Overview
EN ISO 2624:1995 (identical to ISO 2624:1990) - "Copper and copper alloys - Estimation of average grain size" is a metallographic standard published by CEN/ISO that defines accepted methods for estimating the average grain size of copper and copper alloys that are principally single‑phase. The standard specifies three procedures (comparison, intercept/Heyn, and planimetric/Jeffries), rules for reporting results, and guidance on specimen preparation and magnification.
Key topics and requirements
- Scope and specimen preparation
- Applies to copper and copper alloys consisting principally of a single phase.
- Specimens must be prepared to reveal grain boundaries (contrast etch) and representative fields selected (three or more fields for most cases; multiple section orientations for non‑equiaxial structures).
- Comparison procedure
- Direct visual or projected comparison with the standard grain size photomicrograph chart (standard charts reproduced at x75). Most convenient and adequate for commercial purposes.
- Intercept procedure (Heyn)
- Count grains intercepted by straight lines on an image or photomicrograph.
- Practical counting requirements: at least 10 intercepts per line and a minimum of 50 intercepts for normal purposes (200 for referee cases). Grains touched by a line end count as half.
- Average intercept length I = total line length / number of intercepts; to align with planimetric/comparison results multiply I by 1.13.
- Planimetric procedure (Jeffries)
- Count whole and partial grains within a known area (commonly 5 000 mm² area on photomicrograph/graticule). Use Jeffries’ multiplier (f) to convert counts to grains per mm², then compute average grain diameter d = 1/√m (or d = 1/f when using provided multipliers).
- Reporting rules
- Report individual field results or a single representative median value. For mixed grain size distributions, express area percentages of each size or range.
Applications and users
- Routine quality control and acceptance testing in copper alloy production and fabrication
- Metallography and microstructure characterization in research and development
- Failure analysis and process optimization (e.g., annealing, recrystallization assessment)
- Materials inspection laboratories, OEM and supplier material certification, and dispute resolution (where Heyn or Jeffries methods are recommended for higher accuracy)
- Primary users: metallurgists, materials engineers, lab technicians, quality managers
Related standards
- ISO 2624:1990 (original international text) / EN ISO 2624:1995 (CEN adoption)
- Annex A of ISO 2624 references standard photomicrographs taken from ASTM E112 (Standard methods for determining average grain size)
Keywords: EN ISO 2624:1995, ISO 2624, grain size, copper and copper alloys, Heyn intercept, Jeffries planimetric, comparison procedure, metallography, average grain size estimation.