Question

State the number of grains per square inch at a magnification of 100X for ASTM grain size number 8

• A. 64
• B. 128
• C. 256
• D. 512

Hint:

ASTM formula: $N = 2^{n-1}$. For $n=8$, just remember $2^7 = 128$.

Answer 1

The Correct Option is B

Step 1: Concept
The ASTM grain size number ($n$) is defined by the formula $N = 2^{n-1}$, where $N$ is the number of grains per square inch at 100X magnification.

Step 2: Meaning
This standard allows metallurgists to quantify the fineness of the microstructure.

Step 3: Analysis
Given ASTM grain size number $n = 8$. Therefore, $N = 2^{8-1} = 2^{7}$.

Step 4: Conclusion
Calculating the value: $2 \times 2 \times 2 \times 2 \times 2 \times 2 \times 2 = 128$. Final Answer: (B)