HARDENING PROCESSES!

Why is Hardening and Heat Treament Required?

Since the material given to us was a High Carbon Steel, after the manufacturing, hardening can be done to improve the properties of steel and make it more desireable.. The type of hardening processes required, depends on the amount of carbon content in our mild steel sample. For example:

• Mild Steel- 0.4% Carbon.

• Medium Carbon Steel- 0.8% Carbon.

• High Carbon Steel- 1.2% Carbon.

Thus, the process of Hardening a High Carbon Steel specimen is as follows:-

QUENCHING:-

This is the process where the specimen is first made "red hot" and to do this, either it is heated slowly first and then the heat is concentrated to make it red hot or it can be placed in a furnace and allowed to become red hot. The temperature at which our specimen will become red hot is 800 degrees celcius.

Figure 1- Muffle furnace

After that, the specimen is soaked in a mild cold water, whose temperature will be around 22 degrees celcius (room temperature), and tongs are used to hold it. This soaking process is also called as Quenching and here the specimen is rapidly cooled within 5-10 minutes.

Thus Quenching improves the hardness of the material but at the same time, it increases the brittleness as well.

Tempering:-

After the soaking duration is over and the specimen temperature becomes normal, it is then treated by using using a Gas/Air control flame. This is done in order to improve the toughness of the specimen and make it less brittle, though it reduces the hardness of the specimen a little bit.

Figure 2 - Tempering using Flame.

The temperature till which the specimen is tempered is 300 degrees celcius, and at this temperature the specimen starts changing to blue colour, which is an indication that the tempering temperature has been reached. Thus, slow cooling is then performed by either placing it on another steel surface, which conducts away it's heat or by allowing it to cool at room temperature. If left at room temperature, it is allowed to cool for almost a day to get a final, hard and tough steel specimen.

Bibliography:-

Text:-

TechnologyStudent. 2009. Hardening and Tempering. [ONLINE] Available at: http://www.technologystudent.com/equip1/heat1.htm [Accessed 25 November 2015].

Images:-

Figure 1- KERONE, Muffle Furnace. Available at: http://www.infraredheater.in/muffle-furnace.php. [Accessed 25 November 2015].

Figure 2- TechnologyStudent, Tempering. Available at: http://www.technologystudent.com/equip1/heat1.htm. [Accessed 25 November 2015].