Quantitative Metallography Methods

QUANTITATIVEQUANTITATIVE
METALLOGRAPHYMETALLOGRAPHY
N. PRAKASAN
ME METALLURGY

QUANTITATIVE METALLOGRAPHYQUANTITATIVE METALLOGRAPHY
INTRODUCTION
Quantitative Metallography involves
determination of specific characteristics of a
microstructure by making quantitative
measurements on micrographs or
metallographic images.
Quantities so measured include volume
concentration of phases, grain size, particle
size and surface area to volume ratio of micro
constituents.

Methods:
There are two methods used in quantitative
metallography
• Comparison method
• Measurement method

Comparison Method
 It is a quickest method for routine analysis
 In this method, the microstructure image or micrograph
is compared with series of Standard charts.
 In Microscopes, facilities are provided for inserting
standard templates which are reproduced
simultaneously with the object, thus making for easy
and rapid comparison.
 The standard charts and templates have been issued
by ASTM, ISO & SIS for,
• Grain size measurement
• Inclusion rating
• Determination of porosity in sintered carbides
• Classification of graphite structure in Cast irons.

Measurement Methods
 Microscopic measurements can be made either,
• On the virtual image in the microscope
• On the micrograph
• On the ground glass screen
 Advanced microscope with image analyzing facilities
give fully automatic quantitative measurements.
 The measuring methods are,
• By comparison with charts or templates
• By means of square grid

Measurement Methods
Measuring ways are,
• Measuring the area of each individual particle
or grain. Then measured areas are divided
by the square of the linear magnification.
• Drawing straight lines on the image projected
on the ground glass screen or micrograph.
The average grain size is the total length of
the lines divided by number of grains
intercepts and by the linear magnification.

Determination of Particle size and Number
Comparison method,
• When determining particle size and size distribution
of powders, inclusion etc., the area, diameter or
length of each individual particle is measured.
• The standard reference template is placed over the
image projected on the microscope ground glass
screen or micrograph.
• Each particle is then classified in accordance with
such templates.

 Determination of Particle size and Number
 Comparison method, Graphite Shape comparison as per ASTM A
247

Linear analysis
• Drawing straight lines on the image or micrograph,
the length of all intercepts for a certain phase are
summated.
• The Ratio between the summated length and the
total length of the lines is equal to the volume
fraction which occupies the structure.

Point counting method (ASTM E 562)
• A standard grid containing large number of points is
placed on the image or micrograph.
• The number of points which coincide with the phase,
in comparison with the total number of grid points
gives the surface proportion (or volume fraction) of
the phase.
• For accuracy, large number of grid points must be
used.

• The grid consists of 100 points
• 7 “points” were inside the constituent of interest. So,
the point fraction is calculated as:

Determination of Grain size
Comparison method
• It is the simplest method in determining grain size.
• For spherical, equiaxed grains standard charts are
available from ASTM (ASTM E 112).
• For Elongated grains reference charts also available,
but usually other methods like Planimetric and
intercepts methods are used.
• A round , polished and etched specimen surface is
compared with standard charts and templates.

 Comparison method
ASTM E112 Plate II,
Rating of Grain size of
Austenitic Twinned alloy

 Comparison method
ASTM E112 Plate III,
Rating of Austenitic Grain
size of copper alloy

Planimetric method (Jeffries method)
• In this method a Circle or rectangle of known area is
drawn on the image on the ground glass screen or
micrograph.
• A magnification should be selected such that at least
50 grains are thus enclosed.
• In counting, half the number of grains which are cut
the confining lines is added to number of grains
inside the area.
• The average grain area=
Total surface area
No.of grains x surface magnification (M2)

Planimetric method
• The Root of this value is designated as the average
grain size.
• For elongated grains, determination should be made
in three section surfaces which right angles to each
other. The number of grains per cubic millimeter is
N = 0.7 (n1 x n2 x n3)1/2
where, n1, n2, n3 are three planes of intersection

 Determination of Grain size
 Planimetric method (Jeffries method)

 Planimetric method (Jeffries method)
 n1= number of grains completely inside the test circle
 n2= number of grains intercepting the circle
 f = Jeffries multiplier; f = magnification2
/circle area
 Magnification 100X
 NA = Average Grain area

Intercept method
• It is simple and rapid than Planimetric method.
• In this method, the number of grains which are cut by
straight lines are measured.
• The total length of the straight line is divided by the
No. of grains cut by the lines and by the linear
magnification.
• The total length of the straight line drawn should cut
at least 50 grains.
• In elongated grains, measurement is carried out in
three directions at right angles & one is parallel to
elongated direction. The Number of grains/Cmm is
N = 0.7 (n1xn2xn3)

 Determination of Grain size
 Intercept method

References:
Metallurgical Microscopy by Helfrid Modin &
Sten modin,
Standards for Metallography by George F.
Vander Voort, Director, Research &
Technology Buehler Ltd.

Quantitative Metallography Methods

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