7 ialis Incl~nn Inst M e t

Vol 60, No 5, Octobor 2007, p p 4X '? -4 i ) - l

Stress-Strain Properties of Ferritic Steels using Automated Ball-Indentation Testing - Pile-up Eflt'eets Included

V. Karthik, K.V. Kssiviswanethan, A. Vijayuragzlvan, K. Laba slid Haldev Haj Metallurgy aricl i\/later~als Ciro~lp, inci~r;~ C;ar~clllr Centre lor Aloinrc I'ZescatcX-~, 1lalp;lkkatrz

E m a ~ l: karthik@~gcar gov rn (Rcccrvecl 00 Oclober 2006 , [ti scvi\cd for- IT^ 21 . I~ine 21107)

ABSTRACT

The autornatecl Ball-Indentation (131) testing is basetl on repented indelltatloll of' a spherical iruh-ter at a single locattion on a rnets~llic sample. The indentation loacls ancl the cot-responcling ciepths in an indelitaliorl are usecl to extract the key meclzanical flow properties L L S ~ I I ~ well established mathematical relationsl~ips. The tecllnicli~e is alcnast non- destructive xnd an excellct-~t s~lbstitutc for the convet~tional tensile test especially when there is very little volume of specimen available f'os testing. The distortion at the original platlc of surfilce ca~rsecl by t l ~ e material displaced by the indentation is r e f e~~cd lo as the pile-LIP or si~llc-i~~ effect. The pile-LI~ bcbaviour- alters the acliial conlac1 area and herrce the illdentation diameter which is used for calculating tlze stress- strait1 parameters. It is well cstablislled [hat the cxtent of pile- up Is related to the strain harclening coefficient of" tile tnrttcrial. This paper describes the t~lethoclology ibr deriving the plastic stress-strain properties by tsutornatetl ball-inclcntation techxziquc talting into acco~~ti t lhe us~lally ignoreel pile-up effects. Flow properties clerivcci from I-rall-indentation tests using the proposecl tnelhodology were found to be in goocl agreement with those ol' tensile test results for various ferritic steels lilce AlSr 1025 carbon slecl, 2.25Cr-lMo stcel, Mod 9Cr- 1 Mo steel with different work hardening characteristics.

Keywords: Spherical iricleritation, pile-up, strain hardening, fcrr-itic sleels, stl-ess-strain

The evaluation of r~lccharlical properties of' s t r~ l c t~ l r a l cornponerlts is very esset~titil for their coiztinuecl safe operation. When this assessment is done witkiout clist~irbing the stntctural ltltcgrity anel fiinctiotlal capabilities 01' the plant components, the ecoilzornlc benei'its reapccl are e~zor i~ io~ls . This clernancls technlqucs that recl~lirc nlir~ilnum sampling volut-ize atlcl that are simple, non-destructive ancl s~litable for localired l ones. One sirctz tecl-lr~ique is tlle Ball-lnctentation (BI ) testing technique. The BI test is based on repealecl indentation of a spherical i~zcletlter at a single location orr a metallic sample. The inclentation loacls ancl the corresponcling depths are ~lsect to find out ltey tncchanical prope~-tics using well establ i~hect n.latluernatica1 relat ionships ' . The B1 technxcluc is a11 excellent substitute for the conventiotlal tensile tests especially when there is very little volume of

material ava~lablt: fur tesilng llltc liri tlic case of' wcSdt~xcn ts2, ihlled components aricl In alloy cicvclopti~cnt appl ~ c a t l o n s ~ . Tllc use of in-s~tu BI tests Sor rerna~ning lifc cisscssmcnt ot' plant components is also ga i t i~~ig pcll~ularity'k.

2. ABOUT 'IffTB-IE TEST 'rEC1WlNglQklE

I-larcliicss tests ;ire cviclely uxed to provlcle u C L L L I C ~ ~ ~ n e ; ~ ~ ~ i r t : of the flow stress of' the mntcrial. N~~tnerlous lnves t igators 11avc cteveloped al loy specific harciness-strcng~l-u relatlonsl-lips which arc inostiy empirical itz t~nturc. Elarrlt~css tests using spherical lncletttcrs (lilce Brine11 llardrtess) tire ~ ~ n i q u c because tile georneiry of inelentiltion cl~arzges wtkZl increasing penetrtition. C'orzs~cler the inden tation o F a rr~etul surface by a spherical Inclenter of clian~eter D to a clept11 11,. This rcs~llt In a plastic: indentation wllich is a scct~otz of t t ~ c

spherical it~cicntcr with a chorctal cliasuelcr d (big. i t \ ) . Tlrc I'

inclcntation geometry cl/h changes wit11 irrcreasrng penetration of tlzc i~rcle~lter. I-lencu a unique flow stress arlcl a corresponding plast ic strtlirl can be assuciatucl cvr!ti particular incletlt;~tion geometry (d/h). Thus clififerent vrilues. of flow stress ancl plastic strain can be gencralecl for a test tnatcrial using a series of spl~crical indentations ot' ilr ff'el-errt sizes5. This is not possihlc with conical or pysamrdal indenters where georne trically sitrrilar inderlta t l ( ~ i 1 5 a r e procliilcecl anci the ratio d/h and t l~c flow stress esscntlcllly rcmnin constant with increasing penetration of tile ~ricler~ter..

~ a b o r l cletno~~stratecl that the xnenn pressure 1-1 cievclopecl betwcexl the splierical indenter ancl the test ru?atcri:il increases witti increasing load and car1 be relatcci to the flow stress ol' the material as

Where tl = 4 P / rrclp2

cr = Flow strcss

For spherical inelentation, the growtlr o f the inclentatio tr geometry with increasing load occurs in t h e e stages: (i) 'Tlli= elastic regime6, wlierc the cleformation Is reversible iirlcl is described by I-lertz Contact sol~llion with having a cotlstant v a l ~ ~ e of 1 . I ( i i ) The tr;lnsition regime, starting wit11 the initiation of plastic beneath the itrcler~tcr, where the ratic~ l-[lo increases with ct anct (iii) The fi~lly plastic txgimc in

P

488 1 Karthik et a/. Stress-Strain Properties of Ferril~c Steels using A~ilorn~~lecl Ball-Indenlalion "Tesl~ng -- Pile-up Effects lncl~~decl

whrcl~ tlrc plastic ztme expar~ds tc) tlrc hirrlice o f tlic il,cc~ir~t:n ancl tile con t~ ic t p1ess111c I ~ - I C I C ~ : , C S c l ~ i i : to war 11 11;~t~lclling cliaracteristicx :~rbct '1' attartis :I corlhtailt v , l l~~e Tllri rrrcr.cc\ac rn the rncaxi con 1ac.t prec,i,urc cvi th the rncl caikrlg pcrretratio1-I 111 ttie trnrzsxtrcu~ a l~d fi~lly pla?,t~crr.egrrncs makes 11 possible Lo cierivc 1l1c plur3tlc f low propcrtles of t11e rnaterial D~ffcrcnt v;rlues car1 I-rc obtarnccl lior~i tlsc Iite~aturc for tllc pararnctcr y, dur~r-lg t11c tliice \i:~gcs u l ilru irldcntii~loti process 6,7 .

F~r;~ncis st-,it~itic;illy analy/ed t l~e publtsheil cupcr~tncntal clat;~ itrzcl ok-itatrlccl ;L vaiul: \-I' - 2 If7 r l l 11-16 fully p1;tstlc r-egrine

'rhe i t r a ~ r ~ I I I ~p l~cr lca l rnclcx~talron 1s rnaxirr1un\ j~uc;t I-rclow the ccrwtcr 01' the region of corrtact ;~ncl red~ices w1t11 rttclral rlistuncc frtrrn 111~' 2~x15 01' i y i ~ l r ~ ~ e t r y 10 ilbo~it 20CY~ of. the rnaxrn~~ln-1 v a l ~ ~ c at tllc pc1.1j711c1-y c1f i n c i e ~ l t ~ ~ t r ~ n . rfhy: itVC[-;Lge s t ra~n bc l~ea t l~ t l ~ c rndcx~tcr 11ns becr~ clclirlecl in varrous ways. -1 ;ibtrr ' ~huwr3d that

c,, = 0.2 ci,, / D ( 2 )

S~rrcc ihe inilxir~~~irrl strain that call be obtalnccl fro111 dbove cc1Liatror-l I(% 0 2, ttris ccluatron tlas the lin-o~tatiorl [hat i t cannot be uscc8 to ctcscrlbc tllc flow straltr f i ~ r mnterrals with vcry lar-ge slralrl or C ~ O I Z ~ ~ I ~ I C ) ~ Vilrioti~ other cie t'rnitions of tlverztgc htra~n In iricler~kation tcsling have been oiitllnccl by 4hn8. Of ai i the strain cluf~initrons, Ahn stlowed that thc ilse of slicar slra~rx a t Llic cont;~ut cclgc C L C I ' I I ~ C ~ by O 12tnr1-y rewltccl in

bcst ;tgr-ccili"~"t bet WCC"LI fllc " ~ ~ I . c " \ ~ - ! , ~ I z I I ~ C I I I V C ~ ~ler I V C L ~ froin t>,ill-~trderrt;itror~ anct t cns~ le tests frur viirioiis steels testccl 'fhrs clefinlt~on of stiiiili rs

wl~erc tally 1s tlle sl~cat strain at the contact edge (Fig. lb) ;tnd cn. is a ni;ltcrral intlepcntlcnt constant0 cstrrnaterl Lo be 0.17,.

Thus, by peif'or-~tirng spllcrical inclcrrtal~on on a n~ctal l ic samplc wit11 p rogsess~ve ly increasing l o t ~ d s at n single locallon, the flow stress ancl the co~-responding plststic stsalt1 can bc obtalnecl ~ ~ s i r l g the measur-ctl vl-~liics of' inclcritatror~ load (P) and plastic inclentation cliarr~etcr (el ). The true strcss-

P strain data can then be fittccl to sui table c o ~ ~ s t i t t ~ t i v e ecl~lations Irke the !HolloinomiO, L~iclwik or ifocc equations 10

cietcrrrlinc the strain hardening coefficient (n) and tho U'TS.

Several worlicrs ' have resortecl to clirect rneasurctnenl of cl by optical technlclucs. A cyclic bail-~nclcntatic,n test was first cleveloped by ~ 1 1 ~ ct al. ancl then patentccl as A~itomatcd 132111 Incleritation by ~ - l a g ~ a , g ' ~ . Tllc AB1, patented by tl;tggag is bascd on nlultiplc rnclcntation cycles on a trletallic sample at the same locatiorl by spherical inde~~.tcr. tiact1 cycle consists o f loacling, partial inl loading ar~cl reloading secluences as shown 111 F r g 2 Tlic plastic inclcniation clcptli, lip, illtcr corrlplete removal of load 1s obtained by extr;~polatitig tlic partla1 inl loading curve limicarly to -/cr-o loacl. 'The p las t~c indentation d~;trncter dl, is obtained using the Sollowing flcrtz's relatic~ii.

'la

Pelraetratisn Depth, mm

h, - Plastic compenent, he - E&a&jc component

Itrg 3 il/lultrple Loac1111g-Unloacii~lg cur-ve 111 a Rall-inclcntat~ou t c s l

Trans. Indian Insl. Met., Vol. 60, No 5, October 2007

Karthrk el a1 . Stress-Strain Propert~es of Ferr~tlc Steels uslny Auton~alecJ Ball-lnclentat~on Testing - Pile-up Effects lncl~~decl I 489

llavitig f~)uiicl el itcriit~vely an sing ccl. (LC), the tt-ire s(r.ess and P

plastic strain can he obttiicled usirig the eqs , 1 arrd 2. According to Tabor, cq. 4 which is eleveloped with the zlssulnpt~on of an ideal sphe~.ical depression, gives good r c s ~ ~ l t s fbr s l~al low iridentations, but ;t large dlr;crepancy occi~rs For (1eepe1, ~~ide~lt i~t ioi is (el /I) 2 0.7).

L'

Altcrnativcly, one can anilly~c t11u saw loact-clcpth d:~ta In C I I I

incientrit~o~l testlng 111 ter~lls of the conlact depth ?I' anid coiltact racl~us 'a ' . C'orzsrclcring the loacl-rnclc~~tatlon clcpth curve shown In Fig. 3, the cor~t:~ct cleptl~ h is obta~rrccl i ~ s ~ n g thc S ticddon's z ~ ~ i a l ~ s l s ''I.

whcre (I,,,,, is the tnaxltnum inclentation clepth. 11, ~x the intercept inclcntation depth a n d w tlic 111deriter shape parariieter I S 0 .75 for a spherical ~ndentcr . l J s~r ig tlie geometrical rclationsh~p, tlie lncIentt.it~on cor~tact d~arnetcr IS

csi~matcd frorn the tndentat~on contact clcpth ti. (Flg. l b )

cl" is the corltact cliatl~etcr arlcl a'i: 1s the contact racliirs 112 tlic plane of original s~~rfi lce. 7 , The rtlls~lig t~p/cZippiilg 111 01' 1111: circle of coi~tact relative to the o r ~ g i ~ l a l iurfacl: is referl-ccl to the ~ ~ I C - L L ~ / S I I I ~ - I 11

plieriomcnot~. 'The p ~ l e - L I P or s1111c-irz cf'fects C ~ L L ~ I ~ Z ~

~nclei~tatiotl siglllficantly allers the actiial contact area ;~ncf ittlcrcby tlie actual iiicilentat~on cli;imeter. It may be r~otcci that ne~tl ler cq. (4) nor eel. (6) accot~sits fur tllc clianges 111

lnclcntai~orl contact clia11-lctcr C I L I C tc) ~ I I C - L I ~ or s~nk-111 cffcct. Norbury anel S a n i ~ l e l ' ~ t~~easureel the contact circle clla~lleter 011 the recoverccl ~l~clctitation slid calciilatecl its relative lre~ght to the original silr.hce. 'Tlicy fo~lrrcl tilat the ratro of tlrc helght of piIe-LIP tc) peiiekrat~on depth hclow the c ~ r c l e of' corllnct i . c llp,lv/l~c (Pig I b) IS il inaterial colrstiinl a n ~ l 1s depcsldent on ' n ' , the strain linrdc~~ing cuci'ficient. t111 I l 6 el. a1 also eslabi~slicd that the ratlo 1i,7,1e/l~c I S a I I L L I ~ ~ C ~ I C I L ~

constal~t dcper~clc~~t oii1y on *n ' . 1 ' 1 1 ~ rcs~i l t~ng relatlonstlips obtainecl us111g 11on-l111car c l a s t~c~ ty theory arid verlficci by finite elctncr~t computations cvas expressed as

7lie corltirct crrcle lie5 In the plane of Ihc original surI.ace oiily when c2 = !, which [narks tile hounilary betweerr rhc: p ~ l ~ r ~ g ~111 and s~rlhrrrg in. This corrcspor~cls to the strairt lrarclerl~ng exponent of a bout 0.28 lvllrch I \ 111 close agrectnen t \-\. ~tli tlle expcrl~nct~ tal vctl~ie obt;~~ried by Norb~~ry ancl Sati~tlel

Frotn the eel (8), i t can be ~r~fcrrccl that exlerlt of p i l e -LL~ tlepellc.2~ on the work I L ; I ~ C L C I I I I Z ~ c i t l t ~ r ; ~ c t c r ~ s t ~ ~ 01 Llle tnnter~;ri. I f ' '11' 1s very low l i l i ~ 111 ;i cold z/vorki;ccl m;llerlal, the large pla5lic Lone beneati~ the rnclerrlet a ~ l d the s~~~-rountIirrg c8ust1c vo l~ i~nc arc rzot ahlc to dcconnrnoclatc tllc vtrlcltne change clue to the ~ncletiter pcnctr i~t~on ancl lrcr~cc plle LIP o c c ~ ~ r s . 111114

~ I L ~ - L L ~ effects arc nlor e promir~erzt In ~nateri;ils wrth low stra s r ~ harclcning coeff~crelrtti.

kicluat~on 19) gives the roal ll~cientation contact cila~rletcr botween the inclcntcs ancl tttc spcc~men aceourli~ng fc)r. the pile-up el'fects. The actual l~~dct l ta t~or i clla~uctcr- tlfter cclcli toacling-u~~loticling cycle of the load-clcpth c ~ ~ r v c car1 be dctcr~ninecl ililng tlre ecjs. (S), (9) artd kuowing the valuc ol 21'. But since thc strain hartlerirng c o c f f ~ c ~ e n t "1' is tin ~~riltiiown to be tleter.~ninccl frotn strcss-stra1-n rlaki o f the irlclentutlctt~ tcsts, the following ~kcrative proceclurc is usecl In the presorlt cvorli; to deter~iiinc thc ~ I - L I ~ stress-strain cl:~ia. For. each load~ng-unload~ng cycle, knocving tlic val ~l;e u f ir L I S I ~ ~

eel. (5) aricl assu1111ng an i n ~ t ~ a l ~ ia lue of' n, cl i 5 calculated using cq. ( 9 ) I 'hen s rt~ld F ~ , ~ ~ i l c ~ l l a t c d i~srnp ~ q b . ( I ) Le (3) . Flttiiig the stress-stratn data to the ; . ~ p p r ~ p r ~ : ~ l e eotlstititttve ccluat lc)~~, the value of 'n ' 1s calculated arrcl coniparecl with Ihe ln~tial itiput value of 'n ' . l 'he itcrat~oil is conl~r~~iecl ur~trl the assumccl ~ n ~ t i a l value of h' ecluals that calc~~latecl.

For ttie fitmiliar power law I-lolloriinti eclualio11 fitting

'11' 1s calc~~latecl 1'1-om [tie slope of the log-log plc~ts O K t r ~ ~ e stress- s t ra~ti clata. This along will1 tlie strength cocfficbicnt ( 1 0 1s usecl to calc~ilate tlic Ul11rn;itc l'ensilc Strcngtli (o,,,,) us~rig the well know11 expression

wlierc "c' - a numct'lcal invariant For steels lllte the 2.25C'r- 1 Mo ancl 9C'r-1 Mo steels, it has

- Contact rudlLls o f orlglnai sL,rlacc 11mn observed thxt Voic cil~liltioll prov~des 21 better lit lo the

( cl~p/2 ) flow p1opcrt1es17.

a - C'o~ltacl radius it? the plane of pilc ~ip(jd/7,) 0 = I< - 13 exp (-Ce) (12) 111tting this irlvarra~lt kc' to tho experimental clat~i obtainccl by Norbury and Saini~cl for a m11gc of maleriais, I-lill proposed l l I c oil l S alld itle % true uniklrm cloilyatlon are ohkained the Sollotvitlg rclatior~ship f'rom tlie Ihllowing eq~latlons using the li t par;~rncters I<, B

ancl C.

Trans. lncliani Ir~st. Met., Vul. 60, No. 5, October 2007

490 1 Karthrk et a/. : Stress-Strair.1 Prr~perlles 01 Ferrltli: Steels uslrig Aurornateci Ball-IndenlailOn Tesllrig - Pile-UP Effecls Included

AlSl 'I"ypc 1025 0.23 Balance

-----

2 25C'r- I Mc, utccl 0 93 Balalkcc:

1Cl ocl 9C'r- I M(-,

stce b 0 0 5 0 0 8

rrab%e 2 S~irlzrnafy of viir rolls lieat trc;~lnlcnts t r r l 2 25C I - l IW o ;rnrci

MI)LI 9C'r-IMo siecis 33 62

Il)ela~ls of' l-[cat-tre;~lrncnt for PvTocS 2 2511's- I Mo (,keel --

0

I J c ; I I ~ Y I ~ ti) t ~ ~ l l i ) ~ : r i ~ l ~ ~ i . ~ Y Ktkv111. w a k ~ r ~ g f'or 5 r i l i t ~ C

ti~llowctl by nil cluct~cl-~~ng iaricl lctnpcrink ;it E O33KJ 1 tir ---------- 0

e-

&

1 IVbi m

A d

k I 300 o 7 1123 155 w

C

3 I 1-53 1-.I.il

4 1 100 170

3 1173 1 1 0 (3

Dctiiil:s uf 1-Fcat-ireatrnent for 9C'1-18~/!0 s t~e l

rn~cl-cistruelures anci n t cc t~a t l~ca l prupertres. S111cc I ~ I ~ C - L L ~

cffcr:ts arc p~cdornltlant Irk materlnls wlth low sisa~n har-dctzing coeflic~cili "n', ttre heat s in~u ia i~of l s carried o~lt eizsureci a varxcty of rn~crostructi~rcs tvlth w~clc r-ai~gc of strail1 harclcn~iig c i icf t ic~~rl ts (ri =- 61 05 lo 0. IS t

IC3soth cor;vct~t.lorl,tl ~ r n r a x ~ a l ic~lsilc t ~ > 1 ~ , anct ball-induntailorx tet;t:, wcrc pcrhtr-nctl on thci. ,~ s~n~ulateci heats to compare, a r i a l y ~ c arici vitlrdtiie thc b a l ! - ~ l l d i . r ~ ~ t i t i o n ?chi i ~ ~ i ~ r l l c l ~ t e . 'icrlsllc f c h t i wcrt C ~ ~ I I I C C ~ 0111 011 ~ ~ / d ~ i l d ~ ~ ~ i t f tera:,ilc s i ~ c i n ~ c n q (26-rnrn~ gauge; iel~gtii anci 4 ir1a11 c i t ; l ~ r ~ c t e z ) labn~caiccl i?om tile dii-icrcll~ l 1 c L 1 t - l r c a i c c i ; i i~ lc~oslru~. t~~i-cs at a noln~nal strain r a k of 3 x 10-'1 5'' at atnb~crlt Ic~npcr-uturt (298 K) as per ASTWI 1 : - X V l ~ i ~ , ~ n g ti floor lnodel Itlslr.orl 1 195 ~rr-tlvcr~nl tesi.ing rnitcll tnc.

I I3 - ------

I

' I hc arin 01" llic plcsci~l ~ I V C J X . ~ is it) d c ~ n o i ~ s t ~ ~ ; ~ t c i hc LI,SC~U\I?CS:, h 1 0 1 ~ w y i i i g out ar~tomutctl b;~ll-!r~ileni~~i iclr~ tests, n ~ i n i ~ i t ~ i l - ~ oj- tikc t~ ; i l l -1~1~2c .~~~nt lo~1 & i : c h t ~ i c l t i c lor- t:st~rnatrng iilc u r ~ r l i y ~ l a t ~ncch, inrca/ kcst system was d c ~ ~ g i l e c l itncl tlcvclstped :.it ;caksile p10~3Ci-tlCC1 tllld cvOi\/c i i ~ S l ~ l ! t ~ d o i i ) g y i o i ill~~liiiliSg IGC'i!!?. (X'rg 4) $ 1 1 ~ b?211trc tcst systcln 1s a closed loop hzl-vu tltc c I'I'cc LS o f p1 I c - L I P I II a l i 3 x . 1 ~ ing ill^ , i r::>,:,-\l~ ai l) i;yd!allias tc\t ~ n a c l ~ ! n c conhlst111g of LL servo-acluntor witit all rcla tiw!~sllips. ' rhc ; i l i ~ y f l j i l k c ~ ~ l i p i ' t i ~ this si~li ly ai c ArSl I V13I iix pc~srilol;al ttatcr-ctlcc, u iugh prcclslon loact C G [ 1

'P !<ulk~n I i i I*/ ?*I - p- - - -- -- - -- - -- - $;abic i g!vcs the C ~ C I ~ I I C ~ L ~ ~01np0:,111ur1 ol' t h ~ nuatcr~cil

1073 205 sl~rdieil 'T'(; val ldarc arlcl bcnchrtl:~rli the b a l l - ~ n c i c t z t a t ~ m

Trans. Indian Irrst. Met, Vul. 60, No. 5 , October 20137

------- -" ---"- - -

2 2 3 t e c l~ r~~c jue for thc.ic a l loyh, a vancty of h ~ i ~ t lsealrnes~ts, :k:,

2 ---- -- ---- -- s(limir-i~arl;/ed [n '!'ahlc 2, wcrc carr~cd out o n 2.25C't-1N1o simcl

7 1273 22.5 i hIod 9C'r-i i\do [kt-ritic slccl alloy:, to s r m ~ ~ l a t c a rarzgc r r i "

i l g 5 lyplcal ~ i l d c ~ ~ t ~ i i ~ o n luad-dcptll c L I I vu 01 4 icpc;it;~blc

ball-lrldcntatlon tcst 1 x 1 Sol-mecl on AlSl 1025 car bnn stccl

_ .. _I__.X_._._^____. _ _ ,",I_IX.._",.. I__-I - ^ . *. L. / 0.25 % Carbon sirel

k- Mod SCr-l Mo steel

Tensile @ Ball-Indentation (wrttiout accot~rtttny piit' -LIP)

~ - - - ^ l l - I T - " - E - . - T - - 7---"7---~----1----,

O.OO O . O ~ (1.04 0.06 0.08 ( I f ( ) ( 1

I ~g 6 S~~css-Stl;llrl plot of UI tcii ~ , v i t l ~ o i i t T O I I $ I I I C I I I I ~ p ~ i i ' t i ] )

uf.fecl5 ,tipol l~npohctl un ~ C ~ T ) L . C ~ I ~ c tct1411t' .,L~C\&,-'>l!':\il;

Trans Irtdlan Inst Met, Vul. 6'0, No 5, October XJL17

492 1 Karthik ct a/. : Stress-Strain Prloper-t~es of Ferrlllc Steels using MulomaZecl @ail-li1der1tat1nr.l Testing -- Prie-LIP Effects incl~lcied

Ball-I~iclenlation tests were performed at a~nb~t.tir tcr11per;itilre on thc various alloys selected 111 tlits s t i ~ l y 7'1.1~ speclmcrl lor iridcntaaiol~ tcstltlg was 8 lnrn tn cliarnct~r nnci 4 rnrn t hlclt Spccimcrls were EDM wire cut atlcl surt'accs were fir~ally polishccl with l~ixr-1 diasa1or1d paste. MCPTC ttian flve inde~ltat~on tests per spcctmen were peri'ort-ilcd to cxanilnc tlzc reproduc~bility. Thc rcsults of the 8PJI tcsts performed on various alloys and t11e1r cornparkson witll tct~sile pr opert~es rs presenteci ixl tlze foIlo\vlng scctlon.

3 . RESBUL,TS AND DISCUSSICIN

l ;~g~ i r e 5 shows the sepeatablc: lncleutatlon loacl-dcpttl plot uf ;I ~ypical BL tcst ~nclicat[ng exccllcnt reproducibllily wrth a scatter of less tlmn 2% in 1 0 x 1 values at any parlkcular depth. The plastrc rrlderltatlot~ clcptl~s for the cliftercnt Ioadsr~g cycles were first obtained fron: tlzc unloacllng cyclc using cc~. (5) and cunvcrtcd to the indentatkon cl~~lmetcrs using ccl. ( 6 ) . Without ~ o ~ ~ s i d c i - l l ~ g (he pile-up cffects, the stress and corrcspcrndirzg slrairls were c~llculated ~ ~ s l n g cqs. 1 6i 2. ?'he strcss-strain data of the AZSl 1025 carbon steel was f ~ t to i-Iollorrlon powcr law C ~ L I ~ L L O X I wllile those of 2.25C's- I Mo and Mot1 9Cr-1Mo stcels werc f i t to Voce ccyitat~un to clcterrninc tile U'TS ancl tl-LLL' ctn~t'orrn elongallo11 ' F ~ '

1 Mod 9Cr-1 Mo (108) I ---*- Tensile 1 " Bl

I L

True slralw

Fig 7 Strcss-Slrain plot o f fgl tc~C with pile Lap cifect~, accounrcd s~~pcr~~~l r ) a sec i an cot-rciporlding t e ~ l ~ ~ l c sirer,s-stialn plots

Tcible 3 rJonlpalisc)n of [tie sesults of ball-rnclcthrattcri~ tests L i ~ ~ d c(,~lvt.nllrj~l;\l tcrlslle tests for [he various ierritic sleclj.

Figure 6 shows tllc strcs~-slraiz data of BL tcht aiipl;.rimposccl on thc tensile tcst resulis wire11 the raw data c ) t BI te\t :ire a~laiysecl w l t h o ~ ~ t c~iisirllc~~i-i~; thc pile-~ip ei'fectli. For the

Terlstle test lesults

plairl carbon steel w ~ t h 11-0.2, ;I shitl of aboul 10 'i/o In thc

E[,%

0.2 1

0.09 I

0.108

0.074

0.142

0.082.

0.064

0100

0.1 19 -

0.083

0.072

0 057 -

0.054

0 052

---

Mii[crial/[[)

AlSI 1025 carbon stecl

--

strc(,s value is notel-1 {Fig ha) ibr ;i gsvcli strann. 'Tltu l-uglier \tress v a i ~ ~ c s calciilatcd lisiiig cquatlun o -= ?P / i i c t I z ~ 1s ~ 1 1 ~

lo ~ o w c r value of iiic i!idcrliatkon diat~lctcr ci detcrrninctt i'

w i t l~o~i t cons~tlerrng the prtc ill? efSects. Tile p ~ l e - ~ i p effect

LJTSMPa P

432 _______--

altcr the inclentaiior~ c c ~ ~ : l a ~ t .br'ca and tncrc:lse, the ~lct t~al

Ball-lndcntal~on ---

UTSblPa

455

5 19

53 1

6 13

477

683

73 5

640.48

624 32 -.

682.06

736.1 1 -

786 2

805.78

830.20

~~ide!~tntlon contact cfid;nc:ter a:, ~ , l iown In 1:1g. I b

test resulls

E,,(% --

0.193

0.11 1

0. I04 -p

O 079 ---

0.123

0.085

0.06 1 --p

0.085

0.095

0.O6

0 074

0 068 --

0.051 --

0 058 --

10: 1 52 1

539

594

superirnposccl oil the‘ ~i jn .1 c%jaortcfftig tcrlsi le cia ta, L I I C r-csulririg plot (Fig 6b) i h i ) ~ . , i ? ~ t t i i4pliziil[ d ;I~?L! iiiti.*~:ll shlli Sroir-i thc

- I

3

0 'Cl

coric,spcti~ciir:g ic i~ i i i l : pjol i ; . ' l t i ~ rtspcc! to both stmess ;~licl strain \a l i l e~ Thts Ll~oi.;ii h n i t I:?. ihc: i- , t r~lir i to 1~1glicr VLLLLICS

4

suggcxls i h i i t t i i t . I 1 1 i ~ l a t ~ o s l ~ l \ ~ j ~ 5 = 0 2 2Ii,!D dock, not l i i i iy i-ip~c\cnl hi. ~ I - L I C 51izi1ii 'it the ji~cluni~ltiun cclgc ii,i tnriiilrr;ll(, w~lli vcsy Iuw I: i , ~ i ~ i c + , . FhM ailc) lysibs 4)i' 111c ~ r x c i ~ ~ i i t : ~ t ~ , ~ r i j ' i i o ~ ( : i : ~ done by T i n l l a i ' c ' ct a1 has shocvcd tli,it tilt: i i i x j ) I : i>i!~ "tr~ilil co!:-~~puet.tl ;it tl'D=-O 5 fbr ~ ~ I - L L L iitfIcit:nt 11 l;;i!~it?s o i ii 0, ii 25 i t r i d (1 '-; rar1cs.l t,t:t\vc.cn 0 05 L U I ~ 0 15 WII~IL ih+: * + J ! L L ~ C , I L ~ o t t l i ~ ~ ! ~ 10 C L I L ~ ; ~ ~ ~ O I ~ rq = 0 2 1 I 1 1 ?hut. r h t b Jiicfi.p:inciLs\ i i i ti\i. iiall -in~luilk;iril,n rc5uils were .~trn-ib~iri:il $0 r ~ O ~ I - I ~ L ~ , I L , I O I ~ o t' i ~ 1 e l ip cffkcts a!!d i n the dcfiriitlisr~ iii titics p i t ! ~ t l c ,ti;ilil ~-.~,r)t:t~~!lIy ior ~ n a t c r ~ c l i ~ ~ wir,l~ I I - 11. I

480

6

608.69

Trans. Indian Ins;.?. Met., Vol. 60, No. 5, Oc-fobsr 2007

0

5 M

LJ '3

-'tY J

2

- 3

4

5

G -

7

702.16

734.28 --

789.18

801.896

812 98 -

Karll-r~k et a/: : Stress-Stra~n Propert~es of Ferrltic Steels uslng Automated Ball-lndentatlon Testrng - Pile-up Effects Included I 493

2 . 2 5 0 - I M o (ID - 2)

Ball-inden tation P

0 -

[, - ~ - ~ - T ~ ~ y - - , - - - r - - - , - - - - , -~- -~-v , . - -7, I I I

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0 "-, 0.0 0 0.02 0.04 0.06 0.08 0.10

True Sfraira Trrle Strain

Ball-l ndentation I I:-- -- I I I I

Mod 9Cr-1Mo (SP ID : 9) Tensile

0.00 0.02 0.04 tl.416 0,08

l'rue Stn-sirr

Mod 9Cr-I Mo (ID-I) TENSILE

--

700 -

MocI~CJS -1Mo(ID - 11) P Tensile

A R I " B1

I31

900

$00-

700- ei 2 600-

500- L

400- 0

2 300- E-c

200 -

100-

P1g 8 Co~l~pasrsolr of ike strcss-xtr;1111 ctir-vc:, obt:rlnccl born the ball-~nclentatio~~ tests ancl cnnvcnt~onal tcr~silc tcsta for the varloua lieat tleatecl nllcrostrvclurcs of 2 25C'r-1 iVlo a~icl Mocl SrCr--1 Mo steclh

the prcvlous scct~on Llslng the cqs. (91, ( 1 ) & (3 ) aricl the agrccrncni bctwc.cn tlle s t ress-slra~n curve obt;ri-tlecl Srorrt coi~statlts Y=2.87 and cu, = 0.12. Frgurcs 7, 8 ancl table 3 ball-inclcntatioti and those clcrrvcd from converltiorval tetlsile compares tlre flow proportics obtained tiom BI test aticl tllc tcsts. T11c pile-up or sinlc-in causccl nra~nly by tvorlc harctening conventional tensile stress-strain properties for. the varlou:, characteristics has a strong et'i'ect or1 calc~llating the abso l~~ t e materials ulrcler s tidy. values oi' the stress cincl strain values. Also the rcstule Illat

600 - CT

2 50Cl-. e .

M

2 4100 - h -i-r

can cicarly seen ti,nt i n c i u s i o i r of p,lc-up et'fccis and a constant vnluc 01 2.87 Tor tlie constraint filclor 'P = tllo for

tire dcfinitioi, accordirrg to c c , (3) results ill good a rm"g of wodc 11al-dcning expoilctlts in this study matches well with sirnil~tl- studics7. T l ~ c use of new strain cief?nitiotl of

Mod 9Cr-1Ma (ID - 13) Tensrle

8 1

Trans. Indian Inst. Met., Vol. 60, No. 5, October 2007

cd4 300 -

3

E-.l 200 -

100 -

494 I Kart i>~k et a1 Stress-Slr;itri Properties of Fefrrtic Sleels uslng A\rtorr~at~.cl Ball-lrlclcr~iatiun T~~stirig -- Pile-uys Effecis li~cluclecl

0 .12 iany instead coinmonly rl\cci cxpi c s i ~ o l l 0 2 dP!D rcs~ t l t s ~n good agrecrncnt o / xlr-es\-strain balucs ~ v ~ t l i the conr:crktlon;ll lciislle tusk, e,lpoc~ally li11 qteels sl~otvirkg ~jile- up ci'Sei.ts. 1111lnc w ~ l l ~ ihr ivor k d o l ~ c by Sung-l - loo~~ K I ~ ' ct al.

pl'lii~s i~ rnctl~oclology f i ~ r accurately clctcr-rn~rslng the strcss- slrairr propcr t ics f o 1 lei t- i t~c s teels wi th c11ffe1-ci1t worli h~ l rdcn ix~g c h ~ a r d ~ t c r i s t ~ c s us111g ball-ll-~clctit;ltrol~ tcchr~~clltc ti,~s becri ~ ~ t i t t > I ~ b l ~ ~ " ( l -1 11e 111ct1ro~lology also ~ ? ~ c o t ~ t l t s lor'

t11c P I I C - L ~ ~ ~ C ~ ~ - C C ~ S c , x ~ I I ~ ~ ~ ~ c ( ~ by these SLCCII . 'r111s OPCtlS ttp thc L ~ S C F L L I ~ I C S S o f ' the tcchnrcl~rc for a wiclc vai.iety oi' ; t p p l ~ ~ " L i r ~ i ~ w l ~ c r c Iittlc V O I L I I T I C o f ~nalerliil 1s only a\~:~il;iblc for extracllr~g the rnechat~~cal propcr t~es . 'Tt~c fcrr-illc steels l ~ k c 2 751'r- 1 Mu i i ~ ~ l hilocl It)C:t- I Mo sreels x c wiclely ~icccl 21s hig11 t e i ~ ~ p e r ~ l l u i c conlporscnls ol' putver g c i ~ c r a t ~ n g plar~ts CJrlc of' tlic ;tg)pltc;~t~ui~\ ol the ball-~t~cleritatim tecl~n~cluc 1s c l~a r~ tc te r~s i r tg the prirpeily grL~dle[lls 111 the welct 1o111ts of tl~ec,c stcclc S ~ m l l n ~ l y rnechan~cell property tltlgl.adtltron of tllesc stccls cl~ic to aging at clcvatctl te~nper t l t r l re~ can also be dc tc~mincd risrng ball-inclentat~on technicjucl" I f s~ ich an iisscisrncnt IS donc ~vithotrt cl~aturbing thy s t n ~ c ~ ~ i r a l ~ntcgrity c.)F the plant ccln~poricnt ancl ttlercby rnrn~~ni;.ing the tlotvi~ t l ~ r ~ e , therl !lie: cctrnom-nlc hertcfit~ rc;lpt.cl are enorlncrns.

' f h e b a l l - ~ r ~ d c n t a t i o n teclln~clcle has been ~ , u c c e ~ s l ' u l l y bi:nchtz~t~~lcecl tot- cIcter.r-r~~ii~ng tlrc str'css-strain propcrlies ot' tcl.r~Pic slcols w~tiz diffelent work h a r c l e t ~ ~ t ~ g c11:tractcristics. '1-11c: cffccts of pile-LIP t l i t ~ ~ been incorporated iri thC an;ilysis of' bull-rr\clent;it~orr clalt~ l o accurately prcclicl thc tensilc ~ t r e a s - i t r l - l r n proper l ies . 'The cons t ra in t !actors tlsed for c!cliiling the rcprcscntaltvc srress ancl the cur~stui~ts tisccl for clciining lhc a v e r a g e strain ~ ~ ~ a t c h c s well wit11 thc ~ r ~ t c i - n n i i ~ o n a l l y rcpartccl values . T ~ L I S t~a l l - inc ic~ i t :~ l l~ ,n tcchai~ilzac and ~ h c trslirig irrctlzoclology ;~ciitptt:cl i r r t h ~ s study I ~ i i $ / i ~ I I C pc-)tcntlal to be appllcd insit~l and nc~r1-c2estt-~1ut1vcly to cgaluate the mecklanical propaticmOt' stnall volumcs such 2s l~~/clds, heat L~Efectccl zones ancl aged comporIents.

r7 , I atrthlor's alse~ th,lr~l< S h r ~ P .K;~ ly~ lnasund~~-am, Asr,oc~atc Idlrcctor. I n s p c c t ~ o n -rcchnolugre,s Ciroup, I n c l ~ ~ a Gaimdhi A ' ont rc lo r Atornlc Resecti-cli, for h i s kecn i~ i t e rcs t ;snil

crlcuuragclnent in t h i s uoi-k. ' I 11t: Ilulp c ~ f ' Sllri k/l. Sck:ir dtrt-uig thc co~ir sc of L ~ V I lc 1s cluiy acltnuwlcdgcd

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2 Mi~rt!i I< I , Mrtagtla P Q blalliew ivf r>, Sliati V N and f Jaggitg f: MI, /ti/et t f i i /1ori~i / .JOIII tt(11 o# F" e ~ \ i i / ~ ~ H*L~.jel$ ( i i t ~ l ~ I , K ) ~ I I ~ , 76 11994) p 361

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Trans. Indian Inst. Met., Vol. 60, No. 5, October 21307