Heat Treatment process & its types

Heat Treatment

Heat treatment is the heating and cooling of metals to change their physical and mechanical properties,without changing its shape.

Grain structure changes with the application of heat and method of cooling. This induces desired properties in the steel.

It is applicable to plain carbon steel, alloy steel as well as non ferrous materials like aluminum and copper.

Heat treatment enhances properties like Hardness, Toughness, Strength & ductility. 

Types of Heat Treatment Processes

• Hardening
• Tempering
• Annealing
• Normalizing 
• Surface Hardening ( Carburizing & Nitriding )

Hardening

Heating Process : The metal is heated at a high temperature and this temperature is maintained until a proportion of carbon has been dissolved in to the metal.

Cooling Process : The metal is quenched, which involves rapidly cooling it in oil or water.

Results : high strength and wear resistance. However hardening will also increase brittleness

Tempering

Heating Process : It is a low temperature heat treatment process normally performed after hardening( double hardening ).

Cooling Process : cooling in air.

Results : Ductility in increased , tougher and less brittle steel.

Annealing

Heating Process : Heating the metal to a specific temperature.

Cooling Process : cooling slowly at a controlled rate.

Results : Annealing is frequently used to soften metals including iron, steel, copper, brass and silver. It increase ductility and reduce hardness. This facilitates shaping, stamping or forming processes, and allows the metal to be cut more easily. Annealing also enhances electrical conductivity.

Normalising

Heating Process : The metal is heated to a predefined temperature.

Cooling Process : cooled by air.

Results : Greater strength and hardness. Typically, the normalising process is performed on materials that will be subjected to machining.

Carburizing

It is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material such as carbon monoxide. The intent is to make  the metal harder. Not the whole metal-piece but certain outer thickness only can be carburized.

Nitriding

It is a heat treatment process that diffuses nitrogen into the surface of a metal to create a case hardened surface. These processes are most commonly used on low to medium carbon & low-alloy steels.