Ductile cast iron has high fatigue strength due to the spherical shape of graphite, especially after quenching and tempering. Higher toughness can be achieved by austempering. One of the advantages of ductile cast iron in relation to other cast irons is its good wear resistance. In the experiments, samples of ductile cast iron and austempered ductile cast iron were eroded with quartz sand particles at six different angles of impact (15°, 30°, 45°, 60°, 75° and 90°). The test results were presented as the loss of mass which occured during the test. Testing with quartz sand shows that the particle erosion resistance of ductile cast iron was better than that of austempered ductile iron for all impact angles except for 60°. The maximum measured wears of ductile cast iron and austempered ductile iron were at 75°.Nodularni lijev ima veliku dinamičku izdržljivost zbog kuglastog oblika grafita, naročito nakon poboljšavanja. Visoka žilavost može se postići izotermičkim poboljšavanjem. Jedna od prednosti nodularnog lijeva u odnosu na ostale željezne lijevove je njegova dobra otpornost na trošenje. U ovom istraživanju ispitivana je otpornost na erozijsko trošenje nodularnog lijeva i izotermički poboljšanog nodularnog lijeva, česticama kvarcnog pijeska pri šest različitih kutova udara (15°, 30°, 45°, 60°, 75° and 90°). Rezultati ispitivanja prikazani su gubitkom mase tijekom ispitivanja. Rezultati pokazuju da nodularni lijev ima bolju otpornost na erozijsko trošenje od izotermički poboljšanog nodularnog lijeva pri svim kutovima udara osim kod 60°. Maksimalni gubitak mase kod oba materijala zabilježen je pri kutu upada od 75°

Denis Prusac

Krešimir Grilec

Suzana Jakovljević

Hrčak - Portal of scientific journals of Croatia

1IntroductionUvodDuctile cast iron is a cast, pseudo-binary iron-carbonalloy, with graphite mostly in spherical shape [1]. Ductileiron has high fatigue strength due to the spherical shape ofgraphite, especially after quenching and tempering. Ductilecast iron has good bearing properties and resistance to wear,corrosion and oxidation. Special properties (like resistanceto aggressive media) can be achieved with alloying [2].Austempering heat treatment significantly enhances themechanical properties of ductile iron. Known asaustempered ductile iron (ADI), this material offersimproved strength and toughness in comparison to ductileiron [3].The austempering heat treatment process consists ofheating a material into the austenite phase field and then ofquenching it to a lower temperature (the austemperingtemperature) and of holding it at this temperature to allowthe austenite to transform isothermally to an acicular ferritephase, known as bainite, which contains carbides [4].Alloying additions can render ductile irons more suitablefor commercial austempering because certain elementsaffect the solubility of carbon in the austenite, therebyinfluencing bainitic transformation [5].The properties of austempered ductile iron (ADI) canbe varied by changing the austempering temperature. Alower transformation temperature produces a fine, highstrength, wear-resistant structure. A higher transformationtemperature results in a coarser structure that exhibits highfatigue strength and good ductility [6].ADI has important advantages as its heat treatment timeis short due to its chemical composition and microstructuresand intricate shapes can be cast with strength and wearresistance properties similar to those of steels (with 10 %-17K. Grilec, S. Jakovljević, D. PrusacISSN 1330-3651UDC/UDK 620.178.16 : 669.131.7EROSION OF DUCTILE CAST IRON WITH QUARTZ PARTICLESKrešimir Grilec, Suzana Jakovljević, Denis PrusacDuctile cast iron has high fatigue strength due to the spherical shape of graphite, especially after quenching and tempering. Higher toughness can be achieved byaustempering. One of the advantages of ductile cast iron in relation to other cast irons is its good wear resistance. In the experiments, samples of ductile cast ironand austempered ductile cast iron were eroded with quartz sand particles at six different angles of impact (15°, 30°, 45°, 60°, 75° and 90°). The test results werepresented as the loss of mass which occured during the test. Testing with quartz sand shows that the particle erosion resistance of ductile cast iron was better thanthat of austempered ductile iron for all impact angles except for 60°. The maximum measured wears of ductile cast iron and austempered ductile iron were at75°.Keywords: austempered ductile cast iron, ductile cast iron, particle erosionOriginal scientific paperNodularni lijev ima veliku dinamičku izdržljivost zbog kuglastog oblika grafita, naročito nakon poboljšavanja. Visoka žilavost može se postići izotermičkimpoboljšavanjem. Jedna od prednosti U ovom istraživanjuispitivana je otpornost na erozijsko trošenje nodularnog lijeva i izotermički poboljšanog nodularnog lijeva, česticama kvarcnog pijeska pri šest različitihudara (15°, 30°, 45°, 60°, 75° and 90°). Rezultati ispitivanja prikazani su gubitkom mase tijekom ispitivanja. Rezultati pokazuju da nodularni lijev ima boljuotpornost na erozijsko trošenje od izotermički poboljšanog nodularnog lijenodularnog lijeva u odnosu na ostale željezne lijevove je njegova dobra otpornost na trošenje.kutovava pri svim kutovima udara osim kod 60°. Maksimalni gubitak mase kod obamaterijala zabilježen je pri kutu upada od 75°.Ključne riječi: erozija česticama, izotermički poboljšani nodularni lijev, nodularni lijevIzvorni znanstveni članakErozija nodularnog lijeva česticama kvarcnog pijeskaErozija nodularnog lijeva česticama kvarcnog pijeskaTechnical Gazette 17, (2010), 171 -22lower density). In addition, ADI is better than forgedaluminium with respect to weight-strength ratio [3].The improved mechanical properties achieved inaustempered nodular iron could be exploited in theautomotive industry by permitting cast component designswith reduced section size, thereby lowering vehicle weight,and by substituting ductile iron for steel in stringentengineering applications [7]. The major applications ofaustempered ductile iron include power plants, mining, rail-road, automotive, military and agricultural industries [5].ADI has become increasingly important for themanufacturing of components such as gears, crank shafts,cam shafts and rolls [8].Wear is one of the most commonly encounteredindustrial problems, leading to frequent replacement ofcomponents [8].Solid particle erosion is the loss of material that resultsfrom repeated impacts of small, solid particles. In somecases, it is a useful phenomenon, as in sandblasting andhigh-speed abrasive waterjet cutting, but it is a seriousproblem in many engineering systems, including steam andjet turbines, pipelines and valves carrying particulatematter, and fluidized bed combustion systems. Solidparticle erosion can occur in a gaseous or liquid mediumcontaining solid particles. In both cases, particles can beaccelerated or decelerated, and their directions of motioncan be changed by the fluid [9].When the impact angle is low (between 0° and 30°), thiskind of erosion is called the abrasive erosion. On the otherside, if the impact angle is between 60° and 90°, the erosionis regarded as impact erosion [2].Erosive wear occurs by plastic deformation and/orbrittle fracture, dependent upon the material being erodedaway and upon operating parameters. Ductile materials willundergo wear by a process of plastic deformation in whichthe material is removed by the displacing or cutting action ofthe eroded particle. In a brittle material, on the other hand,material will be removed by the formation and intersectionof cracks that radiate out from the point of impact of theeroded particle. The shape of abrasive particles affects thepattern of plastic deformation around each indentation and,consequently, the proportion of the material displaced fromeach impact. In the case of brittle materials, the degree andseverity of cracking will be affected by the shape of abrasiveparticles. Compared with more rounded particles, sharperparticles would lead to more localized deformation andsubsequent wear [10]The experiment was performed on samples of ductilecast iron produced in the Split Shipyard. Samples of ductilecast iron were austempered at the Faculty of MechanicalEngineering and Naval Architecture in Zagreb. Parametersof austempering are shown in Figure 1..2Laboratory investigations2.1Materials descriptionLaboratorijska istraživanjaOpis materijala18Erosion of ductile cast iron with quartz particles K. Grilec, S. Jakovljević, D. PrusacTehni ki vjesnikč , 1717, 1(2010) -22yield and tensile strengths but imparts higher ductility [12].The first temperature corresponds to lower bainite and thesecond one corresponds to upper bainite.A quantitative chemical analysis of ductile cast iron isperformed by a spectrometer method on SPECTRUMAT-750 GDS Leco in the Laboratory for Metal Analysis at theFaculty of Mechanical Engineering and Naval Architecturein Zagreb.2.2Chemical analysisKemijska analizaThere are three phases to the ADI heat treat cycle:austenitizing, quenching and austempering. All three ofthese phases contribute to the final properties. First, thecasting is heated to the austenitizing temperature. The rateof heating has very little or no effect on final properties.Then, the casting is held at this temperature until fullaustenitization is achieved. Full austenitization meansconversion of the entire matrix to face centered cubic (FCC)austenite and the saturation of the austenite to carbon. Thesecond phase of the heat-treat cycle is quenching. There aretwo criteria for a proper quenching: the cooling rate must behigh enough to avoid pearlite formation during quenchingand the desired austempering temperature must be reachedin the casting prior to the beginning of the austemperingreaction (ferrite nucleation).The most important of the three phases of the heat-treatcycle is austempering. Both the temperature and the timeduration of the austempering cycle have a strong effect onthe matrix structure and the mechanical properties [11].When ADI is austempered at lower temperatures, it hasfiner ferrite and austenite and this results in higher yield andtensile strength but with lower ductility. On the other hand,when ADI is austempered at higher temperatures, it hascoarser or feathery ferrite and austenite and this reduces the2.3Microstructural analysisAnaliza mikrostruktureA microstructural analysis was performed in theLaboratory for Metallography at the Faculty of MechanicalEngineering and Naval Architecture in Zagreb. Themicrostructure of a ductile cast iron sample is shown inFigure 2a (ferrite-pearlite matrix) and the microstructure ofan austempered ductile cast iron sample is shown in Figure2b (bainite matrix).Figure 1Slika 1.ADI heat treat cycleToplinska obrada izotermički poboljšanog nodularnog lijevaTable 1Tablica 1.Analysis of chemical composition of ductile cast iron samplesKemijska analiza uzorka nodularnog lijevaMass portion, %C Si Mn P S Cu Ni Mo MgDuctilecast iron2,34 2,72 0,72 0,054 0,011 1,14 0,095 0,016 0,033Figure 2Slika 2.Samples of a) ductile cast iron, b) austempered ductile ironUzorci a) nodularnog lijeva, b) izotermički poboljšanognodularnog lijevaa)b)The microstructure of ADI is upper bainite (it hascoarser or feathery ferrite and austenite).Measurements of hardness were performed in theLaboratory for Testing Mechanical Properties at the Facultyof Mechanical Engineering and Naval Architecture inZagreb. The hardness testing of samples was performedaccording to [13]. Results of the hardness testing are shownin Table 2.2.4Hardness measurementsMjerenje tvrdoće19Technical Gazette , 1717, 1(2010) -22K. Grilec, S. Jakovljević, D. Prusac Erozija nodularnog lijeva česticama kvarcnog pijeskaThere are no significant differences in Vickers hardnessbetween ductile cast iron and austempered ductile ironsamples.Wear resistance, is not an intrinsic property of thematerial but depends upon the tribological system, such asproperties of materials tested, abrasive grit size, testcondition, equipment, and environment [8].In the literature on erosion, materials are broadlyclassified as ductile or brittle, based on the dependence oftheir erosion rate on. Ductile materials, such as pure metals,have a maximum erosion rate at low angles of incidence(typically 15° to 30°), while for brittle materials, such asceramics, the maximum is at or near 90°.Avariety of curvesintermediate between these classical extremes exist and insome cases the same material exhibits behavior that shiftsfrom one extreme to the other, depending on erosionconditions [9].Atest of solid particle erosion resistance, using roundedquartz sand as solid particles, was performed in theLaboratory of Tribology at the Faculty of MechanicalEngineering and Naval Architecture in Zagreb. The particleerosion tester is shown in Figure 3 (details are shown inFigure 4).2.5Test of solid particle erosion resistanceIspitivanje otpornosti na eroziju česticamaTesting parameters:abrasive: rounded quartz grain sand AFS 50/70 (Figure5)revolution: 1440 rev/minvelocity of samples: 24,265 m/stime of testing: 13 min 53 secnumber of impacts: ~20 000impact angles: 15°, 30°, 45°, 60°, 75° and 90°dimension of samples: 18×18×18 mm.Table 2Tablica 2.Vickers hardness HV10Tvrdoće po Vickersu HV10Ductile cast iron Austempered ductile iron1 240 2432 297 3063 254 2794 258 2795 283 2476 240 2707 283 2978 258 2879 283 28710 287 292HV 268 279Figure 3Slika 3.Particle erosion testerUređaj za eroziju česticamaFigure 4Slika 4.Testing of solid particle erosionErozija krutim česticamaFigure 5Slika 5.Erosion particles of quartz sandErozijske čestice kvarcnog pijeska20Figure 6 shows results of particle erosion testing. When the impact angle exceeded 45°, erosion crackswere observed in the erosion surface of ductile iron samples.However, the erosion cracks were not observed for lowimpact angles (< 45°) and for high impact angles (>75°) forductile iron samples. The appearance of the erosion surface(45° impact) shown in Figure 7.At oblique impact angles (30° and 60°), a hard erodentcauses plastic flow in a relatively soft surface of ductile ironand material removal occurs by microcutting andmicroploughing (see Figure 7).Grooves and lip mechanism were observed on the wearsurface (see Figure 8a i 8b). The martensite phase of ADIresults in large brittle cracks in the oblique wear surface(shown in Figure 8). The increased brittleness caused by themartensite not only reduced erosion resistance but alsocreated the erosion peak at 75°.Erosion of ductile cast iron with quartz particlesTehni ki vjesnikč , 1717, 1(2010) -22K. Grilec, S. Jakovljević, D. PrusacFigure 6 shows that particle erosion resistance ofductile cast iron was better than that of austempered ductileiron for all impact angles except for 60°. Ductile cast ironand austempered ductile iron curves have maximum valueat 75°. It was considered that a huge part of the impactenergy is spent on the formation of plastically deformedmaterial regions on the surface of ductile iron and isabsorbed by its high toughness. Austempered ductile ironhas a double-peak erosion curve with fall in erosion at 60°.The martensite and carbides that embrittle the sample couldinduce the peek found at high angles (75°) to occur by brittleerosion [14]. ThisADI sample, will be used as an example todiscuss the wear observations for double peak curves (45°and 75°).In order to examine the erosion mechanism anddamages, top-view of the eroded surfaces of the samplesstructure were observed by Scanning electron microscopy(SEM).2.6Wear surface analysisAnaliza trošene površineFigure 6Slika 6.Mass loss of ductile cast iron and austempered ductile iron(ADI) samplesGubici mase uzoraka nodularnog lijeva i izotermičkipoboljšanog nodularnog lijeva (ADI)Figure 7Slika 7.Wear surface of ductile cast iron (ED – erosion direction)Trošena površina nodularnog lijeva (ED – smjer erozije)Figure 8Slika 8.Wear surface of ADI: (a) 45°, (b) 75°°, (b) 75°Trošena površina izotermički poboljšanognodularnog lijeva: (a) 45a)b)21Figure 9 shows that nodular graphite appeared in theeroded surface at impact angle of 15°. When increasing theimpact angle, nodular graphite becomes less visible.Technical Gazette , 1717, 1(2010) -22Erozija nodularnog lijeva česticama kvarcnog pijeskaK. Grilec, S. Jakovljević, D. PrusacThe stream of erodant particles seemed to have strikedout some nodles of graphite and covered the by iron matrix.During the erosive wear process at oblique impact angles,the nodular graphites are deformed by impingement andploughed out. The shallower nodular graphite is shown to bemore deformed and has been found to play a role in cracknucleation. This effect leads to crack formation towards theeroded surface. Nodular graphites are bent in the directionof impact in the severely deformed areas just below theeroded surface.3Conclusion4ReferencesZaključakOne of the advantages of ductile cast iron in relation toother cast irons is its good wear resistance. However, it mustbe considered that wear resistance depends on wearcondition. Solid particle erosion resistance is function ofimpact angle. Testing with quartz sand shows that theparticle erosion resistance of ductile cast iron was betterthan that of austempered ductile iron for all impact anglesexcept for 60°. Microstructure of tested austempered castiron was upper bainite whose main characteristics are highfatigue strength and good ductility (not wear resistance).The maximum measured wears of ductile cast iron andaustempered ductile iron were at 75°. Austempered ductileiron has a double peak erosion curve with a fall in erosion at60°.The stream of erodant particles striked out some nodlesof graphite and covered the place where it was by ironmatrix. When increasing the impact angle, nodular graphitebecomes less visible. Erosion cracks, lips and many grooveswere observed in the erosion surface of all samples.Literatura[1] Novosel, M.; Krumes, D. Iron-based materials, part I:Casting, Faculty of Mechanical Engineering, Slavonski Brod,1994.[2] Glossary of terms and definitions in the field of friction, wearand lubrication - tribology, OECD Publications, Paris 1969[3] Seker, U.; Hasirci, H. Evaluation of machinability ofaustempered ductile irons in terms of cutting forces andsurface quality. // Journal of Materials ProcessingTechnology. 173(2006), pp. 260-268.[4] Harding R.A. The production, properties and automotiveapplications of austempered ductile iron. // Kovovematerially. 45(2007), pp. 1-16.[5] Narasimha Murthy, K.; Sampathkumaran, P.; Seetharamu, S.Abrasion and erosion behaviour of manganese alloyedpermanent moulded austempered ductile iron. // Wear.267(2009), pp. 1393-1398.[6] ASM Handbook, Vol. 4: Heat Treating, ASM International,1991[7] Shea, M. M.; Ryntz, E. F. Austempering Nodular iron foroptimum toughness. // Transactions of the AmericanFoundrymen's Society. 94(1986), pp. 683-688.[8] Sahin, Y.; Durak, O.Abrasive wear behaviour of austemperedductile iron. // Materials and Design. 28(2007), pp. 1844-1850.[9] ASM Handbook, Vol. 18: Friction, lubrication, and weartechnology,ASM International, 1992[10] Bhushan, B. Introduction to Tribology, John Wiley and Sons,2002[11] Kovacs, B. Heat treating of austempered ductile iron. //Transactions of the American Foundrymen's Society.99(1991), pp. 281-286.[12] Yang, J.; Putanda, K. S. Effect of microstructure on abrasionwear behavior of austempered ductile cast iron (ADI)processed by a novel two-step austempering process. //Materials Science and Engineering. A 406(2005), pp. 217-228.[13] International standard ISO 6507/1, Metallic materials-Hardness test- Vickerstest-Part 1: HV 5 to HV 100, 1982[14] Hung, F. Y.; Chen, L. H.; Lui, T. S.Astudy on erosion of upperbainiticADI and PDI. // Wear. 260(2006), pp.1003-10012.a)b)c)Figure 9Slika 9.Sample surfaces of ductile iron eroded at impact angle:a) 15°, b) 30° c) 45°Površina uzorka nodularnog lijeva erodiranog pod kut m od:a) 15°, b) 30° c) 45°oErosion of ductile cast iron with quartz particles K. Grilec, S. Jakovljević, D. Prusac22 Tehni ki vjesnikč , 1717, 1(2010) -22Authors' AddressesAdrese autoraKrešimir Grilec, assist. prof.Denis PrusacUniversity of ZagrebFaculty of Mechanical Engineering and Naval Architecture10000 Zagreb, Croatiae-mail: kgrilec@fsb.hrUniversity of ZagrebFaculty of Mechanical Engineering and Naval Architecture10000 Zagreb, Croatiae-mail: suzana.jakovljevic@fsb.hrTechnical school ZadarNikole Tesle 9c23000 Zadar, Croatiae-mail: dprusac1@gmail.comIvana Lučića 5Ivana Lučića 5Suzana Jakovljević, assistant

Erozija nodularnog lijeva česticama kvarcnog pijeska

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