62
K. Santhy and D. R. Rajkumar
Graphite
Graphite
Ferrite
Pearlite
(a)
(b)
Fig. 6 Microstructure of ductile cast iron, a before and b after etching
Type A graphite flakes which are randomly distributed and oriented throughout the
ferrite matrix. The ductile cast iron products consist of a pearlitic matrix with ferritic
rings of varying thickness surrounding graphite nodules. Due to the addition of
inoculants such as Ce and slow solidification, small amount of chunky graphite
is also observed in microstructure of ductile cast iron. To avoid chunky graphite,
multiple inoculation will be a better choice. The cast iron composition before and
after addition of inoculants are shown in Table 3. For cast iron, main alloying elements
are carbon(C) and silicon (Si) in iron (Fe). These elements play an important role in
the formation of required microstructure which decides the properties of cast iron.
Even though phosphorous (P) is in trace amount, which helps for the fluidity, it is
maintained minimum. If P is high, it induces the shrinkage porosity. The combined
influence of C, S and P is determined by carbon equivalence (CE) such as
CE = %C +
(%Si + %P)
3
(1)
Table 3 Chemical composition (in wt%) of ductile and grey cast iron before and after adding
inoculants using melt spectroscopy
Element
Ductile iron (wt%)
Grey iron (wt%)
Initial
Final
Initial
Final
Carbon
3.711
3.523
3.859
3.6
Silicon
2.789
2.6
2.316
2.152
Manganese
0.604
0.59
0.468
0.463
Phosphorous
0.032
0.034
0.06
0.048
Sulphur
0.1
0.018
0.041
0.046
Chromium
0.247
0.244
0.085
0.089
Nickel
0.089
0.09
0.032
0.036
Molybdenum
0.018
0.017
–
–
Magnesium
0.056
0.041
–
–
Iron
92.278
92.69
93.139
93.566
K. Santhy and D. R. Rajkumar
Graphite
Graphite
Ferrite
Pearlite
(a)
(b)
Fig. 6 Microstructure of ductile cast iron, a before and b after etching
Type A graphite flakes which are randomly distributed and oriented throughout the
ferrite matrix. The ductile cast iron products consist of a pearlitic matrix with ferritic
rings of varying thickness surrounding graphite nodules. Due to the addition of
inoculants such as Ce and slow solidification, small amount of chunky graphite
is also observed in microstructure of ductile cast iron. To avoid chunky graphite,
multiple inoculation will be a better choice. The cast iron composition before and
after addition of inoculants are shown in Table 3. For cast iron, main alloying elements
are carbon(C) and silicon (Si) in iron (Fe). These elements play an important role in
the formation of required microstructure which decides the properties of cast iron.
Even though phosphorous (P) is in trace amount, which helps for the fluidity, it is
maintained minimum. If P is high, it induces the shrinkage porosity. The combined
influence of C, S and P is determined by carbon equivalence (CE) such as
CE = %C +
(%Si + %P)
3
(1)
Table 3 Chemical composition (in wt%) of ductile and grey cast iron before and after adding
inoculants using melt spectroscopy
Element
Ductile iron (wt%)
Grey iron (wt%)
Initial
Final
Initial
Final
Carbon
3.711
3.523
3.859
3.6
Silicon
2.789
2.6
2.316
2.152
Manganese
0.604
0.59
0.468
0.463
Phosphorous
0.032
0.034
0.06
0.048
Sulphur
0.1
0.018
0.041
0.046
Chromium
0.247
0.244
0.085
0.089
Nickel
0.089
0.09
0.032
0.036
Molybdenum
0.018
0.017
–
–
Magnesium
0.056
0.041
–
–
Iron
92.278
92.69
93.139
93.566