Normalising

 Normalising is similar to full annealing, but cooling established in still air rather than in the furnace.

NORMALISING

1. What is Meant by Normalising?

✓ Normalising is similar to full annealing, but cooling established in still air rather than in the furnace.

✓ Full annealing is an expensive and time consuming process When a reasonably soft and ductile material is required and co savings are desired, then the normalising process is used instead of full annealing.

2. Objects of Normalising

Some of the purposes of normalising are:

1. To refine the grain structure.

2. To increase the strength of the steel.

3. To provide a more uniform structure in castings and forgings.

4. To relieve internal residual stresses due to cold working.

5. To achieve certain mechanical and electrical properties. 

3. Materials

The normalising process is extensively employed for low an medium carbon steels as well as alloy steels.

4. Operation

In normalising, the steel is heated to 50°C to 60°C above its upper critical temperature (i.e., above the A3 line) for hypoeutectoid steel on above the Acm line for hypereutectoid steels, as shown in Fig.2.6. It is held at this temperature for a short time and then allowed to cool in still air.

The normalising process provides a homogeneous structure onsisting of ferrite and pearlite for hypoeutectoid steels, and pearlite nd cementite for hypereutectoid steels.

5. Normalising Vs Full Annealing

The difference between normalising and full annealing is presented Table 2.1.

6. Summary of the Process Treatments

Fig.2.7 provides a graphical summary of the process heat treatments for steel on an equilibrium diagram.