1. FSW ofStainless SteelSUBMITTED TO: PRESENTED BY:DR. NAVNEET ARORA HIMASNHU NAMDEO145420051

2. A Primer on FSWSECTION 12 3. Relevance TodayHelping create cuttingedge devices.3 4. Friction Stir Welding : Frictionat workFriction-stir welding (FSW) is a solid-state joining process (the metal is notmelted) and is used when the original metal characteristics must remainunchanged as much as possible.- Wikipedia4 5. The Process 5 6. How does it works 7 7. 8The two surfaces tobe joined arepreparesA rotating non-consumablecylindrical toolpenetrates thematerialThe two surfaces arejoined due to thefrictional heat. Theheat, though is notsufficient for meltingThe Process 8. Process Parameters The heat generated in the joint area takes it to typically about80-90% of the melting temperature. The heat input is purely mechanical and includes force, friction,and rotation. A simplified model to identify the way heat is generated andtransferred to the joint area is described in the followingequation:Q = FK in which the heat (Q) is the result of friction(), tool rotation speed () down force (F) and a tool geometryconstant (K).9 9. Process Parameters 10 10. Process Parameters Tool rotation and traverse speedsThere are two tool speeds to be considered in friction-stir welding; howfast the tool rotates and how quickly it traverses the interface. Thesetwo parameters have considerable importance and must be chosenwith care to ensure a successful and efficient welding cycle. Tool TiltTilting the tool by 24 degrees, such that the rear of the tool is lowerthan the front, has been found to assist this forging process. It affectsthe bead characteristics and the appearance of the weld.11 11. Process Parameters DownForce / Plunge DepthThe plunge depth is defined as the depth of the lowest point of theshoulder below the surface of the welded plate and has been foundto be a critical parameter for ensuring weld quality. The plunge depthneeds to be correctly set, both to ensure the necessary downwardpressure is achieved and to ensure that the tool fully penetrates theweld. Tool designThe design of the tool is a critical factor as a good tool can improveboth the quality of the weld and the maximum possible welding speed.It is desirable that the tool material is sufficiently strong, tough, andhard wearing at the welding temperature.12 12. Tools 13 13. Why FSW? 14Source: Friction stir welding and processing R.S. Mishraa,, Z.Y. Mab 14. Challenges to FSWof Stainless SteelsSECTION 215 15. Challenges to FSW of SSFSW of Stainless steel 304 had not been progressing as rapidly as foraluminium and other metals because of various reasons some of whichare given below: The wearing out of the tool because of strength of steel and highsoftening temperature of steels. The consequences of phase transformations accompanying FSWhave not been studied in sufficient depth. The variety of steels available is much larger than for any other alloysystem, requiring considerable experiments to optimize the weld fora required set of properties Cost Competitiveness16 16. 17Source: Critical assessment: friction stir welding of steels H. K. D. H. Bhadeshia and T.DebRoy 17. So how do we do the FSWin stainless steels?18 18. FSW in StainlessSteelSECTION 319 19. Addressing the concerns in FSW forStainless Steels1. Tool Material 2. Phase Effects 3. Analysis of JointAn ideal tool would be: Strong enough even at hightemperatures Wear Resistant to bearbrushing up a steel durably Cheap enough for massproductionAvailable options: Diamond PCBN (Boron Nitride)Arbitrary heating and cooling ofsteel is well known to produce alot of undesirable effects inferrous alloys.So studying the effects of stirwelding owing to its peculiartemperature range on theoverall strength of a materiallike steel gains importance.Finally the analysis of the weldjoint is of prime importance, asit leads to the technological aswell as economic results out ofthe process.Based on these tests, is itsfeasibility weighed in terms ofits comparison with otherjoining processes.20 20. 1. Tool Material SelectionWanted in an ideal tool: High Temperature Strength enough to be useful here Wear Resistance and Durability to bear brushing up a steel Cheap enough for mass production owing to continuous consumption21 21. Post-weld analysis of the Tool 22260 feet in 1018 mild steel Solved design issue in driving PCBN 78 tool plunges No visible wear Pin fractured at 262 feetBefore After 200 feet15 mmBead on plateperformed for life study 22. Issues with Tool material selection To apply FSW in steel or other high-temperature materials, thedifficulty is mainly associated with finding proper tool material; amaterial that can withstand the high temperatures that areexperienced during the process. The temperatures are especiallyhigh because of steel being ferrous. Resistance to wear (durability) is one important aspect, especially asmany of the intended applications are considered critical at amicroscopic level; hence there can be no traces of the tool left inthe seam. PCBN is one of the most promising tool materials so far.23 23. We want a hard material!Why not use Diamond? Diamond is soluble in iron, nickel, andrelated alloys at high temperatures, to givecarbides Blending of diamond cutting tools into themetallic components of the movable machineryis relatively a harder task Natural diamond is very rare and being agemstone is quite costly while the artificialdiamond is very difficult to manufacture.So diamond abrasives are preferred only foraluminium alloys, ceramics and stone.24 24. PCBN A material to the rescue!PCBN is one of the most promising toolmaterials so far considering all theprocess requirement parameters. Poly-cBN or PCBN : PolycrystallineCubic Boron Nitride Owing to its insolubility in iron, nickel,and related alloys at hightemperatures, polycrystalline c-BN(PCBN) abrasives are used formachining steel. Boron nitride binds well with metals,due to formation of interlayers ofmetal borides or nitrides making themanufacturing of tools easier, morereliable and a economical.25 25. 2. Phase EffectsArbitrary heating and cooling of steel is well known to produce a lot ofundesirable effects in ferrous alloys.So studying the effects of stir welding owing to its peculiar temperature rangeon the overall strength of a material like steel gains importance.26 26. 27The consequences of phase transformations accompanying FSW have notbeen studied in sufficient depth. In most studies, the steel being friction stir welded becomes locally red hot;the maximum temperature reached is less than 1200 C and the time Dt85taken to cool over the range 800500 C is approx.. 11 s. Austenite will therefore form during the heating cycle and will subsequentlytransform during the cooling cycle. With few exceptions, only elementary mechanical properties have beencharacterised in studies of the FSW of steels; For serious structural applications, it would be necessary to assess fracturetoughness and other complex properties in much greater depth.Commercial adoption wont happen unless it is conclusively shown thatthe the properties of welded materials are appropriate. 27. 28The material from which the tool is made has to survive much more strenuousconditions because of strength of steel and high softening temperature ofsteels.It is apparent that the torment that an FSW tool would have to go through inthe case of steel would be much greater than that for aluminium unlesstemperatures are achieved in excess of some 800 C; the steel must besufficiently plasticised to permit the material flow to enable a sound weld tobe fabricated. Cost effective tool materials which survive such conditions forextended service remain to be developed 28. Phase analysis of materials304 Stainless Steel500x1000xSigma phase observed in bandsAlso observed at grain boundaries between bands29A typical weld beadon 304 SS 29. 3. Analysis of Welded JointsFinally the analysis of the weld joint is of prime importance, as it leads to thetechnological as well as economic results out of the process.Based on these tests, is its feasibility weighed in terms of its comparison withother joining processes.30 30. Added characteristics ofSolid State Joining Minimization of fume generation since the heat generated duringthis process remains below the melting temperature of the material Reduced distortion The ability to form strong joints without filler wire Reduced joint preparation and post-weld clean-up Reduced post-weld inspection and rework Various inherent user- and environmentally-friendly properties, suchas the ability to be automated31 31. Added characteristics ofSolid State JoiningFriction Stir Welding of ferrous alloys offers numerous benefits, such as: Critical Pitting Temperature (CPT) is 20 C higher than arc-weldingprocesses FSW does not introduce harmful inter-metallics FSW retains the proper ratio of austenite and ferrite FSW does not form excessive amounts of martensite FSW creates a matching fusion zone without reinforcement32 32. A vision for the futureThe challenges have been discussed at great length, but it is useful tospeculate on the more difficult task of how a vision for the future maybe achieved:1. The identification of a joining problem for steel which cannot betackled using conventional techniques. This will necessarily be aniche problem dealing with expensive components in order tojustify costs.2. The imaginative development of a tool material specifically suitedto the problem. For example, could the tool be designed so thatany tool material which enters into the weld is benign? Perhaps theconcept of a slowly consumable tool may then not be farfetched.33 33. Potential Applications Underwater WeldingOne potential application of FSW is underwater joining of steels,where FSW would have clear advantages over fusion welding.Underwater pipelines are extremely expensive to place in positionand it is possible that the cost of tooling might then becometolerable. Another is the joining of mechanically alloyed yttria dispersionstrengthened iron based alloy which are currently beinginvestigated for the fusion research programme, and for which thereis no seriously useful joining technology available. These areexpensive materials for an expensive but critically importantapplication.34 34. To Sum-up : Friction Stir Welding is a promising process and has clearadvantages in terms of the mechanical properties of the weldedmaterial. FSW has already found great applications in theAluminium industry. Therefore it becomes imperative to try to use itwith other materials including stainless steels.35 35. Chief ReferencesCritical assessment: friction stir welding of steelsH. K. D. H. Bhadeshia*1 and T. DebRoywww2.matse.psu.edu/modeling/papers/09STWJ_Bhadeshia.pdfFriction Stir Welding of Ferrous and Nickel AlloysCarl D. Sorensen and Tracy W. Nelson Department ofMechanical Engineering, Brigham Young Universitywww.asminternational.org/content/ASM/StoreFiles/05112G_Chapter_6.pdf36Friction Stir Welding of austenitic stainless steelsC. Meran*, O.E. CanyurtMechanical Engineering Department, EngineeringFaculty, Pamukkale University,www.journalamme.org/papers_vol43_1/43149.pdfFriction Stir Welding of Stainless Steel 304: A SurveyPushp Kumar Baghel Research Scholar, Department ofMechanical Engineering, Delhi Technological University,Delhi, Indiahttp://iosrjournals.org/iosr-jmce/papers/vol1-issue2/D0122223.pdf 36. Other Credits http://www.esab.com/de/de/support/upload/FSW-Technical-Handbook.pdf http://ammtiac.alionscience.com/pdf/AMPQ7_3ART02.pdf http://www.aws.org/conferences/abstracts/2003/10d.pdf37 37. ThanksHIMASNHU NAMDEO 1454200538