🔬 Average grain size according to ASTM — comparison procedure with standard charts, planimetric (Jeffries) and intercept (Heyn, circles), result as the grain size number G; ASTM E112

Materials and NDT ASTM E112

Overview

WHAT THE STANDARD COVERS. Scope of ASTM E112-25 according to the publisher's page (store.astm.org, read on 10.10.2026; the page of the active E112-25ε1 has the same scope and significance character for character): measurement of the average grain size by three procedures — comparison, planimetric (Jeffries) and intercept; they may also be applied to non-metallic materials with structures similar in appearance to those shown in the standard charts. They apply chiefly to single-phase grain structures, but can be used to determine the average size of a particular type of grain in a multiphase specimen (1.1). They apply to specimens with a unimodal distribution of grain areas, diameters or intercept lengths (approximately log-normal); bimodal distributions are covered by ASTM E1181, individual very coarse grains in a fine-grained matrix — by E930 (1.2). They deal only with the grain size on the plane of the section, not the spatial grain size (1.3). They describe manual techniques; semi-automatic and automatic image analysis is ASTM E1382 (1.4). They do not establish limits of acceptability of the material (1.5). Arrangement of the standard (1.8): among others, sampling, test specimens, calibration, photomicrographs, comparison procedure, planimetric procedure, general intercept procedures, Heyn procedure (lineal intercepts), circular intercept procedures (Hilliard — single circle, Abrams — three circles), statistical analysis, non-equiaxed grains, specimens with two or more phases, report, precision; annexes: basis of ASTM grain size numbers, conversion equations, austenite grain size in ferritic and austenitic steels, fracture grain size method, requirements for copper and copper alloys, application to special situations.

THREE PROCEDURES (section 4 according to the same page). Comparison — no counting: comparison of the structure with a series of graded images (wall chart, overlays, eyepiece reticle); it has a general tendency to rate the grain as slightly coarser (1/2–1 G number lower), and repeatability and reproducibility are usually ± 1 number. Planimetric — counting grains within a known area; the number of grains per unit area NA gives the number G; a precision of ± 0.25 units is attainable with reasonable effort, results are free of bias, repeatability and reproducibility are below ± 0.5; it requires marking of the counted grains. Intercept — counting the grains intercepted by a test line or the grain boundary intersections with the line per unit length, from which the mean lineal intercept length ℓ and the number G are calculated; precision better than ± 0.25, results free of bias, faster than the planimetric procedure for the same precision. For equiaxed grains the comparison with standard charts is the most convenient and sufficiently accurate for most commercial purposes; for higher accuracy — intercept or planimetric; intercept particularly for elongated grains (4.2). In a dispute the referee procedure is ALWAYS the planimetric one (4.3). The average grain size of heavily cold-worked material should not be estimated; partially recrystallized wrought alloys and lightly to moderately cold-worked material may be treated as non-equiaxed grains (4.4). The standard charts are not used for measuring individual grains — they show a size distribution (4.5).

EDITIONS. The ASTM store (10.10.2026) marks E112-25ε1 as the active edition — E112-25 with an editorial correction (ε1; the page does not describe the correction); the page of E112-25 itself is marked "Historical". Earlier editions include E112-24, E112-13(2021), E112-13 and E112-12. ASTM has no Polish edition of this standard. The micrographic determination of the grain size of steels is also described in PN-EN ISO 643 (a separate entry in this database) — a different document with its own procedures.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database of 10.10.2026 and current PCA documents read on 10.10.2026). In Polish scopes "E112" appears in 13 records at 9 laboratories: AB 019, AB 053 (5 records of one bilingual entry), AB 099, AB 128, AB 490, AB 608, AB 792, AB 1283 and AB 1629; the standard is present in all 9 current PCA documents, no entry is suspended. Editions: E112-25 (AB 490, AB 792, AB 1283, AB 1629), E112-24 (AB 053), E112-13(2021) (AB 099), without a year (AB 019, AB 128, AB 608). The "Laboratories" tab ("ASTM E112") shows 21 laboratories — 8 Polish and 13 Czech (measurement on the production server on 10.10.2026); it does not include the laboratories writing "ASTM E 112" with a space: AB 792 ("ASTM E 112-25") and seven Czech ones.

WHAT THE LABORATORIES TEST (copy and PCA documents). Grain size by optical (light) microscopy in metallic products and materials, steels, steel, cast and structural products, metals and alloys in the cast or wrought form. Procedures stated in the scopes: comparison with the standard charts (AB 019, AB 053, AB 128, AB 490, AB 1629), and beside it intercept and planimetric (AB 1629) or intercept and grain counting (AB 128); AB 099, AB 608, AB 792 and AB 1283 state only optical (light) microscopy, without a procedure.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — the comparison method overstates grain coarseness: the result from the charts is often 1/2–1 G number lower than the real one, and its scatter is ± 1 number; with a requirement close to a class limit the comparison with charts is not conclusive. Second — dispute: only the planimetric method is the referee method (4.3). Third — cold-worked material: the average grain size is not estimated at all; a result for such a specimen is meaningless. Fourth — bimodal distribution or individual coarse grains: this standard does not cover them (E1181, E930) — an average of a mixture of fine and coarse grains is misleading; AB 792 has both of these standards in the same entry as E112. Fifth — the number G from ASTM E112 and a result according to PN-EN ISO 643 are results of two different standards; where one is required, the result of the other must not be given — and eight of the nine laboratories have both standards in the same scope entry.

WHAT WE DO NOT GIVE. We have not read the content of the standard beyond the scope (section 1) and significance (section 4) from the publisher's page — we do not give the formulae for G, magnifications, number of fields and counts, preparation of sections and etching, or conversion tables.

Method principle

On a plane section of a metallographic specimen (light microscope) the average grain size of a single-phase structure is determined: by comparison with graded standard images, by counting grains within a known area (Jeffries, planimetric) or by counting grain boundary intersections with a test line or circle (intercept); the result is expressed as the ASTM grain size number G (ASTM E112-25, 1.1 and 4.1, according to the publisher's page). In a dispute the planimetric method decides.

Applications

• Single-phase metals; a particular type of grain in multiphase structures; non-metallic materials with a similar appearance of the structure (1.1)
• Equiaxed grains — the comparison method is sufficient for most commercial purposes; elongated grains — the intercept method (4.2)
• In the accreditation scopes: 9 Polish laboratories (editions -25, -24, -13(2021) and without a year)

Key parameters

Standard

Standard number

ASTM E112-25ε1

Title (PL)

Metody wyznaczania średniej wielkości ziarna (tłumaczenie tytułu nasze; norma ASTM nie ma polskiego wydania)

Title (EN)

Standard Test Methods for Determining Average Grain Size

Step-by-step procedure

1. Assessment of the suitability of the specimen

   Single-phase structure or a particular type of grain; not for heavily cold-worked material; unimodal distribution (otherwise E1181/E930).

2. Section and observation

   Plane section, revealed grain boundaries, light microscope; we DO NOT GIVE details.

3. Measurement

   Comparison with charts (equiaxed grains, commercial purposes) or counting — planimetric (grains within an area) or intercept (intersections on a line/circle); for elongated grains — intercept.

4. Result

   ASTM grain size number G; state the procedure and the edition of the standard (active E112-25ε1, state on 10.10.2026); in a dispute — planimetric.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Etching of sections — corrosive and toxic reagents; fume cupboard, gloves, goggles
• The standard itself does not address safety concerns; it is the responsibility of the user to establish safety and health practices (1.7)

Frequently asked questions