Overview
EN ISO 7625:2012 (ISO 7625:2012) defines methods for preparing samples from sintered metal materials (excluding hardmetals) for chemical analysis of carbon content. It covers procedures to obtain representative samples for determination of free carbon, total carbon, and combined carbon (calculated as the difference between total and free carbon). The standard is specifically intended for carbon determination by chemical combustion in oxygen with measurement of CO2 (in accordance with ISO 437) and excludes physical methods such as metallography or spectroscopy.
Key topics and requirements
- Scope: Applies to parts with uniformly distributed carbon; does not apply to carburized/decarburized or non-uniformly distributed carbon (e.g., case‑hardened parts) unless sampling is mutually agreed.
- Removal of interfering carbonaceous material:
- Impregnated organic substances (lubricants, oils, waxes) must be removed by Soxhlet degreasing with an appropriate solvent per ISO 2738; the solvent used must be stated.
- Surface carbon deposits (from sintering or heat treatment) must be removed by mechanical treatment.
- Sample preparation methods:
- Produce small fragments by crushing (in an inert mortar) or by dry machining (drilling, milling, turning) using hardmetal or ceramic tools.
- Avoid overheating, oxidation, contamination and loss of fine particles (e.g., free graphite) during handling.
- For drilling, holes should be distributed uniformly over the part; for thick parts, drill from both faces.
- Sampling considerations:
- If segregation is possible, divide the sample into several test portions and report the average.
- Store prepared samples in tightly sealed containers to prevent contamination.
- Precision indicator:
- After degreasing per ISO 2738, results are considered suspect if repeatability > 5% or reproducibility > 10% (95% confidence).
Applications and users
This standard is essential for:
- Quality control and laboratory technicians in powder metallurgy and materials testing labs
- Metallurgists and engineers responsible for sintered component verification
- Manufacturers and suppliers of sintered parts who must certify carbon content
- Purchasers and third‑party inspectors specifying reliable carbon analysis methods
Practical benefits include consistent sample preparation for accurate chemical carbon analysis, improved comparability of results, and reduced interference from surface or pore‑held organics.
Related standards
- ISO 437 - determination of total carbon by combustion and CO2 measurement
- ISO 2738 - Soxhlet degreasing and density/porosity determinations for sintered materials
Keywords: EN ISO 7625, ISO 7625:2012, sintered metal materials, sample preparation, carbon determination, chemical analysis, powder metallurgy, Soxhlet degreasing.
