The finished product of casting is processed to get good properties by heat treatment. Certain properties or desirable condition is obtained by heating or cooling of the metal by without any changing of chemical composition in solid state.
The metal consists of micro structure of grain particals. It is a mechanical and metallurgical process in which, By the changing of grain size or micro structure we can obtain some challenging properties of metal.
Following properties to be obtained by the heat treatment process.
- To Soften metal.
- To increase the hardness and strength of metal.
- To change the magnetic properties.
- To Increase the resistance of wear.
- To change grain size.
- To change the electric properties.
- To Improve machinability and quality of casting.
Considering its different properties in way of engineering, its 1st topic is normalizing
Normalizing
Normalizing process is used to soften the metal. By the normalizing we can achieve highest machinability and improve tensile strength. By this improvement in electric and magnetic properties of metal.
The cold working process like hammering, knockout, bending causes strain on metal, its remove by normalizing.
It used to refine grain structure and uniformity of grain size and composition. It makes the material brittle and unreliable. This process less expensive than annealing.
For Hypo eutectoid steels the heating temperature is 45 to 50 degree above to its upper critical temperature and for Hyper eutectoid steels, the temp. is 45 to 50 above to its lower critical temp. The metal is kept for a while at this temperature and then cooled down by air.
The upper and lower critical temp of steed depends upon the total percentage of carbon consists in steel.
For best quality and machinability it performed after forging and casting.
In Hypo-eutectoid steel less than 0.8% of C in its composition. It is composed by pearlite and α-ferrite and Hyper-eutectoid steel has between 0.8% and 2% of C, composed by pearlite and cementite. It is very important to understand Iron-Carbon phase diagram to understand the Hypo-eutectoid and Hyper-eutectoid.
This process provides a uniform structure consisting of ferrite and pearlite for hypoeutectoid
steels, and for hypereutectoid steels pearlite and cementite.
