sudarsanum S.
David Stanislaus A.
George Easo P.
Goodwin Gene M.
Moyer Carol E.
Jones Deborah
Koehler Robert R.
Siemens Westinghouse Power Corporation
LandOfFree
Superalloys with improved weldability for high temperature... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Superalloys with improved weldability for high temperature..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Superalloys with improved weldability for high temperature... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2464310