melting

1. SUPERALLOYS
MELTING AND PRACTICE

2. VACUUM INDUCTION MELTING
 Flexibility due to small batch sizes
 Fast change of program for different types of steels and alloys
 Easy operation Low losses of alloying elements by oxidation
 Achievement of very close compositional tolerances
 Precise temperature control Low level of environmental pollution from dust
output
 Removal of undesired trace elements with high vapor pressures
 Removal of dissolved gases, for example, hydrogen and nitrogen.

3. BASIC ELEMENTS OF A
VACUUM INDUCTION
MELTING
FURNACE
• A virgin portion, which consists of
material that has never been
vacuum melted
• A refractory portion, which consists
of those virgin elements that are
strong oxide formers and have the
tendency to increase the solubility
of oxides and nitrides in the virgin
charge
• A revert (or scrap) portion, which
consists of both internal and
external scrap that previously has
been vacuum melted

4. DOUBLE-CHAMBER
VACUUM
INDUCTION
MELTING FURNACE

5. TYPICAL REFRACTORIES USED TO LINE VACUUM
INDUCTION MELTING CRUCIBLES

6. MELTING PROTOCOL FOR NICKEL- AND COBALT-BASE SUPERALLOYS

7. SHAPE CASTING WITH VIM

8. POTENTIAL PROCESSING ROUTES FOR PRODUCTS CAST FROM VACUUM
INDUCTION MELTING (VIM) INGOTS OR ELECTRODE

9. VIM Metallurgy - Refining
• Selection of a more stable refractory material
for the crucible lining
• Rinsing of the melt with inert gas
• Minimizing the contact time of the melt in the
crucible
• Exact temperature control to minimize crucible
reactions with the melt
• Suitable deslagging and filtering techniques
during pouring
• Conception of a suitable tundish and launder
system for good oxide removal
• The quantity of the dissolved gas
• The decreased pressure exerted on the bubble
as it rises in the melt
• The bath temperature
• The time it takes for the bubble to rise through
the melt to the surface, which, in turn, is a
function of melt stirring
• The pressure above the melt
• The interfacial tension between the bubble
and the liquid metal.

10. Trace Elements

11. Melting and stirring modes of the vacuum induction melting process

12. Freckle Formation
 Due to high solute contents in Superalloys
impulse to be solidified under controlled
conditions.
 When solidification rates are too slow, the solute
rejected from primary dendrites formed. It is
forming continuous channels of very high solute
content.
 When these channels solidify as ‘‘freckles’, they
are too concentrated in solute to be dissolved by
subsequent heat treatment, and thus form
continuous hard defects

13. Freckle formation
Local solidification time is defined as:
LST =TL –TS / G×R
TL - The liquidus temperature (oC),
TS - The solidus temperature (oC),
G - The temperature gradient (oC/cm)
R - The solidification rate (cm/min).
 Increasing heat extraction or decreasing heat input increases both G and R.
 It decreases LST, and increasing heat extraction or decreasing heat input thus decreases dendrite size.
 When the solidification conditions become sufficiently slow (high LST) that the dendrites and the
separation between them becomes large, the interdendritic regions may combine into a continuous
channel of liquid.
 Freckles occur in regions with high LSTs, that is, in large ingots, solidifying slowly and thus with large
mushy zones (low G.R).

14. VAR – VACCUM ARC
REMELTING FURNACE

15. ELECTROSLAG REMELTING
FURNACE - ESR