Overview
ISO 24476:2024 - Steel - Determination of oxygen - Infrared absorption method after fusion under inert gas (Routine method) specifies a routine laboratory method for measuring oxygen in steel by fusing a test portion in a single‑use graphite crucible under an inert gas (He or Ar) stream and detecting evolved carbon monoxide/carbon dioxide using infrared absorption. The method covers oxygen contents from 0.001 % to 0.02 % (mass fraction) and uses calibration against steel certified reference materials (CRMs).
Key topics and requirements
- Principle: Fusion of a weighted test portion at very high temperature (minimum ~2 000 °C) in graphite crucible under ultra‑high‑purity inert gas (He or Ar, ≥99.999 % by volume, total impurities ≤0.0005 % mass fraction). Oxygen released reacts with carbon to form CO (optionally oxidized to CO2) which is measured by an infrared detector.
- Applicable range: 0.001 % to 0.02 % oxygen (mass fraction).
- Sample preparation: Use solid, uniform samples (slice thickness ~3–4 mm); weigh ~1 g to nearest 1 mg; remove surface oxide by dry filing/grinding (avoid overheating); avoid contact with fingers; analyze promptly or store in desiccator for oxidation‑prone alloys.
- Reagents and materials: Ultra‑high‑purity He or Ar; copper(II) oxide (if instrument oxidizes CO to CO2); magnesium perchlorate for moisture; sodium hydroxide on clay (ascarite) for CO2 absorption; high‑purity acetone for cleaning; single‑use high‑purity graphite crucibles.
- Apparatus: Commercial oxygen analyzers (follow manufacturer instructions), resistive electrode furnaces/graphite crucibles, glass‑wool filters; features of instruments discussed in Annex A.
- Quality controls: Perform duplicate blank tests (degassing at >2 100 °C for blanks), ensure mean blank is acceptably low, subtract blank from readings, build calibration curve using CRMs that bracket expected oxygen levels, run RMs/CRMs periodically to monitor drift.
- Safety: High burn and electrical hazards-use crucible tongs and follow manufacturer safety guidance.
Applications and users
- Routine quality control and process monitoring in steel production and processing
- Metallurgical and chemical analysis laboratories performing oxygen determination in steels
- Third‑party testing labs, certification bodies, and instrument manufacturers validating analyzer performance
- Useful where accurate low‑level oxygen quantification (ppm level) is required for product specification, process optimization, and material certification
Related standards
- ISO 14284 - Steel and iron - Sampling and preparation of samples for the determination of chemical composition (referenced for sampling and sample prep)
- Instrument manufacturers’ manuals and national laboratory practice standards for measurement traceability and safety
Keywords: ISO 24476:2024, oxygen determination in steel, infrared absorption method, fusion under inert gas, oxygen analysis, graphite crucible, helium argon ultra‑high purity, certified reference materials, calibration curve, blank test.
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