Duplex Stainless Steel Fabrication

Duplex Stainless Steel FabricationGary M. CarinciTMR StainlessConsultant forInternational Molybdenum Association1

Promoting molybdenum - as a material with superior properties andperformance in a wide variety of metallurgical, chemical and other productapplications Expanding the applications in which molybdenum is used via: Market development programs Co-operation with consumers, end-users and allied organizations Technical brochures and training seminars to explain the advantagesof using molybdenum-containing products in various industries2

Presentation Overview 3What is Duplex Stainless Steel?Chemical CompositionMechanical cation Cleaning

Types of Stainless Steels4AusteniticType 316FerriticType 430DuplexType 2205

Chemical erritic)162205(duplex)2253

ASTM Mechanical Properties(Minimum 040316L2570402205659525

What is Duplex Stainless Steel?7

Duplex Stainless Steels Consist ofAustenite and Ferrite8

Duplex MicrostructureCourtesy of OutokumpuAusteniteFerrite9

Duplex Stainless Steel Types230423% Cr, 4% NiLDX 210121% Cr, 1% Ni220222% Cr, 2% Ni210221% Cr, 2% NiStandard220522% Cr, 5% NiSuper250725% Cr, 7% NiLean10

Advantages of Duplex 11StrongStress corrosion cracking resistantPitting / crevice corrosion resistantErosion resistantFatigue resistantCost effective (lower nickel contents)

Cutting Stainless Steel12

Cutting Duplex Stainless Steel13 Mechanical Sawing Shearing Abrasive wheel cutting Water-jet cutting Thermal Plasma cutting Laser cutting

Cutting: Sawing 14Similar to austenitic stainless steelPowerful machineProper blade alignmentCoarse toothed bladeSlow to moderate cutting speedHeavy feedGenerous flow of coolant

Cutting, Mechanical Shearing 15More force and heavier equipment will be required toshear stainless steel compared to carbon steelCarbon steel - 1/2” thick shear limitAustenitic stainless steel - 1/4” max.Duplex stainless steel - 3/16” max.

Mechanical Shearing A general clearance guide is to use a clearance of 5% of themetal thickness between shear knivesTo counter the shearing force required for duplex stainlesssteel, the hold down pressure on the clamps may have to beincreased BLADES MUST BE SHARP! 16

Abrasive Cutting 17Abrasive wheels, rotating at highspeed can be used for straightline cutting of sheet and thingauge plate and for cut-offoperations on relative smallsectionsThick section cut-off operationsare usually done wetUse uncontaminated vitrified orresin-bonded wheelsDO NOT INDUCEOVER-HEATING

Cutting: Plasma and Laser 18Same equipment as for 304/316Optimum parameters vary slightly

Bending - Springback19 Duplex stainless steels, with their higher strength andhigher rate of work hardening, require more power tobend than carbon steel Duplex stainless steel must be bent further thancarbon steel to result in the same angle since there ismore springback

Minimum Bending Force3.5Bending Force (kN)3.02.52.01.51.00.50.02022052304Stainless Steel Grades316L

Forming Stainless Steels Duplex stainless steels havehigh work hardening rates the strength increases asthey are formed Greater springback thancarbon steels Avoid contamination fromtooling: Use dedicatedtooling, or provide surfaceprotection21

Avoid Iron Contamination!22

Avoid Contamination fromTooling During Forming 23Ensure particles such as carbon steel or rust arenot pressed into the surfaceAdopt some combination of the followingguidelines: Use dedicated tooling Clean all contamination from the surface oftooling before use Do not use carbon steel tooling - use toolsteel or stainless steel or hard chromeplated tooling Protect the surface of the stainless steel

Cold Forming 24Duplex ductility lower than austenitic avoid sharp bend angle bend radius at least twice the thicknessDuplex much stronger than austenitic higher forces necessary more spring-backDuplex cold works readily Requires more annealing stages than austenitic

Hot Forming25 Avoid critical temperaturerange for sigma phase (1300 - 1800 F) Duplex is very soft between1750 and 2100 F easy to hot form

Hot Forming Temperature RangeGrade26Hot Forming Temperature Range C F22051100 to 9502010 to 174025 Cr Duplex1150 to 9802100 to 179525071200 to 10252190 to 1875Types 304/3161205 to 9252200 to 1700

Hot Forming27 Lower temperature can cause cracking Higher temperature can cause tearing Full solution annealing after hot forming

Minimum Annealing TemperatureGrade C F22051040190025 Cr Duplex104019001025 to 11001875 to 2010Superduplex(depending on grade)28Minimum Annealing Temperature

Machining29

Machining Duplex 30High work hardeningLow thermal conductivityHigh toughness“sticky”Poor chip breaking

General Rules for Machining 31Good edge sharpnessCutting tool with high edge strengthSufficient cutting depthsFrequent insert replacement

ComparisonAustenitic - DuplexAlloy content machinability 32Duplex: harderDuplex: faster strain hardeningHigher tool wearLower machinability

Face Milling with Cemented CarbidesStainless Steelormachining dataLean duplex(2304)2205SuperduplexFeed (per tooth)Depth of cutCarbide Grade33RoughingSpeed (m/min)Speed (sfm)FinishingSpeed (m/min)Speed 0260-36030-50100-16550-70165-2300.2-0.4 mm0.008-0.075 in.0.1-0.2 mm0.004-0.008 in.2-5 mm0.080-0.200 in.1-2 mm0.040-0.080 in.2304, 2205: ISO P20-P402304, 2204: ISO P10-P25Superduplex: ISO P25-P40Superduplex: P20-P30

Summary 34Machinability generally lower than standardaustenitic grades (300-series)Higher forces necessary for machining andformingAdjust parameters to optimize

Duplex Stainless Steel Welding35

Similarities: Austenitic vs. Duplex36 Same pre-weld joint cleaning Remove all debris, dirt, paint and oil Remove water or moisture Same joint preparation Remove heavy oxides Remove rough grinding burrs Same edge geometry Machine or grind edge profile Similar joint design Provide backing gas shielding Ensure full penetration weld

Differences: Austenitic vs. DuplexDuplex weld / HAZ sensitive to: Excessive ferriteSigma phase“You can’t tell from the outside”37

Differences Austenitic vs. Duplex Qualification extremely important 38Appearance of weld gives no indication of qualityWritten procedures and trial welds necessary toassure quality

Differences Austenitic vs. Duplex 39Less thermal expansion - less distortionLess hot crackingSensitive to H2-cracking Remove moisture from joint Store electrodes at elevated temperature Avoid hydrogen in backing or shielding gas

Metallurgy: Phase Balance 40Don’t quench too quicklyNo wash passes or spot weldsIntermediate heat inputFiller metal mandatoryNickel over-alloyed fillerNitrogen in shielding gas is beneficialRemove tack welds in final fabrication

Metallurgy: Sigma Phase 41Don’t cool too slowlyAvoid high heat inputInter-pass temperature 300 FHeat input 15 - 60 KJ/inch (2205)Qualify all welding procedureQualify weld repairs

Welding Processes for DuplexStainless Steel 42Shielded Metal Arc Welding:SMAW, covered electrodes, “stick”Gas Tungsten Arc Welding:GTAW, “TIG”Gas Metal Arc Welding:GMAW, “MIG”Flux Core Arc Welding: “FCAW”Submerged Arc Welding: “SAW”

2205 Welding 43Always use filler metal, even for repairUse 2209 (7 - 9% nickel) filler metalPreheating is not necessaryHeat input 15 - 60 kJ/inchInterpass temperature below 300 FPost-weld heat treatment is not normally necessary.Above 600 F alpha prime precipitation is a concern(885 embrittlement)

Superduplex Welding 44Always use filler metal, even for repairUse 25Cr-10Ni-4Mo-N filler metalPreheating is not necessaryHeat input 15 - 40 kJ/inchInterpass temperature below 200 FPost-weld heat treatment is not normally necessary.Above 600 F alpha prime precipitation is a concern(885 embrittlement)

Dissimilar Metal Welds45 Duplex can be welded to austenitic stainlesssteels and carbon steels E309LMo/ER309LMo or E2209/ER2209 fillerused when welding to austenitic stainless steel E309L/ER309L or E309LMo/ER309LMo fillerused when welding to carbon steels

Welding Consumables Used for Dissimilar Metal Welding2304220525 CrSuperduplex304316Carbon steel462304220525 209309L309LMo220922092209220925Cr-10Ni-4Mo-N 25Cr-10Ni-4Mo-N25Cr-10Ni-4Mo-N 25Cr-10Ni-4Mo-N 25Cr-10Ni-4Mo-N25Cr-10Ni-4Mo-N 25Cr-10Ni-4Mo-N o

Welding Consumables47 Always use a recommended welding product Duplex stainless steel weld fillers are slightlyoveralloyed compared to the base material Composition of consumables is chosen toproduce correct Austenite/Ferrite balance induplex stainless steel welds

Duplex Stainless Steel Shielding Gases48MethodShielding GasesTIGAr or Ar 2 - 3% N2 or Ar 30% HeMIGAr or Ar 2 - 3% N2 or Ar 30% He 1 - 3% CO2 orAr 2 -3 CO2FCAWAr 18 - 25% CO2 or 100% CO2

Good Welding Qualification ToughnessCorrosion resistance e.g., ASTM A 923ASME requirementsMetallographyÎ49Service relevant propertiesare most important

Post Weld Heat TreatmentOnly full solution anneal acceptable! Not normally necessary, except: Autogenous weld (not recommended) Thick weld section with multiple passesto remove sigma phase and restore phase balance50

Post-Fabrication Cleaning Main Objectives are: 51Remove heat tintMake sure there is no surface contamination,such as smeared or embedded ironEnsure there is a strong, continuous, protectivechromium-rich oxide layer all over the surface

Post-fabrication cleaning treatments Blasting (eg. glass beads) Local or large area cleaning Grinding (abrasive discs or flapper wheels) Do not smear (eg. wire brushes) or overheat thesurface (eg. worn abrasives or excessive pressure) Pickling (mixed nitric-hydrofluoric acids) Immersion, spray or paste Electropolishing (electrocleaning) 52Site or shop treatmentBetterresult

Pickling Chemical treatment toremove heat tint, andthe underlyingchromium-depletedlayer and surfacecontamination Covered by:ASTM A 38053Pickling with paste

Spray Pickling54

PicklingAfterBefore55

Duplex Stainless Steel Fabrication HandbookPublication was revisedin 2009 and will beprinted by IMOANew duplex stainlesssteel grades are includedin the revision56

Duplex Stainless Steel Fabrication Handbook. Title: Microsoft PowerPoint - Gary Carinici - Duplex F