Conclusions
The eutectic cell and nodule count of graphite in castings can be predicted when the following parameters are known:
• •
Nucleation coefficients and maximum undercooling.
Chemical composition of cast iron, nucleation co- efficients and cooling rate.
• Chemical composition of cast iron, maximum un- dercooling and cooling rate.
Moreover, knowing the chemistry of the cast iron and the critical cell and nodule count, the chilling tendency index, as well as the chill can be predicted.
SYMBOLS Symbol
A B
B, B1 C
cef
CE CT
CTn D
Fc L
la L
Le Lγ
M N
n(l) ni
N
Nnuc Nn,cr Nv
NL Nn
Nv,n Ns
Nx P
pn P
(l)
fgr fγ
D fc
, B2
The eutectic cell and nodule count are a direct measure of the graphite nucleation potential, while the nucleation coefficients, Ns
and b are an indirect measure. In turn, these parameters determine the quality of the molten cast iron (in terms of the graphite nucleation potential) and hence they incorporate all of the technological fac- tors connected with the melt processing. In addition, this work shows that the melt quality can be linked to found- ry practice through factors such as chill, pre-shrinkage expansion, shrinkage porosity and shrinkage depression, as well as graphite and matrix structure (including me- chanical properties).
Meaning
Mold ability to absorb heat Nucleation coefficient Temperature parameters Specific heat of metal
Effective specific heat of metal Carbon equivalent
Chilling tendency index of flake graphite cast iron Chilling tendency index of ductile iron Diameter of the cylindrical casting
Diffusion coefficient of carbon in austenite Fraction of liquid in mushy zone
Volume fraction of graphite at room temperature Volume fraction of proeutectic austenite Surface area of the casting
Substrate size of incompletely dissolved graphite particles Average size of all graphite nucleation sites Width of the mushy zone in casting Latent heat of graphite eutectic Latent heat of pre-eutectic austenite Casting modulus
Wedge size coefficient Size distribution function
Size distribution function for inoculated iron Cell count per unit area
Nodule or flake graphite count per unit secant length. Nodule count
Cell count per unit volume of metal Nodule count per unit volume of metal
Number, of active sites for nucleation Critical nodule counts at temperature T ≈ Tc
Number of all of the graphite nucleation sites in melt per unit volume, nucleation coefficient Cell or nodule count in mushy zone Parameter for flake graphite cast iron Parameter for ductile iron
Pressure generated during solidification of graphite eutectic
ProductLog(y) Lambert function, also known as Omega function Q
Casting cooling rates of flake graphite at graphite eutectic equilibrium temperature Ts
International Journal of Metalcasting/Summer 10
Definition/Value - -
Eqn. (19) -
Eqn. (20)
Units
J/(cm2 oC s1/2 oC -
J/(cm3 o J/(cm3 o
CE = C + 0.33Si Wt. % Eqn. (29) Eqn. (31) -
s1/2 s1/2 cm
Table 2 --
0.12
Table 2 -
Eqn.(7)
Eqn. (23) -
Table 1 Table 2
Eqn. (17) -
Eqn. (4) -
Eqn. (1) -
Eqn. (1) Eqn. (8)
Eqn. (2) Eqn. (3)
- -
Eqn. (28) Eqn. (30) - -
Eqn. (15)
/o /o
cm2 - - -
cm2 cm cm cm
J/cm3 J/cm3 cm -
cm-4 cm-4 cm-2 cm-1
mm-2
cm-3 cm-3 cm-3
cm-3
(cm o (cm o bar -
oC/s 55
C1/3 C1/3
)/1/2 )/1/2
/s
C) C)
C1/3 C1/3
)
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