ji ca 2010 cast iron

7/30/2019 Ji CA 2010 Cast Iron

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Welding of Cast Irons

Material for May 7th 2010

Lecturer Dr. Jippei Suzuki Graduate School of Engineering Mie UniversityDepartment of Mechanical EngineeringFaculty of Engineering, Mie UniversityKurima-Machiya-cho 1577, Tsu, Mie 514-8507Tel. 059-231-9372Fax. 059-231-9663E-mail [email protected]



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Fe-Fe3C systemmeta-stable system

Fe-graphite systemstable system

T e m p e r a t u r e K

Carbon content mass%

Peritectic point 0.181494℃

(austenite)

(ferrite)

Eutectoid point 0.77(pearlite)

C Eutectic point 4.32(ledeburite)

T e m p e r a t u r e

Primaryaustenite

Primarygraphite

Primary cementite

(cementite)

Fe-C dual equilibrium diagram (Fig.K1)

Cast iron



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Stabilizing graphite (Fig.K2)

White cast iron

Mottled cast iron

Gray cast iron

pearlite

ferrite/pearlite

ferrite

meta-stable

stable

Low CLow Si

High CHigh Si

Rapid coolingThin section

Slow coolingThick section



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Degree of carbon saturation

SC=

SC<1 ; hypo eutectic

SC＝

1 ; eutecticSC>1 ; hyper eutectic

T.C.

4.3－0.3×%Si

Effect of Si (Fig.K3)

C.E.=T.C.+ %Si

or = T.C.+ (%Si+%P)

C.E.; carbon equivalent

T.C.; total carbon content

31

31

C content

eutecticpointSi content

Si



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Relation of structure to carbon and silicon contents of cast iron

Ⅱa; mottled cast iron

Maurer diagram (Fig.K2)

Ⅲ; ferritic cast iron

Ⅱb; pearlitic+ferritic cast iron

Ⅱ; pearlitic cast iron

Ⅰ; white cast iron



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Greiner-Klingenstein diagram (Fig.K5)

0 10 20 30 40 50 60 70

thickness mm

7

6

5

4

C + S

i

%

I IIa IIIIb

III

I; white cast iron, IIa; mottled cast iron, II; pearlitic cast ironIIb; pearlitic+ferritic cast iron, III; ferritic cast iron



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Cast iron Fe-2.5～4.0%C-0.5～3.0%Si(Chemical compositions of cast irons are not stipulated.)low melting point(1147K), good castability,

good absorbent of vibration, wear resistance,good machinability, good lubrication

By luster of fracture surfaceGray cast iron → graphite flakeWhite cast iron →ledeburite+primary Fe3C or austeniteMottled cast iron

By Morphology of graphite

A. Flake graphiteB. Lump graphiteC. Spheroidal graphite

By compositionsLow carbon cast ironHigh carbon cast ironHigh silicon cast ironAlloy cast iron

By the microstructure of matrixFerrite cast ironPearlite cast ironAustenite cast ironBainite cast iron(acicular cast iron)

By mechnical propertiesNormal cast iron(lower 300MPa)

Tough cast iron(over 300MPa)

Gray cast iron

White cast iron

Mottled cast iron

Hypo-eutectic W.C.I. Hyper-eutectic W.C.I.Eutectic W.C.I.

Classification of cast irons (Fig.K6)



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A. Graphite flake

B. Graphite rose

C. Kish graphite(large graphite flake) +small flake(hyper-eutectic iron)

D. Thin graphite between dendrites (eutectic graphite)

E. Graphite fleke between dendrites

A B C D E

Morphology of flake graphite (Fig.K7)



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Gray cast iron

Spheroidal graphite

+Ce, Mg(Mg alloy)

Nodular graphite cast ironSpheroidal graphite cast iron (U.K.)Ductile cast iron (Japan, U.S.A.)

Degree of spheroidization

Spheroidal graphite (Fig.K8)



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Structure of black heart malleable

cast iron (lump graphite)

Whitecast iron

black heartmalleablecast iron

annealing

850～950℃

680～720℃

1st step 2nd step

time

t e m p e r a t u r e First step

decomposition of cementite in ledebriteFe3C → graphite

Second stepdecomposition of cementite in pearlite

Fe3C → graphite

black heart malleable cast iron

pearlitic malleable cast irononly 1st step

Malleable cast iron (Fig.K9)

Example of annealing



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white heart malleable cast iron

White castiron

Heating for decarburization

900～1000℃ long period

Ferrite near the surface

Pearlite interior portionTemper graphite in core

Oxidant or Oxide

white heart

malleablecast iron



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Type of cast iron Weldability

Gray cast iron (graphite flake) normal

Spheroidal graphite cast iron (U.K.)Ductile cast iron (Japan, U.S.A.)

good

Malleable castiron

black heart malleable cast iron difficult

white heart malleable cast iron normal

pearlitic malleable cast iron difficult

Alloy cast iron Ni cast iron normal

Cr cast iron difficult

Generally it is difficult for cast iron to be welded because of its high carboncontent and low ductility.

Change to white cast iron by rapid cooling

Oil remaining in a gap between graphite and matrix (repair welding)→burning the cast before welding

Cracking due to welding thermal stress→peening→pre-heating

Weldability of cast iron (Table K1)



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Shielded metal arc welding

ElectrodeCore wire

pure Ni60%Ni-Fe alloyMonel 20%Ni, 1.5～3.5%Cr, 18%Cu, Fe Bal.mild steelcast iron

Fluxgraphite

Welding without pre-heatingbead length should be about 15mmpeening

Welding with low temperature pre-heating(370 570K)

small heat input

straight short bead (20～50mm)position of the crater

Welding with high temperature pre-heating(about 870K)

cast iron electrodeweaving to slow cooling rate

using furnace after welding to slow cooling

Gas weldingPre-heating over 870KElectrode(filler metal)

cast iron rod high carbon-high siliconFlux

sodium carbonate Na2CO3・10H2Osodium borate Na2B4O7・10H2Osodium bicarbonate NaHCO3

silica sand SiO2

orthoboric acid H3BO3

Welding portion

Welding processes (Fig.K11)

ji ca 2010 cast iron

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