Full Annealing Service

In fact, the actual definition of annealing describes only the full annealing. That is, full annealing consists of heating the steel to a temperature at or near the critical point, holding there for a time period and then allowing it to cool slowly in the furnace itself.

The main objects of full annealing are:
(i) To soften the metal,
(ii) To refine its crystalline structure, and
(iii) To relieve the stresses.

Material: The full annealing is specially adopted for steel castings and steel ingots:
process of Full Annealing

In full annealing, hypoeutectoid steels (less than 0.77% C) are heated to 30 to 60°C above the upper critical point i.e., A3 line (i.e., between 723^oC and 910^oC). This is to convert the structure to homogeneous single-phase austenite of uniform composition and temperature, held at this temperature for a period of time, and then slowly cooled to room temperature.

Cooling is usually done in the furnace itself by decreasing the temperature 10 to 30^oC per hour to at least 30^oC below the A line. Then, the alloy is removed from the furnace and air cooled to room temperature.

Now the resulting structure is coarse pearlite with excess ferrite. In this condition, the steel is quite soft and more ductile.