analysis of annealing hardenig and tempering

1. Heat Treatment
Analysing of Annealing
Hardening Tempering
By
M.Sabari Venkat Narayanan

2. Definition
• Annealing is a heat process whereby a metal
is heated to a specific temperature /colour
and then allowed to cool slowly. This softens
the metal which means it can be cut and
shaped more easily. Mild steel, is heated to a
red heat and allowed to cool slowly.

3. Annealing
 Makes a metal as soft as
possible
 Hypoeutectoid steels (less
than 0.83% carbon) are
heated above upper critical
temp., soaked and cooled
slowly.
 Hypereutecoid (above
0.83%) are heated above
lower critical temp., soaked
and allowed to cool slowly

4. Process of Annealing
• Process Annealing. Low
carbon steels may harden
through cold working.
They can be heated to
around 100 degrees
below lower critical
temp., soaked and
allowed to cool in air.
• Spheroidising. High
carbon steels may be
annealed just below the
lower critical temp. to
improve machinability

5. Full Annealing
• A full anneal typically results in the second most ductile
state a metal can assume for metal alloy. It creates a new
uniform microstructure with good dynamic properties. To
perform a full anneal on steel for example, steel is heated
to 50°C above the austenic temperature and held for
sufficient time to allow the material to fully
form austenite or austenite-cementite grain structure. The
material is then allowed to cool slowly so that
the equilibrium microstructure is obtained. In some cases
this means the material is allowed to air cool. In other cases
the material is allowed to furnace cool. The details of the
process depend on the type of metal and the precise alloy
involved. In any case the result is a more ductile material
but a lower yield strengthand a lower tensile strength.

6. Normalizing
• Normalizing is a technique used to provide
uniformity in grain size and composition
throughout an alloy. The term is often used for
ferrous alloys that have been austenitized and
then cooled in open air.[18] Normalizing not
only produces pearlite, but also sometimes
martensite, which gives harder and stronger
steel, but with less ductility for the same
composition than full annealing.

7. Stress Relief
• Stress relieving is a technique to remove or
reduce the internal stresses created in a
metal. These stresses may be caused in a
number of ways, ranging from cold working
to non-uniform cooling. Stress relieving is
usually accomplished by heating a metal
below the lower critical temperature and then
cooling uniformly

8. Hardening
 Medium and High carbon steels (0.4 –
1.2%) can be heated until red hot and then
quenched in water producing a very hard
and brittle metal. At 723 degrees, the BCC
ferrite changes into Austenite with a FCC
structure.

9. Hardening 0.6% carbon steel
 The metal is heated to over
780 degrees, which allows
the carbon to dissolve into
the FCC Austenite.
 Quenching the metal
quickly in water prevents
the structure from changing
back into BCC.
 A different structure, Body
Centre Tectragonal (BCT) is
formed. It is called
Martensite and is extremely
hard and brittle with a
needle-like microstructure.

10. Quenching
• Quenching is a process of cooling a metal at a
rapid rate. This is most often done to produce
a martensite transformation. In ferrous alloys,
this will often produce a harder metal, while
non-ferrous alloys will usually become softer
than normal.

11. Tempering
 To remove some of the brittleness from
hardened steels, tempering is used. The metal
is heated to the range of 220-300 degrees and
cooled.
 Tempering colours are an indicator of
temperature on polished metals. Colours
range from yellow to brown to violet and blue.

12. Heat Treatments
 A – Normalising
 B – Annealing or
Hardening
 C – Spheroidising or
Process Annealing
 D - Tempering