Materials Science and Engineering A 528 (2010) 583588

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Materials Science and Engineering A

journa l homepage: www.e lsev ier .co

Effect o echof gray

M.M. Jaba Department o ehran,b Razi Metallur d, Tehr

a r t i c l

Article history:Received 4 JulReceived in reAccepted 10 S

Keywords:Gray cast ironCooling rateDASSDASeHB

d andast irrite ae) ahly delso de decr

1. Introduction

Gray casrial with ovtraditionallexibility oand wide raof GCI depecess, inoculGCI is charamatrix. Fougraphite aenhance thmorphologydeterminin

The as-cprocess andMatrix micreutectoid remechanismand the cooresult of eutmechanical

CorresponE-mail add

ments on mechanical properties of iron might be related to theirinuence on eutectoid transformation [57].

0921-5093/$ doi:10.1016/j.t iron (GCI) remains the most important casting mate-er 70% of the total worlds production tonnage [1]. It isy chosen in many industrial applications because of itsf use, good castability, low-cost (2040% less than steel)nge of achievable mechanical properties. The structurends on chemical composition before the casting pro-ants and cooling conditions [2]. The microstructure ofcterized by graphite lamellas dispersed into the ferrousndry practice can inuence nucleation and growth ofkes. So that size and type of graphite akes or (them),e desired properties. The amount of graphite and size,

and distribution of graphite lamellas are critical ing the mechanical behavior of GCI [24].ast microstructure is governed by the solidicationsolid state transformation (eutectoid reaction). The

ostructure depends on the conditions under which theaction occurs. Among the variables that inuence theof the eutectoid reaction are the chemical compositionling rate through the eutectoid temperature range. Theectoid transformation have key role in determining theproperties of cast iron. Thus, the effect of alloying ele-

ding author. Tel.: +98 9143107797; fax: +98 21 66036012.ress: jabbaribehnam@gmail.com (M.M. Jabbari Behnam).

Although there is sufcient information available onmicrostructural characteristics of cast iron, however effect ofthem on mechanical property (hardness) is not formulated. Thishas led to a series of experiments to nd the effect of coolingrate on DAS and SDAS, and also e. Besides the effect of theseparameters on mechanical property (HB) is evaluated.

The effect of high cooling rates in producing ne structuresresults in development of high-strength cast alloys. The under-cooling of a melt to a lower temperature increases the numberof effective nuclei relative to the growth rate, the latter beingrestricted by the rate at which the latent heat of crystallization canbe dissipated [8]. The rening inuence of an enhanced cooling rateapplies both to primary grain size and to substructure. Thus, thereis a marked effect upon DAS, SDAS and e over a wide range ofcooling rates.

The eutectic solidication initiates at certain locations andcontinues by radial growth with the simultaneous separation ofgraphite and austenite from the melt. Furthermore, the lower thetemperature of formation, i.e. the greater the amount of undercool-ing thener is the graphite formed. SunandLoper [9] showed thatintensive supercooling both constitutional and thermal lead tothe development of cellular dendritic growth of the graphite into aform recognized as exploded graphite. The microstructures of grayiron and ductile irons are determined by cooling rate, composition,nucleation andgrowth conditions existing during solidication and

see front matter 2010 Elsevier B.V. All rights reserved.msea.2010.09.087f cooling rate on microstructure and mcast iron

bari Behnama,, P. Davamia,b, N. Varahrama,b

f Materials Science and Engineering, Sharif University of Technology, P.O. Box 11365, Tgical Research Center, No. 8, Fernan St., Sorkhehesar Road, Km 21 Karaj Makhsous Roa

e i n f o

y 2010vised form 29 August 2010eptember 2010

a b s t r a c t

This paper presents the results obtaineand mechanical tests involving gray cof cooling rate on the primary dendthickness of ferritecementite layer (bothDAS and SDAS and alsoe are higrate increases. More attempts were athat HB increases as DAS, SDAS and m/locate /msea

anical properties

Iranan, Iran

the deductionsmade froma series ofmicrostructural studieson which was sand cast using a variety of modules. The effectrm spacing (DAS), secondary dendrite arm spacing (SDAS),nd the hardness (HB) were evaluated. Results show that thependent on the cooling rate, and they decreases as the coolingone to correlate the HB with DAS, SDAS and e. It was foundeases.

2010 Elsevier B.V. All rights reserved.

584 M.M. Jabbari Behnam et al. / Materials Science and Engineering A 528 (2010) 583588

Fig. 1. Plot ofabsolute temp

the transfordendriticallof these invconcluded fto cooling rcooling rate

As the dand growthhas the keinuence ofor the seincreases apto 1.8101temperaturperature ac

D = D0 exp

where D0 isQd is the acis illustrate

So as thdiffusion raextensively

Mechandependentmatrix, althtion, size, shmatrix, hav[14] evaluation for calphase fractiamount on

1 Tensile str2 Yield stres

Table 1Nominal composition of melt used in this work.

Element C Si P S Mn Cu

Amount (wt%) 3.43.6 1.21.3 0.130.15 0.101 0.64 0.48

on:

cp(5

ple eharnons a

BSi

54 +

167

drichiches noin thho inicalpeci

+ f (

erim

y iroast adesratemetacq

rmemols. Ththe logarithm of the diffusion coefcient versus the reciprocal oferature for several metals [12].

mation deeds of austenite. DAS in alloys that solidiedyhavebeen investigatedbyZhanget al. [10]. The resultsestigations are in general agreement. Pande et al. [11]rom their investigation that SDAS can easily be relatedate and have the same behavior of DAS in relation with.evelopment of GCI microstructure is in the nucleationclassication, so the temperature and its variation

y effect on it. Temperature has a most remarkablen the diffusion coefcients and rates. For example,lf-diffusion of Fe in -Fe, the diffusion coefcientproximately six orders of magnitude (from 3.01021

5 m2/s) in rising temperature from 500 to 900 C. Thee dependence of diffusion coefcients is related to tem-

equati

HB = eSim

relateequati

HB = H

HBSi =

HBSipe =Goo

tion wincludditionones wmechain the sbelow:

HB = A

2. Exp

Grawere csamplecoolingtial geoto datatransfoin CO2samplecording to [12]:

( Qd

RT

)

temperature-independent preexponential (m2/s) andtivation energy for diffusion (J/mol). This phenomenond in Fig. 1.e undercooling decreases (by decrease of cooling rate)te increases and the carbon atoms can diffuse moreby the time. This results in coarse grains (akes).

ical properties of cast in room temperature are moreto solidication microstructure and related phases inough different parameters such as chemical composi-ape anddistribution of graphite, pearlite/ferrite ratio ine signicant effects [13]. Venugopalan and Alagarsamyted the effect of alloy elements and conducted an equa-culating mechanical properties (TS1 and YS2) versuson. Yu and Loper [15] investigated the effect of pearliteHardness (Brinell) in ductile iron and come to the below

ength.s.

embedded.All these sasoftware (ahardness Brin Table 2.

CoolingRelated coo

for eaching rate dethe eutectic(11001000

3. Results

3.1. Dendri

Effect ofandb respedecrease. Ring resultstemperatur

3 Analog to.01 + %pearlite)quations were suggested by Svensson et al. [16] to cor-ess of iron to Si content (between 1.7 and 4.9). Thesere written below:

f + HBSipe (1 f)

37Si

+ 31Sih and Shaws [17] investigations results were an equa-calculate the ultimate tensile strength. Their formulat only composition of elements, but also cooling con-e form of cast bar radius. Yang et al. [18] were the rstncluded the cooling rate of alloy in the formulation ofproperty (Brinell hardness). This cooling rate (R) was

al temperature (900 C). Their formulawas summarized

%alloy elements) + f (R900)

ental procedure

n specimens with the composition shown in Table 1t 1420 C. To obtain different cooling rates, a step formigned which is illustrated in Fig. 2a. To calculate reals, ve thermocouples embedded in the middle of spa-ry of each step. These K-type thermocouples connecteduisition system (DAQ) in personal computer by A/D3

r (schematically showed in Fig. 2b). The body is moldedd box. After casting, the bulk cut into metallographicese samples are cut in places which thermocouples areFig. 2a and b show the location of samples in body.mples then are analyzed by commercial image analyzequinto) to obtain microstructure parameters, and alsoinell testwas done. Details of each step are summarized

curvesobtained fromthermocouples are shown inFig. 3.ling rates are summarized in Table 3step. It is clear that by increase of module, the cool-

creases. Cooling rates are calculated just a little belowtransformation temperature and in the constant rangeC).

and discussion

te characteristics (DAS and SDAS)

cooling rate on DAS and SDAS are illustrated in Fig. 4actively. As the cooling rate increases, bothDASandSDASapid cooling produces ne dendrites, while slow cool-in large and coarse dendrites. Thus solidication over ae range is the primary requirement for dendrite growth.digital.

M.M. Jabbari Behnam et al. / Materials Science and Engineering A 528 (2010) 583588 585

ation

Primary austhe eutecticalongside wthe eutecticsection mayand SDAS a

The corrwritten bel

DAS = (78.4

SDAS = 2.

3.2. Ferrite

The austtic cells thathought thevent. Thesurroundedwithin theresults in meutectic groby the samoccurring ainstability ivection curheat extrac

Phasech+ Fe3C phtheeutecticthrough thelamellae ofduring the tis approximand the cemappear dark

Table 2Details of each

Step numbe

12345

500

700

900

1100

1300

3002001000

me (s)

Fig. 3. Cooling curves of cast body obtained from thermocouples.

ed cooling rates for each step.

S1 S2 S3 S4 S5

g rate ( C/s) 1.90 3.14 8.87 13.53 17.67

aries are indistinguishable, which layers appear dark at highcation. Mechanically, pearlite has properties intermediaten the soft, ductile ferrite and the hard, brittle cementite.ct of cooling rate on eutectoid layer thickness is shown ins it seen from thediagram, increase of cooling rate redounds

rease of thickness in eutectoid. Results are shown for four, since in the S5 section there was no good detectable metal-hic picture for eutectoid. Behavior of eutectoid thickness onFig. 2. (a) Designed sample for getting different cooling rates, (b) schematic illustr

tenite dendrites readily grow from the liquidus belowtemperature. Growth of dendrites may also continueith the eutectic as the temperature decreases throughrange to the solidus. Therefore, undercooling in thicklead to longer dendrites and higher interaction. DAS

re shown in Fig. 5 for S4.elation between DAS and SDAS whit cooling rate (R) isow:

8)R0.61

47 Ln(R) + 93.30

cementite layers

enite-FG eutectic solidieswith the formation of eutec-t are more or less spherical in shape. It is generallyat each eutectic cell is the product of a nucleationeutectic cell is made of interconnected graphite platesby austenite. The degree of ramication of graphitecell depends on undercooling, Higher undercoolingore graphite branching. The leading phase during thewth is the graphite. Graphite spacing is determinede parameters as for regular eutectics, with branchings a response to interface instability. In turn, interfaces determined by localized changes in composition, con-rents, crystallographic orientation different from thetion direction, and a change in temperature gradient.anges thatoccuruponpassing fromthe region into thease eld are relatively complex and similar to those forsystems. Themicrostructure for eutectoid that is cooledeutectoid temperature consists of alternating layers orthe two phases ( and Fe3C) that form simultaneously

Tem

pera

ture

(.c)

Table 3Calculat

Step

Coolin

boundmagnibetwee

EffeFig. 6. Ain decpointslograpransformation. In this case, the relative layer thicknessately 81. The thick light layers are the ferrite phase,entite phase appears as thin lamellae most of which. Many cementite layers are so thin that adjacent phase

step in designed model.

r Label Geometricmodule (cm)

Dimensions(LmmWmmHmm)

S1 1.5 15083.555S2 1 15052.524.2S3 0.75 15051.515.8S4 0.5 15051.510S5 0.25 15048.55

the basis of

e = 0.863RFig. 7 sh

calculating

3.3. Hardne

Hardnesplastic defoare performseveral reaspecial sperelatively inof A/D conversion and data acquisition system (DAQ).cooling rate formulated as below:

0.16

ows the metallographic pictures of image analysis forthe thickness of ferritecementite layers.

ss evaluations

s is a measure of a materials resistance to localizedrmation (e.g., a small dent or a scratch). Hardness testsed more frequently than any other mechanical test forsons; they are simple and inexpensive (ordinarily nocimen need be prepared, and the testing apparatus isexpensive), the test is nondestructive (the specimen is

586 M.M. Jabbari Behnam et al. / Materials Science and Engineering A 528 (2010) 583588

10

20

30

40

50

60

20151050D

AS

(m

)

R (.c/s)

a b

2

3

4

5

6

7

8

20151050

SDA

S(m

)

R (.c/s)

Fig. 4. Effect of cooling rate on (a) dendrite arm spacing (DAS) and (b) secondary dendrite arm spacing (SDAS).

Fig. 5

neither fracthe only debe estimate

Fig. 8 shples. The coformation ois consideradecreased smottled zonand whitethe sectionthere is a copears, the mgraphite, recooling rate(constant to

0.

0.

0.7

0.8

0.9

e (

m)

ig. 6.

grapcoolual carserrate. Metallographic picture of step 4 showing DAS and SDAS.

tured nor excessively deformed; a small indentation isformation) and other mechanical properties often mayd from hardness data, such as tensile strength.ows the effect of cooling rate on hardness of the sam-oling rate is highest at the S5 step. This results in the

F

type AAs thea gradof a cocoolingf white iron, a mixture of iron carbide and pearlite thatbly harder than gray iron. When the cooling rate hasufciently to allow the formation of some graphite, ae appears. The mottled zone, which is a mixture of gray

iron, has a lower hardness than the white iron tip. Assize increases, the white iron gradually disappears, andrresponding drop in hardness. As the white iron disap-icrostructure becomes a mixture of ferrite and type Dsulting in the low hardness. A further decrease in the(8.513.5 C/s) results in low increase in hardnesssomehow) as the microstructure shifts from type D to

HB = 170.9Effect of

hardness isand e resudecrease, in

Kumruoproperties ovalues obtaand limit thues from th

Fig. 7. Metallographic pictures for (a) S2 with R=3.14 C/s, a5

6

1612840

R (.c/s)

Effect of cooling rate on thickness of ferritecementite layers.

hite and the matrix converts from ferrite to pearlite.ing rate decreases, the hardness is reduced because ofonversion of the pearlite to ferrite and the formationgraphite structure. Correlation between hardness andis as below: 0.067R + 0.147R2

DAS, SDAS and thickness of ferritecementite layers onlaid in Figs. 9 and 10 respectively. Increase of DAS, SDASlts in decrease of hardness. When all these parametersfact sample faces with ne structure.

glu [5] evaluated the mechanical and microstructuref chilled cast iron camshaft. To investigate the hardnessined in this study to apply them to industrial elementse cooling range, cooling rates and related hardness val-e Kumruoglus work were obtained using point value

nd (b) S5 with R=1.90 C/s.

M.M. Jabbari Behnam et al. / Materials Science and Engineering A 528 (2010) 583588 587

160

180

200

220

20151050

Har

dnes

s (H

B)

R (.c/s)

Fig. 8. Effect of cooling rate on hardness.

160

180

200

220

Har

dnes

s (H

B)

DAS SDAS

measuringbtrates the cNote that twere conve

To limitpare our dacomparison

166

170

174

178

182

186

0.90.80.70.60.5

Har

dnes

s (H

B)

e (m)

Fig. 10. Relation between hardness with thickness of eutectoid layers.

4.3

1.9

Cooling rate ranges0 10 20 30 40 50 60DAS, SDAS(m)

Fig. 9. Relation between hardness with DAS and SDAS.

yGetDataGraphDigitizer software. Fig. 11a andb illus-ooling curve and hardness value of lobe in camshaft.he hardness values are in Rockwell scales, which theyrted to Brinell scale using ASTM E140-97.our proposed formulation in industrial use we com-ta with the Kumruoglus work. The cooling rate rangesis shown in Fig. 12.

50

Fig. 12. Compmodel.

From Figour proposewe comparshown in Fi

Fig. 11. (a) Cooling curve and (b) hardness values of lobe in camshaft w27.4

17.67from literature

this paper3025201510

R (.c/s)

arison of cooling rate ranges between industrial results and proposed

. 12 we come to this point that the industrial range ford formula, is between 4.3 and 17.67 C/s. In this range,

e the hardness value between those two data, which isg. 13.

hich was measured by Kumruoglu [5].

588 M.M. Jabbari Behnam et al. / Materials Science and Engineering A 528 (2010) 583588

160

180

200

220

20151050

Har

dnes

s (H

B)

R (.c/s)

proposed formula from literature

Fig. 13. Comparison of hardness value between proposed formula and literature inthe subscription cooling rate range.

4. Conclusion

Evaluation of gray cast iron with different cooling condition(rate) showSDAS, e anDAS, SDAS aing rate decbecomes rebecause of care clear anbehavior wuses, propoliterature fohardness vamentwith eused in indmethod canwere drawn

1. Dendritecooling r

DAS = (7

2. Secondardecrease

SDAS =

3. Thickness of ferritecementite layers in the gray cast ironincreased as the cooling rate increased

e = 0.863R0.16

4. The hardness Brinell (HB) decreases as DAS, SDAS and eincrease. Also it shows the below behavior whit cooling rate:

HB = 170.9 0.067R + 0.147R2

Acknowledgment

This work has been nancial supported by the Razi Metallurgi-cal Research Center (RMRC) for advanced manufacturing and dataacquisition system.

References

[1] D.M. Stefanescu, Mater. Sci. Eng. A A413414 (2005) 322333.[2] L. Collini, G. Nicoletto a, R. Konecna, Mater. Sci. Eng. A 488 (2008)

539.Davis, ASM Metals Hand Book, vol. 9, ASM International, 1985, pp.135.ills, et al., ASM Metals Hand Book, vol. 9, ASM International, 1985, pp.

228.. Kumr. Haq

. Salazater. E.H. Se. Sun,. Zhancess. T. Pand. Cal

nt of1, 126uo, D89) 21lagar

. Yu, SSven

. Piowt IronCast

36.. Shaang,rostrundrys that the cooling rate has remarkable effect on DAS,d hardness Brinell (HB). It is found that HB decreases asnd e increase. The HB however, decreases as the cool-reases, screening a direct relationship. But this behaviorverse in a special cooling rate range (8.513.5 C/s)hange in graphite type in the structure. All these resultsd a lot of piece of data are indifferent literature, but theiras formulated. To limit cooling rate ranges for industrialsed formula was compared with experimental data inr camshaft. The valid range is 4.317.67 C/s and thelue in this range for proposed formula is in good agree-xperimental data in literature. So these formulas can beustrial scales. In addition, the presented experimentalbe used for other commercial alloys. The formulationsas follow.

arm spacing (DAS) in the gray cast iron decreases as theate increased.

8.48)R0.61

y dendrite arm spacing (SDAS) in the gray cast irons as the cooling rate increased:

2.47Ln(R) + 93.30

529[3] J.R.

127[4] K. M

219[5] L.C[6] M.M[7] F.R

J M[8] K.W[9] G.X

[10] L.YPro

[11] K.S[12] W.D

me200

[13] X. G(19

[14] D. A[15] C.R[16] I.L.

T.SCasand29

[17] G.M[18] Y. Y

micFouuoglu, Mater. Des. 30 (2009) 927938.ue, J Mater. Process. Technol. 191 (2007) 360363.ar, M. Herrera-Trejo, M. Castro, N.J. Mndez, T.J. Torres, N.M. Mndez,ng. Perform. 8 (1999) 325329.ah, J. Hemanth, S.C. Sharma, Mater. Des. (1995) 175179.C.R. Loper, Trans. Am. Foundry Soc. (1983) 91841.g, Y.H. Jiang, Z. Ma, S.F. Shan, Y.Z. Jia, C.Z. Fan, W.K. Wang, J. Mater.echnol. 207 (2008) 107111.e, S.K. Pande, P. Premkumar, Indian Foundry J. (1979) 2540.lister, Fundamentals of Materials Science and Engineering, Depart-Metallurgical Engineering, the University of Utah, 5th edition,146..M. Stefanescu, L. Chuzhoy, M.A. Pershing, G.L. Biltgen, AFS Trans. 974223.samy, A. Venugopalan, AFS Trans. 98 (1990) 395400..K. Loper, AFS Trans. 96 (1988) 811822.sson, M. Wessen, A. Gonzalez, in: V. Voller, L. Katgerman,onka (Eds.), Modeling of Structure and Hardness in NodularCastings at Different Silicon Content, Proceeding of Modeling

ing; Welding and Advanced Solidication Process VI, 1993, pp.

w, W.F. Goodrich, AFS Gray Iron Research Committee 5-H, Cast Facts.A. Louvo, T. Rantala, The effect of alloying and cooling rate on thecture and mechanical properties of low-alloy gray iron, 57th World

Congress, September 2328, 1990.

Effect of cooling rate on microstructure and mechanical properties of gray cast ironIntroductionExperimental procedureResults and discussionDendrite characteristics (DAS and SDAS)Ferritecementite layersHardness evaluations

ConclusionAcknowledgmentReferences