Heat Treatment

Topics: Steel, Metallurgy, Austenite Pages: 2 (503 words) Published: May 26, 2012
Name: Lucas Ng Boon Siang (6)
Class: N06

Report on Chapter 4 (Heat Treatment Of Steels)

Heat treatment is a metalwork process in which metals undergo heating and cooling only to obtain desirable properties for the metal. These properties include increasing hardness, strength, toughness and ductility. Different types of heating processes are used depending on the carbon content and also the desired application of the metal. The different processes include Annealing, Normalising, Hardening and Tempering. Finally, the product that results from the process will depend on the rate of cooling if the heating is done slow enough to reach structural equilibrium at the max temperature of the metal.

Normalising is firstly used to produce harder and stronger steel. Next they are also used to fine the grains and homogenise the structure of the material. Lastly they improve machinability greatly. Firstly the steel is heated gradually above its Upper Critical Temperature (UCT) which is roughly about 300 degree Celsius. It is then left in the furnace until it has reached uniform temperature throughout before it is withdraw from the furnace and cool in still air. Structural changes in normalising occurs heating above Lower Critical Temperature (LCT). The pearlite will change to fine‑grained austenite. On further heating, remaining primary ferrite will be absorbed by new austenite crystals. Then the change is complete at the UCT, and the final structure contains uniformly fine‑grained austenite. Lastly cooling the material in still air, the structure changes back to uniformly fine­ grained pearlite and ferrite.

The heat treatment process of annealing has three principal processes namely Full Annealing, Spheroidisation Annealing and Stress Relief Annealing. Full Annealing process is used to produce softer and higher ductile steels where a coarse pearlitic microstructure is obtained. Spheroidisation Annealing is a process which is normally used on high carbon-steels...
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