Welding of Stainless SteelsPROGRAM STUDI TEKNIK BANGUNAN KAPALJURUSAN TEKNIK BANGUNAN KAPALPOLITEKNIK PERKAPALAN NEGERI SURABAYA2014
Stainless steelsStainless steels = Cr containing steel alloysCr content is min. 10.5% and max 30% Cr makes the steel 'stainless' = improved corrosion resistance, due to a chromium oxide film that is formed on the steel surfaceThis extremely thin layer is also self-repairing in the presence of oxygenand damage by abrasion, cutting or machining is quickly repairedC : 0.03 % - 1,2% 0Corrosion Rate (mm/year)% Chromium51000.10.2Fig. 1 - In any normal oxidising environment a protective coating of passive chromium rich oxide film is automatically formed on stainless steel.Fig. 2 - When scratched, damaged or machined this protective film is denuded exposing the steel to the atmosphere.Fig. 3 - The protective coating is quickly restored through the rapid self-repairing quality of the chromium rich film.
Stainless steelsPasivitas Pada Stainless SteelsPasivitas dikarenakan oleh adanya lapisan oksida yang bersifat self-repairing dengan karakteristik :Kompak, lapisan kontinyu memerlukan ~ 11wt% Cr.Pasivitas meningkat dengan meningkatnya Cr hingga ~17wt% Umumnya stainless steels mengandung 17-18wt% CrPada Duplex SS Cr 22-27%Ketahanan korosi tergantung pada kestabilan lapisan oksidaUntuk lingkungan yang berbeda dioptimalkan oleh alloying dengan unsur lainContoh; Ni, Mo, N, CuPengelompokan Stainless Steels Berdasarkan mikrostruktur Stainless steels (SS) dapat dikelompokkan atas:Feritik SSAustenitik SSDuplex (Feritik-Austenitik) SSMartensitik SSPrecipitation Hardening (PH) SSMikrostruktur stainless steels (sangat tergantung dari komposisi) dapat diprediksi menggunakan diagram Schaeffler-Delong Schaefler Diagram
Diagram Schaeffler-DelongChromium Equivalent = %Cr + 1.5%Si + %MoNickel Equivalent = %Ni + 30(%C + %N) + 0.5(%Mn + %Cu + %Co)
Family of SS
Effect of Alloying ElementsUnsur paduan berkontribusi terhadappembentukan fasa ferrite-austeniteFerrite stabilizer (misal: Cr, Mo, W, V)Austenite stabilizer (misal: C, Cu, Ni, Mn, N)pembentukan fasa kedua (precipitate) yang melibatkan unsur Cr, Mo, W, Cu, NSigma phaseChi phase
Sangat penting untuk mengetahui pengaruh elemen paduan terhadap complex metallurgical systemEffect of CarbonIron + carbon =increasing the hardness and strength of iron. In austenitic and ferritic stainless steels a high carbon content is undesirable, especially for welding carbide precipitation brittleEffect of ChromiumChrom :To increase resistance to oxidation. This resistance increases as more chromium is added. Duplex Stainless SteelCr = ferrite former and sigma phase (carbide former)Cr > 22%increase in pitting and crevice corrosion resistance Cr < 27 % in order toretain ductility, toughness and corrosion resistance
Effect of NickelNi = austenite former (austenite promoting element)To balance the microstructure to ferrite/ austenite ratioAffects the corrosion and mechanical propertiesExcessive Ni: increase in austenite contentPromoting a greater conc. of ferrite stabilizer element (Cr, Mo) in the remaining ferrite (not change to the precipitation of sigma phase)
Effect of Mo and NMolybdenum (Mo): Strong ferrite former, similar effect as Cr does on propertieswhen added to austenitic stainless steelsimproves resistance to pitting and crevice corrosion especially in Cl and S containing environments
Nitrogen (N): N = austenite forming element increasing the austenite stability Yield strength is greatly improved without sensitization (e.g. carbon) Effect of Mn and CuManganese (Mn): to improve hot working properties and increase strength, toughness and hardenability. Mn = austenite forming element used as a substitute for nickel in Austenitic SS e.g. AISI 202 as a substitute for AISI 304
Copper (Cu): Cu = normally present as a residual elementin a few alloys to produce precipitation hardening properties or to enhance corrosion resistanceEffect of W W = minor elements improving corrosion resistanceThe addition of W causes easy to form inter metallic phase compare with W-free duplex SSW =like Cr and Mo promotes sigma phase formationpromote of Chi phase
Effect of Alloying on SS PropertiesPropertyCCrNiSMnSiPCuMoSeTi or NbCorrosion Resistance-X-----Mechanical Properties---High Temperature Resistance-X-----MachinabilityXX------WeldabilityXX-X-X--Cold WorkabilityXXX------Ferritic Stainless Steel (Generasi I)
Ferritic Stainless Steel (Generasi II)
Aplikasi Ferritic Stainless SteelAplikasi SS 430 Produk Flat Rolled (plate, sheet and coil)Refrigerator cabinet panelsLinings for dish washers
Aplikasi SS 409 Automotive exhaust systems Catalytic converters
Austenitic Stainless SteelsTipikal: 18%Cr, >8%Ni, 40Martensitic Stainless SteelMerupakan paduan chromium dan karbon yang mengalami distorsi struktur kristal bcc (body centered cubic) pada saat proses pengerasannya.Komposisi :Cr: 10,5 18 %C : > 1,2 %Sifat : - ferromagnetik- hardenable- tahan terhadap korosi pd lingkungan tertentu
Precipitation Hardening SSPrecipitation hardening stainless steel pertama kali dikembangkan pada tahun 1940 oleh United State Steel CorporationAdanya chromium dan nickel yang terdapat dalam baja dapat menciptakan very high tensile strengths. Keuntungan baja ini adalah dapat dibuat pada dalam kondisi "solution treated.Dapat dikeraskan dengan proses "ageing" yang dapat mengurangi distorsi pada komponen.
Aplikasi PH Stainless SteelAplikasi precipitation hardening stainlesssteel :Aerospace hardwareA-286 high temp untuk mesin jetTurbin wheelFanFastenerStrength and Ductility of Stainless Steel
Toughness of Stainless Steel
Properties of Stainless SteelAlloy GroupMagnetic Response1Work Hardening RateCorrosion Resistance2HardenableAusteniticGenerally NoVery HighHighBy Cold WorkDuplexYesMediumVery HighNoFerriticYesMediumMediumNoMartensiticYesMediumMediumQuench & TemperPrecipitation HardeningYesMediumMediumAge HardenAlloy GroupDuctilityHigh Temperature ResistanceLow Temperature Resistance3WeldabilityAusteniticVery HighVery HighVery HighVery HighDuplexMediumLowMediumHighFerriticMediumHighLowLowMartensiticLowLowLowLowPrecipitation HardeningMediumLowLowHighProperties of Stainless Steel
Properties of Stainless Steel
Welding stainless steelsAll SS types Weldable by virtually all welding processesProcess selection often dictated by available equipmentSimplest & most universal welding processManual SMAW with coated electrodesApplied to material > 1.2 mmOther very commonly used arc welding processes for SSGTAW, GMAW, SAW & FCAWOptimal filler metal (FM)Does not often closely match base metal compositionMost successful procedures for one family Often markedly different for another familyWelding stainless steelsSS base metal & welding FM chosen based onAdequate corrosion resistance for intended useWelding FM must match/over-match BM content w.r.tAlloying elements, e.g. Cr, Ni & MoAvoidance of crackingUnifying theme in FM selection & procedure developmentHot crackingAt temperatures < bulk solidus temperature of alloy(s)Cold crackingAt rather low temperatures, typically < 150 CSheet1KOMPOSISI KIMIA FERRITIC STAINLESS STEEL GENERASI IKOMPOSISI WT %UNSTYPECCrMoLAIN2S429004290.1214.0-16.0--S430004300.1216.0-18.0--S43020430F0.1216.0-18.00.60.06P;0.15 min SS43023430FSe0.1216.0-18.0-0.15 min SeS434004340.1216.0-18.00.75-1.25-S436004360.1216.0-18.00.75-1.25Nb+Ta = 5x%C minS442004420.218.0-23.0-S446004460.223.0-27.0-
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Sheet1KOMPOSISI KIMIA FERRITIC STAINLESS STEEL GENERASI IIKOMPOSISI WT %UNSTYPECCrMoNiLAIN2S405004050.0811.5-14.50.1-0.3 AlS409004090.0810.5-11.750.5Ti = 6xCmin to 0.75%max409Cb0.0212.50.20.4 NbS441004410.02180.30.7 Nb, 0.3 TiAL4330.02190.30.4 Nb, 0.5 Si, 0.4 CuAL4660.0111.50.20.2 Nb, 0.1 TiAL4680.0118.20.20.2 Nb, 0.1 TiYUS436S0.0117.41.20.2 TiS430354390.0717-190.5Ti = 0.2 + 4(C+N)min to 1.0max12SR0.2121.2 Al, 0.3 Ti18SR0.04182.0 Al, 0.4 TiK419704060.0612.0-14.00.52.75 - 4.25 Al , 0.6 Ti
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