Overview
ISO 10720:1997 - "Steel and iron - Determination of nitrogen content - Thermal conductimetric method after fusion in a current of inert gas" specifies a laboratory method for measuring nitrogen content in steel and iron. The method uses inert‑gas fusion (helium) to extract nitrogen as N2, followed by detection with a thermal conductimetric (catharometer) gas analyser. It is applicable to nitrogen levels from 0.0008 % (m/m) to 0.50 % (m/m).
Key topics and technical requirements
- Principle: Fusion of a test portion in a single‑use graphite crucible under a helium stream (e.g., ≈2 200 °C), extraction of nitrogen as N2, separation and measurement by thermal conductivity.
- Applicable range: 0.0008 % to 0.50 % nitrogen (m/m).
- Sample preparation: Degreasing (e.g., acetone), controlled test portion masses (approx. 1.0 g for ≤0.10 % N; ≈0.50 g for >0.10 % N), and sampling per ISO 14284.
- Calibration and standards: Use potassium nitrate standard solutions for calibration; prepare calibration graphs by plotting net analyser response vs. micrograms of nitrogen. Perform routine blank tests and apply blank corrections.
- Reagents and consumables: High‑purity helium, pure iron reference material (low N), copper(II) oxide or platinum oxidation tube when organic contaminants are suspected, drying/absorbent agents (Mg(ClO4)2 or CaSO4), sodium hydroxide on support.
- Apparatus: Single‑use graphite crucible, nickel capsule, resistive electrode furnace (commercial analyzers), flowmeter and helium purification, thermal conductivity detector (catharometer).
- Quality and safety: Follow manufacturer instructions for instruments; conduct dummy/trial runs after changing reagents/filters; use crucible tongs and protective measures (risk of burns).
- Precision: Interlaboratory testing (14 laboratories) was performed; repeatability/reproducibility vary with nitrogen level (logarithmic relationship).
Applications and who uses this standard
- Metallurgical and materials laboratories performing routine or certification testing of steels and irons.
- Steel producers and foundries for quality control of alloying and interstitial impurity levels.
- Research & development groups studying nitrogen effects on mechanical properties and microstructure.
- Instrument manufacturers and service engineers for calibration, validation, and performance checks of inert‑gas fusion analysers.
- Compliance and certification bodies requiring traceable nitrogen measurements according to an international standard.
Keywords: ISO 10720, nitrogen content, steel and iron, inert gas fusion, thermal conductimetric, helium fusion, catharometer, nitrogen analysis, metallurgical testing.
Related standards
- ISO 14284 - Sampling and preparation of samples for chemical composition of steel and iron
- ISO 3696 - Water for analytical laboratory use
- ISO 5725 series - Accuracy (trueness and precision) of measurement methods
- ISO 385‑1, ISO 648, ISO 1042 - Laboratory glassware specifications
This standard provides a validated, reproducible procedure for precise nitrogen analysis in ferrous materials, suitable for laboratory accreditation and industrial quality control.