Methods Of Grain size Determination

Stereology is the process of sampling and counting material using specific protocols to obtain an estimate of a quantitative parameter, such as number, length, volume, etc. Obtaining accurate estimates is a critical component of producing a study outcome with statistical validity.

There are many methods to find the size of a given grain by its microstructure.

Grain size is an important parameter which determines mechanical properties and corrosion behaviour of a material. Grain size has a measurable effect on most mechanical properties. For example, at room temperature, hardness, yield strength, tensile strength, fatigue strength and impact strength all increase with decreasing grain size

ASTM grain size number (n) is related with the number of grains that you can count in 100X magnification (N) by the relation, N=2^(n-1) . So ASTM grain size number increases with decreasing grain size.

The intercept method suggested by Heyn in 1903 [1] is considerably faster to perform manually which has made it popular, despite the fact that there is no direct mathematical connection between the mean lineal intercept length and G. Both straight lines and circles have been used as templates, plus other shapes.

One of the simplest techniques to estimate an average grain size is the intercept technique. A random straight line is drawn though the micrograph. The number of grain boundaries intersecting the line are counted. The average grain size is found by dividing the number of intersections by the actual line length.