1、09FTM14AGMA Technical PaperDesign, Developmentand Application of NewHigh-PerformanceGear Steelsby J.A. Wright, J.T. Sebastian,C.P. Kern, and R.J. Kooy,QuesTek Innovations LLCDesign, Development and Application of New High-Performance Gear SteelsJames A. Wright, Jason T. Sebastian, Chris P. Kern, and
2、 Richard J. Kooy, QuesTekInnovations LLCThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractQuesTekInnovationsLLCisapplyingitsMaterialsbyDesigncomputationaldesigntechno
3、logytodevelopanew class of high strength, secondary hardening gear steels that are optimized for high-temperature,low-pressure (i.e., vacuum) carburization. The alloys offer three different levels of case hardness (with theabilityto“dial-in”hardnessprofiles,includingexceptionallyhighcasehardness),an
4、dtheirhighcorestrength,toughness and other properties offer the potential to reduce drivetrain weight or increase power densityrelative to incumbent alloys such as AISI 9310 or Pyrowear Alloy 53. This new class of alloys utilizes anefficient nanoscale M2C carbide strengthening dispersion, and their
5、key benefits include: high fatigueresistance (in contact, bending, scoring); high hardenability achieved via low-pressure carburization (thusreducingquenchdistortionandassociatedmanufacturingsteps);atemperingtemperatureof900Forhigher(providinguptoa500Fincreaseinthermalstabilityrelativetoincumbentall
6、oys);andcoretensilestrengthsinexcessof225ksi. FerriumC61tisonealloyinthisfamilyandiscurrentlyusedintransaxleringandpinionsfor SCORE 1600 class off-road racing cars as well as process equipment applications; C61 is also beingexamined in a Army SBIR program as a potential replacement for 9310 in CH-47
7、 Chinook helicopter mainrotormastapplications,yieldingaprojectedpotentialweightsavingsof1525%. Secondly,FerriumC64tisbeing developed under a Navy STTR program aimed at rotorcraft gear transmission applications in order toreduce weight, improve fatigue performance, and improve high temperature operat
8、ing capability relative totheincumbentalloyPyrowearAlloy53. Lastly,FerriumC69tcanachieveacarburizedsurfacehardnessofHRC 67 (with a microstructural substantially free of primary carbides) and has exceptionally-high contactfatigue resistance, which makes it a candidate for applications such as camshaf
9、ts and bearings as well asgear sets.ThistechnicalpaperhasbeenreviewedandapprovedforpublicreleasebytheU.S. ArmyandtheU.S. NavalAirSystemsCommand“NAVAIR”. NAVAIRPublicRelease09-812DistributionStatementAApprovedfor Public Release; Distribution is Unlimited.Copyright 2009American Gear Manufacturers Asso
10、ciation500 Montgomery Street, Suite 350Alexandria, Virginia, 22314September 2009ISBN: 978-1-55589-967-73Design, Development and Application of New High-Performance Gear SteelsJames A. Wright, Jason T. Sebastian, Chris P. Kern, and Richard J. Kooy,QuesTek Innovations LLCIntroductionCarburized steel g
11、ears are widely used for powertransmission in rotorcraft, transportation vehicles,agricultural and off-road equipment, industrialrotatingequipment,andthousandsofotherapplica-tions. Commonly-used alloys such as AISI 9310(AMS 6265) and Pyrowear Alloy 53 (“X53”) (AMS6308; UNS K71040) have functional li
12、mitationswhich may not meet all of the performancerequirements arising in next-generationequipment. Increasing demands to reduce energyconsumption, material use, and environmentalimpact are driving the need for dramaticperformance improvements in gear steel manufac-turing and performance. For exampl
13、e, the GearIndustry Vision for 2025 (published in 2004 byAGMA, ASME and other leading governmental,professional and commercial interests) identifiedstrategic goals such as “Increase power density by25% every 5 years”.1 Or as another example, theU.S. Navy estimates that a 20% increase in gearenduranc
14、e could provide $17 million/year in costsavings to the Defense Logistics Agency alone.2Pasteffortstoincreasethepowerdensity,reliability,or endurance performance of gears have includedstudiesofhardtribologicalcoatings;however,manypotential coatings do not work well due to process-ing constraints or p
15、oor adhesion to the underlyingalloy.3, 4, 5 Powder alloy approaches have alsobeen studied, but are often inadequate for fatigue-limited applications due to the higher fraction ofoxide inclusions and porosity, which can act asfatigue initiation sites. Many improvements in thefatigue performance of co
16、mmonly-used alloyshave been made using surface processingtechnology advancements such as superfinishing,shot peening, laser shock peening, or cavitationpeening, but these do not improve the intrinsiccharacteristics of the base alloys. This papersummarizes a first-principles-based, integratedcomputat
17、ional materials design approach that isbeing used to create next-generation, high-performance base alloys with improvedperformance and reduced manufacturingcomplexity and variability.Overview of computational materialsdesign technologyNew materials have historically been discoveredeither by chance o
18、r by intricate and costly cycles oftrial and error, yielding a limited understanding ofoptimization and design. The limitations of the pastapproacharewidelyknown,andnumerousnationalstudies over the past decade have consistentlyemphasized that traditional empirical materialdevelopment methods have no
19、t kept pace withmodern design-based product developmentefforts. One result is that a number of renownedmaterials companies have all but dropped theirlabor-intensive internal research and developmentprograms due to their prohibitive cost, and haveinstead refocused their efforts on reducing costs toma
20、nufacture and process generic materials.The use of powerful computational tools, propertydatabases and intellectual expertise tocomputationally design and create new materials isa rapidly-emerging alternative approach. Thesetechniquescanbeusedtoquicklyandeconomicallydesign and develop unique materia
21、ls as integratedsystems, in order to deliver optimal performancerequirements for a given application. The SteelResearch Group (SRG) at Northwestern UniversityofEvanston,ILpioneeredthistechnologybeginninginthemid-1980s. Thestrategicimportanceofcom-putational materials design to the national missionwa
22、s set forth in 2000 when the U.S. PresidentsOffice of Science and Technology identifiedcomputational design of materials as one of fivecritical technologies for the coming decade.6QuesTek Innovations LLC (QuesTek) of Evanston,ILwasfoundedin1997andisbuildingontheSRGsinitial efforts by using QuesTeks
23、proprietaryMaterialsbyDesigntechnology tocomputational-ly design many new materials, include iron-,copper-, aluminum-, nickel-, niobium- and4titanium-based materials. Dr. Gregory B. Olson,the Wilson-Cook Chaired Professor in EngineeringDesign at Northwestern Universitys Department ofMaterials Scienc
24、e and Engineering, is QuesTeksChiefScienceOfficerandafounderofthecompany.QuesTek was one of only a few commercial firmshighlighted in 2008 by the U.S. National ResearchCouncil as examples of firms utilizing IntegratedComputational Materials Engineering (ICME) forIntegrated Manufacturing, Materials,
25、andComponent Design.7QuesTeks computational materials designapproach considers material design goals and de-sired performance in the context of a materialsystem. This approach integrates materialsprocess-structure and structure-property modelsin a systems-based framework in order to meetspecific, de
26、fined engineering needs, and alsoaddress manufacturing processes and materialqualification hurdles (including prediction ofmanufacturing variation). Like any other designeffort, judicious decisions regarding key trade-offsamong many competing requirements are oftenneeded. Combinations of properties
27、must beconsidered within specified process, cost, environ-mental and life-cycle constraints. Advancedcomputational modeling tools provide valuablescientific understanding in order to optimize suchtrade-offs in an efficient and knowledgeablemanner, and typically provide enough fidelity to notonly det
28、ermine the favorability of one designsolution over another but also to search for designoptima in previously-unexplored terrain.Some of the SRGs and QuesTeks work hasfocused on computationally designing next-generation, high-performance gear steels, in orderto significantly improve performance prope
29、rtiessuch as strength, corrosion resistance, wear resist-ance and fatigue resistance while designing forrobust, efficient and flexible processing paths. ThenewresultingalloysareinaclassofQuesTekalloystermed Ferrium alloys.Design and overview of Ferrium gearsteel alloysFerrium C61t,C64t and C69t are
30、three newalloysbeingusedorconsideredforpowertransmis-sion applications. All of these alloys utilize anefficient nanoscale M2C carbide strengtheningdispersion within a Ni-Co lath martensitic matrix.Utilizing their suite of computational models,QuesTek designed these alloys considering thecomplex inte
31、rplay of critical design factors includ-ing: martensitic matrix stability (Mstemperature);M2Ccarbidethermodynamicstabilityandformationkinetics; matrix cleavage resistance; andembrittling phase thermodynamic stability.The hierarchicalrelationships betweenProcessing,Structure, Properties, and Performa
32、nce are sum-marizedbyQuesTekintheformofa“DesignChart,”which serves as the template for alloy design (seeFigure1). Theperformanceofthealloyisembodiedin the combination of properties outlined in thecolumn on the right. The design processdetermines suitable microstructural concepts tomeet these propert
33、y goals, as indicated by themiddle column. Available processing paths toaccessthemicrostructuralobjectivesarequantifiedintheleftcolumn. Thelinksbetweenthesubsystemblocks in the flow-block diagram representprocess-structure and structure-property modelsrequiredtoquantitativelydesignanalloytomeetthede
34、sired material performance objectives.Asithasdoneinitsotherdevelopmentprograms8,QuesTek and its partners utilized its custom stage-gate process, as graphically illustrated in Figure 2,to design and develop the Ferrium alloys in a rapidmanner while minimizing development costs. Theprocess begins by w
35、orking with the key stakehold-ers, such as gear designers and manufacturers, toestablish specific system property goals and proc-essing constraints. Within thesecustomer-definedobjectives,QuesTekapplieditscomputationalmod-elstoexploreviablemicrostructuralconcepts. Withthe most promising concept sele
36、cted, the alloy de-signplanisreviewedforitsviabilitypriortoproceed-ing to the design phase.QuesTeks Materialsby Designprocess is iterative,with review meetings at critical decision pointsthroughout the modeling, design, and prototypingtasks. Aftercompletingtheinitialmodelingandpro-totype designs com
37、plete, QuesTek procures sub-scale ingots to validate the proof-of-concept withmaterial testing and microstructural characteriza-tion. Having achieved the design goals with sub-scale material, QuesTek proceeds to full-scalecommercial production. For example, QuesTekprototyped Ferrium C64 with one rou
38、nd each ofsub-scale and intermediate-scale prototypes priorto the finalized commercial-scale production.5Figure 1. The “Design Chart” used by QuesTek to design the Ferrium C64 alloy. The hierarchicalrelationships between processing, structure, properties, and performance are summarizedgraphically an
39、d serve as the template for alloy design.Figure 2. Overview of QuesTeks custom stage-gate process showing the development of a newmaterial from identification of the customer-defined needs through qualification and componentdemonstration.6The objective of the final phase of QuesTeks alloydevelopment
40、processistodevelopmaterialsdesignallowables of the alloy and manufacture full-scalecomponents. These two tasks may be executed inparallel depending upon the specific situation at thetime. Multiple heatsof thealloy maybe requiredforstatistical development of materials designallowables. In the case of
41、 the gear steels, thisincludes rotating gear and rig testing to providestatistically validated fatigue design data. Themajority of the work in the qualification phase of de-velopment is performed by our manufacturingpartners and leading adopters of the material.QuesTeksdesignmethodologyyieldedanumbe
42、rofattractive material properties for C61, C64 and C69alloys. A tabular and graphical summary of keyproperties vs. common incumbent materials isshown in Figure 3 and Figure 4.Figure 3. Tabular comparison of core properties (typical)Figure 4. Graphical comparison of core properties and design targets
43、7These properties, and the material processingroutes available with these materials, yield perfor-mance features such as the following:Greater core strengthThese alloys exhibit core steel tensile strengths(UTS) of 229 ksi or more, which is a +35% increasevs. conventional gear steels and allows signi
44、ficantreductions in part size and weight, particularlywhere structural components are integrated withgearing into single components.Greater surface fatigue resistanceThese alloys demonstrate high surface fatigueresistance,whichleadstoincreasedcontactfatigueand bending fatigue performance. Generallys
45、peaking, increasing the surface hardness withoutcreating embrittling features (such as intercon-nected primary carbides) increases surface fatigueresistance. Since surface fatigue resistance canoften be a limiting factor in gear design, increasedsurface fatigue resistance can enable eithersmaller, l
46、ighter power transmission units or higherpower throughput in a given unit size.High surface hardenability, designed to usehigh-temperature, low-pressure (i.e. vacuum)carburization methodsThese alloys were specifically designed to achievehigh surface hardenability and use high-temperature, low-pressu
47、re (i.e., vacuum) carbu-rization and gas quenching processing methods,the combination of which can permit significantreductions in manufacturing costs and schedulesdue to:S Shorter processing times at higher carburizingtemperatures.S Elimination of the secondary hardening and oilquench process step,
48、 and the associated costsofcustompressquenchdies,liquidquenchants,rapid transfer mechanisms, hydraulic systems,etc.S Reduction of excess grinding labor, excessstock removal waste and part scrap waste, byreducingpartquenchdistortionandavoidingtheintergranularoxide(IGO)formationinherentinapre-oxidatio
49、n step - the slower gas quenchprocess is far less severe and far more spatiallyuniform than a rapid liquid quench.S Enhanced manufacturing flexibility and control,due to the ability to “dial in” the depth and profileof case carburization.For example, the high hardenability of Ferrium C61when compared to a conventional baseline gearsteelaswellasa premiumgear steelis illustratedinFigure 5.Figure 5. Hardenability comparison for center of an air-cooled bar between legacy baselinesteel, curren
