Calculate ASTM grain size number (G) from grain count measurements per ASTM E112 standard using the Heyn intercept or planimetric methods
Input Parameters
Results
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ASTM Grain Size Number G
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Average Grain Diameter
μm
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Grains per mm² (actual)
Note: ASTM grain size number G: higher = finer grains. G=5 is coarse, G=8 is fine, G=10+ is very fine. Fine grain size improves toughness and yield strength.
Reference
ASTM E112 Grain Size:
N_A = 2^(G-1) grains per sq inch at 100× magnification
G = 1 + log2(N_A)
Average grain diameter d ≈ 1/√(N_A per mm²)
Typical structural steels: G = 5 to 10 (finer = higher G = better toughness)