# Heat Treatment of Metals and Alloys Questions and Answers – Steels – Determination of Austenitic Grain Size

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

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

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

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=2N-1
b) N=2n-1
c) n=2N
d) N=2n

Explanation: n=2N-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 mm2 at 1X magnification, na and ASTM grain size number, G?
a) G = -2.9542 + 1.4427 ln na
b) G = 2.9542 + 1.4427 ln na
c) G = -2.9542 – 1.4427 ln na
d) G = −3.9542 + 1.4427 ln na

Explanation: G = −2.9542 + 1.4427 ln na gives the correct relationship between ASTM grain size number and number of grains per mm2 at 1X magnification. It is the modified version of n=2N-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

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 mm2 in steel at 1X whose ASTM grain size number is 4.
a) 204
b) 124
c) 2.07
d) 20.7

Explanation: By formula we know that G = -2.9542 + 1.4427 ln na. In this equation, if we put G=4, then we get
ln na = (4+2.9542)/1.4427
Or, na= exp ((4+2.9542)/1.4427)
Hence, na = 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

Explanation: From the formula n=2N-1
Putting N=4, we get n=24-1
Hence n=23=8.

9. We have steel with ASTM grain size number 9. What is the average area of the grain in inch2?
a) 4.9×10-7 inch2
b) 3.9×10-7 inch2
c) 3.9×10-11 inch2
d) 4.9×10-11 inch2

Explanation: We know that n=2N-1, putting N=9 we get
n = 28 = 256 grains per inch2 at 100X magnification
At 1X magnification, n=256/((0.01)*(0.01)) grains per inch2.
Hence, average grain area= (0.01*0.01)/256 = 3.9*10-7 inch2.

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