Overview
ISO 2624:1990 - "Copper and copper alloys - Estimation of average grain size" specifies standardized procedures and reporting rules for estimating the average grain size of copper and copper alloys that consist principally of a single phase. The standard defines three accepted methods (comparison, intercept/Heyn, planimetric/Jeffries), specimen-preparation requirements, counting rules and recommended reporting formats. Annex A provides the normative standard grain-size charts (reproduced at ×75).
Key topics and technical requirements
- Scope: Applies to single‑phase copper and copper alloys; sub‑grains, minor phases and inclusions are ignored for grain-size estimation.
- Specimen preparation: Sections must be prepared to reveal grain boundaries (contrast etch) and representative fields chosen.
- Three procedures
- Comparison procedure: Project a photomicrograph and compare visually with the standard chart (most convenient and adequate for commercial use). Charts reproduced at ×75; Table 2 gives equivalent grain diameters for other magnifications.
- Intercept procedure (Heyn): Count grains intercepted by straight lines on an image. Recommended when higher accuracy or non‑equiaxial structures are present. Lines should yield at least 10 intercepts per line, with a minimum total of 50 intercepts for normal testing and 200 for referee purposes. Grains touched by the end of a line count as half.
- Planimetric procedure (Jeffries): Count whole and partial grains within a known area (commonly 5 000 mm²). Use the Jeffries multiplier f (Table 1) and the relation given in the standard (d = 1/f for average grain “diameter” as expressed in the document) to calculate equivalent grain diameter.
- Non-equiaxial materials: Prepare three sections at right angles; use intercept method and report results per principal direction.
- Reporting: Report per-field results or the median of fields. Mixed grain sizes should be expressed as area percentages of constituent sizes.
Applications and who uses this standard
- Metallurgists and materials scientists use ISO 2624 to quantify microstructure for process control and research.
- Quality control and inspection labs apply the methods to verify annealing, recrystallization and grain‑size requirements in supplied copper products.
- Manufacturers of copper alloys rely on these procedures for specification compliance, production monitoring and supplier acceptance.
- Failure analysis and R&D teams use standardized grain‑size data to correlate microstructure with mechanical and electrical properties.
Related standards and notes
- Annex A reproduces standard grain‑size photomicrographs (×75) - derived from ASTM E112 reference plates noted in the document.
- For contractual disputes, ISO 2624 recommends using the intercept (Heyn) or planimetric (Jeffries) procedures because they provide higher accuracy than the comparison method.
Keywords: ISO 2624, grain size, copper alloys, metallography, Heyn intercept, Jeffries planimetric, comparison procedure, standard grain size charts, microstructure, photomicrograph.
