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1、WeldingdefectFromWikipedia,thefreeencyclopediaJumpto:navigation,searchAweldingdefectisanyflawthatcompromisestheusefulnessofaweldment.AccordingtotheAmericanSocietyofMechanicalEngineers(ASME),weldingdefectcausesarebrokendownasfollows:45percentpoorprocessconditions,32percen
2、toperatorerror,12percentwrongtechnique,10percentincorrectconsumables,and5percentbadweldgrooves.[1]Contents·1Majorcauseso1.1Hydrogenembrittlemento1.2Residualstresses·2Typeso2.1Cracks§2.1.1Arcstrikecracking§2.1.2Coldcracking§2.1.3Cratercrack§2.1.4Fusion-linecrack§2.1.5Hatc
3、rack§2.1.6Hotcracking§2.1.7Underbeadcrack§2.1.8Longitudinalcrack§2.1.9Reheatcracking§2.1.10Rootandtoecracks§2.1.11Transversecracko2.2Distortiono2.3Gasinclusiono2.4Inclusionso2.5Lackoffusionandincompletepenetrationo2.6Lamellartearingo2.7Undercut·3Referenceso3.1Bibliograph
4、y·4ExternallinksMajorcausesHydrogenembrittlementMainarticle:HydrogenembrittlementResidualstressesMainarticle:ResidualstressThemagnitudeofstressthatcanbeformedfromweldingcanberoughlycalculatedusing:[2]WhereEisYoung'smodulus,αisthecoefficientofthermalexpansion,andΔTisthete
5、mperaturechange.Forsteelthiscalculatesouttobeapproximately3.5GPa(510,000psi).TypesCracksDefectsrelatedtofracture.ArcstrikecrackingArcstrikecrackingoccurswhenthearcisstruckbutthespotisnotwelded.Thisoccursbecausethespotisheatedabovethematerial'suppercriticaltemperatureandt
6、henessentiallyquenched.Thisformsmartensite,whichisbrittleandmicro-cracks.Usuallythearcisstruckintheweldgroovesothistypeofcrackdoesnotoccur,butifthearcisstruckoutsideoftheweldgroovethenitmustbeweldedovertopreventthecracking.Ifthisisnotanoptionthenthearcspotcanbepostheated
7、,thatis,theareaisheatedwithanoxy-acetylenetorch,andthenallowedtocoolslowly.[3]ColdcrackingResidualstressescanreducethestrengthofthebasematerial,andcanleadtocatastrophicfailurethroughcoldcracking,aswasthecasewithseveraloftheWorldWarIILibertyships'hulls.Coldcrackingislimit
8、edtosteelsandisassociatedwiththeformationofmartensiteastheweldcools.Thecrackingoccursintheheat-affected
