Case hardening

2. Case hardening
 Case hardening is a heat treatment
technique in which the steel surface is
processed by the addition of carbon ,
nitrogen or both to the surface of the steel
part in order to provide a hardened
case(layer) of a definite depth of 0.03mm.
 This is called case hardening.
 This technique used only for low carbon
steels

3. CARBURISING
 Carburizing is a method of introducing,carbon
to ferrous alloy such as low carbon steels in
order to produce a hard case(surface).
 Carburizing is also called as cementation.
 process:
 Low carbon steel is heated at 870 to 925 0C In
contact with gaseous , solid or liquid carbon
containing substances for several hours.
 Thus high carbon steel surface is obtained
followed by quenching.

4. NITRIDING
 Nitrogen is added instead of carbon to the
surface of the steel.
 Process:
 The piece to be case hardened is put into a
furnace and heated to between 950° and
1,200°F and, at the same time, is exposed to
ammonia gas. The heat of the furnace causes
the ammonia to break down into nitrogen and
hydrogen. Some of the nitrogen combines with
the elements in the steel to form chemical
compounds called nitrides in the outer layer of
the steel.
 These nitrides give the surface its hard, wear-
resistant qualities.

5. CYANIDING
 CYANIDING can be used to obtain a hard
superficial case on low-carbon steels.
 process
 The process involves the introduction of both
carbon and nitrogen into the surface layers
of the steel.
 Steels to be cyanided normally are
heated(850 0C) in a molten bath of cyanide
carbonate- chloride salts and then
quenched water.

6. Induction hardening

7.  Induction hardening is a process used for the surface
hardening of steel and other alloy components.
 The parts to be heat treated are placed inside a
copper coil and then heated above their
transformation temperature by applying an
alternating current to the coil. The alternating current
in the coil induces an alternating magnetic field within
the work piece, which if made from steel, caused the
outer surface of the part to heat to a temperature
above the transformation range.
 Parts are held at that temperature until the
appropriate depth of hardening has been achieved,
and then quenched in oil, or another media,
depending upon the steel type and hardness desired.

8. Flame hardening

9. working
 Flame hardening is similar to induction
hardening, in that it is a surface hardening
process. Heat is applied to the part being
hardened, using an oxy- acetylene (or
similar gas) flame on the surface of the steel
being hardened and heating the surface
above the upper critical temperature before
quenching the steel in a spray of water. The
result is a hard surface layer ranging
from0.050" to 0.250" deep.