Grain size is normally quantified by a numbering
system. Coarse 1-5 and fine 5-8. The number is
derived from the formula N=2n-1 where n is the
number of grains per square inch at a magnification
of 100 diameters. Grain size has an important
effect on physical properties. For service at
ordinary temperatures it is generally considered
that fine grained steels give a bettercombination of
strength and toughness, whereas coarse grained
steels have better machinability.