The document discusses different methods for measuring grain size in polycrystalline materials: - Comparison method involves comparing the actual grain structure to standard images and assigning an ASTM grain size number, with lower numbers indicating larger grains. - Heyn's intercept method measures the average number of grains intercepted along a fixed line length, with the intercept length giving the average grain diameter. - Jefferies planimetric method counts grains within a defined area on a micrograph, using the magnification to determine grains/mm2 and calculate average size. Examples are given for problems using each method to determine grain size from measurement data. The methods are compared for applicability based on grain shape and measurement approach.

1. A1MET201
Metallurgy and Material Science
Jagadeesh N B.Tech, M. Tech (NIT -W) Materials
Faculty of Materials and Manufacturing Sciences
MVGR College of Engineering-Autonomous
Vizianagaram-535005
njagadeesh@mvgrce.edu.in

2. Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
2

3. Concept of Cooling Curves
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
3

4. Concept of Cooling Curves
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
4

5. Concept of Cooling Curves
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
5

6. Concept of undercooling

7. Grain Boundary Formation

8. Steel Grain Structure

9. Grain Structure of Austenitic SS

10. “Cu” Grain Structure

11. Brass (Cu+Zn) Microstructure

12. Concept of Grain Boundary
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
12

13. Concept of Grain Boundary
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
13
A grain boundary is the interface between two grains,
or crystallites, in a polycrystalline material.
In the Process of crystallization the crystals growing in
size will meet another crystal forming grain boundary.
Grain boundaries are 2D defects in the crystal
structure, and tend to decrease the electrical and thermal
conductivity of the material.

14. Differently oriented crystallites in a
polycrystalline material
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
14

15. The internal interfaces that separate neighboring
disoriented single crystals in a polycrystalline solid
Most solids such as metals, ceramics, and
semiconductors have a crystalline structure, which
means that
 they are made of atoms which are arranged in a
three-dimensional periodic manner within the
constituent crystals
Most engineering materials are polycrystalline in
nature in that they are made of many small single
crystals which are disoriented with respect to
each other and meet at internal interfaces called
grain boundaries
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
15

16. Grain Boundary
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
16
+ or -

17. Grain boundaries play an important role in
controlling the electrical and mechanical properties
of the polycrystalline solid
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
17

18. Hall-Petch Equation
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
18

19. A 2D representation of a perfect single crystal with
regular arrangement of atoms
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
19

20. Schematic drawing of a poly-crystal with
defects
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
20

21. Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
21

22. Defects have a profound impact on
the various properties of materials
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
22

23. Grain Size measurement
Comparison method
Heyn’s Intercept method
Jefferies Planimetric method
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
23

24. COMPARISON METHOD
This method is applicable for equiaxed grains
Here the grain size is reported by ASTM(American
Society for Testing of Materials) grain size no.
In this we write
 N= 2 n-1
 “N” is no. of grains per sq. inch at 100x magnification
“n” is ASTM grain Size no.
Jagadeesh N, B. Tech, M. Tech (NIT W),
Assistant Professor
24

25. ASTM Grain Size numbers

26. COMPARISON METHOD
• Usually the actual structure is compared at a standard
magnification of 100x for steels and 75x for Cu based alloys
• In general
 ASTM grain size no. below 3 represents coarse grained steel
 ASTM grain size no. above 6 represents reasonably fine
grained steel
 ASTM grain size no. greater than 8 are ultra fine grained steel

27. COMPARISON METHOD
Problem:
If the ASTM grain size no. is 8, calculate the average
grain diameter in microns assuming the grains to be
spherical.

28. HEYN’S INTERCEPT METHOD
 This method is used mainly when the grains are not equiaxed
 This method consists of finding out the no. of grains
intercepted by a line of fixed length.
 The magnification is such that the area covered is at least 0.5
mm2 on the actual sample.
 The grains touched by the end of the line are counted as half
grains
 Counts are made on at least three fields to assure a reasonable
accuracy
 The length of the line in mm divided by the average no. of
grains intercepted by that line gives the average intercept
length or grain diameter

30. HEYN’S INTERCEPT METHOD
Problem:
Heyn’s method was used to measure the grain size of a
particular material. The no. of grains intercepted by a line
of total length 100cm at 100x magnification were 196.
Find the average grain size in microns

31. JEFFERIES PLANIMETRIC METHOD
 It is used for measuring the grain size of equiaxed grains
 Results of this method are preferred over the Comparison
method
 In this method a circle or rectangle of a known area (usually
5000 mm2 ) is drawn on a photo micrograph
 The magnification employed should be such that at least 50
grains should be seen in the field
 The total no. of grains are counted in this known area which is
the sum of grains included plus half the grains intersected by the
circumference or perimeter of the area.
 Now, total no. of grains per sq. mm are determined by the
corresponding magnification factor (f, Jefferies multiplier)

32. relationship between magnification, m and Jefferies multiplier,
f

33. JEFFERIES PLANIMETRIC METHOD
Problem:
Jefferies method was used to measure the grain size
of a metal. Measurements of grains was done in an
area of 5000sq.mm at 100x magnification. The no.
of full grains were 20 and half grains were 38.
Assuming grains to be spherical, find the average
grain size in microns

34. Compare all the three methods of Grain
Size Measurement