06 Properties cast ıron summary

8/8/2019 06 Properties cast ron summary

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CAMSDM Lecture 6:CAMSDM Lecture 6:

Properties of Steels IIProperties of Steels II

Dr Tim SercombeSchool of Mechanical Engineering

The University of Western Australia

Room:2.12Phone:6488 3124

email::[email protected]
mailto:[email protected]:[email protected]


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RecapRecap

Steel is an alloy of?

Classes of steel

Plain carbon (low, med or high C) Low alloy (typical high strength grade)

High alloy (tool and stainless steels)

Strength/hardness increases with %C Toughness and ductility decrease.


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Heat TreatmentHeat Treatment

These are equilibrium(slow cooled)microstructures.

We can alter structure(and thereforeproperties) by heattreatment

Re-heat treatment canalso erase priortreatments.

0.5%C

0.95%C


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QuenchingQuenching

Heat to austenitic regionand quench rapidly

Forms martensite Extremely hard, but brittle

Not particularly useful

Temper

Re-heat to 200-500oC forup to 10h

Small decrease inhardness/strength

Regain some ductility andtoughness

Austenitise

Quench to room temperature


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Example PropertiesExample Properties

%C


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Steel ProductsSteel Products Nearly all carbon and alloy steels can be produced

either as cast products or wrought products.

Castings: Casting is used to produce near-finishcomponents.

Wrought products are produced more as semi-processed raw materials for further fabricationinto components. usually produced by any or combination of rolling,

extrusion, drawing and forging. Common forms available are bars, tubes, sheets, coils,

wires, I-beams, angles. Most structural and mild steels, stainless steels arefound in these forms.

Tool steels: usually produced by casting and forgingand are available as bars, rods and forged shapes.


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Grey iron

Nodular ironWhite iron

Malleable iron

Metal Alloys

Non-ferrousFerrous

Carbon Low Alloy High Alloy

Cast ironsCast ironsSteelsSteels

Low-C

Medium-C

High-C

Tool (Mo,V,W,Cr,Ni)

Stainless (Cr, Ni)

High-

strengthlow-alloy

Classes of MetalsClasses of Metals


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Cast irons

Steels

Fe-C Phase DiagramFe-C Phase Diagram


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Cast IronsCast Irons

High C content ~2-4%

Lower melting temperature than steel (~300oC lower)makes them more suitable for casting

Developed in China ~500 BC.

Not widely used in western world until ~1700 and thedevelopment of the steam engine


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Types of Cast IronTypes of Cast Iron

From a microstructural view point, cast irons canregarded as steels embedded with a carbon-rich phase.

This C-rich phase be either graphite or cementite (Fe3C).

Graphite offers no strength nor toughness and acts likevoids in the iron.

Cementite is very hard and brittle.

Formation of graphite of Fe3C depends on alloying content Eg. Addition of 2% Si causes the Fe

3C to become unstable and

graphite forms instead.


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Types of Cast IronTypes of Cast Iron

Grey iron: graphiteflakes embedded in

ferrite matrix,cutting the

continuity of thematrix and rendering

the metal highbrittleness.

Nodular iron:graphite nodules in

ferrite matrix,significantly

improving toughnessand ductility of the

metal

White iron:cementite platesembedded in pearlitematrix, renders themetal high hardnessand brittleness.

Malleable iron:

graphite clustersconverted fromdecomposingcementite in whiteiron, significantlyimproving toughnessand ductility of themetal

Normally, a cast iron product is grey iron, but it is not the only type available


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Grey Cast IronsGrey Cast Irons

Fe-1.8%Si-0.5%Mn-3.4%C

Properties

Cheap excellent castability high damping capacity good metal-metal wear resistance

when lubricated

strength much higher in compressionthan in tension brittle in tension. UTS:


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St

ress

Strain

Grey iron

Mild steel

Tensile stress-strain

behaviour of grey cast iron

Grey Irons - ApplicationGrey Irons - Application

Grey irons are by far the most producedamong all cast irons.

Used primarily for their low cost andexcellent castability.

Typical applications include: engine cylinders, pistons, gear box casing, transmission casing, machine tool bases, balance weight of large cranes, large diameter underground pipework.

They are used always under compressiveloading conditions. They are unsuitablefor taking tensile loads or bending loads.


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Nodular (Ductile) IronsNodular (Ductile) Irons Fe-1%Ni-0.4%Mn-0.06%Mg-3.4%C

Produced by inoculating (addition of RE or Mg tomolten metal just before casting) grey iron. Thisconverts graphite flakes into granules or nodules

These irons are much stronger andtougher than grey irons, but moreexpensive

They are produced and used for

high specification applications.


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Nodular Irons - ApplicationsNodular Irons - Applications

Typical applications include: gears,

Crankshafts

pump bodies pressure valves

rollers.

Properties Yield Strength: 365MPa

UTS: 500MPa,

ductility 18%

Hardness: 170 HB


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White Cast IronsWhite Cast Irons

Fe-0.7%Si-0.6%Mn-3.4%C

White irons contain relatively less C and Si.

Cementite (Fe3C) is formed instead of graphite. This makes the alloy very hard andbrittle, practically useless as structural material.

The high hardness, however,renders them high resistance

to abrasive wear.


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White Cast Irons - ApplicationsWhite Cast Irons - Applications

White irons are produced mainly for two purposes: Intermediate product for producing malleable irons

As abrasive wear resistant components, such as ball mill lining tiles,

slurry pipe elbows, slurry pump bodies

Properties

Yield Strength:


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Malleable Cast Irons - ApplicationsMalleable Cast Irons - Applications

They are suitable for castings of thin thickness But they are expensive to produce, largely due to the

heat treatment.

Typical applications include gear box, and diff casings, clamps pipe fittings

Properties Yield Strength: 230MPa

UTS: 360MPa

Ductility: 12%

Hardness: 130 HB


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Cast Iron SummaryCast Iron Summary

Cast Irons are a class of ferrous alloys with very high(2-4%) carbon contents.

Classed depending on microstructure

Grey: Graphite flakes in ferrite matrix

Brittle in tension, good in compressionCheap

Nodular: graphite nodules instead of flakesMuch higher strenght and ductility

White: Fe3C forms instead of graphite

Very hard, but brittleUsually only used in wear applications

Malleable:Heat treating white CI decomposes Fe3C into graphiteIncreased strength and toughness.

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06 Properties cast ıron summary