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  • 8/9/2019 Jominy Experiment Report

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      Kasırga,

    28.11.2006 – 04.12.2006

    Instructor: Prof. Dr. Ahmet ARAN

    0

    HÜSE!N "ASIR#A

    0$0040$2$#R%&P

    '

    (A)ERIA* )ES)IN# *A'%RA)%R REP%R)

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    )A'*E %+ ,%N)EN)S

    I. Intro-ucton

    1. Definitionsa. Hardness

     b. Hardenabilityc. Jominy Test

    II. E/erment Proce-ure

    1. Objective2. !amination

    a. !"erimental #$i"ments b. Descri"tion of t%e &"ecimen

    c. !"eriment

    III. Dt An3ss

    1. Hardness 'eas$rements

    I. Resuts

    1. Hardness (al$es2. Hardenability )$rve of t%e &"ecimen

    . Dscusson

    1. val$ation of t%e Hardenability of t%e &"ecimen2. *elation +eteen 'icrostr$ct$re and Hardness-. ffects of lloy lements on Hardenability

    a. )arbon b. Ot%er lloy lements

    I. ,oncuson

    II. )5es n- +ures

    III. References

    1

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    I. IN)R%D&,)I%N

    1. DE+INI)I%NS

    . HARDNESS&im"ly stated, %ardness is t%e resistance of a material to "ermanent indentation. /t

    is im"ortant to recognie t%at %ardness is an em"irical test and t%erefore %ardness is not amaterial "ro"erty. T%is is beca$se t%ere are several different %ardness tests t%at ill eac%determine a different %ardness val$e for t%e same "iece of material. T%erefore, %ardness is testmet%od de"endent and every test res$lt %as to %ave a label identifying t%e test met%od $sed.

    Hardness is, %oever, $sed e!tensively to c%aracterie materials and to determineif t%ey are s$itable for t%eir intended $se. T%e most common $ses for %ardness tests is toverify t%e %eat treatment of a "art and to determine if a material %as t%e "ro"erties necessaryfor its intended $se. stablis%ing a correlation beteen t%e %ardness res$lt and t%e desired

    material "ro"erty allos t%is, maing %ardness tests very $sef$l in ind$strial a""lications.

    5. HARDENA'I*I)

    &im"ly stated, %ardenability is a meas$re of t%e ca"acity of t%e steel to %arden inde"t% $nder a given set of conditions.

    it% a more detailed definition, %ardenability is t%e ability of steel to "artially or com"letely transform from a$stenite to some fraction of martensite at a given de"t% belo t%es$rface, %en cooled $nder a given condition. 3or e!am"le, a steel of a %ig% %ardenability cantransform to a %ig% fraction of martensite to de"t%s of several millimeters $nder relatively

    slo cooling, s$c% as an oil #$enc%, %ereas a steel of lo %ardenability may only form a%ig% fraction of martensite to a de"t% of less t%an a millimeter, even $nder ra"id cooling s$c%as a ater #$enc%. /n order to form a f$lly martensitic str$ct$re, t%e steel m$st be #$enc%ed ata rate t%at is e#$al to or greater t%an a critical cooling rate. /f t%e #$enc% is indeed fast eno$g%and t%e "art is t%in t%en one can $s$ally ass$me t%at t%is cooling rate can be ac%ieved t%ro$g%t%e %ole cross4section, "rod$cing a f$lly %ardened "art. Hoever, t%is may not be t%e casefor t%ic sections beca$se t%e interior cools more sloly t%an t%e s$rface. +$t if one co$ldmodify t%is steel s$c% t%at critical cooling rate is loer t%en t%ic "ieces can be %ardenedt%ro$g%o$t and even t%icer "ieces can be %ardened to a considerable de"t%. T%is is of great

     "ractical im"ortance not only in terms of o$r ability to "rod$ce a f$lly %ardened "art 5%ic%ill also be f$lly brittle6 b$t beca$se s$bse#$ent tem"ering ill be s$ccessf$l in "rod$cing

    t%e desired strengt% and d$ctility t%ro$g%o$t t%e "art. Hardenability t%erefore describes t%eca"acity of t%e steel to %arden in de"t% $nder a given set of conditions.

    &teels it% %ig% %ardenability are needed for large %ig% strengt% com"onents, s$c%as large e!tr$der scres for injection molding of "olymers, "istons for roc breaers, mines%aft s$""orts, aircraft $ndercarriages, and also for small %ig% "recision com"onents s$c% asdie4casting mo$lds, drills and "resses for stam"ing coins. Hig% %ardenability allos sloer #$enc%es to be $sed 5e.g. oil #$enc%6, %ic% red$ces t%e distortion and resid$al stress fromt%ermal gradients.

    &teels it% lo %ardenability may be $sed for smaller com"onents, s$c% as c%iselsand s%ears, or for s$rface %ardened com"onents s$c% as gears.

    Hardenability s%o$ld not be conf$sed it% %ardness, as s$c%, or it% ma!im$m%ardness. T%e ma!im$m attainable %ardness of any steel de"ends solely on carbon content.T%e %ardenability of steel is governed almost entirely by t%e c%emical com"osition 5carbon

    2

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    and alloy content6 at t%e a$stenitiing tem"erat$re and t%e a$stenite grain sie at t%e momentof #$enc%ing. /n general, t%e %ardenability of steel is im"roved t%ro$g% alloying and all alloyadditions e!ce"t cobalt ill im"rove t%e %ardenability of steel. )oarse grain sie and%omogeneity of t%e a$stenite also im"rove t%e %ardenability. &$c% factors as time at t%ea$stenitiing tem"erat$re and "rior microstr$ct$re are sometimes very im"ortant variables

    %en determining t%e basic %ardenability of a s"ecific steel com"osition.Hardenability can be meas$red $sing t%e Jominy end 7 #$enc% test.

    c. 7%(IN END – &EN,H )ES)

    Knoledge abo$t t%e %ardenability of steels is necessary to be able to select t%ea""ro"riate combination of alloy steel and %eat treatment to man$fact$re com"onents of different sie to minimie t%ermal stresses and distortion. T%e most direct meas$re of t%e%ardenability of steel is t%e 8critical cooling rate9. Hardenability is also demonstrated in cases

    %ere large "art fails to f$lly %arden. One can meas$re t%is in terms of t%e de"t% of f$ll%ardening, t%e diameter of bar %ic% ill j$st %arden to t%e center and t%e de"t% %ere t%emicrostr$ct$re consists of :0; martensite. more convenient and very idely $sed met%odof meas$ring %ardenability is t%e Jominy end4#$enc% test develo"ed by Jominy and+oege%old in 1

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    5. Descrton of the Secmen

    /n t%e e!"eriment, a sam"le of medi$m carbon steel "remac%ined to a s%a"e of acylindrical long bar it% a lengt% of 100 mm. and a diameter of 2: mm. is em"loyed as t%es"ecimen. 5&ee 3ig$re //.26

    Figure II.2 – Standard size Jominy end-quench test specimen

    c. E/erment

    T%e standard4sie Jominy test s"ecimen is "laced into t%e electric f$rnace "re%eated to a tem"erat$re of

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    Figure II.3 – ustenitizing tempe-

    rature of a medium car!on stee".

    Figure II.# – Schematic i""ustration of the

    Jominy end – quench test

    fter t%e s"ecimen is removed from t%e fi!t$re, it is "re"ared for t%e %ardnessmeas$rements by grinding t%e s$rface $ntil obtaining a 2 mm eig%t gro$nd section along t%elengt% of t%e s"ecimen 5&ee 3ig$re //.26. 3inally, *ocell ) %ardness meas$rements aremade it% 2 mm intervals along t%e grinded section, and t%e readings of H*) is recorded for data analysis.

    III. DA)A ANA*SIS

    1. HARDNESS (EAS&RE(EN)S

    Determined meas$rements of t%e %ardness of a s"ecimen in Jominy end 7 #$enc%test enable a %ardenability c$rve of %ardness vers$s distance from t%e #$enc%ed end to be

     "lotted. T%is c$rve "rovides basic information on t%e %eat treatment of t%e s"ecimen incorrelation it% %ardness, diameter of t%e "art, and cooling rates by t%e aid of TTT 5Time4Tem"erat$re4Transformation6 and ))T 5)ontin$o$s4)ooling4Transformation6 diagrams. Datafrom t%e Jominy end #$enc% test can be $sed to determine %et%er "artic$lar steel can bes$fficiently %ardened in different #$enc%ing media, for different section diameters.

    I. RES&*)S

    1. HARDNESS A*&ES

    7omn3 Dstnce9

    ;mm<

    Hr-nessHR,

    7omn3 Dstnce9

    ;mm<

    Hr-nessHR,

    2   59   28   214   53   30   21

    :

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    6   48   32   20,5

    8   43,5   34   20

    10   37   36   19

    12   32   38   19

    14   30   40   19

    16 27,5   42   19

    18   26   44   18,5

    20   23   46   18,5

    22   22,5   48   18,5

    24   22   50   18

    26   21,5

    $a!"e I%.1 – &etermined hardness 'a"ues

    2. HARDENA'I*I) ,&RE %+ )HE SPE,I(EN

    Figure I%.1 – (ardena!i"ity cur'e of )oc*+e"" hardness 'ersus distance from the

    quenched end ,Jominy distance

    >

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    . DIS,&SSI%N

    1. EA*&A)I%N %+ )HE HARDENA'I*I) %+ )HE SPE,I(EN

    val$ating t%e %ardenability c$rve of t%e s"ecimen 5&ee 3ig$re /(.16 it can be saidt%at t%e s"ecimen %as a c$rve t%at dro"s off #$icly meaning it %as a lo %ardenability 7 onlyvery %ig% cooling rates "rod$ce all martensite.

    D$e to t%e fact t%at if different steels of same sie are #$enc%ed $nder identicalconditions 5standardied for a Jominy test6, t%eir cooling rates or Jominy distances are t%esame, t%e /&/ n$mber of t%e s"ecimen $sed in t%e e!"eriment can be g$essed by com"aringits %ardenability "ro"erties it% t%e steels s%on in t%e folloing fig$re 53ig$re (.16.

    Figure %.1 – $he hardena!i"ity cur'es for se'era" stee"s

    3rom t%e %ardenability c$rve of t%e s"ecimen 5&ee 3ig$re /(.16, a %ardness of H*) 2@.: corres"onds to a Jominy distance of 1> mm. 510A1> in.6. /f ass$med t%e sameJominy distance, t%e ot%er steels s%on in 3ig$re (.1 %ave t%e folloing %ardness at t%ecritical locationB

    • 10:0 C H*) 2 E =-=0 C H*) >0• 100 C H*) -> E >=0 C H*) :2

    • =-20 C H*) -1 E

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    direct relation beteen t%e cooling rate and t%e distance from t%e #$enc%ed end 5Jominydistance6. /n a Jominy test, an a$stenitied steel bar is "laced into a fi!t$re and s"rayed at oneend ater. T%is "roced$re "rod$ces a range of cooling rates 7 very fast at t%e #$enc%ed end,almost air cooling at t%e o""osite end. T%at is cooling rate decreases %ereas t%e Jominydistance increases 5&ee 3ig$re (.26.

    Figure %.2 – oo"ing rate – Jominy distance cur'e

      f$rt%er relation is beteen t%e cooling rate and t%e microstr$ct$re of t%e steel.T%is relation can be e!"lained by e!amining t%e TTT 5Time4Tem"erat$re4Transformation6and ))T 5)ontin$o$s )ooling4Transformation6 diagrams of t%e steel 5&ee 3ig$re (.-6.

    Figure %.3 – $he $ diagram ,so"id "ines for a 1/xx stee" compared +ith the

    $$$ diagram ,dashed "ines

    3ig$re (.-

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     !amining t%e diagram 53ig$re (.-6, it% a ra"id cooling it%o$t c$tting t%e noseof t%e diagram, a microstr$ct$re containing 100; martensite can be obtained %ereas some

     "earlite andAor bainite is "rod$ced it% a slo cooling. T%at is, as t%e cooling rate decreasest%e formation of t%e martensite in t%e microstr$ct$re also decreases.

    T%ere are anot%er relation beteen t%e microstr$ct$re and %ardnessB +eing a$nstable microstr$ct$ral constit$tion res$lted from t%e s%a"e of t%e crystal lattice, martensite%as a %ig% %ardness com"ared to bainite and "earlite constit$tions. T%is sit$ation increases t%e%ardness of t%e steel, too. T%e ty"es of micro constit$tes "rod$ced as a res$lt of transformation, can be arranged in an order of martensite, bainite, and "earlite according tot%e decreasing %ardness5&ee 3ig$re (.=6.

    Figure %.# – $he $$$ ,$ime-$emperature-$ransformation diagram for a

    eutectoid stee"0 +here =ear"ite0 =ainite0 and =artensite. $he su!scripts

    4s5 and 4f5 indicate the start and finish of a transformation.

    T%ese relations can be s$mmaried and com"o$nded lie t%atB as t%e distance fromt%e #$enc%ed end increases, t%e cooling rate decreases 5&ee 3ig$re (.26 %ic% "revents t%eformation of an all martensitic microstr$ct$re 5&ee 3ig$re (.-6, and red$ces t%e %ardness of t%e steel 5&ee 3ig$re (.=6.

    )onsidering t%e relation beteen t%e %ardness and Jominy distance t%emicrostr$ct$re of t%e s"ecimen $sed in t%e e!"eriment can be "redicted. T%at is, beca$se t%ecooling rate and t%e %ardness is %ig%est at t%e ero Jominy distance, t%ere e!ists a 100;martensitic microstr$ct$re, and as t%e %ardness decreases 5&ee Table /(.16 in t%e distant

    sections of t%e bar, it can be said t%at "ro"ortion and formation of t%e martensite decreases int%at sections %ere t%e formation and amo$nt of bainite and "earlite increases.

    <

    3ig$re (.=

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    $. E++E,) %+ ,AR'%N > %)HER A**% E*E(EN)S %N HARDENA'I*I)

    lloying elements are added to steels d$e to folloing reasonsB4 to "rovide solid4sol$tion strengt%ening of ferrite

    4 to ca$se t%e "reci"itation of alloy carbides rat%er t%an t%at of 3e-)4 to im"rove corrosion resistance and ot%er s"ecial c%aracteristics of t%e steel4 to im"rove hr-en5t3.

    T%e term %ardenability describes t%e ease it% %ic% steels can form martensite.T%is relates to %o easily e can form martensite in a t%ic section of steel t%at is #$enc%ed.it% a more %ardenable steel martensite can still be formed it% a relatively slo cooling./m"roving %ardenability it% alloying is t%erefore im"ortant in steels.

    . Effect of ,r5on ;,< ,ontent on Hr-en5t3

    )ontrolling t%e %ardness of t%e martensite, carbon is t%e "rimary %ardening elementin steel. /n steels it% less t%an 0.2; ), t%e 3)) 53ace )entered )$bic6 a$stenite transformsto a s$"ersat$rated +)) 5+ody )entered )$bic6 martensite. /n %ig%er carbon steels, t%emartensite reaction occ$r as 3)) a$stenite transforms to +)T 5+ody )entered Tetragonal6martensite beca$se d$ring t%e transformation from 3)) a$stenite to t%e +)) ferrite, t%einterstitial carbon on t%e face of t%e a$stenite lattice is tra""ed ca$sing an $nstable tetragonalstr$ct$re to be "rod$ced. s t%e carbon content of t%e steel increases a greater n$mber of carbon atoms are tra""ed, and beca$se martensite is not an e#$ilibri$m "%ase, t%eseincreasing $nstabilities as martensitic constit$tions increase t%e %ardness of t%e steel.

    /ncreasing t%e carbon content increases t%e %ardness of steels $" to abo$t 0.>t;.Hoever, at %ig%er carbon levels t%ere occ$rs a negative side4effectB t%e formation of 

    martensite is de"ressed to loer tem"erat$res and t%e transformation from a$stenite tomartensite may be incom"lete, leading to retained a$stenite. T%is com"osite microstr$ct$re of martensite and a$stenite gives a loer %ardness to t%e steel, alt%o$g% t%e micro%ardness of t%emartensite "%ase itself is still %ig% 5&ee 3ig$re (.:6.

    Figure %.6 – 7ffect of car!on content on hardness

    5. Effect of %ther Ao3n Eements on Hr-en5t3

    /n general, t%e %ardenability of steel is im"roved t%ro$g% alloying. ll alloyingelements, e!ce"t cobalt, incl$ding )r 5c%romi$m6, 'o 5molybden$m6, 'n 5manganese6, &i

    5silicon6, Fi 5nicel6 and ( 5vanadi$m6 im"rove t%e %ardenability of steel by retarding t%e

    10

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     "%ase transformation from a$stenite to ferrite and "earlite. T%e most commonly $sed elementsare )r, 'o and 'n.

    T%e retardation is d$e to t%e need for redistrib$tion of t%e alloying elements d$ringt%e diff$sional "%ase transformation from a$stenite to ferrite and "earlite. T%e sol$bility of t%eelements varies beteen t%e different "%ases, and t%e interface beteen t%e groing "%ases

    cannot move it%o$t diff$sion of t%e sloly moving elements. T%ere are #$ite com"le!interactions beteen t%e different elements, %ic% also affect t%e tem"erat$res of t%e "%asetransformation and t%e res$ltant microstr$ct$re. &teel com"ositions are sometimes describedin terms of a carbon e#$ivalent %ic% describes t%e magnit$de of t%e effect of all of t%eelements on %ardenability. T%is im"roving effect of alloying elements can be seen byconsidering t%e alloy com"osition table of several steels 5Table (.16 and e!amining t%efolloing fig$re 53ig$re (.>6 ill$strating t%e %ardenability c$rves of several alloy steels%aving same carbon content of 0.=0;.

    $a!"e %.1 – omposition of se"ected ISI-S7 stee"s

    11

    Table (.1

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    Figure %.8 – (ardena!i"ity cur'es of se'era" ISI stee"s +ith same content

    ,/.#/wt93or e!am"le, according to t%e table 5Table (.1 7 )om"osition of selected

    /&/A& steels6, >=0 steel contains less alloying elements t%an t%e =1=0 steel, and =1=0steel contains less alloying elements t%an =-=0 steel. )om"aring it% t%e fig$re 53ig$re (.=6it can be seen t%at t%e =1=0 steel is more %ardenable t%an t%e >=0 steel, and t%e =-=0 steel%as t%e %ig%est %ardenability, %ic% certifies t%e im"roving effect of alloying elements on%ardenability.

    I. ,%N,*&SI%N

    Knoledge abo$t t%e %ardenability of steels is necessary to be able to select t%ea""ro"riate combination of alloy steel and %eat treatment in man$fact$ring and design.

    Jominy end #$enc% test is t%e standard met%od $sed to meas$re t%e %ardenability of steels,%ic% is a meas$re of t%e ca"acity of t%e steels to %arden in de"t% $nder a given set of conditions.

    II. )A'*ES AND +I#&RES

    III. RE+EREN,ES

    G1 D.*. seland, “The Science and Engineering of Materials”, I.I I%$le T%omson I$b.,:t% edition, 200>.

    G2 niversity Of )ambridge, retrieved from%tt"BAA.msm.cam.ac.$Adoit"omsAtl"libAjominyA, on Fovember 2

    G- Key to &teel, &teel Database, retrieved from http://www.key-to-steel.com/,on Fovember 2

    G= /nstron, retrieved from %tt"BAA.instron.com.tr , on Fovember -0, 200>G: ran, ., “Malzeme Bilgisi Ders Notları”, 'aina 3altesi, LTM.

    G> “Material Testing Laboratory Manal”, /T, 200>.

    G@

    G

    G