Manufacturing: Surface Finishing

Heat Treatment -

Case-hardened Pliers

Heat Treating is controlled heating and cooling of a solid metal or alloy by methods designed to obtain specific properties by changing the microstructure. Heat Treating takes place below the melting point of the metal and changes in microstructure take place within the solid metal. Changes in microstructure are due to the movement of atoms within crystal lattices in response to heating or cooling over a period of time.

The ability to tailor properties by heat treating has contributed greatly to the usefulness of metals and their alloys in an assortment of applications such as sheet metal for cars and aircraft.

Heat treating processes include annealing, normalizing, tempering, stress relieving, solution treating, age hardening, and bright hardening. Quenching, or cooling from a higher temperature, is an integral part of many heat treating processes when hardening is involved.

Regardless of the reason for the heat treating, the basic process is the same and has three steps.

1. Heat the metal to a specific temperature
2. Hold the metal at that temperature for a specific amount of time
3. Cool the metal in a specific manner

Basic Processes

The following heat treatment processes are the most commonly used:

1. Annealing
   
2. Normalizing
   
3. Stress Relieving
   
4. Tempering
5. Quenching
6. Hardening