Question

For an ASTM grain size number of 8, approximately how many grains would be visible per square inch at a magnification of 100$\times$?

• A. 64 grains/in$^2$
• B. 100 grains/in$^2$
• C. 128 grains/in$^2$
• D. 256 grains/in$^2$

Hint:

Use the formula \( N = 2^{(G - 1)} \) to find the number of grains per square inch at 100$\times$ magnification for ASTM grain size number \( G \).

Answer 1

The Correct Option is C

The ASTM grain size number (G) is related to the number of grains per square inch at 100$\times$ magnification (N) by the formula: \[ N = 2^{(G - 1)} \] Given: \( G = 8 \)
Substitute into the formula: \[ N = 2^{(8 - 1)} = 2^7 = 128 \] Therefore, at 100$\times$ magnification, there would be approximately 128 grains per square inch.
This standard method is commonly used in metallography to estimate grain sizes quickly and accurately.