ISO 7625:2012

Overview

ISO 7625:2012 specifies how to prepare samples from sintered metal materials (excluding hardmetals) for chemical analysis of carbon content. It covers preparation methods for determining free carbon and total carbon by combustion in oxygen with CO2 measurement (chemical method in accordance with ISO 437). Combined carbon is calculated as the difference between total and free carbon. This standard does not apply to physical carbon-determination methods (e.g., metallography or spectroscopy) or to materials with non-uniform carbon distribution unless sampling is agreed between supplier and purchaser.

Key topics and requirements

• Scope: Applies to sintered parts (excluding hardmetals) where carbon is uniformly distributed and present in forms listed by the standard.
• Chemical analysis method: Preparation is intended for combustion/CO2-based carbon measurement per ISO 437.
• Removal of interfering carbonaceous substances:
  • Degreasing by Soxhlet extraction using an appropriate solvent (record the solvent used) in line with ISO 2738 when organic liquids/waxes are present in pores or on surfaces.
  • Mechanical removal of surface carbon deposits (e.g., from sintering or heat treatment).
• Sample preparation techniques:
  • Crushing in a non-contaminating mortar, or
  • Dry machining (drilling, milling, turning) using ceramic or hardmetal tools; avoid overheating, oxidation, and contamination.
  • For drilling, holes should be distributed uniformly and, if necessary for thick parts, drilled from both faces.
• Handling fine particles: Take care not to lose fine constituents (e.g., graphite) during manipulation.
• Storage: Keep prepared fragments in airtight containers to prevent contamination.
• Validity limits: Results may be questionable if repeatability exceeds 5% or reproducibility exceeds 10% at 95% confidence after degreasing per ISO 2738.

Applications and users

ISO 7625:2012 is relevant for:

• Metallurgists and materials engineers in the powder metallurgy industry
• Quality control and materials testing laboratories performing carbon analysis on sintered parts
• Suppliers and purchasers agreeing on sampling when carbon distribution is non-uniform (e.g., cemented or decarburized surfaces)
• R&D teams characterizing sintered components for performance or failure analysis

Practical benefits include improved accuracy of free/total carbon measurements, standardized sample handling to avoid contamination, and consistent procedures for contract testing and certification.

Related standards

• ISO 437 - Carbon determination by combustion (CO2 measurement)
• ISO 2738 - Sintered permeable materials - determination of density, oil content and open porosity (referenced for Soxhlet degreasing)

Keywords: ISO 7625:2012, sintered metal materials, sample preparation for chemical analysis, carbon content determination, combustion analysis, Soxhlet degreasing, powder metallurgy testing.