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Introduction to Ferrous Materials (I) WS 2017/18Lecture 6Cast IronsDr. Javad MolaInstitute of Iron and Steel Technology (IEST)Tel: 03731 39 2407E-mail: mola@iest.tu-freiberg.de1

Fe-C Phase DiagramDashed lines:Fe-Gr. diagramStable systemIntroduction to Ferrous Materials (I) WS 2017/18Solid lines:Fe-Fe3C diagramMetastable system LPeritectic reactionSteels๐œน ๐‘ณ๐’Š๐’’.Steelsandcastirons๐Ÿ๐Ÿ’๐Ÿ—๐Ÿ“ ๐‘ช , ๐ŸŽ.๐Ÿ๐Ÿ” ๐’˜๐’•%๐‘ชAustenite Fe3C / Gr.๐œธEutectoid reaction๐‘ญ๐’† ๐‘ช๐œธีœ๐œถ แ‰Š ๐Ÿ‘๐‘ฎ๐’“.Ferrite Fe3C / Gr.Eutectic reactionCastirons๐‘ณ๐’Š๐’’. ีœ ๐œธ แ‰Š๐‘ญ๐’†๐Ÿ‘ ๐‘ช๐‘ฎ๐’“.SteelCast IronASM Handbook: Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, Materials Park, Ohio, 1992.2

Carbon Equivalent Concept๐‘ช๐‘ฌ %๐‘ช Introduction to Ferrous Materials (I) WS 2017/18Si displaces theeutectic point to lowercarbon concentrations.The Carbon Equivalent(CE) equation belowtakes into account theeffect of Si and P onthe displacement of theeutectic point. Eutecticcomposition is wherethe CE is equal to 4.3.(%๐‘บ๐’Š %๐‘ท)๐Ÿ‘Pseudo-binary Fe-2.5 wt.%Si-C Phase DiagramASM Handbook: Volume 15: Casting, ASM International, Materials Park, Ohio, 1992.3

Hypo-eutectic(primary formation aboveeutectic temp.)4.3%CEutecticHyper-eutectic(primary Fe3C or Gr. formationabove eutectic temp.)Liq. Gr. (kish Gr.)Liq.Liq. Liq. Fe3C1150 C๐‘ณ๐’Š๐’’.๐Ÿ๐Ÿ๐Ÿ“๐ŸŽ ๐‘ช , ๐Ÿ’.๐Ÿ‘ ๐’˜๐’•.%๐‘ช๐‘ญ๐’† ๐‘ช๐œธ แ‰Š ๐Ÿ‘๐‘ฎ๐’“.White iron (ledeburite)Gray ironGraphitizationpotential low๐œธ๐’‘๐’“๐’Š๐’Ž๐’‚๐’“๐’š (๐‘ญ๐’†๐Ÿ‘ ๐‘ช ๐œธ)๐‘ญ๐’†๐Ÿ‘ ๐‘ช๐’‘๐’“๐’Š๐’Ž๐’‚๐’“๐’š (๐‘ญ๐’†๐Ÿ‘ ๐‘ช ๐œธ)Graphitizationpotential high๐œธ๐’‘๐’“๐’Š๐’Ž๐’‚๐’“๐’š (๐‘ฎ๐’“. ๐œธ)๐‘ฎ๐’“.๐’‘๐’“๐’Š๐’Ž๐’‚๐’“๐’š (๐‘ฎ๐’“. ๐œธ)723 C34wt.%C564Introduction to Ferrous Materials (I) WS 2017/18Constitution of Cast Irons

Cast Irons: OverviewPearlite Gr. Gr.(cooling througheutectoid interval)Gray castironSlowFerrite Gr.Graphite shapeHighFlakeLiquidcast alMottledcast iron Fe3C Gr.Low Fe3CSolid-statetransformation(cooling througheutectoid interval) Fe3C Gr.Cool througheutectoidintervalFastPearlite Temper Gr.Hold aboveeutectoidintervalPearlite Fe3CWhite ironReheat aboveeutectoidinterval Fe3CSlowFerrite Temper Gr.Malleable ironASM Handbook: Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, Materials Park, Ohio, 1992.5Introduction to Ferrous Materials (I) WS 2017/18FastSolid-statetransformation

Introduction to Ferrous Materials (I) WS 2017/18Cast Iron: Applications6

Decreasing graphitization potentialIntroduction to Ferrous Materials (I) WS 2017/18Graphitization; Role of Alloying ickelHigh graphitization adiumHigh negative graphitization potentialASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996.7

Chemical CompositionIntroduction to Ferrous Materials (I) WS 2017/18Carbon and silicon composition ranges ofdifferent classes of cast irons and steels.4.32.0ASM Handbook: Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, Materials Park, Ohio, 1992.8

The tendency of an iron to solidify as white or gray iron may be evaluated bycasting a wedge-shaped specimen. The fracture surface is then examined andthe distance from the wedge tip to the end of the white zone is measured. Thelarger the white zone, the higher the tendency of the steel to solidify as white iron.Gray๐‘ณ๐’Š๐’’. ีœ ๐œธ ๐‘ญ๐’†๐Ÿ‘ ๐‘ช ๐‘ฎ๐’“. Mottled๐‘ณ๐’Š๐’’. ีœ ๐œธ ๐‘ญ๐’†๐Ÿ‘ ๐‘ชThinner section,higher cooling rate๐‘ณ๐’Š๐’’. ีœ ๐œธ ๐‘ฎ๐’“.WhiteG.F. Vander Voort, Metallography, Principles and Practice, ASM International, 1984.9Introduction to Ferrous Materials (I) WS 2017/18Wedge Test

Wedge TestASM Handbook: Volume 15: Casting, ASM International, Materials Park, Ohio, 1992.Introduction to Ferrous Materials (I) WS 2017/18Gray IronFe-3.52 C-2.55 Si-1.01 Mn-0.215 P-0.086 S10

ationrangeCast nVolume change upon solidification (%)SteelExpansionupon freezinggray ironsallows toproduceriserlesscastingsCarbon, mass-%(Eutectic)TemperatureSchematic illustration of three shrinkageregimes in most alloys: in the liquid;during freezing; and in the solid stateJ. Campbell, Castings, Butterworth Heinemann, 2nd Edition, 2003.The volume change on freezingof Fe-C alloys.11Introduction to Ferrous Materials (I) WS 2017/18Expansion during Graphite Formation

Primary above eutectoidtemperature, pearlite ( Fe3C) below eutectoidtemperatureLedeburite( Fe3C right after eutecticsolidification, pearlite Fe3C below eutectoidtemperature)12Introduction to Ferrous Materials (I) WS 2017/18White Cast Iron

High hardness and abrasion resistance Low Carbon Equivalents (CEs) Usually used after alloying with Cr (high-Cr white iron) or Ni Cr (Ni-hard whiteiron) for higher hardnesses The high hardness originates from a hard martensitic matrix and the presenceof a large fraction of hard alloy carbides such as M3C and M7C3 (M denotesCr, Fe, )Example compositions of high-alloy white 3.61.3 max0.8 max3.3-3.51.4-41.0 maxNi-Hi Cr2.5-3.61.3 max1.0-2.25.0-7.07.0-11.01.0 max12%Cr2.4-2.80.5-1.51.0 max0.5 max11.014.00.5-1.020%Cr-Mo-LC2.0-2.60.5-1.51.0 max1.5 max18.023.01.5 max25%Cr2.3-3.00.5-1.51.0 max1.5 max23.028.01.5 maxASM Handbook: Volume 15: Casting, ASM International, Materials Park, Ohio, 1992.13Introduction to Ferrous Materials (I) WS 2017/18White Cast Iron

Typical graphiteshapes according toASTM A247 standard.SpheroidalCompactedImperfect spheroidalCrabIntroduction to Ferrous Materials (I) WS 2017/18Gray Iron: Graphite ShapesTemperExplodedFlakeASM Handbook: Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, Materials Park, Ohio, 1992.14

Introduction to Ferrous Materials (I) WS 2017/18Gray Iron (Iron with Flake Graphite)Graphite flakes in a ferritic matrix Graphite flakes in FG iron can take various shapes, sizes, and orientations depending oncomposition and casting conditions Excellent damping capacity Brittle Good machinability because of easy chip formation and cutting tool lubrication by graphite Good heat conduction due to interconnected graphite flakes The matrix microstructure depends on the cooling conditions through the eutectoid interval(usually pearlite or ferrite rather than martensite) Graphitization is aided by the inoculation process. Inoculation agent (usually ferrosilicon orgraphite) which is added to the melt just before casting promotes the nucleation of graphiterather than cementite during solidification.ASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996.15

Introduction to Ferrous Materials (I) WS 2017/18Ductile Iron (Iron with Spheroidal Graphite)Graphite nodules in a ferritic matrix Also known as spheroidal graphite (SG) iron or nodular ironGraphite is more or less spherical in shapeThe size and the number of graphite nodules per unit area influences mechanical propertiesHigher ductility than gray ironThe matrix microstructure depends on the cooling conditions through the eutectoid interval(usually pearlite, ferrite or a mixture of both although martensite formation is also possible athigh cooling rates) Spherical graphite is achieved by the addition of elements such as Mg. The process of Mgaddition to the melt is challenging because of its ready evaporation.ASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996.16

Ductile IronElement categoryElementSpheroidizer:Magnesium, calcium, rareearth elements (cerium,lanthanum, etc.), yttriumNeutral:Iron, carbon, alloyingelementsAnti-spheroidizer:Aluminum, arsenic,bismuth, tellurium, titanium,lead, sulfur, antimonyIntroduction to Ferrous Materials (I) WS 2017/18Influence of minor elements on graphite shapeThe amount of Mg required to produce spheroidal graphite is 0.03-0.05 wt.%. In practice,however, more Mg is required to account for the recovery rate of the technique used for the Mgaddition and to compensate for the Mg loss due to the MgS formation;Mg added 0.75 S net Mg level needed for spheroidizationRecovery of Mg in the Mg addition technique utilized(fraction of Mg which actually enters the melt)ASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996.17

Ductile IronIntroduction to Ferrous Materials (I) WS 2017/18Bullโ€™s-eye microstructures in SG ironFe3C-free ferriticlayer next tographite nodulesPearlitic matrixAs cast iron cools throughthe eutectoid interval, Cdiffusion to the alreadyexisting graphite nodulescauses an Fe3C-free layernext to the graphite nodules18

Matrix TypesIntroduction to Ferrous Materials (I) WS edductile iron (ADI)19

Austempered Ductile Iron (ADI)Introduction to Ferrous Materials (I) WS rmation(austempering)TemperatureTemperatureFerrite GraphitePearliteMsBainiteMartensiteTime1 ksi 7 MPaTimehttp://www.totalmateria.com/page.aspx?ID CheckArticle&site kts&NM 24320

Introduction to Ferrous Materials (I) WS 2017/18Compacted Graphite IronCompacted graphite in a ferritic matrix Also known as CG iron or vermicular graphite iron Graphite shape intermediate between spheroidal and flake Microstructure of CG iron is free of flake graphite and the amount of spheroidal graphite is lessthan 20% Properties intermediate between FG and SG Produced by the addition of Mg in amounts lower than needed to obtain SG or by combinedaddition of spheroidizing and anti-spheroidizing elements (for example Mg Ti addition)ASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996.21

Introduction to Ferrous Materials (I) WS 2017/18Malleable IronTemper graphite in a ferritic matrix Also known as temper graphite (TG) iron Production method: Solidification as white iron (therefore not applicable to heavy sections) Subsequent reheating and holding at temperatures between eutectoid and eutectictemperatures (typically 950 C) for cementite decomposition to temper graphite (1st stage) Controlled cooling to obtain the desirable matrix microstructure (2nd stage) Graphite morphology and mechanical properties similar to SG Applicable to thin sections where solidification as ductile iron is not possible Small amounts of elements such as Bi and Te are used to suppress graphite formation duringsolidification (0.01 wt.% Bi, 0.0005-0.001 wt.% Te) Elements such as B and Al are used to speed up the cementite decomposition during the 1 st heattreatment stage (0.001 wt.% B, 0.005 wt.% Al)ASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996.22

Introduction to Ferrous Materials (I) WS 2017/18Malleable Ironundissolved cementiteTemper carbon graphite surroundedby ferrite in a matrix of pearliteExample of incomplete malleablizationheat treatment.23

Driveline yokesConnectingrodsSteering gearhousingDiesel pistonsASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996.24Introduction to Ferrous Materials (I) WS 2017/18Mealleable Iron: Automotive Applications

Graphite flakes act as internal defects and cause stress concentration. Stressconcentration is especially pronounced in the case of flake graphite.GraphiteflakeJ. Peterseim, Lecture notes for Materials Engineering II (Werkstofftechnik II), FH Mรผnster.Graphitenodule25Introduction to Ferrous Materials (I) WS 2017/18Stress Concentration at Graphite Flakes

Vibration oads/2011/03/Reducing-Gear-Noise.pdfIntroduction to Ferrous Materials (I) WS 2017/18Relative damping behaviors of steel, ductile &malleable irons and gray iron26

Rough comparison of the properties of steels and gray cast ironsSteelGray Cast IronCarbon contentless than about 2 wt.%more than about 2 astabilitylowhighConsumptionhighlowGraphite hWeldabilityhighlow27Introduction to Ferrous Materials (I) WS 2017/18Steel vs. Cast Iron

28Introduction to Ferrous Materials (I) WS 2017/18

ASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996. WS 2017/18 23 Malleable Iron ... heat treatment. undissolved cementite. WS 2017/18 24 Mealleable Iron: Automotive Applications ASM Specialty Handbook: Cast Irons, ASM International, Materials Park, Ohio, 1996. Driveline yokes Connecting rods Diesel pistons ...