4 years ago
- Normalizing process is a heat treatment process for making material softer but does not produce the uniform material properties as produced with an annealing process.
- The most common reason for the normalizing process is to adjust mechanical properties to suit the service conditions.
- The other purpose of the normalizing is:
- To relieve the internal stresses,
- To refine the grain structure, and
- To improve the machinability.
- Normalizing involves heating steel to above 50°C above the upper critical temperature, (for hypo-eutectoid steel) and to 50°C above the lower critical temperature (for hyper eutectoid steel).
- Holding at this temperature for a shorter time to prevent grain growth and finally, cooling in air.
- The time allowed should be sufficient so that the temperature is equalized throughout the section.
- The structure produced by normalizing is similar to that of annealing. But air cooling is faster than furnace cooling. Thus the normalized steels possess fine grains than annealed steels.
- The normalized structure of low-alloy steel consists of sorbite (fine pearlite) and fine ferrite.
- The increased rate of cooling in normalizing results high hardness and low ductility than annealed steel –> machinability will be easy.
- Normalizing is usually performed after forging or casting, to put steel in the best condition for machining or hardening.