Metal is heated to modify its physical and mechanical properties without changing its form. Changing these properties in metal manufacturing is essential as it improves required characteristic of metal while allowing for further processing to take place.
Heat treatments involve controlled heating and cooling of metals. For instance, steel is generally given heat treatment for use in multiple commercial applications.
What do heat treatments do?
- Increase strength
- Improve ductility
- Increase elasticity
- Increase hardness
- Increase machinability
- Enhance formability
The cooling procedure has different effects on metal. When steel is cooled down quickly it increases the hardness, whereas the quick cooling stage of annealing softens aluminium. Annealing and tempering are one of the most important types of heat treatment.
What is annealing and how does it work?
Annealing is a heat treatment process which involves heating steel to a specified temperature and then cooling it at a slow rate.
Annealing is done to:
- Soften steel for cold working
- Increase machinability
- Improves electrical conductivity
Annealing also re-establishes ductility. During the cold working procedure, the metal becomes so hard that any more work will result in breaking. Annealing metal beforehand reduces the risk of cracking while cold working.
Generally, annealing is used for steel, although, other metals including aluminium, brass etc can be subject to a procedure known as solution annealed.
During the annealing process, the metal is heated to a specific temperature which encourages re-crystallization. This stage repairs any defects caused by deformation of the metal. The metal is held at a temperature for a specific period of time and then it is cooled down to room temperature.
The cooling process is done slowly to produce a superior micro-structure, thus improving softness. This is often done by dipping the hot steel in sand, ashes or other materials with low heat conductivity, or by turning off the oven and letting the steel cool with the furnace.
What’s Tempering and How does it Work?
Tempering is basically done to improve the toughness of iron alloys, mainly steel. Before the tempering process, steel is too brittle for most of the applications. It is generally done after hardening to decrease extra hardness.
Tempering is done to modify:
- Structural stability
During tempering, the metal is heated to a specific temperature. The temperature is set depending on the amount of hardness needs to be reduced. Low temperature generally reduces brittleness and maintains hardness, while higher temperature reduces hardness increasing machinability.