Can You Explain Case Hardening?


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It is a method of hardening the surface of mild steel to a depth varying up to about 1/16 inches. We know that heating and quenching has no appreciable effect on low carbon steel, but if we can convert the surface of mild steel into high carbon steel we may harden it by heating and quenching in the usual way. Now the question is what takes place in case hardening? Now the operation is divided into two main parts
1- Converting the outer shin( known as case) to a high carbon steel (carburizing)
2- Hardening this case and refining the core

Now coming to the first step which is to increase the carbon content of the case, the steel is packed in cast iron or steel boxes together with a substance rich in carbon such as charcoal granules. At this temperature the carbon infuses into the surface of the metal converting it into high carbon steel. At the end the box is allowed to cool slowly and when removed the steel parts consists of a case of high carbon.
To refine the core it is first heated to about 900 degree centigrade and then quenched in oil after which the case is hardened by heating to about 770 degree centigrade.

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