# What is the average grain diameter (in mm) for the grain size ASTM grain size 12?

What is the average grain diameter (in mm) for the grain size ASTM grain size 12?

#### SOLUTION

According to ASTM standard E1112, ”standard test methods for determining average grain size is

n = 2 G – 1

where:
n = the number of grains per square inch at 100X magnification, and
G = the ASTM grain size number.

Average Grain diameter (d, in mm)

$\dfrac{1}{{\sqrt {\dfrac{{n \times {{10}^4}}}{{645}}} }}$

Given ASTM grain size 12, thus,

n = 212 − 1 = 211 = 2048

Therefore, average grain diameter will be

$\dfrac{1}{{\sqrt {\dfrac{{2048 \times {{10}^4}}}{{645}}} }}$

= 0.0056 mm.

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