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Mechanical Performance ofAustempered Ductile Iron

David K. Matlock and George Krauss DU. 21

.... , .,.... ..

ARL-CR-1 17 April 1994

Prepared byAdvanced Steel Processing and

Products Research CenterDepartment of Metallurgical and Materials Engineering

Colorado School of Mines, Golden, CO 80401

under contractEEC9147146

(National Science Foundation) DTI G Q U ECTED 2

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Mechanical Performance of Austempered Ductile Iron Contract No.EEC9147146

S. AUTHOR(S) ((National ScienceFoundat i,)n

David K. Matlock and George Krauss

7. PERFORMING ORGANIZATION NAME(S) AND ADORESS(ES) 6. PERFORMING ORGANIZATION

Advanced Steel Processing and Products Research REPORT NUMBER

CenterDept. of Metallurgical and Materials Engineering

Colorado School of Mines, Golden, CO 804019. SPONSORINGjMONITORING AGENCY NAME(S) AND ADORESS(ES) 10. SPONSORING,•ONITORING

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13. ABSTRACT (MAaxtnnum 2X wr)

Plates of Austempered Ductile Iron (ADI) containing, in mass pct, 3.7 C, 2.7Si, 0.97 Ni and 0.27 Mn were heat treated to ASTM 897 Grade 1 and 3 tensileproperties and subjected to tensile testing at temperatures between -80 and120 0C. Room temperature yield and ultimate tensile strengths metspecifications but values of elongation were lower than expected. The retained

austenite contents contributed to lowered yield strengths during lowtemperature testing and increased ultimate tensile strengths and ductilitiesduring high temperature testing. These changes in properties were related tothe effects of temperature on the strain-induced transformation of austeniteto martensite. The lower than expected ductility of the ADI specimens wasrelated to microporosity, differences in graphite nodule distributions,differences in strain hardening related to austenite stability, and the

ductile-to-brittle fracture transition of the matrix ferrite with decreasing

temperature.

14. SUBJECT TERMS 1S. NUMBER OF PAGES

Ductile iron, Austempering, Mechanical properties, 35

Austenite transformation 16. PRICE CODE

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1.0. INTRODUCTION

Austempered ductile irons (ADI) are alloyed nodular cast irons whichafter solidification are subjected to austenitizing and isothermaltransformation (austempering) heat treatments (1,2). During isothermalholding, austenite first transforms to acicular or bainitic ferrite and carbonis rejected into austenite adjacent to the ferrite. The high silicon of thecast iron prevents cementite formation, and the enriched austenite, sometimesreferred to as reacted austenite (3), is quite stable and coexists with theacicular ferrite to provide good combinations of strength and ductility (4).Adjustments in austenitizing and austempering temperatures are used to produceADI grades of various strength and ductility levels (5). The gradedesignations, minimums in strength and ductility, and anticipated hardnessranges are summarized in Table 1. These data show that depending on heattreatment, tensile sterengths between 125 ksi and 220 ksi can be obcained.Extended heating in the austempering range could cause the retained austeniteto decompose to ferrite-carbide microstructures with reduced toughness (5).

TABLE 1 - Summary of Tensile Properties for Standard ADI Grades as Specifiedin ASTM 897-90 (5).

Grade Tensile Yield Elongation* TypicalStrength* Strength* MX) Hardness

(ksi) (ksi) (BHN)

1 125 80 10 269-321

2 150 100 7 302-363

3 175 125 4 341-444

4 200 155 1 388-477

5 230 185 N/A 444-555

* Minimum Values

Recent studies of intercritically annealed and isothermally transformedlow-carbon steels show that retained austenite plays an important role inmechanical behavior (6-9). Depending on test temperature, the austenite maytransform at low strains and significantly affect yielding behavior, or theaustenite may be stable to high strains and enhance ultimate strength anddefer necking instability.

The effect of test temperature on the mechanical behavior of theferrite-austenite-nodular graphite microstructures of ADI has receivedrelatively little attention. Therefore, the purpose of this investigation wasto evaluate mechanical performance of ADI by tensile testing over a range of..........temperatures, from cryogenic to well above room temperature. The selectedrange of temperatures represents conditions to which ADI tank components mightbe subjected in climates ranging from desert to arctic.

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2.0 EXPERIMENTAL PROCEDURE

The research program involved three specific phases identified asfollows:

Phase I Microstructural and hardness analysis of as-cast plates andlaboratory heat treated coupons.

Phase II Mechanical property study on laboratory heat treatedsamples.

Phase III Mechanical property study on commercially heat treated Grade1 and Grade 3 samples.

Experimental castings were prepared by Wagner Casting Company, Decator,Illinois, as either 0.5 inch (12.7mm) or 1.0 inch (25.4 mm) thick plates withthe following composition (in wt. pct.): 3.7 C, 2.7 Si, 0.97 Ni, 0.27 Mn,0.057 Mg, 0.003 Mo, 0.87 Cu, 0.009 P, 0.009 S, and 0.03 Cr. Two 8 x 8 inchplates of each thickness were received in the as-cast condition for Phase Iand Phase II studies. The material for Phase III was received in commerciallyheat treated conditions.

2.1 Phase I

The as-received microstructures of each thickness plate were evaluatedwith standard light metallographic techniques on samples etched in nital. Toevaluate the effect of aging time on hardness, cube samples, 1 inch square,were cut from one of the 1 inch thick plates and heat treated with thefollowing procedure: austenitize at 900 0C for 120 min.; quench into a 3700Csalt bath and age for 15, 30, 45, 60, 90, and 120 min. followed by an aircool.

2.2 Phase II

The effects of strain rate and test temperature on the tensileproperties of laboratory heat treated samples were evaluated on samples fromthe 0.5 inch. thick as-cast plates. The two plates were cut into eight equalsections, each 4 inch x 4 inch square, and six of the sections were heattreated with the following procedure: pretreatment of 90 min. at 6350Cfollowed by a furnace cool; austenitize at 9000C for 120 min.; quench into a3451C salt bath for 90 min. followed by an air cool. Coupons (0.5 x 0.5 x 4.0inches) were cut for tensile samples and prior to machining the hardness wasmeasured on each coupon; the measured values for all coupons were between 32HRC and 38 HRC. Round tensile samples with a 1.2 inch long by 0.25 inchdiameter gage section, were machined from the heat treated coupons. The gagesections were ground to an 8 p-inch finish.

Tensile tests were performed on a screw-driven testing machine at -80,-30, 23, 70, and 120 °C and a constant crosshead speed of 0.02 in/mmn. The

2

test system was equipped with a special test frame which allowed the samplesto be submerged in heating or cooling fluids (7). For tensile testing at -80and -300C, temperature was maintained with a controlled refrigerated alcoholbath. The 23 0 C tests were performed in air and the elevated temperature testswere performed in a constant temperature oil bath. Strain was directlymeasured with a submersible extensometer attached to the tensile samples andload-strain tensile data were recorded on a computer-based data acquisitionsystem. Selected tests at 230C were also performed at 0.2 in/min. At leastthree samples were tested at each test condition. The microstructures wereevaluated in the as-polished condition on as-received samples and sectionsthrough the tensile fracture surfaces. The graphite nodule size distributionsand average sizes were determined from polished samples with a Leco imageanalyzer.

2.3 Phase III

Four 8 inch x 8 inch square plates were received commercially heattreated to either Grade 1 properties with an average hardness of 33 HRC orGrade 3 properties with an average hardness of 42 HRC as specified by ASTM897-90 (5). For each heat treated condition, one plate was 0.5 inch thick andone was 1.0 inch thick. Ten~ile tests were performed with the same proceduresoutlined for Phase II above.

As part of Phase III, retained austenite measurements were obtained onall samples. An approximate method, based on x-ray diffraction measurements,as calibrated against the volume fraction of a "known" samples in which theaustenite volume percent was obtained from Mossbauer measurements, wasutilized. The specific procedures were as follows: obtain as a calibrationsample a laboratory heat treated coupon with a high volume fraction ofretained austenite; measure the retained austenite content on the calibrationsample with Mossbauer spectroscopy; for the calibration sample and each testsample obtain the x-ray diffraction pattern for a scan from approximately 26of 600 to 800 and determine the peak height intensities for the (200) ferritepeaks (Ia) and the (220) austenite peaks (17); for each test sample determinethe apparent volume fraction of austenite, fy-app, defined as Ii/(Ia + IL); forthe calibration sample determine the ratio of the actual austenite volumefraction (as obtained from Mossbauer measurements) to f 7 -app and define thisratio as a calibration factor f; finally determine the actual volumefraction, f., defined as f x f7-app' It was estimated that this technique willpredict an austenite volume fraction within about 10% of the quoted level(e.g. f 7 = 20% ± 2%).

To evaluate the effects of strain on austenite transformation duringdeformation at room temperature, samples of the 0.5 inch thick plates of boththe Grade i and Grade 3 materials were deformed by rolling on a laboratoryrolling mill.

3

3.0 RESULTS

3.1 Phase I

Light micrographs of the as-cast microstructures are shown in Fig. 1.Figures la and lb present two magnifications of the 0.5 inch thick plate andFigs. lc and id present corresponding results for the 1 inch plate. The as-cast microstructures are independent of plate thickness and consist ofspherical graphite nodules surrounded by ferrite in a pearlitic matrix. Theeffects of time during austempering at 370 0 C on the heat treatedmicrostructures for samples austempered for 15, 45, 60, and 120 minutes areshown in Fig. 2 and on hardness are shown in Fig. 3. The heat treatedmicrostructures are essentially independent of time and consist of graphitenodules in a matrix of acicular ferrite and austenite. This matrixmicrostructure is sometimes referred to as "ausferrite" (2). Figure 3 showsthat the hardness is high for the 15 minute austempered sample and isessentially constant for all other tempering times. Also shown in Fig. 3 isthe effect of austempering time on samples of an 1.5 pct Ni-0.3 pct Mo alloyheat treated at 900 0C (10). A similar high hardness for short times andhardnesses which are essentially independent of time for longer times wereobtained for both alloys.

3.2 Phase II

The laboratory heat treated samples exhibited smooth tensile stress-strain curves with minimal variability in measured flow stresses but withsignificant variability in total ductility. As an example, Fig. 4 presentsfour stress-strain curves for samples tested at 1201C and 0.02 in/min. Thetotal ductility varied between 1.9 and 20%.

The effects of test temperature on the tensile stress-strain behaviorfor samples deformed at 0.02 in/min are shown in Fig. 5. Results for thesamples with the highest ductility at a given test temperature have beenselected. In general, with a decrease in temperature, the peak ductilitydecreased and the strength increased. The results of the tensile testsperformed in Phase II are summarized in Table 2 which includes the yieldstrengths at an offset strain of 0.2%, ultimate tensile strengths, tensileductilities, reduction in areas at fracture, and the average samplehardnesses. For these samples at least 5 hardness tests were obtained withinthe grip section of each tensile sample; the typical total variation inhardness within one sample was approximately 3 HRC units.

Selected results of the Phase II metallography study on deformed tensilesamples are presented in Figs. 6 and 7. Figure 6 includes micrographs whichshow cross sections of tested tensile samples. The micrographs were obtainedat a location adjacent to the fracture surfaces which are evident at the topof each micrograph. The microstructure consists of graphite nodules,microporosity, and microcracks. The micrographs illustrate the range ingraphite nodule distributions observed in this study. For samples whichexhibited low ductilities, the microcracks are associated with themicroporosity. However, for samples which exhibited high ductilities,

4

microcracks also nucleated at graphite nodules.

In Fig. 7, quantitative metallographic analysis of the graphite nodulesize distributions for the four micrographs in Fig. 6 are presented. In eachbar chart the dashed line indicates the average nodule size distribution forall of the samples. For the micrographs shown here, the sample shown in Fig.7b (and Fig. 6b) exhibits a size distribution which is similar to the average.In contrast, Fig. 7c (and Fig. 6c) shows a sample with a higher density oflarge graphite particles while the sample in Fig. 7d (and Fig. 6d) shows ahigher density of fine particles.

3.3 Phase III

Tensile properties of the commercially heat treated samples tested at0.02 in/min are summarized in Tables 3 to 6 for the Grade 1 (33 HRC) and Grade3 (42 HRC) materials. Each table includes data for one heat treat grade andplate thickness. Data include yield strength, ultimate tensile strength,total tensile elongation, and reduction in area at fracture. Representativetensile curves for the Grade 1 and Grade 3 materials are presented in Figures8 to 11. In each figure stress-strain curves for the samples which exhibitedthe maximum ductility at each test temperature in the temperature rangp of -801C to 1201C are presented. Also, each figure includes a presentation of thecomplete stress strain curves in part "a" and in part "b" a plot on anexpanded strain scale to illustrate the effects of temperature on the onset ofyielding. All samples exhibited continuous yielding behavior. As shown inFigs. 8 and 9 for the Grade 1 material, the deformation behavior isessentially independent of plate thickness but depends on test temperature.At -80 0 C the Grade I material exhibits a low yield strength and a high initialstrain hardening rate. With an increase in test temperature, the yield stressincreases and the initial strain hardening rate decreases. In contrast, forthe Grade 3 material the deformation behavior is essentially independent ofplate thickness and test temperature.

The effects of test temperature on tensile properties are summarized inFigs. 12 and 13 in which the yield stresses and ultimate tensile strengths foreach grade type and plate thickness are plotted versus test temperature.Figures 12a and 12b show that for the Grade 1 material the yield stressincreases with test temperature while the ultimate tensile strengths areessentially independent of test temperature. In contrast to the Grade 1material, Figures 13a and 13b show that for the Grade 3 material there is noapparent temperature dependence of either the yield stress or ultimate tensilestrengths.

3.4 Analysis of Retained Austenite

Retained austenite measurements were made on the as heat treatedmaterials for each experimental phase and as a function of imposed rollingstrain for samples of the Grade 1 and Grade 3 materials in Phase III. Theretained austenite measurements on the heat treated ;amples are summarized inTable 7. In Phase I for the samples austempered at 3700C the retained

austenite volume fractions were essentially constant in the range of 20 to25%. The material austempered at 345°C in Phase II exhibited approximately38% austenite while the Grade I and Grade 3 materials of Phase III exhibitedvolume fractions of 27 and 19% respectively. Also shown in Table 7 is theretained austenite measured on a sample removed from a tank track section.

The effects of imposed rolling strain on strain-induced transformationof austenite in the Grade 1 and Grade 3 materials of Phase III are shown inFigure 14. For both materials the volume fraction of austenite decreased withan increase in strain. Also, at high strains both materials exhibitedessentially the same retained austenite content of approximately 6% forsamples strained 19% by rolling. This deformation-induced transformation ofaustenite documented in the rolling experiments is expected.

6

4.0 DISCUSSION

Figure 15 summarizes all combinations of ultimate tensile strengths andelongations for ADI specimens tested in the Phase II and Phase III experimentsof this investigation. The data are compared to a band of expected ultimatetensile strength-elongation combinations for ADI published by Gundlach andJanowak (1). The lower boundary of the band corresponds to minimum values ofroom temperature properties tabulated for ADI specimens in the ADI ASTMspecification and summarized in Table 1 (4). While the Grade 1 and Grade 3ultimate strengths measured in this investigation generally meet therequirements of the ASTM specification, the elongations of most specimens arebelow the expected values.

There may be a number of explanations for the lower than expectedductilities of the ADI specimens. Documented variations in nodule sizedistributions and microporosity are possible causes of fracture initiation andreduced elongation. Segregation at intercell boundaries, which leads to largevolumes of unreacted austenite and to reduced ductility, does not appear to bea factor in the specimens examined in this study. Another factor which mightaccount for reduced ductility is the effect of low-temperature testing asdescribed below.

Apart from ductility, the flow strengths and strain hardening behaviorof the ADI specimens are significantly affected by test temperature. Inspecimens with high retained austenite contents, yield strength decreases withdecreasing test temperature in contrast to the behavior of specimens withstable microstructures. The reduced yield strengths are associated with thestrain-induced austenite transformation to martensite, a process that, becauseof the associated volume increase, increases the effective strain measuredduring yielding (11). However, as shown in Figure 8, the strain-inducedmartensite causes rapid strain hardening and increased strain hardening at lowplastic strains. The latter behavior is most pronounced in the Grade Ispecimens with high retained austenite. In Grade 3 specimens with lowerretained austenite, yielding behavior is effectively insensitive to testingtemperature, Figure 13.

At higher testing temperatures, the mechanical stability of the retainedaustenite increases, and there is little effect of austenite transformation onyield behavior. However, with increasing strain the austenite eventuallytransforms, and if the strain-induced transformation occurs around the pointof necking instability, the enhanced strain hardening effectively defersnecking and increases ductility (6-9). The latter effect appears to beoperating in the specimens tested above room temperature where the highestelongations measured in this investigation were observed.

In addition to a change in strain hardening behavior, the fracture modein the ferrite between graphite nodules changed with test temperature fromvoid coalescence at high temperatures to cleavage at temperatures at orbelow -301C. To illustrate this point, Fig. 16 presents SEM photographs ofthe tensile fracture surfaces of Phase II samples tested at 1200 C (Fig. 16a)and -30 0 C (Fig. 16c). Also shown in Figs. 16b and 16d are the correspondingcross sections of the fracture surfaces (similar to those presented in Fig. 6)

7

for the 120'C and -30 0C samples respectively. The fracture of the 1201Csample is associated with well defined void coalescence (Fig. 16a) and necking

(Fig. 16b). In contrast, fracture of the -30'C sample exhibits cleavage in

the matrix (Fig. 16c) and a relatively flat fracture surface with limitednecking (Fig. 16d). Since Fig. 15 includes all of the data of this study,while the ASTM results are for room temperature tests, the transition to

cleavage fracture at low temperatures may contribute to the decreasedductilities observed in the samples of this study in comparison to the minimumvalues quoted by ASTM.

5.0 CONCLUSIONS

1. The temperature dependence of the strain-induced transformation ofretained austenite to martensite in ADI specimens plays animportant role in establishing deformation behavior.

2. At low testing temperatures, the strain-induced transformation ofretained austenite occurs at low strains, reduces yield strengths,and increases strain hardening rates at low strains.

3. At high testing temperatures, the strain-induced transformation ofretained austenite occurs at high strains and the associated

increases in strain hardening increase ductility.

4. There is a transition in fracture mode of the ADI matrix fromductile to brittle as test temperature is decreased below room

temperature.

4. The elongations measured for ADI specimens except for specimens

tested above room temperature, were generally lower than expected.The lower ductilities were related to microporosity, differencesin graphite nodule distributions, and a transition in strainhardening and fracture behavior at low testing temperatures.Further work is necessary to develop detailed correlations ofmicrostructure with fracture phenomena of ADI.

6.0 ACKNOWLEDGEMENTS

The authors acknowledge the discussions and assistance of Dr. Mani ofWagner Casting Company, Decator, Illinois. The assistance of Dr. Dong Won Ohwith the testing is greatly appreciated.

7.0 REFERENCES

1. R.B. Gundlach and J.F. Janowak, "A Review of Austempered Ductile IronMetallurgy", in First International Conference on Austempered DuctileIron, American Society for Metals, Metals Park, OH, 1984,p. 1-12.

2. B.V. Kovacs, Sr., "Austempered Ductile Iron - Fact and Fiction", ModernCastings, vol. 80, no. 3, March, 1990, pp. 38-41.

3. B.V. Kovacs, Sr., "A Simple Technique to Identify Various Phases inAustempered Ductile Iron," Modern Castings, vol. 77, no. 6, 1987, pp.34-35.

4. D.J. Moore, T.N. Rouns, and K.B. Rundman, "The Relationship BetweenMicrostructure and Tensile Properties in Austempered Ductile Irons", AFSTransactions, vol. 95, 1987, pp. 765-774.

5. "Austempered Ductile Iron Castings," ASTM Specification No. A 897-90.

6. Y. Sakuma, D.K. Matlock, and G. Krauss, "Intercritically Annealed andIsothermally Transformed 0.15 pct C Steels Containing 1.2 pct Si-l.5 pctMn and 4 pct Ni: Part I. Transformation Microstructure, and RoomTemperature Mechanical Properties", Metallurgical Transactions A, vol.23A, 1992, pp. 1221-1232.

7. Y. Sakuma, D.K. Matlock, and C Krauss, "Intercritically Annealed andIsothermally Transformed 0.15 pct C Steels Containing 1.2 pct Si-l.5 pctMn and 4 pct Ni: Part II. Effect of Testing Temperature on Stress-Strain Behavior and Deformation-Induced Austenite Transformation",Metallurgical Transactions A, vol. 23A, 1992, pp. 1233-1241.

8. W.C. Jeong, D.K. Matlock, and G. Krauss, Materials Science andEngineering 1993, "Observation of Deformation and TransformationBehavior of Retained Austenite in a 0.14 pct C - 1.2 pct Si - 1.5 pct .AnSteel with Ferrite-Bainite-Austenite Structure", Materials Science andEngineering, vol. A165, 1993, pp. 1-8.

9. W.C. Jeong, D.K. Matlock, and G. Krauss, "Effects of Tensile TestingTemperature on Deformation and Transformation Behavior of RetainedAustenite in a 0.14 pct C - 1.2 pct Si - 1.5 pct Mn Steel with Ferrite-Bainite-Austenite Structure", Materials Science and Engineering, vol.A165, 1993, pp. 9-18.

10. J.F. Janowak and P.A. Morton, "A Guide to Mechanical Properties Possibleby Austempering 1.5%No-0.3%Mo Ductile Iron", Report No. XGI-84-03, AI"iaxMaterials Research Center, Ann Arbor, Michigan, 1984.

11. K.J. Grassl, S.W. Thompson, D.K. Matlock, and G. Krauss, "Toughness ofMedium-Carbon Forging Steels with Direct Cooled BainiticMicrostructures", 31st Mechanical Working and Steel ProcessingConference Proceedings, vol. 27, Chicago, Illinois, October 22-25, 1989,ISS-AIME, Warrendale, PA, 1990, pp. 137-143.

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'A'ab~ t. 4 u. s~tc. *t * S

est a'sQ r*4.*~*V. -- IW '.u

A .~ k, )* -*

WN 'A 0 u4 yu

ZAP'. (A -4~¶ad.4p a -., w1 - Z

Ar-0 -sit z@' t

r. x*,.e 4,t*4 *f a

*W 0.

~~~~~~~~~~~ i•671a 4, 'u A~.. O.

*q. S. 41Scu0St be *4 .* t. &~ *

-INI

44 *

-'~-,'~ 'u

E E;

L IT, -. 4

. -4

i~s$~.~ J'

4-.'N P0

4r0

4ft- a1 3

40

a:35

COCOwz

< 30-

I

o Phase I Samples (370 0C Austemper)* 1.5%Ni-0.3%Mo (Janowak and Morton)

250 50 100 150

AUSTEMPERING TIME (MIN)

Figure 3: A summary of the effect of austempering time on the hardness ofPhase I samples austempered at 3701C. Also shown are the resultsof Janowak and Morton (10) on 1.5%Ni-0.3ZMo alloy.

18

200

CO)AD121

"CO . AD129150

O AD138w

(9100zWU Phase II

Z 50 1200C0z 0.02 in/minULJ

0

0 5 10 15 20

ENGINEERING STRAIN(%)

Figure 4: Tensile stress-strain curves for four Phase II samples ofaustenitic ductile iron tested at 120 0C at a crosshead speed of0.02 in/min.

19

200

0O .80oCS• ~1200C ,

0O 150CO,LLJ • • • - 70°C

,23OC0O -30oC

(.D 100z

Z 500. Phase IIzZ 0.02 in/min

0

0 5 10 15 20

ENGINEERING STRAIN(%)

Figure 5: A comparison of the effect of test temperature on the stress-strain curves for Phase II samples which exhibited the maximumductility at each test temperature.

20

go ** a , c

04-146' -4 En

dogUo too** b~

0 0.

-~~~~3 *. .OCO* .

&.C 0 * ,

00

*. * * 0 - S4j.. :

00 41 0 Q)

tip ~ ~ 4604

wo - cn m co-

400

40*0*% * * 0

.'* ~-(A '-4

- 0 *4.e0 410 41r - 4b~ 0.

C~ ~ ~~ * @ *4* "

4b 0 -0. *, !m - -r-- 4qw i 0 .060* S S we 45. ~S~ 0.

*~~~~j *.***...0? 09 0 oI~ * %6 CL Go.' C

* ~~~ 0 C4 . 4 -

00F ese 0 0 o

og 00' ~0-4 *~ 0

goo* 0.

CTJ OF

* ~ .. S*.

50 i , , , , , I 50 , , , ,

Phase II Phase II40 ADI13 40 AD1384 40

S30 30

Z zLU LU

M D

020 020

10 10

0 0-0 20 40 60 80 100 0 20 40 60 80 100

GRAPHITE SIZE (Qm) GRAPHITE SIZE (Am)

a b

50 , 50 , , , ,

Phase II Phase II

40 ADI22 40 AD134

o30 o30z z

020 0 20

LL, , .LL10 10

0 .. 00 20 40 60 80 100 0 20 40 60 80 100

GRAPHITE SIZE (Am) GRAPHITE SIZE (Am)

C d

Figure 7: Graphite nodule size distributions for the Phase II mticrographsshown in Figure 6. The average distribution from an analysis of20 samples is also shown by the dashed line in each graph. (a)Sample ADII3, 1201C, 134ksi UTS, (b) Sample ADI38, 120'C, 152ksiUTS, (c) Sample AD122, -80°C, 109ksi UTS, (d) Sample AD134,80'C, 163 ksi. Light micrographs, unetched.

22

200

CO,ýe 150 1302C 230CU)• 1 200CCO ,

I.-

a 1 00 ./800C

z

W Phase IIIz Grade 1o 50z Thickness: 0.5 inch

0.02 in/min

0 5 10 15 20ENGINEERING STRAIN(%) a

200

ýe 150.3000 2300Cl,

o 100

z

z Phase IIIz Grade. 1W Thickness: 0.5 inch

0.02 in/min

0 . . . I . . I . . . . 1 . i0 1 2 3 4 5

ENGINEERING STRAIN(%) b

Figure 8: The effect of test temperature on tensile properties: Phase III,Grade 1, 0.5 inch thick plate. (a) complete stress strain curvesfor selected samples which exhibited the maximum ductility at eachtest temperature. (b) expanded low strain behavior of samplesshown in part "a".

23

200

C', -800C150 300C

C13 1200CLU

=: . 23oCp- 70°C

o100_z

a:'" Phase IIIz Grade 13 50 Thickness: 1.0 inchzW 0.02 in/min

0 5 10 15 20

ENGINEERING STRAIN(%) a

2 00 . . . , . . , . . . , . .

S"80°C -30°C,•150 1200C • <

I-t

03 70oC 230C

a 100

z(' 1 0-80°C

,, -30oCUz Phase IIIO 50 Grade 1z,, Thickness: 1.0 inch'

0.02 in/0nin

0 1 2 3 4 5ENGINEERING STRAIN(%) b

Figure 9: The effect of test temperature on tensile properties: Phase III,Grade 1, 1.0 inch thick plate. (a) complete stress strain curvesfor selected samples which exhibited the maximum ductility at eachtest temperature. (b) expanded low strain behavior of samplesshown in part "all.

24

200-80C 0230-700C1200C

COX, 150

LUn-

I--CO

a 100z

w Phase IIIz Grade 3

0 50 Thickness: 0.5 inchzW 0.02 in/min

0

0 5 10 15 20

ENGINEERING STRAIN(%) a

200200

e -.800C12C

S150UO

CIO

0 100z

lu Phase III0 Grade 3z Thickness: 0.5 inchW 0.02 in/min

0 1 2 3 4 5

ENGINEERING STRAIN(%) b

Figure 10: The effect of test temperature on tensile properties: Phase III,Grade 3, 1.5 inch thick plate. (a) complete stress strain curvesfor selected samples which exhibited the maximum ductility at eachtest temperature. (b) expanded low strain behavior of samplesshown in part "a". 25

200 .0o ,C

230C~800C

C, 12000- 150

CO

0 100z

wwz Phase IIIO 50 Grade 3zw Thickness: 1.0 inch

0.02 in/min

0 | I .I j

0 5 10 15 20

ENGINEERING STRAIN(%) a

200

230° 0C"23

, 150 7 00CC 1200C

I-o 100z

z Phase III

O 50 Grade 3Lu Thickness: 1.0 inch

0.02 in/min

0

0 1 2 3 4 5

ENGINEERING STRAIN(%) b

Figure 11: The effect of test temperature on tensile properties: Phase III,Grade 3, 1.0 inch thick plate. (a) complete stress strain curvesfor selected samples which exhibited the maximum ductility at eachtest temperature. (b) expanded low strain behavior of samplesshown in part "a". 26

160

CO,~120

ým 100C-

80 c3 Phase III c ILGrade 10YILThickness: 0.5 inch. - UTS

60 . .IIII .. . II . a-100 -50 0 50 100 150

TEMPERATURE (00)

160

S120

CO 0CO,

S100C,,

80 rhsII

Thickness: 1.0 inch60 - 1. . I I . . . ' I.. b

-100 -50 0 50 100 150TEMPERATURE (00)

Figure 12: The effect of test temperature on thie yield stress and ultimatetensile strength for all. of the Phase III, Grade 1 tensile samples(a) 0.5 inch thick plate. (b) 1.0 inch thick plate.

27

200

180U U

COS 160

CO

030LU 0r"140 -_IF

120 Phase IIIGrade 3 o YIELDThicknes's: 0.5 inch m UTS

1 0 0 . . . . I . .I . . . . I . . I . . a

-100 -50 0 50 100 150

TEMPERATURE (0C)

200 ,

I180

03 II

160__ U

wn- 140

120 a Phase III 0

Grade 3 o YIELD

Thickness: 1.0 inch n UTS

100 b-100 -50 0 50 100 150

TEMPERATURE (0C)

Figure 13: The effect of test temperature on the yield stress and ultimatetensile strength for all of the Phase III, Grade 3 tensile samples(a) 0.5 inch thick plate. (b) 1.0 inch thick plate.

28

30

O Phase III

- 25 o Grade 10 * Grade 3W

S20zI-Co,. 15

0wz 10 U

W EQli

"C 5

0 j , , ,

0 5 10 15 20ROLLING STRAIN (%)

Figure 14: The effect of rolling strain on the retained austenite volumefraction from Phase III, Grade 1 and Grade 3 samples.

29

200 AUSTEMPERED 1400• A

0"•5 180 1

101200S160-, [

140--

8000120 8a

L11008 -

w3 Phase II 600 wI- 80-I

S Phase III (Grade 1)

60 A Phase III (Grade 3) 400

400 , 1 ,0 5 10 15 20

% ELONGATION

Figure 15: Summary of ultimate tensile strengths and ductilities for all ofthe Phase II and Phase III tensile samples. Also shown are theresults, in the highlighted band, from a series of ductile ironsas reported in the literature (1).

30

ft.

.44Ito S

0 ..

0104-40 . , 0 dp a o 0C(

'0 go0 40

-Z 14 0

0 0 4 -C o * z

.04w** '-

0 0.. .40

040.

O'j'

-6* -00 E540# 0*9 -0 4-4 -

40-40

-0 0

AN ftCj W 'S1A. toC 0

~ It' M~~~'S~~c M~*% . ~G O 5

-" E-~J - L4.

. ~ 44 44

(n14

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No. ofCopies To

1 Office of the Under Secretary of Defense for Research and Engineering, The Pentagon, Washington, D.C. 20301

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2 ATTN: DTIC-FDAC

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Ductile Iron Society, North Olmstead, OP, 44070,1 ATTN: Mr. Jack Hall

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34