Defects and Property Failure

Prévia do material em texto

Defects & Cause.
Defects Root Cause
Shrinkage
Rusty charge: very high chilling tendency in this iron
low content of CE
EFFECT OF SUPERHEATING
Metal Holding
Excess magnesium
Under inoculation or over inoculation
High Pouring temp
Chunky graphite
High Purity charge materials
Metal Holding 
High CE
High %RE(rare earth)
High Pouring Temp
Mech Failure
Poor Charge Mix
Fadding
ELEMENT SEGREGATION TENDENCY
Blow Hole Low Pouring Temp
Slag inclusion
Rusty charge materials
Poor Pouring Practice
Types of shrinkage
Decrease in volume of the metal as it solidifies
Outer sunks:
Outer sunks (pull downs, sinks) can be seen 
from the outside of the casting, usually as a 
smooth depression in the casting surface.
Macro shrinkage:
Macro shrinkages are usually found 
inside the casting and close to heat 
centers. They appear as larger holes,
Defect size >5mm 
Micro shrinkages:
Micro shrinkages are smaller cavities 
with irregular surfaces. Defect size 
<3mm also called porosity
Shrinkage
 Rusty charge: 
very high chilling tendency in this 
metal
 High Magnesium:
Very high chilling tendency in this 
metal
High magnesium content acts 
to promote carbidic 
microstructures and increase 
shrinkage
Shrinkage
Effect of Superheating:
the temperature of any melt is increased above 
the normal melt temperature (high 
superheat), nucleation has been reduced. 
Holding:
The longer the hold times, at any 
temperature, the greater the loss of 
nucleation.
Shrinkage
Under inoculation: 
Not enough to precipitate Carbon as a graphite
Over inoculation:
Too many nucleation points are active early in the solidification
feeders become inactive and contraction takes place, there is no graphite
Chunky Graphite
Entrapment of gases in the cavity while pouring. 
Occurrence: were the casting thickness is more
High RE:
Excessive cerium in the metal will cause the chunky 
graphite.
Wall thickness < 25 mm Ce 0,020 – 0,015 %
25 – 50 mm Ce 0,015 – 0,010 %
50 – 100 mm Ce 0,010 – 0,005 %
100 – 250 mm Ce 0,005 – 0,002 %
250 mm Ce 0,002 – 0,000 %
High Purity Charge material:
Charge more than 50% sorrel PI cause there is no trace 
element eg: Pb,Bi,Sb etc
High Pouring Temp & Holding:
Both will affect the nucleation of SG to form CHG.
High CE:
Increased volume of the graphite
Mechanical Failure
Exploded Graphite
 Excess, rare earths can
cause exploded graphite.
 At very high carbon equivalent 
(CE).
 Exploded graphite is normally 
found in thicker section
castings with slow cooling 
rates.
 High purity charges are used 
which are low in detrimental 
tramp elements such as lead, 
bismuth, antimony, titanium etc
Mechanical Failure
Graphite Flotation
 At very high carbon 
equivalent (CE).
 The nodules, being of a 
lower density than the 
matrix, tend to float 
towards the surface of 
the casting. 
CE
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V1/V
V2/V
Slag Inclusion
A product resulting from the action of a flux on the oxidized non-metallic constituents of molten metals.
Occurrence: Any place of the casting Rusty Charge: 
Charge containing oxide products 
(e.g:Rust CRS & Borings), that one 
oxidize the metal. it will cause Heavy 
slag formation in the metal. 
 Pouring Practice:
Slag should be removed thoroughly.
Metal level should be maintained 75% 
of basin capacity during the pouring. 
Min 300Kg metal maintained in the 
Basin
Material Charge Mix Slag
steel 1-2%
DI Returns 5-10%
Pig iron 0.12%
rusty scrap 12%
Borings 25%
Dross
Non metallic inclusion is called Dross
Occurrence: Surface of the casting
• Non metallic inclusion:
Excess residual Mg (>0.050%)in the metal 
react with oxygen & sulphur to form 
Mgo,Mgs respectively. It will appear on the 
surface of the casting.
• Low pouring Temp:
mg easily react with Si to form Mgsi2
(During Inoculations)
• Turbulence:
Rapid flow of metal into the mould
Will cause Dross 
Blow Hole
Entrapment of gases in the cavity while pouring.
Occurrence: Any place of the casting
Low Pouring Temp:
Gas molecules not easily escape from the 
mould at low temp.
Ti & Al content in metal:
it will promote the evolution of the gas in 
the metal.
Requirements for cast-on sample as per standard 
DIN 1563-2003-02[5]
Material designation
Walll 
Impact 
Mea
n(J)
Impact 
Individual
(J)
Min. tensile Min. Yeild 
% Elong
thickness, 
t(mm)
strength(N
/mm2)
strength(N/
mm2)
EN-GJS-350-22U-LT
Impact at - 40 ± 2℃
< 30 12 9 350 220 22
30 < t ≤ 60 12 9 330 210 18
60 < t ≤ 
200
10 7 320 200 15
EN-GJS-400-18U-LT
Impact at - 20 ± 2℃
< 30 12 9 400 240 18
30 < t ≤ 60 12 9 390 230 15
60 < t ≤ 
200
10 7 370 220 12
Mechanical Failure
The following Metallurgical defect Can 
cause the Mechanical failure.
1.Fading
2.Exploded Graphite
3.Chunky Graphite
4.Compacted Graphite
5.Graphite Flotation
6.Spiky Graphite
Mechanical Failure
Fading
 Holding the metal after 
treatment will cause 
Fading 
 High Sulphur content in 
the bath
 Inadequate inoculation
Mechanical Failure
Compacted Graphite
 Incorrect weighing 
of the nodulariser. 
 Although a long 
holding time in the 
ladle or excessive 
temperatures. 
Mechanical Failure
Spiky Graphite
 Excess, Trace elements 
such as lead, bismuth, 
titanium and antimony 
present in the metal to 
form Spiky Graphite.
ASTM A48 (Class 30, 35, 40? Gray Iron Castings 
ASTM 159 or SAE J431 ( G4000, G3500, G3000, G2500, G1800) Automotive Gray Iron Castings 
ASTM A319 Class I, II, III Gray Iron Castings for Elevated Temperatures
ASTM A436 (DIN 1694, BS 3468) Ni-Resist Castings, Austenitic Gray Iron Castings 
DIN 1691 (GG10, GG15, GG20, GG25, GG30, GG35) 
EN 1561 （EN-GJL-200, EN-GJL-250, EN-GJS-300, EN-GJS-350,EN-GJS-400, 
EN-GJS-500, EN-GJS-600, EN-GJS-700) , 
ISO 185
SG IRON
ASTM A536 (60-40-18, 65-45-12, 80-55-06?100-70-03, 400-15, 500-7, 600-3) Ductile Iron Casting 
ASTM A439 (DIN 1694, BS 3468) Austenitic Ductile Iron
ASTM A897 Austempered Ductile Iron ADI 
ASTM A571 Low Temp, Pressure-Containing 
DIN 1693 (GGG-30, GGG-40, GGG-50, GGG-60, GGG-70, GGG-80) 
EN 1563 (EN-GJS-400-15, EN-GJS-450-10, EN-GJS-500-7, 
EN-GJS-600-3, EN 1563 EN-GJS-400-18-LT) 
SAE J434（D4018, D4512, D5506?D5504?D7003, D700, D800, D400) 
ISO 1083, BS 2789 
Grey & SG iron