Grain size (and grain boundary area) are important modulators of
material properties and behavior. A quantitative measurement
procedure has been established by the American Standard for
'l'esting and Materials (ASTM). For grain size, reference nets
with various grain size numbers (GS# or n) are used for
comparison with observations through a microscope at lOOx
magnification (Refer to Figure 3). The number of' grains N per
square inch at lOOx magnification is calculated using the
formula: N = 2n-i. A large grain size number indicates more
grains and more grain boundary area per unit volume. For grain
boundary area, the following equation is utilizd for calculalion:
Sy = 21'~ , where PL is the number of intercepts of grain
boundary per unit length viewed at a known magnification (of a
simple shape whose perimeter is easily calculable (e.g. circle,
square, etc.) and Sy is the grain boundary area per unit volume