06 properties cast ıron summary
TRANSCRIPT
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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.