The basic knowledge of heat treatment

Definition of heat treatment

* The process of processing metal parts by heat treatment, which includes heating to standard temperatures, holding heat and cooling at different rates.
 

Heat treatment of steel achieves 2 purposes

* Achieving desired quality (Hardness, permeability layer thickness, microstructure, etc.)
* In the same part when heat treatment mechanical properties another inner surface


 

The iron-carbon phase diagram

 

Basic heat treatment methods

Normalizing
• Heat the part to a temperature 40-50^oC above the upper critical point, hold that temperature, and then cool in still air.
Annealing
• Heat the part to a temperature between 40-50^oC above the upper critical point, hold that temperature, and then cool in still air.
Austemper
• Heat the part to a temperature 40-50^oC above the upper critical point, keep that temperature and then cool it at 232-427^oC until it is completely transformed into Bainite
Isothermal annealing
• Heating the part to a temperature 40-50^oC above the upper critical point, keeping it at that temperature and then cooling it to a temperature below the A1 line (50-100^oC) keeping the heat and then cooling it in still air
Spheroidizing annealing
• Heating the part to the circulating temperature above and below the temperature of the A1 line forms a spherical Cemanite organization.

Methods of heat treatment and microstructure of metals

 

Typical microstructure after quenching

 

Change the microstructure of the part surface layer

 

Change Layering improves the mechanical properties of steel