土木工程專業(yè)英語(yǔ) 課件 2.3 2.4 Steel Materials Steel Types

Chapter2-3

SteelMaterialsMaterialPropertiesofSteelConstituentsIron

(about99%)Benificialalloyelements

Carbon–increasestrengthSilicon–strong

oxygenabsorberManganese–weakoxygenabsorberCopper–corrosionresistanceChromium–corrosionresistanceHarmfulelementsOxygen&Sulphur–hotbrittlenessPhosphorous&Nitrogen–coldbrittlenessHydrogen–hydrogen-inducedbrittlenessSteelAttributes

Strength

Abilityofamaterialtoresiststresses-yieldstrength,ulitmate(ortensile)strength

Stiffness

Abilityofamaterialtoresistdeformation-slopeofthematerial’sstress-straincurve

Toughness

Abilityofamaterialtoabsorbenergybeforefailure–theareaunderthematerial’sstress-straincurve

Ductility

Abilityofamaterialtoundergolargeinelastic,orplastic,deformationbeforefailure–percentelongationorpercentreductioninareaofthespecimentestedinuniaxialtensionStress-StrainCurveLowcarbonsteelHighcarbonsteelSteelTypesCarbonsteels

mainingredients–carbon&manganese;smallamountofsiliconandcopper,i.e.Q235.Highstrengthlowalloysteels

enhancedstrength–morealloyingagentssuchaschromium,copper,nickel,siliconetc,andothersinadditiontobasicelementsofiron,carbon,andmanganese,i.e.Q345,Q390andQ420.Quenchedandtemperedalloysteels

heattreatedbyquenching,andtemperingtoenhancestrength.Reducedductilityandplasticity.DesignConsiderationsFatiguecausedbyfluctuatingloadsoccursthroughinitiationandpropagationofacrackweldedconnectionshavegreatesteffectonfatiguestrengthbuttwelds>continuousfilletweld>intermittentfilletweldresidualstress&stressconcentrationtensilestress-fatiguecrackpropagationfatiguelifedeterminedbyhotspotstressrange–S-NcurveFatiguefailureofaweldedtubularjointS-NcurvesBrittlefractureFractureoccursatlowstressbelow0oCCharpytestImpacttoughnessAbruptofcrosssectionStressconcentrationResidualstresscausedbyweldingFireprotectionSolidcasingHollowcasingProfilecasingIntumescentpaintCorrosionprotectionMetalliccoatingPaintingSurfacepreparationiscriticalSteelSectionsRolledandFormedSectionsI-sectionH-sectionChannelsEqual&unequalanglesStructuralteesCircular,square&rectangularhollowsectionsCompoundSectionsCoverplatestrengtheningCombiningtwoseparaterolledsectionsConnectingtwomemberstogethertoformastrongcombinedmemberBuilt-upSectionsFormedbyweldingplatestogetherI,HandboxmembersaremostlyusedUsedtosustainheavyloadsCold-rolledOpenSectionsFormedbycoldrollingSuitableforthinsteelplateApplication–purlins,side&sheetingrailsothersBriefreviewforsteelmaterials

ConstituentsIron,carbon,silicon,manganese,…Oxygen,sulphur,phosphorous,nitrogen,hydrogen,…MaterialpropertiesWhatmechanicalpropertiescanyoufindfromtheStress-Straincurves？Strength-yieldstress,ultimate(tensilestrength)Stiffness–plasticityToughness–areaunderthestress-straincurveDuctility–percentelongationorpercentareareductionSteeltypesCarbonsteelsHighstrengthlowalloysteelsQuenchedandtemperedalloysteelsReviewDesignconsiderationsFatigue–whichprincipalfactorscausedthefatiguefailuredevelopingrapidly?Highstressconcentration–causedbyabruptsectionsorflawsResidualstress–causedbyweldingBrittlefractureFireprotectionCorrosionprotectionSteelsectionsRolledandformedsections-Whatisthe