HEAT TREATMENT
Dr. Maryam Abduladheem
Lecture 1
HEAT TREATMENTS
Heat treatment is the process of heating (but
never allowing the metal to reach the molten
state) and cooling metal in a series of specific
operations which changes or restores its
mechanical properties.
STAGES of HEAT TREATMENT
• Stage l — Heat the metal slowly to ensure a uniform
temperature.
• Stage 2 — Soak (hold) the metal at a given temperature
for a given time.
• Stage 3 — Cool the metal to room temperature.
Heat treatment process Variables includes:
1.Heating temperature
2.Cooling temperature
3.Heating rate
4.Cooling rate
5.Soaking time
6.Environment
* Heat
treatment may use for:
1- Final product to alter the properties (in general).
2- To facilitate the manufacturing processes such as
the rolling process.
IRON-CARBON PHASE DIAGRAM
It’s defined as:A map of the temperature at which different phase changes
occur on very slow heating and cooling in relation to Carbon
content. is Isothermal and continuous cooling transformation
diagrams for plain carbon and alloy steels.
Various Transformation Reactions and development of
Microstructure
• Peritectic Reaction:

L+⇌
• Eutectic Reaction: Eutectic of austenite and
cementite is known as ledeburite

L ⇌  + Fe3C
• Eutectoid Reaction: Eutectoid of ferrite and
cementite is known as pearlite. The ferrite and
cementite phases occur as alternate layers

 ⇌  + Fe3C
• When Fe-alloy of
0.77% of C is
cooled slowly it
transforms from
single phase of
austenite to
pearlite structure.
 ⇌  + Fe3C
Microstructure of hypoeutectoid steel
Microstructure of hypereutectoid steel