Heat treatment could be any one of a variety of controlled
heating operations used to change the physical properties of a metal; there are
five different types of heating processes. These would be case hardening,
normalizing, hardening and tempering. Even though they all differentiate in
results, they all share three simple steps: heating, soaking and cooling.
The first step in a heat-treatment process would be heating.
The steal is heated to its final temperature. This helps in keeping a uniform temperature
in the part being heated. This reduces cracking and distortion.
When a piece of metal is heated to the temperature in which
a change in structure takes place, it has to stay at that particular temperature
until the entire part has been evenly heated. The more mass it has, the longer
it will take for t to be completely soaked, this is known as soaking.
After the metal part has been soaked, the last step us to
cool. This process may force the structure to stay the same, revert to its original
form or even change from one chemical composition to another. These changes are
all predictable and for this reason metals can now be made to suit certain
structure to increase the level of their, hardness, strength and ductility.
This is the process of hardening the surface of metal
objects while the deeper metal underneath stays soft, this will form a thin
layer of harder metal called the case. For other metals like iron and steel
that have low carbon content the process would involve infusing additional
carbon into the surface layer. Generally case hardening would be done after it
has been formed into its final shape, carbon and alloy steels are suitable for
Annealing the exact opposite of hardening, it relieves
internal stresses, softens them and makes it more ductile. It is the process
where a metal is heated to very high temperature; it would be held there for a
period of time usually between hours and days and allowed to cool. For this
process to go perfectly, the process should be slow down in steels and other ferrous
metals. Condition in the furnace is controlled firmly to assure the expected changes
are going to take place.