Effects of Alloying Elements (Mo, Ni, and Cu) on the Austemperability of GGG-60 Ductile Cast Iron

metals

Article Effects of Alloying Elements (Mo, Ni, and Cu) on the Austemperability of GGG-60 Ductile Cast Iron

Erkan Konca 1,* ID , Kazım Tur 1 and Erkin Koç 2 1 Department of Metallurgical and Materials Engineering, Atılım University, Ankara 06830, Turkey; [email protected] 2 Ay Döküm Machine Industry and Trade Inc., Ankara 06930, Turkey; [email protected] * Correspondence: [email protected]; Tel.: +90-312-586-8785

Received: 22 June 2017; Accepted: 15 August 2017; Published: 22 August 2017

Abstract: The interest in austempered ductile irons (ADI) is continuously increasing due to their various advantageous properties over conventional ductile irons and some steels. This study aimed to determine the roles of alloying elements Ni, Cu, and Mo, on the austemperability of GGG-60 ductile cast iron. Two different sets of GGG-60 (EN-GJS-600-3) samples, one set alloyed with Ni and Cu and the other set alloyed with Mo, Ni, and Cu, were subjected to austempering treatments at 290 ◦C, 320 ◦C, and 350 ◦C. A custom design heat treatment setup, consisting of two units with the top unit (furnace) serving for austenitizing and the 200 L capacity bottom unit (stirred NaNO2-KNO3 salt bath) serving for isothermal treatment, was used for the experiments. It was found that austempering treatment at 290 ◦C increased the hardness of the Ni-Cu alloyed GGG-60 sample by about 44% without causing a loss in its ductility. In the case of the Mo-Ni-Cu alloyed sample, the increase in hardness due to austempering reached to almost 80% at the same temperature while some ductility was lost. Here, the microstructural investigation and mechanical testing results of the austempered samples are presented and the role of alloying elements (Mo, Ni, and Cu) on the austemperability of GGG-60 is discussed.

Keywords: ADI; austempering; molybdenum; nickel; copper; alloying; GGG-60; cast iron

1. Introduction Austempering is an attractive thermal process as it can turn a cast iron of appropriate composition into a new engineering material with signiﬁcantly increased strength and usable ductility [1]. Wear resistance and fatigue properties of austempered ductile irons (ADIs) are also superior so that they can replace wrought alloys in certain engineering applications [2,3]. Similar to austempering of steels, austempering of cast irons also consists of three steps: (i) austenitizing of the cast iron matrix, (ii) rapid cooling to the isothermal treatment temperature, and (iii) isothermal treatment usually in the range of 250 ◦C–450 ◦C[1–5]. However, differing than that of steels, austempering of cast iron does not aim to be a complete bainitic transformation. During the austempering of cast iron, part of the austenite matrix ﬁrst transforms into ferrite and therefore the remaining part of the austenite becomes carbon-enriched; this is called a high carbon austenite (γhc). This resulting microstructure, known as ausferrite, is responsible for the outstanding mechanical properties of ADIs [2]. If the material is kept at the austempering temperature for a longer time, then the carbon-rich austenite (γhc) decomposes into ferrite and cementite to complete the bainitic transformation, and the mechanical properties start to deteriorate [6,7]. The so-called “processing window” refers to the range of austempering conditions (temperature and duration) where the ductile cast iron matrix has completed its transformation into an ausferritic microstructure (stage 1 reaction) but has not yet started to transform into a bainitic microstructure (stage 2 reaction) during isothermal treatment [4,8,9].

Metals 2017, 7, 320; doi:10.3390/met7080320 www.mdpi.com/journal/metals Metals 2017, 7, 320 2 of 9

The purpose of adding alloying elements into ADI is first to ensure that the austenite-to-pearlite transformation is avoided during cooling to the isothermal treatment temperature, and then to affect the austenite decomposition kinetics and mechanisms during the isothermal treatment to obtain the desired ausferritic microstructure mentioned above [10,11]. However, before these alloying elements affect the mentioned solid-solid phase transformations of the ductile cast iron matrix, they first influence the preceding solidification behavior to change the size (i.e., nodule count) and nodularity of graphite [12,13]. Therefore, the alloy design (i.e., which elements to be added and how much of them) of cast iron to be austempered should be made such that the effects of alloying on both the cast structure (graphite nodule count and nodularity) and austempering behavior are optimized together [12]. Nickel, copper, and molybdenum are by far the most widely used alloying elements in both conventional and austempered ductile irons [5,8,14–25]. Ni and Cu are austenite stabilizers with low affinity towards carbon. Mo, on the other hand, is a ferrite stabilizer with strong affinity towards carbon and is very effective in increasing hardenability. Cast irons containing engineered combinations of these alloying elements are expected to exhibit enhanced mechanical properties after suitable austempering treatment. The objective of this work is to contribute to the exploration of the roles of alloying elements, namely Mo, Ni, and Cu, in their combined use on the austempering behavior of conventional ductile cast iron. Rather than working on some impractical experimental alloys, the studied alloy compositions were selected to be within the conventional ductile iron compositions.

2. Materials and Methods Two spheroidal graphite cast iron alloys (Alloy O and Alloy M) conformal to GGG-60 (EN-GJS-600-3) were prepared using an Indemak brand induction furnace with a 150 kg capacity at Ay Döküm Machine Industry and Trade Inc. (Ankara, Turkey) and poured into the molds of rectangular blocks. Then, these blocks were sliced into dimensions of about 25 mm × 25 mm × 200 mm in order to obtain samples for tensile tests after austempering under various conditions. The chemical compositions (in wt %) of these two cast iron alloys are given in Table1. Basically, Alloy O contains Ni (0.37%) and Cu (0.52%) as alloying elements, whereas Alloy M contains 0.21% Mo in addition to Ni (0.21%) and Cu (0.41%). As Alloy M is alloyed with Mo and has reduced Ni content, the comparison of its austempering behavior with those of Alloy O should indicate the role of Mo in austemperability.

Table 1. Chemical compositions (wt %) of the ductile cast iron alloys studied.

Alloy C Si Mn P S Ni Cu Mo Mg Cr Al Ti Fe O 3.64 2.20 0.03 0.039 0.010 0.37 0.52 <0.001 0.05 0.01 0.01 0.004 bal. M 3.76 2.19 0.14 0.041 0.013 0.21 0.41 0.21 0.04 0.01 0.01 0.008

The sample to be austempered needs to be quickly cooled from the austenitizing temperature down to the austempering temperature, such that there will be no time allowed for any phase transformation to take place between these two temperatures. The use of an agitated salt bath is a very effective method for this purpose. In addition, a salt bath provides a suitable medium for isothermal treatment. In this study, a custom designed heat treatment setup was used for the austempering treatments. This setup contains two units, where the top unit (furnace) serves for austenitizing and the bottom unit (salt bath) serves for isothermal treatment. The top unit is placed on a motorized tilting stage that allows quick transfer of the samples to the bottom unit through the guides. The bottom unit is a 200 L capacity, temperature-controlled salt bath ﬁlled with Petrofer AS135 heat treatment salt (NaNO2-KNO3). The salt bath is continuously stirred during operation using a motorized mixer, which ensures both efﬁcient heat removal from the sample at the time of quenching and uniform temperature in the bath during the isothermal treatment. Metals 2017, 7, 320 3 of 9

In this study, in order to focus on the effects of alloying elements on the austempering behavior, the temperatureMetals 2017, 7, 320 and duration of austenitization for all samples were ﬁxed at 850 ◦C and3 of 90 9 min, respectively. Three different austempering temperatures of 350 ◦C, 320 ◦C, and 290 ◦C were used for a respectively. Three different austempering temperatures of 350 °C, 320 °C, and 290 °C were used for constant duration of 90 min. Austempering conditions which are graphically presented in Figure1 a constant duration of 90 min. Austempering conditions which are graphically presented in Figure 1 and listedand listed in Table in Table2 are 2 are selected selected to to be be within within the the “processing“processing window” window” based based on onprevious previous studies studies on on similarsimilar materials materials [1,3 [1,3–6,14–16].–6,14–16]. MetallographicMetallographic examinations examinations were were performed performed on on unetched unetched and and 2% 2% nital nital etched etched polished polished sample sample surfacessurfaces using using a Nikon a Nikon LV 150 LV optical 150 optical microscope microscope (Nikon (Nikon Corporation, Corporation, Miyagi, Miyagi, Japan). Japan). ImageJ ImageJ software (v151k,software U.S. National (v151k, U.S. Institutes National of Institutes Health, Bethesda,of Health, Bethesda, MD, USA) MD, [26 USA)] was [26] used was to used determine to determine the nodule countsthe from nodule the counts unetched from the polished unetched samples. polished Five samples. Brinell Five hardness Brinell hardness measurements measurements (HBW (HBW 2.5/187.5) were2.5/187.5) taken using were an taken EMCO using M4U an EMCO 025 G3M4U universal 025 G3 universal hardness hardness testing testing machine machine (EMCO-TEST (EMCO-TEST GMBH, GMBH, Kuchl, Austria) for each sample. Tensile testing of the samples according to ASTM E8 were Kuchl, Austria) for each sample. Tensile testing of the samples according to ASTM E8 were done using done using Alşa brand tensile testing machine (Alşa Laboratuar Cihazlari, Istanbul, Turkey) at Ay Al¸sabrand tensile testing machine (Al¸saLaboratuar Cihazlari, Istanbul, Turkey) at Ay Döküm in order Döküm in order to obtain yield and tensile strength (i.e., ultimate tensile strength) values of the to obtainsamples yield in MPa and and tensile their strength ductilities (i.e., in percent ultimate elon tensilegation strength)in length (% values EL). Three of the samples samples were in used MPa and theirin ductilities each test condition. in percent elongation in length (% EL). Three samples were used in each test condition.

850°C 90 min. Austenitizing Q

350 - 290°C

Temperature 90 min. A Salt Bath ir c o o l in g

Room Temp. Time FigureFigure 1. 1.Graphical Graphical representation representation of of the the heat heat treatment treatment conditions. conditions.

TableTable 2. 2.Austempering Austempering conditions of of the the samples. samples. Experiment # Temperature (°C) Duration (min) ◦ ExperimentExp. 1 # Temperature 350 ( C) Duration 90 (min) Exp.Exp. 2 1 320 350 90 90 Exp.Exp. 3 2 290 320 90 90 Exp.All samples 3 were austenitized 290 for 90 min at 850 90°C. All samples were austenitized for 90 min at 850 ◦C. 3. Results

3. Results3.1. As-Cast Samples The as-cast microstructures of Alloy O and Alloy M samples are presented in Figure 2. It can be 3.1. As-Castseen that Samples both samples have typical bull’s eye structures but to different extents. Alloy M has a lower 2 graphiteThe as-cast nodule microstructures count (356 versus of Alloy488 nodules O and per Alloy mm M) and samples more ferritic are presented matrix surrounding in Figure2 the. It can nodules. It is known that Mo has an adverse effect on nodule count [13,27]. With a higher count of be seen that both samples have typical bull’s eye structures but to different extents. Alloy M has a graphite nodules (488 nodules per mm2) and a more pearlitic matrix microstructure, the average as- lower graphite nodule count (356 versus 488 nodules per mm2) and more ferritic matrix surrounding cast hardness of Alloy O, measured from a cross-section, was 236 HB, whereas Alloy M had a the nodules.hardness Itof is215 known HB. The that surface Mo has hardness an adverse of the samples, effect on as nodule measured count after [13 0.5,27 mm]. With grinding, a higher were count 2 of graphite243 HB and nodules 202 HB, (488 respectively. nodules per Tensile mm tests) and showed a more that pearlitic the as-cast matrix Alloy microstructure, O had a tensile strength the average as-castof 677 hardness MPa with of 5.7% Alloy EL O, whereas measured Alloy from M has a a cross-section, tensile strength was of 576 236 MPa HB, with whereas 11.3% EL. Alloy M had a hardness of 215 HB. The surface hardness of the samples, as measured after 0.5 mm grinding, were 243 HB and 202 HB, respectively. Tensile tests showed that the as-cast Alloy O had a tensile strength of

677 MPa with 5.7% EL whereas Alloy M has a tensile strength of 576 MPa with 11.3% EL. Metals 2017, 7, 320 4 of 9

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(a) (b) (a) (b)

(c) (d) (c) (d) Figure 2. Optical images of the as-cast microstructures of (a) Alloy O (100×), (b) Alloy O (200×), (c) Figure 2. Optical images of the as-cast microstructures of (a) Alloy O (100×), (b) Alloy O (200×), FigureAlloy M 2. (100×) Optical and images (d) Alloy of the M (200×)as-cast (2% microstructures nital etched). of (a) Alloy O (100×), (b) Alloy O (200×), (c) (c) Alloy M (100×) and (d) Alloy M (200×) (2% nital etched). Alloy M (100×) and (d) Alloy M (200×) (2% nital etched). 3.2. Austempered Samples-Microstructural Examination 3.2. Austempered3.2. Austempered Samples-Microstructural Samples-Microstructural Examination Examination Optical images of the microstructures of Alloy O and Alloy M samples austempered at 350 °C, Optical320 °C,Optical and images 290images °C of are theof thegiven microstructures microstructures in Figure 3. Obviously, ofof AlloyAlloy O O as and and a resultAlloy Alloy ofM M thesamples samples austempering austempered austempered treatment, at 350 at the°C, 350 ◦C, 320 ◦320ferritic-pearliticC, and°C, and 290 290◦C are°Cmatrices are given given of in thein Figure Figure as-cast3 .3. Obviously,samples Obviously, shown asas a in result Figure of of the the2 austemperinghave austempering transformed treatment, treatment, into new the the ferritic-pearliticferritic-pearliticcomplex microstructures matrices matrices of the of with as-castthe as-castmainly samples samples ausferri shown showntic in characteristics. Figure in Figure2 have 2 have transformedAs transformedexpected into [6,11], newinto new complexthe complex microstructures with mainly ausferritic characteristics. As expected [6,11], the microstructuresmicrostructures with became mainly finer ausferritic as the austempering characteristics. temperature As expected was lowered; [6,11], the this microstructures is especially so for became microstructuresAlloy M samples. became finer as the austempering temperature was lowered; this is especially so for ﬁner as the austempering temperature was lowered; this is especially so for Alloy M samples. Alloy M samples.

(a) (d) (a) (d)

Figure 3. Cont.

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(b) (e)

Figure 3. Optical images of the microstructures of Alloy O (a–c) and Alloy M (d–f) samples Figure 3. Optical images of the microstructures of Alloy O (a–c) and Alloy M (d–f) samples austempered austempered at 350 °C (a,d), 320 °C (b,e), and 290 °C (c,f) (1000×, 2% nital etched). at 350 ◦C(a,d), 320 ◦C(b,e), and 290 ◦C(c,f) (1000×, 2% nital etched). 3.3. Austempered Samples-Hardness 3.3. Austempered Samples-Hardness The average hardness values of the Alloy O and Alloy M samples after austempering are given Thein Table average 3. Apparently, hardness the values austempering of the Alloy treatment O and drastically Alloy M increased samples the after hardness austempering of all samples. are given in TableThe3 hardness. Apparently, of Alloy the O austempering samples was measured treatment as drastically299 HB, 322 increasedHB, and 341 the HB hardness after austempering of all samples. The hardnessat 350 °C, of320 Alloy °C, and O 290 samples °C, respectively. was measured When as compared 299 HB, to 322 the HB, as-cast and hardness 341 HB of after 236 austemperingHB, these at 350values◦C, 320 correspond◦C, and to 290 26.5%,◦C, respectively.36.4%, and 44.4% When increase, compared respectively. to the as-cast hardness of 236 HB, these The hardness values of austempered Alloy M samples exhibited even more dramatic increases. values correspond to 26.5%, 36.4%, and 44.4% increase, respectively. The hardness of Alloy M samples was measured as 335 HB, 336 HB, and 389 HB after austempering The hardness values of austempered Alloy M samples exhibited even more dramatic increases. at 350 °C, 320 °C, and 290 °C, respectively. When compared to the as-cast hardness of 215 HB, these The hardnessvalues correspond of Alloy to M 55.8%, samples 56.3%, was and measured 79.9% increase, as 335 respectively. HB, 336 HB, and 389 HB after austempering at 350 ◦C, 320 ◦C, and 290 ◦C, respectively. When compared to the as-cast hardness of 215 HB, these values correspondTable 3. toHardness 55.8%, of 56.3%, the as-cast and and 79.9% austempered increase, samples respectively. as the average of five tests for each. Brinell Hardness Table 3. HardnessSample of the as-cast and austempered samples as the average of five tests for each. Alloy O Alloy M As-cast 236 ± 3.5 215 ± 4.2 Brinell Hardness Exp. 1 Sample 299 ± 6.0 335 ± 5.1 Exp. 2 322Alloy ± 8.4 O Alloy 336 M ± 23.4 Exp. 3 As-cast 341 236 ± 21.4± 3.5 215 ± 3864.2 ± 22.0 Exp. 1 299 ± 6.0 335 ± 5.1 3.4. Austempered Samples-TensileExp. Tests 2 322 ± 8.4 336 ± 23.4 Exp. 3 341 ± 21.4 386 ± 22.0 The tensile test results of the austempered Alloy O and Alloy M samples are given in Table 4. For the Alloy O samples, the tensile strength values were 992 MPa, 1018 MPa, and 1027 MPa after 3.4. Austempered Samples-Tensile Tests The tensile test results of the austempered Alloy O and Alloy M samples are given in Table4. For the Alloy O samples, the tensile strength values were 992 MPa, 1018 MPa, and 1027 MPa after Metals 2017, 7, 320 6 of 9 austempering at 350 °C, 320 °C, and 290 °C, respectively. When compared to the as-cast tensile Metals 2017, 7, 320 6 of 9 strength of 677 MPa, these values correspond to 46.5%, 50.2%, and 51.6% increase, respectively. Noticeably, the improvements in tensile strengths of the samples were not accompanied by decreases inaustempering % EL. On the at 350contrary,◦C, 320 %◦C, EL and values 290 ◦ C,also respectively. slightly improved When compared from 5.7% to thefor as-castthe as-cast tensile sample strength to 5.8%,of 677 6.7%, MPa, and these 6.3% values for the correspond samples austempered to 46.5%, 50.2%, at 350 and °C, 51.6% 320 °C, increase, and 290 respectively. °C, respectively. Noticeably, the improvementsThe increase in in tensile tensile strength strengths values of the of samples the austempered were not accompanied Alloy M samples by decreases were even in %more EL. significant;On the contrary after, %austempering EL values also at 350 slightly °C, 320 improved °C, and from 290 5.7%°C, the for tensile the as-cast strengths sample of to the 5.8%, Alloy 6.7%, M samplesand 6.3% increased for the samples to 1035 austempered MPa, 1065 MPa, at 350 and◦C, 1311 320 ◦MPa,C, and respectively. 290 ◦C, respectively. These values correspond to 79.7%,The 85.1%, increase and in127.8% tensile respective strength increased values of when the austempered compared to Alloy the as-cast M samples tensile were strength even of more 576 MPa.significant; On the after other austempering hand, the % at EL 350 values◦C, 320 of◦ C,the and Alloy 290 M◦C, samples the tensile decreased strengths from of the8.3% Alloy EL for M austemperingsamples increased at 350 to °C 1035 to 3.5% MPa, EL 1065 for austempering MPa, and 1311 at MPa,290 °C. respectively. The increase These in strength values and correspond decrease into ductility 79.7%, 85.1%, of Mo andalloyed 127.8% ADIs respective with decreasing increases austempering when compared temperature to the as-cast was previously tensile strength observed of in576 similar MPa. studies On the as other well hand, [24]. the % EL values of the Alloy M samples decreased from 8.3% EL for austempering at 350 ◦C to 3.5% EL for austempering at 290 ◦C. The increase in strength and decrease Table 4. Tensile test results of the as-cast and austempered samples as the average of three tests for each. in ductility of Mo alloyed ADIs with decreasing austempering temperature was previously observed in similar studies as well [24].Alloy O Alloy M Yield Strength Tensile Yield Strength Tensile Sample % EL % EL Table 4. Tensile(MPa) test resultsStrength of the as-cast (MPa) and austempered samples(MPa) as the averageStrength of three (MPa) tests for each. As-cast 426 ± 5.1 677 ± 7.3 5.7 ± 0.7 356 ± 4.7 576 ± 6.9 11.3 ± 1.0 Exp. 1 707 ± 12.6 Alloy 992 ± O14.1 5.8 ± 0.8 863 ± 16.5 Alloy 1035 M± 24.2 8.3 ± 1.3 Exp.Sample 2 724 Yield± 16.5 1018Tensile ± 17.9 6.7 ± 1.0 937Yield ± 17.3 1065Tensile ± 19.5 4.2 ± 1.1 Exp. 3 Strength 739 ± 14.2 (MPa) Strength 1027 ± 16.5 (MPa) 6.3% ± EL0.8 Strength 1169 ± 21.5 (MPa) Strength 1311 ± 23.2 (MPa) 3.5% ± EL 1.4 As-cast 426 ± 5.1 677 ± 7.3 5.7 ± 0.7 356 ± 4.7 576 ± 6.9 11.3 ± 1.0 3.5.Exp. Effects 1 of Austempering-Temperature 707 ± 12.6 992 ± 14.1 and Alloying 5.8 ± 0.8 863 ± 16.5 1035 ± 24.2 8.3 ± 1.3 Exp. 2 724 ± 16.5 1018 ± 17.9 6.7 ± 1.0 937 ± 17.3 1065 ± 19.5 4.2 ± 1.1 Exp.In 3order to 739 gain± 14.2 a clear picture 1027 ± of16.5 the results, 6.3 ± the0.8 variation 1169 ± of21.5 hardness, 1311 tensile± 23.2 strength, 3.5 and± 1.4 EL % values of the as-cast and austempered samples are visually presented in Figures 4a–c, respectively. From3.5. Effects Figure of Austempering4a, it is evident Temperature that Mo has and a Alloyinghigher hardenability-promoting effect than Ni and Cu. In all three austempering temperatures, Mo alloyed Alloy M with reduced Ni and Cu contents reached higherIn hardness order to gainvalues a clearthan pictureAlloy O, of which the results, was alloyed the variation only with of hardness,Ni and Cu. tensile strength, and % EL valuesThe effect of the of as-cast Mo on and hardenability austempered is also samples reflected are visuallyin tensile presented strength values; in Figure 13114a–c, MPa respectively. of tensile strengthFrom Figure attained4a, it by is evidentAlloy M that after Mo austempering has a higher 290 hardenability-promoting °C is significantly higher effect than than thatNi of andAlloy Cu. O (1027In all threeMPa) austemperingtreated at the temperatures,same temperature Mo alloyed (Figure Alloy 4b). M with reduced Ni and Cu contents reached higherIt hardnessshould be values notedthan that AlloyAlloy O, M which austempered was alloyed at 290 only °C with comfortably Ni and Cu. meets the strength and ductilityThe requirements effect of Mo on of hardenabilityADI Grade 1200 is also of Euro reflectedpean instandard tensile strengthEN 1564 values;[28] and 1311 falls MPa between of tensile ADI ◦ Gradestrength 2 and attained 3 of ASTM by Alloy A897/A897M-03 M after austempering [29]. 290 C is significantly higher than that of Alloy O (1027When MPa) austempered treated at the at same 350 temperature°C, Alloy M (Figureexhibits4 b).higher ductility than Alloy O (8.3% EL vs. 5.8% ◦ EL inIt Figure should 4c) be for noted a comparable that Alloy strength M austempered (1035 MPa at vs. 290 992C MPa). comfortably These results meets mean the strengththat a wider and rangeductility of mechanical requirements properties of ADI Grade can be 1200attained of European by Alloy standardM by choosing EN 1564 the [appropriate28] and falls austempering between ADI conditions.Grade 2 and 3 of ASTM A897/A897M-03 [29].

(a) (b)

Figure 4. Cont.

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(c)

Figure 4. (a) Hardness, ( b) tensile strength, and ( c) %EL EL % (elongation in length) values of the as-cast and austempered samples.

Another observation to point out which is in line with some previous studies [1,25] is that the When austempered at 350 ◦C, Alloy M exhibits higher ductility than Alloy O (8.3% EL vs. relatively higher Ni and Cu content of Alloy O enables the conservation of its ductility even after 5.8% EL in Figure4c) for a comparable strength (1035 MPa vs. 992 MPa). These results mean that austempering at lower temperatures, which is not the case for Alloy M. This suggests that a new Mo- a wider range of mechanical properties can be attained by Alloy M by choosing the appropriate Ni-Cu alloyed ductile iron with an increased Ni content can be designed to attain higher strength valuesaustempering with less conditions. sacrifice in ductility after austempering. Another observation to point out which is in line with some previous studies [1,25] is that the 4.relatively Summary higher Ni and Cu content of Alloy O enables the conservation of its ductility even after austempering at lower temperatures, which is not the case for Alloy M. This suggests that a new Mo-Ni-CuTwo sets alloyed of ductile ductile cast iron iron with samples, an increased one alloyed Ni content with can 0.37% be designed Ni and 0.52% to attain Cu higher and the strength other valuesalloyed with with less 0.21% sacriﬁce Mo, in0.21% ductility Ni, and after 0.41% austempering. Cu, were cast and then subjected to austempering treatments at 350 °C, 320 °C, and 290 °C. 4. SummaryWhen their as-cast states are compared, the Mo-Ni-Cu alloyed ductile iron was softer due to its higher ferrite-containing microstructure with coarser graphite nodules. Two sets of ductile cast iron samples, one alloyed with 0.37% Ni and 0.52% Cu and the other After austempering, all samples exhibited significant increases in strength. The Mo-Ni-Cu alloyed with 0.21% Mo, 0.21% Ni, and 0.41% Cu, were cast and then subjected to austempering alloyed ductile iron had higher hardness, yield, and tensile strengths compared to the Ni-Cu alloyed treatments at 350 ◦C, 320 ◦C, and 290 ◦C. ductile iron for all three austempering temperatures, proving the better performance of Mo as a When their as-cast states are compared, the Mo-Ni-Cu alloyed ductile iron was softer due to its strengthener. higher ferrite-containing microstructure with coarser graphite nodules. The ductility of the Mo-Ni-Cu alloyed ductile iron, however, decreased as the austempering After austempering, all samples exhibited signiﬁcant increases in strength. The Mo-Ni-Cu alloyed temperature was lowered. On the contrary, the ductility of Ni-Cu alloyed ductile iron slightly ductile iron had higher hardness, yield, and tensile strengths compared to the Ni-Cu alloyed ductile increased rather than decreased with the decreasing austempering temperature. iron for all three austempering temperatures, proving the better performance of Mo as a strengthener. It is anticipated that by properly combining these alloying elements, it is possible to engineer The ductility of the Mo-Ni-Cu alloyed ductile iron, however, decreased as the austempering ADIs to reach to various strength-ductility levels. temperature was lowered. On the contrary, the ductility of Ni-Cu alloyed ductile iron slightly increased Acknowledgments:rather than decreased The withauthors the are decreasing thankful austemperingto Özdemir Dinç temperature. for his help with the metallographic sample preparation.It is anticipated The publishing that costs by properly have been combining covered most thesely by alloying Ay Döküm elements, Inc., with it ais minor possible contribution to engineer from ADIsAtılım toUniversity. reach to various strength-ductility levels.

Acknowledgments:Author Contributions:The Erkin authors Koç are designed thankful the to Özdemircomposition Dinç of for the his alloy help samples with the and metallographic poured them sample and preparation.performed tensile The publishing testing. Kaz costsım Tur have and been Erkan covered Konca mostly designed by Ay and Döküm performed Inc., withthe austempering a minor contribution experiments, from Atılımanalyzed University. and interpreted the data, and wrote the paper.

AuthorConflicts Contributions: of Interest: TheErkin authors Koç designeddeclare no the conflict composition of interest. of the Th alloye founding samples sponsors and poured had themno role and in performedthe design oftensile the study; testing. in Kazım the collection, Tur and Erkananalyses, Konca or interpretation designed and of performed data; in the the writing austempering of the manuscript, experiments, and analyzed in the and interpreted the data, and wrote the paper. decision to publish the results. Conﬂicts of Interest: The authors declare no conﬂict of interest. The founding sponsors had no role in the design Referencesof the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results. 1. Blackmore, P.A.; Harding, R.A. The Effects of Metallurgical Process Variables on the Properties of Austempered Ductile Irons. J. Heat Treat. 1984, 3, 310–325. 2. Keough, J.R.; Hayrynen, K.L. Designing with Austempered Ductile Iron (ADI). AFS Proc. 2010, 2010, 10– 129.

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