Table Of ContentI30THBRKAL TajWSFORIUTIQB OF AUSEB&ITS
BY MAGNETIC PSEMSASiLlfl METHOD
by
3 3 2 83
A thesis
Submitted t® the Departaent of M^talitargj
ij& Partial Falfp^t^t of tbs
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RequireiiamtiV for: tli@ Deg^eaM of
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faster of Seleses* In JfeialXorglcal Snglxseering
MQHTiKA SCHOOL Of MIIiES
Butte Moiitana
$
Feb. U, 195Q
UMI Number: EP33456
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TABLE OF QOSTSHTS
mm
iBtroduetiosi
Ha&ure of Iiarostigatiw^ . . . • * . * * *• o . . . . . .* . 1
Xmpm*tmm of Studj* . . . . • , * * . • . . . • • . . . . •• 2
History oi* the Process * * * * * « • * * • * * * . » » * • *« 2
Isottmraal Transforoaticci Brooe^s
1 Typieal Isothermal fr^mSoTimtxmi Diagram. . . . . . . . .. 9
SigM£i&axim* * * * . • • • • • *• • . • • • . *• 13
BcrrLnr or Different Methods of Isothermal Studies * • . . 16
Apparatus wad Materials
Baals oJT S^-teetixm . . . . . . . . . . . . . . . . . . . . .. 18
AtEst^nltlsirig Furoae** . . . . . . . . . . . . . . . . . . .. If
Qo«i)cb£ias«43sa^h Fornaoe * • « * « • « • * * « « . » * * » « »» 22
f ramformtioia Furna®* . . . . . . . . . . . • . . » • » . .• 22
M^natlc SOTieii* . . . . . . . . . . . . . . . . . . . . . .. 27
Jfttjdliary Equlp«wit . . . . . . . . . . . . . . . . . . . .. 29
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Mr%m i®r Bstdllag Spec&rens* . . . . . . . . . . . . . . .. 31
Preltolaai^f Work . . . . . . . . . . . . . . . . . . . . . .. 33
Saqperiamts ©n Steel X~916$* . . . . . . . . . . . . . . . .. 1*2
Isothermal fraaafei^tioa tea . . . . . . . . . . . . . . .. 1$
Essmlta of Ia¥#atigatl<m m& Mi@ttitm
BesuXts and Qelmlatimm . . . . . . . . • • * . . . . . . .. Ii8
Dlaciaaaio^ . . . . . . . . . . . . . . . . . . . . . . . . .. 58
Smgg^mtloa far Patera Work • • • . » * , • » • • , * • • » •• 60
Bibliogmpkj* • • « • . . • . • . . • . . . . . . • . . . . , . .• 62
ii
TABLE Of CGBSSSIS C(KTJXmH
FA®
^ctoowledg^nt . . . . . . . . . . . . . . . . . . . . . . . . . .. 6k
imimms
I The lrm Irm^arbicte Bquilifer im Diagram . . . . . . . . . .. ?
II A I&deaX Isotherm! ¥ra&s£onat log* Diagram . . . . . . . . .. H
III S#etion through xte !Era^sror^atioB end
QaanetiSiig-bath furnaces* . . . . . . . . . .. . • . . . . •. 25
I? Line Diagram of Electrical Conmefcim^ . . .. . . . . . . .. 28
V Magnetising foroe v& Flux Density Curro. . . • . . . . . . .. 36
1% Isothermal feaasforaatioaa Curve for
X-£L65 Steel *b XX8O0F . * » . « • « * . . .. . . , • . . .• 50
?II I-T Diagram of Steel X-9165* • . • • . . • .. . . . . . . .. 57
FLAXES
I Austsni-tising Fura&ee . . . . . . . . . . . . . . . . . . . .. 20
II Conpldte S*i Up for Isothermal Stadias* . . . . . . . . . . .. 21
III 'BranaforatatioQi and Qn^meibdag-feath Furnaces
with t&e&r aeeessorias . . . » * . * » » * •. . . . * . . .. 23
TAMES
I (ftranelH&tt&l B^rmoec^ple Chart • « • • » • • • » « • • • •• I4X
II Xsotlianial Study B&% of Steel X~?!65 at llSO^F . * . * . . •. h&
III Data for Calonlattog tbs Bsg&miHg and did of
Trma£®rm%xm of Steel X-9165 at H80°F. • « • • » « • « . «» 52
If Isothermal frmsformation lines of stteX 1-9X65
at Different Seapsrattu** « » • » « , * ,« . . . . . . * • ., $k
¥ Hardnsss ?alu#s of the ?»d&ets of Aunteuite
fraasfc^^atic^ at Constant T*japerature . . # . • . . . . . .* 56
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X
ISOBIBBHAL miflBFCRMATXCH €F AUSTM1TE
BI HAtMSflC PERMEABILITY METHOD
DRfiODUCTIOB
Mature of Investigation
This work jmoluidss tha setting up of a suitable apparatus for
studying the Isotnerntal Transformation of Austenite by tiie 3fagBeti@
Itexroabllitar method* as well as Tsrification of the Tij^-f^mperatui^e-
fransformation data obtataM from this se*t*up for steal X-9165 of
MlX^iOO series with the data obtained for the SUM steal bj MetaXlo-
graphic isetfaod*
The apparatus as dereloped was found to be quite satiefaetorjj, but
time, aa nail as arterial* was laeking for isproving its efficleney by
cutting down the magfietio loaves to a sii&ijsuBU
Tfaa purpose of this tbesia is to dsaeriba tb& apparatus a&d eupXaim
t&a pro^adura and eaXoulatia&s iav&Lved to dstarssttiing Wamtf^rsmtim
rates by the oagpetio pex^abilitj method and to sfaoir the results
obtained with the <teralop@d sqplgmnt, It is hoped that by this preseatd~
%±m further research is this dJra^tion niH be stisuXatsd sod that the
f
nagaetic parasability ratttaod could mmntn&IXy mplsim the tiss ooriau^iBg
®d laborious »tallop*apM.e itethod of Baisa m& DmrenpoT% for stamping
ths isotliarnial transforation of auataaits*
2
3J^ortanoe of Study
f he i^ortanoa attached by i^tallurgists to the iaothariml trans-
foraatioa characteristics of ferrous materials is eTicteneed hj the large
nmimr of papers presented to the last few years ®n the effects of
Tariatioiss in these characteristics on the structural and aieebaiiLeal
properties of steal, Bala and his eo-*orkera in their early papers
reported studies of the suberitieaX ira&sforsatien of atateetoid »stenite
m& established tte fandliar *?^-0urr®w as representing the transforation
oimraoteriaties of eutectoid auste&ite an a ta^eratur# TO* logarithmic
tiae plot, md showed variati«s in the shape ®£ the TOTTS ftr Tarious
alley steels* Buzidreds of different steals haw minne then be#n sub
jected to isathei^al d&tentin&tiais md today the steal industry depeixds
mostly <m the ^S-ourires^ for teat traatisent*
In all the S-mtrre detexatinatixans* hwewr, the avrtalXograplde
3sethod deirelopsd by Bmin md Barostport in the f®ar 1^30 is still b#tog
fallowed* Steee this method is Tery labor icns» an attempt Mnm made to
develop a shorter mathod based CK the ®ag»0ti0 changes *idi a^i^^^iy
tte trmsfcrmtim* This Betted wraXd make it pcssi3ai# to deiendne a
traxiadroraMtiea curve in a a»eh shorter tisne irith f^wer sttBt&a*, aaad with
greater aacuraagr than is pc^sibl© 'with the aetaltegraphic asthod,
History mi the Iscthermal
TrwrnCmtoaskim Froeese
1 phrasal of the dbr^&oig^ieaX bibliography of isetsXXurgicaX
literature *m isothermal trsasf ormatic^ studies giTOB by BaTe^port1
WsrtSSi Superscripts refer to bibliography at the asd.
3
repeals that the investigation on the isothermal transformation of
austenite conducted by the Besearch Engineers of United States Steel
Corporaticm at Eearay, I. J in Becei&er 1929, marks tte real beginning
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of isotheraial studies* The results of these studies ware summarised in
a technical paper ifhieh was presented by Bain and Daveaport2 at the
Septeitfeer 1930 Chicago meeting of xta& Ircai and 3te#X Biirision of the
African I&siitute of Mining and Metallurgical Engineers* Jhis paper
was one of tho aoot outstandii^ contributions to the steel industry both
from a theoretical wad praetio^ point of view* Poll<MiBg this publican
tion several aotaXXurgists began work in this field* This is evidenced
by the large nw&heT of papers presented in the las* few je&r® on the
effects of variations of time* temperature* and ecmpos&tim., on the
structnr&l «md mechanical properties of the different decomposition
products of austenite*
The trend prior to tte worlc of Bain and Davenport was to investigate
the affects due to Tariations la the cematitution of thai steel* as re**
vaaled by studies* involving, on the one handy condition of presumed
eipiXibr:BK% and en the other hand* condition in i&ich the influence of
time and of tesiperatere coiiM ncrt be readily separated or evaluated*
E^erien^e in tte bsat treatment of steely hgaraver* revealed that to
ord^r to get at the jfcra&aBmtalg of the subject of heat treatment of
steal* a syateawti* effort had to be nada to disentangle the influence
of tise and of te^erature by studying each one separately* In order to
do this, one factor (time or tesp^ratyr#) h&d to be held ccmstant ubile
the other one wm varied in sons predetermined maimer* ContinnoiJis
cooling failed to iseet these requdteeoettta, since, with mj given cooling
rate, both time and teiiperatwe are ehsoging similtaneously and it is
impossible to evalszate tte separate influence of either factor. In tte
k
investigation conducted at the ¥• S. Steel Research Laboratories to
December 1929* the teaperature wm kept constant and the effect of time
on the transforation of mistsnite HIM studied*
3n tte discission that followed the presentation of Budn aid Daven
ports p^BT^ cm the transformation of ansteaite at sub-critical te^era-*
tnras, Robertson, tte well taowi English metaHxirgist, questioned the
correctness of the isothermal transformation diagram of Bain md Davenport
in the region of oartensite formatim i«e*, beloar Ms temperature. This
controversial issue was subsequently studied at greater length by several
KtaHnrgists and all tte evidence &v&iXable-M**5, indicates that marten-
site foras only on cooling and does not form by isothermal transforB$atiim
as do pearlite and batoite Ifence, the portion of the isotberiaal diagram
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(better )m®mi as S-*carve because o£ tte sh^e of the diajp*am) below Ms
5
temper atere, should be draam as a series of isotharosl lines, each indicat
ing a greater percentage of transformation to siartensits with a decrease
in teisperatmre,
In 19lil, Grange and Kiefer^ reported studies of the tranaformation
of anstanite ithaii cooling at constant rate and shewed its general relation-*
gb% to the isotharsial trsnsferiaation* Btaring the war period* extensive
research *ork ir&s coridneted to find out a relationship between transfora
tion ^t constant te^^ratere and transformation en continuous cooling*
Maiming and Lorig? succeeded in finding a mtheiti&iieaX relatiensh%
betireen initial transfoa^tiois during continuous cooling and initial
transformatdon at constant t^^erature fhair results wre in good ^ i »-
#
mxA with end*^imehBd h^rdenability tests« Other notable publio&tima
in this field are by Holloiaon, Jaffe aid Iortan§, Liedholm and Coons? and
several others*
Even though the e^s&ct coalitions vatoSvr utiich the S-mrve determine
$
tions are stadte, cannot be duplicated in actual heat^troataent practice
anting to the large sise of the steel articles that are generally beat**
treated, still the S~eurves serve m very useful guides in the heat-
tx^ateent of steels For this rem®& there has been an increasing demand
t
for the S-eurves for varieties of steel.
6
ISOffiSRIttL TRAMSFOSMATia OF ATJSTBfiflfB
theory
Shan carbon or lo^-aLloy steels are suitably heated, the ferrite
(alpha iron solid solaticai) and the carbide of nhich they are eeiiipesed,
react together to form a single solid solution of carbon (md other
elements) 5n %mmm iron mhieh has been given the nasse lfAn#tenite« after
the Sogllsh ssatolXn&ist Sir Roberts Aostisu This inaction begins only
at a certain a&aiMua te^erature called the euteetoid tei^>eratiare# the
first ferrite mid carbide thus to react together do so in definite
proportions kmmn as tha eutectold composition* With further heating.
the paroeutoctodLd eoastltu^it that is present in excess is dissolved in
the oB&tenite -until exhausted* bettor the excess eonstittient is ferrite
m Sa the case of %poeMtactoM steels or oarbide if the steel is tgper~
eniectoid^ tte procedure is much tte aam* Gn nlm eooll&g, the bottom
geneous auotenite e^qpela the e;»ess of proeutectoid ferrite or carbide
as tte cas# «ay be «rtil tha eutectoid composition is reached* the
rem^tim ^pon heating it reversed impost ocmUjag and accordingly an
aqgulXibriuBa digram of ttdat process am be constructed^
Snob an e^dXS^ri^ digram of irei>4rcn carbide is given en page ?
(diagram I) * It MIX be seen from the diagram timt auatanite is ccupletely
atabla in tte mm betawaa the OSS line {A3 *r Ao*) and the seUdta** It
is partially stable la the woe befetean A3 car Aot and % line and ecm~
plately unstable bel^ the Aj line* In actuiX prwtice* however* dne t@
fmi3^re of attaining eqaUiteiaam eooditioBS* tte traaaforaatira tespirm-
tnree are found to be slightly lower en coding arad higher m heating*
flaws instead of tte theoretical trmsfcrmti®n teiqpermtureii k% and A3 we
