Heat treatments of materials

Heat treatments of materials

Heat treatments of materials

Heat treatment is a process wherein the material is heated and then cooled in a predetermined manner ( controlled way). 

Through this method, it is possible to change the physical and mechanical properties of metal without changing its shape.

Purpose of heat treatment:-

usually, heat treatment performed to improve the properties of the material or get the desired ability of the material such as ductility, toughness, hardness, strength softness, etc. Through this process, the properties of the metal are changed as required.

Steps in Heat Treatment

There are three steps involved in heat treatment such as:

Heating Temperature is raised in this segment in a controlled manner to the required extent.

Soaking(Holding)In this segment, the temperature is kept constant for a specified time after the temperature rises to the required extent.

Heat treatments of materials

CoolingTemperature is reduced in this segment and the metal is brought to room temperature

Types of heat treatment

Types of heat treatments are as follows:

Quenching(Hardening)

-By this method, the metal is heated to the required temperature and then rapidly cooled which is called quenching or quenching hardening. In this process, oil or water is used for rapid cooling.




Effect on the material after quenching-By this method the hardness and strength of the metal increases but the brittleness decreases.

Tempering

Heat treatments of materials

-In this process, the material is heated at the required temperature and then cooled in the airway (room temperature environment. 

Effect on the material after Tempering-

By this process, the internal stress is reduced along with brittleness decreased.

ANNEALING

With this method, the material is heated to the required temperature and then held at that temperature for a required time frame, then cooled slowly. For this purpose, ash, sand is used or kept in the furnace by lowering the temperature.

Effect on the material after annealing-

Annealing is used for relieving internal stresses, increase ductility, fine grain structure(softness)

Normalizing

By this method, the metal is heated to the required temperature and then the temperature is kept constant for a specified time then cooled in air,

Effect on the material after normalizing 

this method reduces the internal stresses caused by welding or machining operations as well as increasing the toughness .

Carburization

It is a heat treatment process wherein steel or iron is heated to a temperature, below the melting point, in the presence of a liquid, solid, or gaseous material that decomposes so as to release carbon when heated to the temperature used.

Heat treatment in welding

The main purpose of heat treatment in welding operations is to remove the stresses that come in the metal due to welding. If this stress is not removed then there is a possibility of cracking in the joint.

Heating& Soaking

Soaking temperature for carbon steel material-620℃. (±20℃)

Soaking period for carbon steel material- 1 hour

Soaking temperature for alloy steel material -720℃. (±20℃)

Soaking period for alloy steel material- 2 hours

Conclusion

Usually the rate of heating and colling for Carbon steel is 150℃/hour, and the rate of heating and cooling for alloy steel is 100℃/hour.