This set of Heat Treatment of Metals and Alloys Multiple Choice Questions & Answers (MCQs) focuses on “Steels – Determination of Austenitic Grain Size”.

1. What is the full form of ASTM?

a) American Standard for Testing Materials

b) American Standard of Testing Materials

c) American Society of Testing Materials

d) American School of Testing Materials

View Answer

Explanation: ASTM stands for the American Society of Testing Materials. ASTM grain size number is used to measure the grain size.

2. Which of the following statements is correct for the grain comparison method?

a) It can be used for all types of grains

b) It can be used for equiaxed grains

c) It does not use ASTM grain size number

d) The grain size is obtained in a microscope of 50X magnification

View Answer

Explanation: Grain comparison method is the simplest method of measuring grain size. In this method, grain size is measured as ASTM number. This method is used for equiaxed grains.

3. Which of the following grain size numbers belong to the category of untwined grains?

a) 0.12

b) 0.5

c) 0.2

d) 0.02

View Answer

Explanation: Untwinned grains include grain size numbers 00, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, and 10. 0.2, 0.12, 0.02 grain size numbers belong to the category of twinned grains which are contrast etched at 75X.

4. Which one of the following formulae shows the correct relationship between numbers of grains per square inch at 100X magnification, n and ASTM grain size number, N?

a) n=2^{N-1}

b) N=2^{n-1}

c) n=2^{N}

d) N=2^{n}

View Answer

Explanation: n=2

^{N-1}gives the relationship between numbers of grains per square inch at 100X magnification, n and ASTM grain size number, N. This formula is very important for calculating the grain size number.

5. Which one of the following formulae shows the correct relationship between numbers of grains per mm^{2} at 1X magnification, n_{a} and ASTM grain size number, G?

a) G = -2.9542 + 1.4427 ln n_{a}

b) G = 2.9542 + 1.4427 ln n_{a}

c) G = -2.9542 – 1.4427 ln n_{a}

d) G = −3.9542 + 1.4427 ln n_{a}

View Answer

Explanation: G = −2.9542 + 1.4427 ln n

_{a}gives the correct relationship between ASTM grain size number and number of grains per mm

^{2}at 1X magnification. It is the modified version of n=2

^{N-1}equation.

6. As the ASTM grain size number increases, the average diameters of grain as the sphere at 1X mm increases

a) True

b) False

View Answer

Explanation: As the ASTM grain size number increases, the average diameters of grain as the sphere at 1X mm decreases. However, the number of grains per square inch increases.

7. Calculate the number of grains per square mm^{2} in steel at 1X whose ASTM grain size number is 4.

a) 204

b) 124

c) 2.07

d) 20.7

View Answer

Explanation: By formula we know that G = -2.9542 + 1.4427 ln n

_{a}. In this equation, if we put G=4, then we get

ln n

_{a}= (4+2.9542)/1.4427

Or, n

_{a}= exp ((4+2.9542)/1.4427)

Hence, n

_{a}= 124.

8. Calculate the number of grains per square inch in steel at 100X whose ASTM grain size number is 4.

a) 16

b) 8

c) 4

d) 2

View Answer

Explanation: From the formula n=2

^{N-1}

Putting N=4, we get n=2

^{4-1}

Hence n=2

^{3}=8.

9. We have steel with ASTM grain size number 9. What is the average area of the grain in inch^{2}?

a) 4.9×10^{-7} inch^{2}

b) 3.9×10^{-7} inch^{2}

c) 3.9×10^{-11} inch^{2}

d) 4.9×10^{-11} inch^{2}

View Answer

Explanation: We know that n=2

^{N-1}, putting N=9 we get

n = 2

^{8}= 256 grains per inch

^{2}at 100X magnification

At 1X magnification, n=256/((0.01)*(0.01)) grains per inch

^{2}.

Hence, average grain area= (0.01*0.01)/256 = 3.9*10

^{-7}inch

^{2}.

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