FULL ANNEALING
The term annealing, until and unless specified means full annealing. The process consists of heating steel to austenitic region and then cooling very slowly. For hypo eutectoid steel a temperature 30-50° C above the UCT is employed. Steel is held at this temperature to a predetermined time and then cooled very slowly either in the furnace itself or in a container made of a heat insulating material. Since the cooling rate s are very slow, the equilibrium conditions predicted as per the equilibrium diagram are achieved. The steel is heated above UCT in order to achieve homogenized austenitic structure.
Highly enriched alloy steels require a higher annealing temperature, than plain carbon steels. For eutectoid steel, a complete austenitic structure can be obtained by heating the steel above LCT. This process is normally not used for hyper eutectoid steels. The reason for this is that heating above UCT followed by slow cooling will result in considerable coarsening of austenite grains and formation of lamellar pearlite and cementite network formation through the grain boundaries. Such a structure has inherent brittleness and poor mechanical properties.
Full annealing
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