KEVOS® MAKEOS · Materials
Grain Size Acceptance (Field Readings, Average ASTM Grain Size, Spread, Specification)
From several microscope field readings, what is the average ASTM grain size number, how much do the fields vary, and does the material meet the grain size specification?
Acceptance of a material for grain size from up to five fields: the average of the readings (grains per square inch at 100×, grains per mm² at 1× or mean lineal intercept), the ASTM grain size number G from the average and from each field, the equivalent counts and intercept length (as the grain size tool), the spread between the coarsest and finest field, against the specified G range and your largest acceptable spread.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Measurement | choice | What was measured in each field. |
| Field 1 reading (0 = unused) | Reading in field 1. | |
| Field 2 reading (0 = unused) | Reading in field 2. | |
| Field 3 reading (0 = unused) | Reading in field 3. | |
| Field 4 reading (0 = unused) | Reading in field 4. | |
| Field 5 reading (0 = unused) | Reading in field 5. | |
| Specification | ||
| Coarsest grain size allowed (lowest G) | G | Lowest grain size number the specification allows (coarsest grains). |
| Finest grain size allowed (highest G) | G | Highest grain size number the specification allows (finest grains). |
| Largest spread between fields | G | Largest difference in G between fields you accept before treating the structure as mixed. |
Method and formulas
- G = 1 + log₂ n₁₀₀; G = 3.3219 log N_A − 2.954; G = −6.6439 log (ℓ̄ in mm) − 3.288 (as the grain size tool).
- Readings are averaged, then G is found from the average; each field’s G gives the spread.
- Accept when the average G lies within the specified range.
- Example: the average reading gives G 6.991, with fields from G 7.1293 to 6.858.
Limitations
- Equiaxed, single-phase grains; elongated or duplex structures need the full standard’s methods.
- Five fields give only a rough average; the standard sets field counts for a given precision.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Accept bar or forgings against a grain size requirement
- Average several fields for a test report
- Spot a duplex (mixed) grain structure
Who it is for
- Metallurgists
- Quality engineers
- Lab technicians
What you get
- Average reading and grain size number
- Each field’s G and the spread
- Against the specification
Interpreting the result
- Each step of one in G halves or doubles the number of grains per unit area.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 369–380. Topic reference; no source tables or recommended settings are reproduced.
- ASTM E112 Standard Test Methods for Determining Average Grain Size
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