Spheroidizing

Spheroidizing - Mechanism
The
solubility of carbon in ferrite, which is
very low at room temperature (0.02% C),
increases considerably up to the Ac1
temperature
At temperatures close to Ac1, the diffusion of
carbon, iron, and alloying atoms is so great
that it is possible to change the structure in
the direction of minimizing its energy
content
Spheroidizing - Process
Prolonged
heating at a temperature just bel
ow the lower critical temperature, usually foll
owed by relatively slow cooling
In the case of small objects of high C steels,
the spheroidizing result is achieved more ra
pidly by prolonged heating to temperatures
alternately within and slightly below the critical
temperature range
Tool steel is generally spheroidized by heating
to a temperature of 749°-804°C and higher for
many alloy tool steels, holding at heat from 1 to
4 hours, and cooling slowly in the furnace
CASE HARDENING
Case
hardening or surface hardening is the
process of hardening the surface of a
metal, often a low carbon steel, by infusing
elements into the material's surface,
forming a thin layer of a harder alloy.
Case hardening is usually done after the
part in question has been formed into its
final shape
Case-Hardening - Processes
Flame/Induction
Carburizing
Nitriding
Cyaniding
Carbonitriding
Hardening
Flame and induction hardening
Flame
or induction hardening are processes in
which the surface of the steel is heated to high
temperatures (by direct application of a flame,
or by induction heating) then cooled rapidly,
generally using water
This creates a case of martensite on the
surface.
A carbon content of 0.4–0.6 wt% C is needed
for this type of hardening
Application Examples -> Lock shackle and
Gears