高强电脉冲和磁脉冲对冷轧中碳钢组织细化的影响余文鹏硕士论文.docx
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高强电脉冲和磁脉冲对冷轧中碳钢组织细化的影响余文鹏硕士论文
学校代码：
10488
学号：
08102033
硕士学位论文
题目
高强电脉冲和磁脉冲对冷轧中碳钢
组织细化的影响
专业
材料学
研究方向
金属材料的相变与强韧化
姓名
余文鹏
导师
吴开明
定稿日期：
2011年5月10日
SchoolCode:
10488
StudentID:
08102033
WuhanUniversityofScienceandTechnology
MasterThesis
Subject:
EffectofElectropulsingandMagneticpulsingonGrainRefinementofCold-RolledMediumCarbonSteels
Major:
MaterialsScience
ResearchField:
PhaseTransformationsonSteels
MasterCandidate:
YuWenpeng（余文鹏）
Supervisor:
Wukaiming（吴开明）
Date:
May10,2011
分类号：
密级：
UDC：
硕士学位论文
EffectofElectropulsingandMagneticpulsingonGrainRefinementofCold-RolledMediumCarbonSteels
余文鹏
指导教师姓名：
吴开明教授
武汉科技大学
申请学位级别：
硕士
专业名称：
材料学
论文定稿日期：
2011年5月10日
论文答辩日期：
2011年5月24日
学位授予单位：
武汉科技大学
学位授予日期：
答辩委员会主席：
郭爱民教授级高工
评阅人：
张莉芹副教授
王红鸿副教授
OriginalityStatementandCopyrightAuthorization
摘要
高强的电脉冲分别作用于热轧态和冷轧态的中碳钢，产生了完全不同的效果。
对于冷轧态的样品，电脉冲起到了明显的细化组织的效果，提高了样品的抗拉强度和伸长率。
对于热轧态的样品，电脉冲对样品的作用效果不明显。
这说明在电脉冲影响组织的过程中，位错起到了非常重要的作用。
上述现象可以用组织转变的热力学和动力学基本理论来解释。
在室温条件下，不同电流密度和不同峰值场强的高强电脉冲和磁脉冲作用在冷轧态和热轧态中碳钢65Mn和30CrMo样品上。
实验结果表明：
同热轧态的样品相比，冷轧态的65Mn和30CrMo在电脉冲的作用下，抗拉强度提升，塑性明显改善。
从显微组织观察结果可以看出，电脉冲处理后冷轧组织中的珠光体团和铁素体尺寸明显小于没有经过电脉冲处理的样品，也小于电脉冲处理热轧态的样品。
珠光体组织的局部可见珠光体片出现球化。
珠光体团的细化效果随着电脉冲电流密度增加逐渐加强。
这种组织细化效果的机理可能跟电脉冲作用下增加的电致形核率有关。
高强磁脉冲在室温下作用于冷轧态和热轧态中碳钢65Mn和30CrMo样品上，直至峰值磁场强度提高至35T，样品的显微组织也没有出现可以观察到的变化。
由此可见，在本研究中未发现高强磁脉冲对组织的细化作用。
本文讨论了经典的形核理论在电脉冲作用下发生的改变和作用机理，电脉冲导致的过冷度改变继而影响形核过程也进行了讨论。
电脉冲所产生的电磁力和焦耳效应也都被考虑可能会是影响形核的因素。
组织细化效果的机理可以认为是电脉冲降低了形核势垒，从而增加了形核率。
在室温条件下，冷轧态中碳钢的组织得到细化，不太可能是电磁力或者焦耳热效应的结果。
电脉冲降低形核势垒是组织细化的主要原因，而且细化效果跟电脉冲的周期和峰值电流密度有关。
关键词：
钢；显微组织；珠光体；电脉冲；磁脉冲；组织细化
Abstract
Applicationofelectropulsingtothehot-rolledandcold-rolledmediumcarbonlowalloysteelshasgeneratedcompletelydifferenteffects.Forcold-rolledsteelsamples,electropulsingtreatmentcausedmicrostructurerefinementandhencetheincrementsoftensilestrength,yieldstrengthandelongation.Forhot-rolledsteels,theeffectofelectropulsingwasfoundtobenegligiblysmall.Thisprovestheimportanceofdislocationsinthemicromechanismofelectropulse-inducedmicrostructuretransformationinmetals.Theexperimentalobservationsareexplainedwithintheframeworksofthermodynamicsandkineticsofmicrostructuretransformation.
Electropulsingandmagneticpulsingwereappliedtohot-andcold-rolledmediumcarbonsteel30CrMoand65Mnwithvaryingpeakelectricvoltagesandcurrentsatroomtemperature.Themechanicalpropertytestresultsofcold-rolled30CrMoand65Mnshowedthattheelongationandareareductionofthespecimenstreatedwithelectropulsingincreased,comparedwiththatwithoutthetreatmentofelectropulsing.Microstructuralobservationsrevealedthatthepearlitecoloniesandferritegraininthespecimentreatedwithelectropulsingwassmallerthanthatwithoutthetreatmentofelectropulsing.Itwasalsofoundthatthelamellarstructureofpearlitewasrefined.Thegrainrefinementofpearlitewasmoreobviouswhentheappliedelectriccurrentdensityincreased.Thegrainrefinementmaybeattributedtoadditionalfreeenergyforthenucleationofpearliteprovidedbyelectropulsing.Thehot-rolledspecimenshadnonoticablechange.Magneticpulsingalsohadnonoticableeffectonmicrostructureinmediumcarbonlowalloysteel.Itislikelythatthestrengthofthemagneticpulsingwasnotsostrongenoughtoinducethemicrostructuretransformation.
Accordingtoclassicalsolidificationtheoryandthemechanismsofsolidificationmicrostructureunderpulsedelectriccurrent,theeffectofundercloolingdegreeonnucleationratewasdiscussed.TheinfluenceofelectromagneticstresseffectandJouleheateffectonundercoolingdegreewereinvestigated.Therelationbetweenelectriccurrentandundercoolingdegreewasdevived.Theeffectofelectropulsingonnucleationratewasduetonucleationpotentialbarrierdecreasedbyelectropulsing.Theelectropulsinginfluencedthemicrostructureofthecold-rolledsteelatroomtemperature,whichwasnotdeterminedbytheeffectofelectromagneticstresseffectandJouleheateffectonundercoolingdegreechange.Electropulsingreducedthenucleationpotentialbarrierandincreasedthenucleationrateandthusmademicrostructurerefinement.
Keywords:
Steel;Microstructure;Pearlite;Electropulsing;Magneticpulsing;Grainrefinement
Contents
OriginalityStatementandCopyrightAuthorizationI
AbstractIII
Keywords:
IV
ContentsV
NomenclatureIX
Chapter1Literaturereview1
1.1Overview1
1.2Effectsofmagneticfieldonsolidification2
1.3Effectsofmagneticfieldheattreatment3
1.4Effectsofelectropulsingonsolidification7
1.5Effectsofelectropulsingheattreatment12
1.6EffectsofelectropulsingonFe-basealloyatroomtemperature15
Chapter2Materialsandexperimentprocedures19
2.1Materials19
2.2Equipmentofelectropulsinggenerator19
2.3Equipmentofmagneticpulsinggenerator21
2.4Procedureofelectropulsingtreatment22
2.5Simulationofconductivityofferriteandcementite23
2.6Pearlitecolonysizemeasurements24
2.7Opticalmicroscopyandscanningelectronmicroscopy（SEM）25
2.8Mechanicalpropertiestext25
2.9Hardnesstest26
Chapter3Effectsofelectropulsing28
3.1Introduction28
3.2Experiments29
3.3Themicrostructureobservationsandanalysis30
3.4Mechanicalproperties34
3.5Micromechanism37
3.6Effectofelectropulsingondislocation38
Chapter4Effectsofmagneticpulsing40
4.1Introduction40
4.2Experimental40
4.3Resultsanddiscussion42
Chapter5Conclusions47
References48
Acknowledgements55
Publicationlist56
Nomenclature
AC
Alternatingcurrent
A
Areaofcrosssection
Bx
Broadeningindiffractionpeak
B
Burgervector
C
Capacitance
Ci
Capacitanceofcapacitori
Cα
Carboninferriteinat%
T
Crystallitesize
ΔGem
Changeinelectromagneticfreeenergyofthesystem
J
Currentdensityinasmallelement
DC
Directcurrent
vd
Driftvelocity
Σ
Electricconductivity
D
Electricdisplacementfield
E
Electricfield
Φ
Electricpotential
EM
Electromagnetic
F
Electromagneticfreeenergy
Fdv
ElectromagneticfreeenergyofvolumeelementdV
IECP
Electropulsingcurrent
dW
Elementalworkdone
Ceq
Equivalentcapacitance
σeq
Equivalentconductivity
Je
Equivalentcurrentdensity
Fe
Forceduetoelectricfield
Jf
Freecurrentdensity
aα
Latticeparameterofferrite
L
Length
B
Magneticfield
Μ
Magneticpermeability
A
Magneticvectorpotential
H
Magnetizingfield
NA
Opticalaperture
μ0
Permeabilityofspace
R
Positionvector
Φi
Potentialatpointindexedi
σrs
Residualstress
Ri
Resistanceofconductingelementindexedi
Q
Resistiveheatgenerated
ρr
Resistivity
SEM
Scanningelectronmicroscope
G
Shearmodulus
dV
Smallvolumeelement
SF
Stackingfault
Ρ
Totalchargedensity
J
Totalcurrentdensity
Δ
Vectordifferentialoperator
Vosc
Voltageintheoscilloscope
Λ
Wavelength
jx,jy,jz
X,y,zcomponentofcurrent
rx,ry,rz
X,y,zcoordinateofpositionvector
Chapter1Literaturereview
1.1Overview
Improvingthepropertiesofsteelsbygrainrefinementisonekindoftraditionalbutaneffectivemethod.Grainrefinementstrengtheninghasbeenutilizedformanykindsofsteels.Elctropulsingandmagneticpulsingtreatmentisarapidandnonequilibriumprocesswhichhasbeenappliedwidelyinmaterialtreatmentforover30years.Withtherapiddevelopmentofelectricpulsegeneratormanufacturingtechnology,itisnotdifficulttoobtainapowerfulelectropulsinggenerator.Thispromotestheresearchactivitiesonelectropulsingandmagneticpulsingeffectsonmaterialsheattreatment.
Inrecentyears,itisreportedthatelectropulsinghasspecialeffectssuchaselectricplasticity[1],crackhealing[2],castingstructurerefinement[3,5],enhancementofcorrosionresistance[4],extendingoffatiguelives[6].Sinceitsdiscovery,manyworkshavebeendoneontheapplicationofelectropulsinginthegrainrefinementofliquidsteelorsolidifiedstructure[7-12].Burstein[13]utilizedelctropulsingtotreatstainlesssteel.Itwasfoundthatelctropulsingcausedtheamountofmartensitegreatlyreducedorevendisappeared.Thisphenomenonissocalledelectrochemicalinducedannealing.Conrad[13,14]etal.alsoreportedthatthegrainrefinementwasobservedincold-workedCubyelectropulsingtreatmentduringannealing.Bymeansofthistreatmentsomeperfectfine-grainswereobtained,aslatercalledsparkannealing[15].
Theimprovementofphysicalandmechanicalpropertiesofsomehard-to-deformmetalsundertheinfluenceofanexternalmagneticfieldhasbeeninvestigatedforthelast30years.Untilnowthemagneticfiledtreatmenttechnologyhasnotbeenappliedwidelyinthefieldofengineering.Ithasbeenthoughtthatitissuccessfulinrelaxingstresses[16-19],andimprovingfatigueproperties[20,21]andsomeotherphysicalproperties[22]ofmetalsinvirtueofchangingdislocationsubstructures.Meanwhile,staticmagneticfieldandpulsedmagneticfieldhavebeingappliedinmoltenmetalsolidificationandheattreatmentprocess.Mostofthesestudiesonelectropulsingandmagneticpulsingweredoneinthecourseofheattreatmentathighertemperaturesorinmoltenmetal.Theeffectofmagneticpulsingongrainrefinementhasreceivedlessattentionintheresearchliteraturethaniswarranted.Thepresentworkaimstoinvestigatetheeffectofelectropulsingonthegrainrefinementofamediumcarbonlowalloysteelatroomtemperatureandtoprovidenewinsightsintoelctropulsingeffectandtoexploreitsfurthe
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