AmlysisofFreeNagrNtSitheetmter

hrdiItoji

DrE

realel

te Steel bLtd

197819iIIgqshilIbCity

YiPf

2ndKDMillisrldSyOSitbOmtileIpon

HiltonIIslandSC

r2t221998

118

ABSlACr

Anev concept vhichfree magnesium might be thekey phase onthe graphite

SPheroidiZationinspheroidal graphiteirons would be proposed and verifiedin this

StudyThechilledsamples containedthedifferentamountofmagnesiumvereprepared

and chemicallyanalyzed onthetotal andinclusivephase usingInductivelyCOupled

Vacuum Plasma SpectrometerFree magnesium was cLalculated as the balance of their

ValuesFree magneSium stepwISeincreased as total magnesiumincreasedOn the other

handinclusivemagnesium tasalmost equalamongthechilledsamplesThesaJneSeries

Ofchilled saJnples asthe above vere also analy21ed using spectroJneterin conjunction

Vithpulsehight distributionanalysis systemThegood relationship betweenthe

Pulse behaviourand the value of free magnesium vas obtainedSimilar tototal

magnesiutnin conventional wayThe nodularityand the tensileproperties of5mY

block shoved the good relationship to the value of free magnesium

IW

In the metallurgical point of vievmagneSiuJnis the deoxidier and desulfurizer

element forliquidironIf magnesiun was added the amount over the stoichiometric

COmpOSition against the free oxygen and sulfer contentmagneSium would exceedin

liquidiron as both the agentsThe excessive amount of magnesium is defined free

magnesiuJninthis studyAccording to the site theoryl2proposedbythe authorit

isconsideredthatmostof freemagnesium wouldhaveto begasstate andexistasgas

bubbleinliquidiron because of thelow boiling point andless solubilityGas

bubbleis considered as aninitial site tonucleateand grov spheroidalgraphiteThe

trace ofmagnesiumgasbubbleparticipatinginspheroidalgraphitehaveanalytically

VerifiedOn the other handthe rest of magnesium would exist asinclusions such

119

as oxideSulfideOXySulfideMany researchers have believed that thoseinclusions

act as the nuOleous for the spheroidal graphite formationtlovevernObody found the

evidence howinclusions affaired spheroidal graphite to grow the final formThe

resultsin this study would show which phase ofJnagneSium affaired the f0rnation of

Spberoidal grapbite

The elements vhich have strong tendency to form stable precipitates are rather

easy to analy2e their metallic phase using SpeCtrOmeterin conjunction with pulse

hight distribution analysis system3Thisis because thereis big differencebetveen

the metallic phase and precipitates on the spectrumintensityin such elementsThe

SPeCtrumintensity detected at the analyzed spot containinginclusionsis much higher

than that containing only metallic phasen the systemeaCh spectrumintensity

detected during discharging is exchanged for pulse hight and arranged into the

distributionThe pulsehight distribution vould appear tvo peaks in the case of

magnesiumOneis for the area vithinclusive tnagnesium and show an unclear peak

Anotheris for the area with only metallic magnesium and shovs a clear peakThe

prinCiple for the phase analysis on magnesium uslng SpeCtrOmeter Vith the PDA system

is schematicallyillustrated as shovnin Fig1

In this paperthe analytical procedure of free magnesium VOuld beintroduced

and thenl the result vould be coaLPared with the nodularity and thetensileproperties

m

Base iron vas smelted inlow rrequency induction furnaceAfter chemical

COmPOSition was adjustedtheliquidiron was once superheated over1500for about

five minutesSince tap weight vasdifferent amOng heatstaptemPerature VaS Changed

attherangefrom1405to1480Thisisbecausesomeheats veretappedonlyfor

120

theexperimentationbutsomeothersweretappedforpracticalcastinginfoundryltOO

Nodulizationandinoculationwereconducted bysandvitchmethodduringtappingFe

Si55Mg and Fe75Si alloys wereused foreachagenThechilled samples for

analysisveretakenfrommagnesiumtreatedliquidironsMetalmoldforthesampleis

ShovninFig2Thetotal magnesiumcontent wasstepvise adjusted thedifferent

COntent aJnOngSeVenheats addingdifferentamount ofFeSi55galloyTheaimed

COntentVaSraPidlycheckedwiththesame spectrometerasusedforthefreemagnesium

analysisbutbyconventional procedureTosurvey thedegree ofdeoxidationin

liquidirons vithdifferentmagnesiumlevelsfreeoxygenvasmeasuredineachheat

afterthemagnesiumtreatment usingEelectr0mOtiveforceprobe50mmYblock

VaSCaStinfuranbonded sandmoldineachheatIt took aboutthreeminutesfromthe

finish of the magnesium reaction to the cast

Totalmagnesiumvasanaly2iedusingInductivelyCOuPledVacuumPlasmaSpectroneter

ICPInclusivemagnesiumwashoweveranalyzedbycomplicatedDethodAtfirst

inclusions such as oxideSulfidenitride in the chilled samples were

electrOlytically extracted usingtheapparatus shovninFig3Theelectrolytical

extractionvasconductedaseachsatnplelosttheweightofaboutO5gThemagnesium

COntentinextractedinclusions vasthen analyzed usingICPTheprocess ofthe

electrolytical extractionandtheanalysisisshowninFigFreemagnesium was

Calculated according to Formulal

FreeMgTotal MgInclusive Mg1

TheotherchilledsamplesintheseriesofheatsvereanalyedusingSpeCtrOmeter

inconjunctionvithpulsehightdistributionanalysissysten3FortotalJnagneSium

themiddlevalueinthetotalfrequencydistributionisselectedandinvestigatedthe

COrelation againstthechemically analyzedvalueForfreemagnesium ontheother

handthefrequencydistributionofmetallicmagnesiumisintegratedandthevaluewas

investigated thecorelation againsttheanalyed valueSince predischarge was

121

COnductedateveryanalysisT thecorltaminationofthearLalyzedsurface hadnottobe

COnSideredThesequence forthemagnesium phaseanalysissetinspectrometeris

ShovninFig5Thevoltage fordischarge andthewavelength fordetectingthe

luminousspectrumofmagnesiumwassetat330Vand2802mmrespectively

Tensileproperties of50mmYblockineachmagnesiutnlevel vasexaminedatthe

POSitionshovninFig6The microstructure WaSeXamined attheholder ofevery

tensile test piece

1Sampling

Thechemical composition ofchilled sanples andthe freeoxygen contentin

magnesiumtreatedliquidirons areshowninTablelTheresidualmagnesiumCOntent

COuldbecontrolledforeveryheatasapproximatelyaimedThedeereaseofsulferand

freeoxygencontentwasobservedineveryheatafterliquidtreatmentForexaJnPle

thecheaLicalciOmPOSitionincludingfreeoxygenofbaseironforheatNo5isshownin

Tablel

Themicrostructure OfzmalyzedsurfaceisshovninFig7AlthoughJnagneSium

treatedliquidironsverepouredintometalmoldSPheregraphiteprecipitatedatthe

analyZedsurfaceandthediameterwas35Mostofinclusionwasthesi2ieOfO55

PmBigincilusion about20VaS rarelyobservedBesides spheregraphite and

inclusionthesimilarsieOfvoidvereobservedThenumberofspheregraphiteat

thecenterareawasgreaterthanthatattheperipheryarea

2CP analysis

TheresultofICPanalysisontotalandinclusivemagnesiumareshowninTable2

ThecalculatedvalueoffreemagnesiumisalsoshovninTable2Thetotalmagnesium

COntentVaSquiteaclosetotheresult ofconventionalemissionspectmmanalysisas

122

ShovninTablelTherewas nobigdifference ontheinclusive magnesiun content

amongthechilledsamplesalthoughthetotalmagnesiumcontentvasstepvisedifferent

Inotherwordsthedeoxidationdegree wasconsidered tobenearlyequal amongthe

Series ofmagnesiumtreatedliquidironsaSShownintheresult ofthefreeoxygen

measurementThe siEnilar condition was forecast on the desulfuriation

3Emission spectrum analysis

Anexample ofthepulseprofile onmagnesiuninsampleNo6isshovninFig8

Theintensity fromfree magnesium was about halfofthe maximuJn Valueinthis case

Ontheotherhandtheintensityfrominclusivemagnesiumvas overaboutseventyper

CentOfmaximumvalueTheplotsofchemicalanalysisvaluetospectrumintensityon

bothtotal andfreemagnesium areshowninFig9Therevere good relationships

betveentheminbothphasesofmagnesiunnotherwordsl gOOdcalibrationcurvewas

ObtainedforbothnthecaseoftotalmagnesiumcurVethedataobtainedinthis

Study vere additionally plotted on conventional one

Theanalysismark vasobservedusingSEMTheSEMphotographisshowninFig10

As theresultI manySpOtS Vith eraterlike hollow vere observedThehollovs were

formed by vaporiZing the saJnPle surraCe during dischargingThe analytical

informationvasget fronthereItissaidthatthediameterandthedepthareabout

thesameandare520pnHoveverl thereweresomanyhollowswhichthesi21eWaSOut

Ofthis range

4MicroandmechanicalpropertiesintestsamPles

ThemicrostruCture Of50mmYblockineachmagnesiumlevelisshovninFig11

Spheroidalratioincreased vithincreasingthefreemagnesiumcontentTherewasno

relation tothe content ofinclusive magneSium on that ratioItseemed that

SPheroidalratio almostsaturated vhenthecorltent Offreemagnesiumexceededabout

0030massagainstthesulfurrange OfO0120015massThis wasalsotrueofthe

tensileproperties asshovninTable3Allpropertieschanged viththecontentof

123

free magnesium

SI

Althoughledeburite cementite was alsoextracted vith oxideSulfideand nitride

vhen magnesiumininclusion vas analyZiedl this would notinfluence the above

experimental resultsThereis the fundamental reason whyledeburite cementite would

not contain magnesiumMagnesium atom hadlittle possiblity to form the

substitutional andinterstitial type solid solutioninledeburite cealentite because of

the atomic si2eThediameterof magnesiumatom3205ismuch biggerthanthatof

iron atoJn285and carbon atoml55The results of emission spectruEn

analysissupport that magnesium had almost no solubilityinto cetnentitelattice

showing good corelation to chemical analysisIfmagnesium could resoIveinto

ledeburite cementitemagneSium might evenly distributein cementite and the content

ofinclusivemagnesium vould be much higher thanthis studygnesium also had

almost no solubilityinto austenltebecauseof the same reason asledeburite cementite

Itis considered that free magnesium could distribute at theinterfacial site betveen

ledeburite cementite and austeniteMost of free magnesium vould exist as gas bubble

as mentioned inintroductionIfit was truethe distribution of free magnesiuD

vould be dotted vith spots as a trace of gas bubbleFor exaJnplemany VOids vere

actually observedin this studyThe precipitationofmagnesium carbide might have no

chanceinchilledsamplebecauseitwasunstableoverabout660

Accordingto thedetailobservation recentlyreportedby TSkaland7thesize

ofmagnesium ciOntainedinclusiorlin30mm sample was mentioned as O2Opn

YIgaraShi8also reportedit was aboutl0In this studyIinclusion was O520

ThesefigureSarealltheresultof2dimensional2DobservationThemeasured2D

124

diametersdAcanbeconvertedinto3Dvaluesdvthroughformula92

dvda22

Theactualsie muStbe surelybigger thanthepore ofnucleopore filter02

Magnesiumcontainedinclusioninchilledsamplesvouldbeallextractedandchemica11y

analyzed exactly

The analysis result of free magnesiumcorrelated vith the nodularity and

mechanicalproperties butthatofinclusivemagnesium didnotThismeansthatthe

COntentOffreemagneSiumisanindispensable factorforthegraphitespheroidization

butthat ofinclusivemagnesiumisnotTheprecisequalitycontrol ofspheroidal

graphite castiron shouldbe discussed and conducted withthe content offree

EnagneSium

Magnesiumisthebestelementforthe graphite spheroidi2iationinliquidstate

becauseofthevaporization andsolubility behaviouratthetemperaturerange from

the magnesium treatment to the solidification finish

lFreemagnesium asmetallicphaseinchilled sample couldbeanalyzed withhigh

aCCuraCy uSlngSpeCtrOmeterinconjunctionvithpulsehight distributionanalysis

SyStem

2When total tnagnesiumincreasedfLree magnesiuEn alsoincreased butinclusive

magnesium had almOSt nO Change

3Whenfreemagnesiumincreasedthenodularityandtensilepropertiesalsoincreased

125

1HItofujiqStudy on Graphite Spheroidi2ationinCastIronsP The Thesis of

Doctors Degreein Kyoto University1993

2HtofujiProposalofSite TheoryAFS TransVol1041996P79

3JOnoFukuiandNImamuraEmissionSpectrochemicalAnalysisbyPDAMethodW

Shimadzu Criticism1978615

4MSaekiIEnissionSpectrumAmalysisTheNewestPhaseAnalysisorSteel1979

107

5SNagasakiMetalsDataBookITheJapanInstituteofMetals197Ll8

6TBMassalskiWBinaryAlloyPhaseDiagramS2ndEditionASMIntVol11992

859

7TSkalandGraphiteNucleationMechanismsinDuctileCastIronI1stKeithD

Millis World Symposium onIuetileIron1993

8YIgarashiSOkadaExamination ofSpheroidal GraphiteinMgTreatedIron

UtiliZingtheLatestMicroanaly21ingApparatusHitachiMetalsTechnicalReport

Vol13199765

9RFullmanTransAIMEVol19719537

I vish to express appreciation to MrMakotoFujino for his operation of

SpeCtrOmeterandtoMissChiaki Takanoforherkindsupport

126

LISTFIE nTItS

Fig1Principle ofphase analysis for magneSiuminchi11edsample ofspheroidal

graphiteironIllustrationforaluminiumanalysisinreference3wasarranged

ror magneSium

Fig2Steelmold and boardforsampling

Fig3Apparatus for electrolytic extraction

Fig4Flov chart of electrolytical extraction and deternination forinclusive

magnesium

Fig5Sequencesetinspectrometerformagnesiumphaseanalysis

Fig6SchematicillustrationofYblocikandtensiletestpiecesmm

Fig7MicrostruCtureOfanaly2iedsurfaceinchi11edsampleNo62Nitaletch

Fig8ExampleofpulseprofiledetectedbydischargingSampleNo6

Fig9Calibrationcurveformagnesiunphaseanalysisbyemissionspectrometer

Fig10SEMphotographofanalysismarkinchilledsampleNo6

Fig11Microstructure Of50mmYb10CkineachnagnesiumlevelResultofchemical

analysisis described

LISTl S

Tablel Results of converltional emission spectrum analysis and free oxygen

measureentin magnesiutn treatedliquidirons

Table2ResultsofchemicalanalysisvithICPmethodonmagnesiumPhases

Table3RelationshipamongfreeMgcontentnOdularityandtensileproperties

127

l

SpectruninteASity

ImnN

128

ncue

Ctning ince

Surfge Of gys sgpe

HmddU

TOt

TOtpunmber

Nnn

Free

Chemicy

Chemil gy

FPrpeOphaeanayragneumnOhFedampeOspherOdagrapherOn

HuuratOnrarumanaySnrerenOeOS arrangedragneS

110

251

l

45

mold 25

15

5

board 12 28 Amalyissurface 20

Fig2Steel mold and board for saJnpling

129

130

Fu Apparatur eeOtrOyEO eXt30iOn

dli 0ind

Umieelni

Ulie Vibtil

mSis

On

lm1iqCaeid

v1sa1mvd11i

CmtdiAem2

10

ilWilt

ionWm

i

ii

eri

2Xma

1Fil

Acid resolution 3H2l

H3ml

1bricadd

FigFdeibiondioniii

131

3000SeOAr Fluse5min

800SeOPreburn

OySeCIntegration

1500SeePreburn

1500SeCIntegration

30pSeCCleaning of Welectrode

62mm Xcone300

Display or result

Fig5Sequencesetinspectrometerformagnesiumphaseanalysis

Test piece14GL50

Fig6SchematicillustrationofYblockandtensiletestpiecesmm

132

aCenter

bPeriphery lOpn

Fig7MicrostructureOfanalyzedsurfaceinchilledsampleN062Nitaletch

133

Time series profile Date O13098Time ll06

J

FMG

2802nm

1512

umerOf pulse

1024

Hum8r Of pul308

tl

FreemCdistriutior Date O13098Time ll05

AGNo53FCIS

Fig8Example ofpulse profile detected bydischargingSample No6

134

mtmax0

max09

Fig9ioncmriumisbylissionspmeter

135

aLov magnifieation

30bHigb magnirieation

Fig10SEMphotographofanalysismarkinchilledsampleNo6

136

a00114TMg00038FMg

r

1

l I

lOO

b00185TMg00120FMg

Fig11MicrostruCtureOf50mm Yblockineach magnesiumlevel

Result of chemical analysisis described

137

J

f

C00316Mg002FMg

d00368Mg00309FMg

Fig11Continued

138

r

ll

e00500TMg025FMg

t

r005TMg00467FMg

Fig11Continued

139

Tablel ResultsormVentiordemissionmmanabsisandfteeoxygenEneaSuWt

inmaliumbqdirorB

le No miealition Ommlt

CSiPS

1 382011000150011 0199113

2 3231020000120022 0102191

3 325602107001401 01326

3226602100013000 0102181335

5Ibse 352180010019 0931371

5 320160810008 009Z1363

6 3522BO12000120 0721

bk23diamlysisvi

mkdonmaium

No ss

behion

1 0011 0 00038

2 00185 065 00120

3 016 00075 01

0368 059 0039

5Ibse

5 0 000 0l

6 049 00082 007

140

Table3RelationshipamongfreeMgcontentnOdularity

and tensile properties

FreeMg Nodu Tensileproperties

Proof Tensile Elongation

1arity StreSS Strengtb

Mass Nmm2 mm2

00038 7 89 107 28

00120 9 276 388 77

0021 89 328 50 182

00309 87 33 520 216

0025 89 317 82 225

00467 82 329 488 225

4points average

141