ji ca 2010 cast iron
TRANSCRIPT
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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)