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外文翻译--结构钢的焊接性.doc

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外文翻译--结构钢的焊接性.doc

附录1英文原文Lecture2.6WeldabilityofStructuralSteelsThelecturebrieflydiscussesthebasicsoftheweldingprocessandthenexaminesthefactorsgoverningtheweldabilityofstructuralsteels.SUMMARYThefundamentalaspectsoftheweldingprocessarediscussed.Thelecturethenfocusesonthemetallurgicalparametersaffectingtheweldabilityofstructuralsteels.Asteelisconsideredtoexhibitgoodweldabilityifjointsinthesteelpossessadequatestrengthandtoughnessinservice.Solidificationcracking,heataffectedzoneliquationcracking,hydrogeninducedcracking,lamellartearing,andreheatcrackingaredescribed.Theseeffectsaredetrimentaltotheperformanceofweldedjoints.Measuresrequiredtoavoidthemareexamined.1.INTRODUCTION1.1ABriefDescriptionoftheWeldingProcessWeldingisajoiningprocessinwhichjointproductioncanbeachievedwiththeuseofhightemperatures,highpressuresorboth.Inthislecture,onlytheuseofhightemperaturestoproduceajointisdiscussedsincethisis,byfar,themostcommonmethodofweldingstructuralsteels.Itisessentiallyaprocessinwhichanintenseheatsourceisappliedtothesurfacestobejoinedtoachievelocalmelting.Itiscommonforfurtherfillermetaltobeaddedtothemoltenweldpooltobridgethegapbetweenthesurfacesandtoproducetherequiredweldshapeanddimensionsoncooling.Themostcommonweldingprocessesforstructuralsteelworkuseanelectricarcmaintainedbetweenthefillermetalrodandtheworkpiecetoprovidetheintenseheatsource.Ifunprotected,themoltenmetalintheweldpoolcanreadilyabsorboxygenandnitrogenfromtheatmosphere.Thisabsorptionwouldleadtoporosityandbrittlenessinthesolidifiedweldmetal.Thetechniquesusedtoavoidgasabsorptionintheweldpoolvaryaccordingtotheweldingprocess.Themainweldingprocessesusedtojoinstructuralsteelsareconsideredinmoredetailbelow.1.2TheMainWeldingProcessesa.ManualMetalArcweldingMMAInthisprocess,thewelderusesametalstickelectrodewithafusiblemineralcoating,inaholderconnectedtoanelectricalsupply.Anarcisstruckbetweentheelectrodeandtheweldareawhichcompletesthereturncircuittotheelectricitysupply.Thearcmeltsboththeelectrodeandthesurfaceregionoftheworkpiece.Electromagneticforcescreatedinthearchelptothrowdropsofthemoltenelectrodeontothemoltenareaoftheworkpiecewherethetwometalsfusetoformtheweldpool.Theelectrodecoatingoffluxcontributestothecontentoftheweldpoolbydirectadditionofmetalandbymetallurgicalreactionswhichrefinethemoltenmetal.Thefluxalsoprovidesalocalgaseousatmospherewhichpreventsabsorptionofatmosphericgasesbytheweldmetal.Therearemanytypesofelectrodes.Themaindifferencesbetweenthemareinthefluxcoating.Thethreemainclassesofelectrodeareshownbelow1.RutileGeneralpurposeelectrodesforapplicationswhichdonotrequirestrictcontrolofmechanicalproperties.Theseelectrodescontainahighproportionoftitaniumoxideinthefluxcoating.2.BasicTheseelectrodesproduceweldswithbetterstrengthandnotchtoughnessthanrutile.Theelectrodeshaveacoatingwhichcontainscalciumcarbonateandothercarbonatesandfluorspar.3.CellulosicThearcproducedbythistypeofelectrodeisverypenetrating.Theseelectrodeshaveahighproportionofcombustibleorganicmaterialsintheircoating.b.SubmergedArcWeldingSAWThisprocessusesabarewireelectrodeandafluxaddedseparatelyasgranulesorpowderoverthearcandweldpool.Thefluxprotectsthemoltenmetalbyformingalayerofslaganditalsostabilisesthearc.Theprocessisusedmainlyinamechanicalsystemfeedingacontinuouslengthofwirefromacoilwhilsttheweldingleadismovedalongthejoint.ASAWmachinemayfeedseveralwires,onebehindtheother,sothatamultirunweldcanbemade.Submergedarcweldingproducesmoreconsistentjointsthanmanualwelding,butitisnotsuitableforareasofdifficultaccess.c.GasshieldedweldingInthisprocess,abarewireelectrodeisusedandashieldinggasisfedaroundthearcandweldpool.Thisgaspreventscontaminationoftheelectrodeandweldpoolbyair.Therearethreemainvariationsofthisprocessasshownbelow1.MIGmetalinertgasweldingArgonorheliumgasisusedforshielding.Thisprocessisgenerallyusedfornonferrousmetals.2.MAGmetalactivegasweldingCarbondioxideusuallymixedwithargonisusedforshielding.Thisprocessisgenerallyusedforcarbonandcarbonmanganesesteels.3.TIGtungsteninertgasArgonorheliumgasisusedforshieldingandthearcstruckbetweentheworkpieceandanonconsumabletungstenelectrode.Thisprocessisgenerallyusedforthinsheetworkandprecisionwelding.1.3WeldedJointDesignandPreparationTherearetwobasictypesofweldedjointsknownasbuttandfilletwelds1.SchematicviewsofthesetwoweldtypesareshowninFigure1.Theactualshapeofaweldisdeterminedbythepreparationoftheareatobejoined.Thetypeofweldpreparationdependsontheweldingprocessandthefabricationprocedure.ExamplesofdifferentweldpreparationsareshowninFigure2.Theweldjointhastobelocatedandshapedinsuchawaythatitiseasilyaccessibleintermsofboththeweldingprocessandweldingposition.Thedetailedweldshapeisdesignedtodistributetheavailableheatadequatelyandtoassistthecontrolofweldmetalpenetrationandthustoproduceasoundjoint.Operatorinduceddefectssuchaslackofpenetrationandlackoffusioncanbedifficulttoavoidifthejointpreparationanddesignpreventgoodaccessforwelding.

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