Spheroidizing is a heat treatment process which results in a structure consisting of globules or spheroids of carbide in a matrix of ferrite

1. SPHEROIDIZING

2. • Spheroidizing is a heat treatment process
which results in a structure consisting of a
globules or spheroids of carbide in a matrix of
ferrite.
• The degree of spheroidization depends on
heat treatment temperature and holding time.

3. • The process can be completed in short time by
increasing the treatment temperature.
• With high spheroidization temperatures,
dissolved carbide particles can reappear as
lamellar during cooling.

4. Methods
Some methods to get spheroidized
structures.

5. Method 1
• Heating of steel just below the lower critical
temperature
• Hold at this temperature for prolonged period
and followed by slow cooling.

6. Method 2
• Heating and cooling steel alternately just
above and below the lower critical
temperature.
• Isothermal annealing is also used for this
process.

7. • In it heating of steel to a temperature above
the lower critical temperature, followed by
slow cooling to a temperature below the
lower critical temperature.
• Hold steel at this temperature for a period till
the shape of all carbide particles changes into
spheroids.

9. • Eutectoid steels are heated about 20-30 °C
above the lower critical temperature.
• Hypereutectoid steels are heated 30-50 °C
above the lower critical temperature.
• Medium carbon steels can be spheroidized
either by heating just above or below the
lower critical temperature.

10. • High carbon steels and alloy steels are
frequently spheroidized in order to improve
ductility and machinability.
• Low carbon steels are generally not
spheroidized.