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Nickel alloys and stainless steels for elevated temperature service: weldability considerations Reprinted with permission from Proceedings from Materials Solutions '97 on Joining and Repair of Gas Turbine Components ASM International, September 1997, Indianapolis, Indiana NiDI NICKEL DEVELOPMENT INSTITUTE NiDI Reprint Series NQ 14 053 D.J. Tillack The material presented in this publication has been prepared for the general information of the reader and should not be used or relied on for specific applications without first securing competent advice. The Nickel Development Institute, its members, staff and consultants do not represent or warrant its suitability for any general or specific use and assume no liability or responsibility of any kind in connection with the information herein. Proceedings from Materials Solutions '97 on Joining and Repair of Gas Turbine Components 15 -18 September 1997, Indianapolis, Indiana Nickel Alloys & Stainless Steels for Elevated Temperature Service: Weldability Considerations D. J. Tillack Tillack Metallurgical Consulting, Inc. Huntington, WV ABSTRACT: occur during the welding operation, such as undercut, The gas turbine is one of the most demanding porosity, slag inclusions, lack of fusion and insufficient applications for materials, particularly the hot sections penetration. These are associated with the welding of the turbine. The welds that join the various process but are also influenced by the material being components of the turbine must withstand the same welded and the filler metal material. An example high pressures and temperatures. Complicating this would be the relatively sluggish nature of a nickel alloy requirement is the fact that gas turbine materials can weld puddle, which necessitates opening up of the be metallurgically complex and can be a challenge to weld joint to allow proper manipulation of the filler weld. The actual welding of these materials is not metal. The second group of weld-associated defects particularly difficult as long as established guidelines are metallurgical in nature, such as microfissuring in are followed, but microfissuring and strain-age the HAl or weld metal. There are times when a weld cracking can be a problem. By being aware of the defect involves both categories, such as the centerline role of residual elements and the effect of stress on cracking of a weld which can be part welding the weld area, many of these materials can be procedure (improper weld bead contour, for example) welded successfully. and part metallurgical (high levels of deleterious trace elements, for example). A MODERN GAS TURBINE ENGINE relies heavily on Austenitic Materials Used in austenitic materials, primarily nickel-base alloys, to Gas Turbines withstand the aggressive conditions encountered during operation of the turbine. Not only do these The modern gas turbine engine has made materials need to be strong at elevated temperatures, tremendous strides since Sir Frank Whittle developed they also need to be able to withstand the corrosive the first gas turbine in the late 1930s. Temperatures, environment of the combustion gas stream. There is pressures and stresses have increased steadily; these also a need for metallurgical stability and reliability, advancements have been made possible by improved since these components will be expected to provide design, new alloy developments and advances in trouble-free service for thousands of hours. metal processing/fabrication. An example of the While these austenitic materials do possess very influence of processing innovations is the attractive properties, the expected design life of the improvements in alloy 718 properties created by triple components fabricated from these alloys can only be melting. achieved if the welds used in their construction are of Table 1 lists many of the alloys used in the suitable quality. Not only must the design of the compressor, combustor and turbine sections of a components be optimized to resist the stresses modern gas turbine engine. Included are designations imposed during service, but the welds themselves as to whether the alloys are usually used in the need to be deposited and positioned properly to wrought or cast condition and whether the achieve desired results. compositions are solid solution or precipitation­ There are two main categories of weld­ hardenable. associated defects. The first group include those that 29 Table 1a Compositions of precipitation-hardenable nickel and iron alloys for gas turbines Alloy UNS Composition - Weight % Name No. Ni Co Cr Fe Mo Nb AI Ti W Zr B Other 706 N09706 42 16 40 2.9 .2 1.8 718 N07718 52 19 3 5.2 .5 .9 X-750 N07750 73 15.5 7 1 .7 2.5 MA754 N07754 78 20 .3 .5 .6 VP3 Re 41 N07041 55 11 19 10 1.5 3.1 .005 Re 95 61 8 14 3.5 3.5 2.5 3.5 .05 .010 .15C U-500 N07500 54 18 18 4 2.9 2.9 .05 .006 U-700 53 18.5 15 5.2 4.3 3.5 .030 Waspaloy N07001 58 13.5 19.5 4.3 1.3 3 .06 .006 w o 214 N07214 75 16 3 4.5 .1- .01- N-155 R30155 20 20 21 30 3 1 .8 2.5 1.5Mn•.15N 80A N07080 76 19.5 1.4 2.4 .06 .003 90 N07090 59 16.5 19.5 1.4 2.4 .06 .005 105 53 20 15 5 4.7 1.2 .10 .005 115 60 13 14 3.3 4.9 3.7 .04 .160 Discaloy K66220 26 14 54 2.7 .1 1.7 .005 .9Mn•.8Si 901 N09901 43 12 36 6 .2 2.8 .015 903 N19903 38 15 41 3 .7 1.4 909 N19909 38 13 42 4.7 1.5 .001 .4Si 783 R30783 29 34 3 26 3 5.4 .1 A-286 S66286 26 15 54 1.3 .2 2 .015 1.3Mn..5Si 17-4PH S17400 4 17 75 .3 4Cu \Iote: all cart on levels are U.1 UUfo or below_ urlless otherwise noted - maximum Table 1b Compositions of wrought solid solution nickel, cobalt, and iron alloys for gas turbines Alloy UNS Composition - Weight % Name No. Ni Co Cr Fe Mo Nb AI Ti W 8 Other Hast. 8 N06635 67 16 1 15 .3 .02La Hast. X N06002 47 1.5 22 18 9 2 .6 230 N06230 57 5' 22 2 .3 14 .005 .48i, .02La 242 65 8 25 556 R30556 21 20 22 29 3 .1 .3 2.5 .5Ta, .02La 600 No6600 76 15.5 8 601 N06601 61 23 14 1.3 617 N06617 55 12.5 22 9 1 625 N06625 61 21.5 2 9 3.6 .2 .2 L-605 R30605 10 51 20 15 1.5Mn 188 R30188 22 40 22 14 .03La 75 N06075 75 20 5 .4 263 N07263 51 20 20 6 .4 2 .13C HR-120 N08120 37 25 33 .7 .004 .2N HR-160 N12160 37 29 28 2 2.758i 800H N08810 33 21 46 .4 .4 .8Mn 330 N08330 35 19 45 1.28i 803 865803 35 27 37 .3 .4 Note: all carbon levels are 0.10% or below, unless otherwise noted , = maximum Table 1c Compositions of cast polycrystalline nickel and cobalt alloys for gas turbines I Alloy ~Cr ~ 8 IC I Other I IN-100 64 15 10 3 5.5 4.7 .06 .014 .18 1V IN-713 75 12 4.5 5.9 .6 .10 .010 .12 2Nb IN-738 62 8.5 16 1.8 3.4 3.4 2.6 .10 .010 .17 1.8Ta..9Nb IN-792 61 9 13 2 3.2 4.2 3.9 .10 .020 .21 3.9Ta IN-939 49 19 22 1.9 3.7 2 .10 .009 .15 1.4Ta. 1Nb 8-1900 65 10 8 6 6 1 .08 .015 .10 4.3Ta X-40 10 56 25 8 .010 .50 FSX-414 10 53 29 7 .010 .25 MAR-M 247 60 10 8 .6 5.5 1 10 .09 .020 .16 3Ta. 1.5Hf MAR-M 509 10 49 24 .2 7 .60 7.5Ta 31 Making the Weld Table 2. Effect of grain size on recommended welding processes B The shape and contour of the weld beads themselves can be instrumental in whether or not the weld will be crack free. Even if the welds are properly Gas Gas Shielded made, residual stresses from the welding operation Grain Metal Electron Tungsten Metal may cause problems, such as distortion or cracking. Alloy Sizeb Arec Beam Arc Arc The effect of welding on the base material is another 600 Fine X X X X potential source of problems, particularly with the Coarse X X metallurgically complex alloys that are often specified 617 Fine X X X X Coarse X in gas turbines. Post-weld annealing or stress­ 625 Fine X X X X relieving practices are another potential source for Coarse X X problems. 706 Fine X X X The welding process that is used the most in Coarse X 71B Fine X X X joining gas turbine components is the Gas Tungsten Coarse X Arc process, or GTAW. This welding process allows BOO Fine X X X X greater control of the heat input and provides the Coarse X X X ability to use very low heat input, which is often AISI Type 316 Steel Fine X X X X Coarse X X necessary when joining many of the more difficult-to­ AISI Type 347 Steel Fine X X X X weld turbine alloys. Also, this process uses bare wire Coarse X X as the filler metal, which avoids slag-related problems associated with flux coated electrodes used in the a. Processes marked Xare recommended.
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