ASTM E562-19e1 is the standard test method for determining the volume fraction of constituents in a microstructure using a systematic manual point count on polished, planar sections. The method utilizes a grid to count points falling within specific phases, providing a statistical average and a 95% confidence interval for accurate material analysis. Purchase the standard from ASTM International ASTM International
Headline: The Grid, Not the Eye: How a 100-Point Count Became the Gold Standard for Phase Volume Fractions
Instead of measuring the area of phases (which requires expensive image analysis software), E562 uses point fraction.
Choose a magnification that clearly distinguishes the phase of interest from all others. The rule of thumb: the spacing between grid points should be such that no feature is counted more than once, but small enough to sample the structure adequately. The standard suggests that the grid spacing should be roughly the size of the features of interest.
Quantifying graphite nodularity or flake graphite area fraction.
Before diving into the methodology, it is essential to decode the title: astm e562-19e1
This standard supersedes previous versions (E562-11, E562-08, etc.) and is recognized globally across industries that require microstructural analysis.
For each field, compute:
[ V_V(field) = \fracP_pP_t \times 100 ]
Then average over all fields:
[ \barV_V = \frac\sum V_V(field)n ]
Where ( n ) = number of fields examined.
Most people assume that if you want to know how much of a material is porosity, ferrite, or graphite, you’d use a computer. But ASTM E562-19e1 defends a deceptively simple, manual method: the manual point count. It’s a testament to how systematic random sampling and basic statistics can outperform intuition—and even some automated systems—in metallography and materials science.
To understand why point counting works, one must revisit stereology. ASTM E562 rests on the Delesse principle (1847), which states that the area fraction of a component on a two-dimensional plane through a material is an unbiased estimator of its volume fraction in the three-dimensional material.
Mathematically: [ V_V = A_A ]
Where:
But how do we measure ( A_A )? Instead of measuring areas directly (which is tedious), we use point counting: if you randomly place a grid of test points on the microstructure, the fraction of points that fall on the phase of interest approximates the area fraction.
[ A_A \approx P_P = \fracP_pP_t ]
Where:
Thus, by counting “hits” on the phase of interest, you directly estimate volume fraction. ASTM E562 formalizes this approach, specifying grid geometry, counting rules, and statistical targets.