制造工程与技术(热加工)英文版joining-processes-and-equipment(3)

§29TheMetallurgyofWelding;WeldingDesignandProcessSelection焊接冶金，焊接设计与工艺制定29.1IntroductionWeldjointscanbegottenbytheweldingprocessesdescribedinchapter27andchapter28.Isthejointstrongenough(good),so-soorfail?Becauseoftheheatingprocess,theremustbesomemetallurgicalandphysicalchanges（冶金与物理变化）inthematerials.otherpropertystrength,ductility,andtoughnessofaweldedjointmechanicalpropertyForexample,therateofheatapplicationandthethermalpropertiesofmetalsareimportant,inthattheycontrolthemagnitudeandthedistributionoftemperaturesinthejoint.Themicrostructureandgrainsizeoftheweldedjoint（焊接接头的微观结构与晶粒尺寸）dependontheamountofheatappliedandtheconsequenttemperaturerise,onthedegreeofpriorcoldworkofthemetals（冷加工程度）,andontherateofcoolingaftertheweldisproduced.Controlofsuchfactorsisessentialtothecreationofreliableweldsthathaveacceptablemechanicalproperties.Weldqualitydependsonmanyfactors,amongthemthegeometryoftheweldbeadandthepresenceofcracks,residualstresses,inclusions,oxidefilmsandsoon.Weldqualitythemicrostructureandgrainsizeoftheweldedjoint焊接接头的微观结构与晶粒尺寸thegeometryoftheweldbead焊道的几何因素defectsinjoint接头缺陷Temperatureanditsdistribution温度分布heatingdurationathightemperaturecoolingTemperatureisdecisive29.2TheweldedjointThreedistinctzonescanbeidentifiedinatypicalfusion-weldjoint:①basemetal;母材②heat-affectedzone(HAZ);热影响区③weldmetal.焊缝Figure29.1Characteristicsofatypicalfusionweldzoneinoxyfuelgasandarcwelding.ThemetallurgyandpropertiesoftheHAZandweldmetaldependstronglyonthemetalsjoined,焊接金属theweldingprocess,焊接方法thefillermetalsused,ifany,填充金属andtheprocessvariables.焊接参数•themetalsjoined,焊接金属Temperaturedistributionforweldingofdifferentmaterialsundersameenergyinputandsameweldingspeed.•theweldingprocess,焊接方法Energydensityforfusionwelding•Compareoftheenergydistributionof(a)arcs,and(b)theconsumablearcwithflame(a)(b)•theprocessvariables.焊接参数ProfilesofweldbeadandHAZ.differentweldingcurrentandvoltageforCO2welding—gasmetalarc29.2.1SolidificationoftheWeldMetal焊缝凝固Weldmetal:Meltingduringweldingandthencooleddown(solidification).Thesolidificationprocessoftheweldmetalissimilartothatincastingandbeginswiththeformationofcolumnar(dendritic)grains.relativelylongandparalleltotheheatflow.orperpendicular(垂直于)tothesurfaceofthebasemetal(shallowweld).(a)(b)Figure29.2Grainstructurein(a)adeepweld(b)ashallowweld.Notethatthegrainsinthesolidifiedweldmetalareperpendiculartothesurfaceofthebasemetal.Inagoodweld,thesolidificationlineatthecenterinthedeepweldshownin(a)hasgrainmigration,whichdevelopsuniformstrengthintheweldbead.Thesolidificationofweldingpoolunder:a)lowspeedweldingb)highspeedweldingcolumnar(dendritic)grains.Grainstructureandsizedependonthespecificalloy,thespecificweldingprocessemployed,(coolingvelocity)andthespecificfillermetal.Thewaytoimprovethemechanicalpropertiesofthejoint:Theproperselectionoffiller-metalcomposition,controlofcoolingrate,oradoptionofheattreatmentsfollowingweldingCoolingratesmaybecontrolledandreducedbyapreheatingofthegeneralweldareapriortothewelding.Theweldmetalhas,basically,acaststructureand,becauseithascooledslowly,ithascoarsegrains（粗大晶粒）.29.2.2Heat-AffectedZone(HAZ)热影响区Ithasamicrostructuredifferentfromthatofthebasemetalpriortowelding,becauseithasbeensubjectedtoelevatedtemperaturesforaperiodoftimeduringwelding;ThepropertiesandmicrostructureoftheHAZdependon(Thermalcycling)①therateofheatinputandcooling,and②thetemperaturetowhichthiszonewasraisedCarbonsteelMartensite马氏体Pearlite珠光体Cementite渗碳体ferrite铁素体Austenite奥氏体annealing,normalizing,quenching,andtemperingThesizeofHAZdependontemperaturedistribution.温度分布Figure29.4Schematicillustrationofvariousregionsinafusionweldzone(andthecorrespondingphasediagram)for0.30%carbonsteelThestrengthandhardnessoftheHAZdependpartlyonhowtheoriginalstrengthandhardnessofthebasemetalwasdevelopedpriortothewelding.Theheatappliedduringweldingrecrystallizes(再结晶）theelongatedgrainsofthecold-worked（冷轧拉长的晶粒）basemetal.①Grainsthatareawayfromtheweldmetalwillrecrystallizeintofineequiaxedgrains（等轴晶）.②Grainsclosetotheweldmetal,ontheotherhand,havebeensubjectedtoelevatedtemperaturesforalongerperiodoftime，consequentlytheywillgrow.Thisgrowthwillcausetheirregiontobesofterandtohavelessstrength.③Forsomematerialsunderacertainweldingprocesses,hardenregionwillappearaftercooling.Quenching淬火29.3WelddefectsAsaresultofahistoryofthermalcyclinganditsattendantmicrostructrualchanges,aweldedjointmaydevelopvariousdiscontinuities.不连续性Weldingdiscontinuitiescanalsobecausedbyinadequateorcarelessapplicationofestablishedweldingtechnologiesorbysubstandardoperatortraining.（不按焊接工艺执行或缺乏焊工培训）29.3.1Porosity气孔Porosityinweldsiscaused①bygasesreleasedduringmeltingoftheweldareabuttappedduringsolidification,析出性气孔②bychemicalreactionsduringwelding,or反应性气孔③bycontaminants.污染物侵入性气孔Mostweldedjointscontainsomeporosity,whichisgenerallyintheshapeofspheresorofelongatedpockets.（球形或长型）Thedistributionofporosityintheweldzonemayberandomortheporositymaybeconcentratedinacertainregion.Theclassificationofporosityrelatedtogas?Porosityinweldscanbereducedbythefollowingpractices:a.properselectio