Overview
ISO 9556:1989 specifies an infrared absorption method after combustion in an induction furnace for the determination of total carbon content in steel and iron. The standard covers the full analytical workflow-principle, reagents, apparatus, sampling, procedural steps, calibration, expression of results and test reporting. The method is applicable to carbon contents from 0.003% (m/m) to 4.5% (m/m). Informative annexes provide international inter‑laboratory precision data, a graphical representation of repeatability/reproducibility, and features of induction furnaces and carbon analysers.
Key topics and requirements
- Analytical principle: Combustion of a weighed test portion in a high‑frequency induction furnace under pure oxygen, with evolved CO2/CO measured by infrared (IR) absorption.
- Scope limits: Valid for carbon contents 0.003%–4.5% (m/m).
- Reagents: e.g., CO2‑free water, oxygen (≥99.5% m/m), pure low‑carbon iron for blanks, standard solutions (sucrose or sodium carbonate) for calibration.
- Apparatus: Induction furnace, IR carbon analyser, micropipette, tin capsules, ceramic crucibles, desiccator and certified volumetric glassware.
- Calibration & blanks: Use calibration series (sucrose, sodium/barium carbonate or reference materials) and blank tests with pure iron; instrument readings are converted to milligrams of carbon via a calibration graph.
- Procedure controls: Pre‑ignition of crucibles, oxygen purification (catalyst and drying), dust collection, and instrument stabilization before measurement.
- Precision & validation: Precision data (repeatability and reproducibility) were derived from multi‑laboratory trials (22 laboratories). Annex B gives graphical precision curves; ISO 5725 principles used for statistical treatment.
- Reporting: Test report must identify sample/lab/date, cite ISO 9556, present results and units, note any deviations or unusual observations.
Applications and users
- Quality control in steel and iron production: Incoming material inspection, process control and final product certification.
- Metallurgical and analytical laboratories: Routine carbon analysis for alloys, ferrous samples and research.
- Inspection and certification bodies: Compliance verification against material specifications.
- R&D and failure analysis: Accurate total carbon quantification for microstructure/property correlation.
- Typical users: steelmakers, foundries, contract testing labs, national metrology/standards labs and academia.
Related standards
- ISO 377 - Sampling of steel and iron (referenced for sampling).
- ISO 5725 - Precision of test methods (used for repeatability/reproducibility assessment).
- Other laboratory glassware standards referenced for volumetric accuracy.
This standard is essential when accurate, traceable measurement of total carbon in ferrous materials is required, especially where results must be comparable across laboratories and conform to internationally recognized procedures. Keywords: ISO 9556:1989, total carbon content, infrared absorption method, induction furnace, carbon analysis, steel and iron, laboratory calibration, precision.
Open preview (PDF)Steel and iron — Determination of total carbon content — Infrared absorption method after combustion in an induction furnace