Question

In a 1 square inch area on a 200X micrograph you count 11 grains. Calculate the ASTM grain size number. (The ASTM grain size number should be accurate to two decimal places.)

Correct Answer: 2.34 +/- 2%

In a 1 square inch area on a 200X micrograph you count 24 grains. Calculate the ASTM grain size number. (The ASTM grain size number should be accurate to two decimal places.) Correct Answer: 2.68 +/- 2% *******BOTH OF THESE ARE CORRECT. HOW DID THEY COME TO THESE ANSWERS************

Answer 1

Answer: 1

Counting each grain on an edge as one half, there are 11/2 = 5.5 edge grains.

Counting each corner grain as one quarter, there is 1 corner grain. therefore, n = 5.5/2 = 2.75

For ASTM grain size number, N, defined by

n = 2^N−1 or N = 1 + ,

therefore,

therefore, N= 2.45 +/- 2%

Answer: 2

Counting each grain on an edge as one half, there are 24/2 = 12 edge grains.

The 1 square inches at 200X would be 4 square inches at 100X

Counting each corner grain as one quarter, there is 1 corner grain. therefore, n = 12/4 = 3

For ASTM grain size number, N, defined by

n = 2^N−1 or N = 1 + ,

therefore,

therefore, N= 2.58 +/- 2%