Austenite Grain Size

          We have read that grain size is of prime importance in the behavior of metals under different loads. Grain size is also a very important factor in relation to the various physical properties of steel. Usually, grain size refers to austenite grain size. While deciding the rate at which steel is to be heated, one must take into consideration the effect of austenite grain growth or increase in temperature. Increase in austenite grain size may have the following effects:

1. Helps to improve the strength of steel after heat treatment, in fine grains.
2. Help to improve machining finishes and machinability.
3. Mechanical properties, e.g. Creep strength, tensile strength and hardenability increases.
4. Quenching cracks and distortion in fine grains reduces.
5. Improves the fabrication properties of a fine-grained steel. One may heat it to higher temperature without the fear of over heating, i.e. appreciabl coarsening of grains.

Grain size is governed by the following factors:

1. Composition of steel.
2. Nature and amount of deoxidizers
3. Heat treatment processes, environment and working temperatures
4. Metallic and non-metallic inclusions
5. Mechanical working processes, e.g. rolling, forging, etc.
6. Grain size, heating and cooling time and tendency to grain growth.