Overview
EN ISO 4945:2018 - titled Steel - Determination of nitrogen - Spectrophotometric method (ISO 4945:2018) - is a CEN-endorsed international standard that specifies a laboratory spectrophotometric procedure for determining nitrogen in steel. The method covers nitrogen mass fractions from 0,0006 % to 0,050 % for low-alloy steels and 0,010 % to 0,050 % for high-alloy steels. It is not applicable to materials containing silicon nitrides or to steels with silicon content above 0,6 %.
Key Topics and Requirements
- Analytical principle: Dissolution of a test portion in hydrochloric acid; fuming of the acid-insoluble residue with sulphuric acid (and potassium sulfate and copper(II) sulfate); alkaline steam distillation to liberate ammonia; trapping ammonia in dilute sulphuric acid; formation of a blue-coloured phenol-based complex (with sodium hypochlorite and sodium nitroprusside); spectrophotometric measurement at about 640 nm.
- Applicable range: 0,0006–0,050 % N (low-alloy steels); 0,010–0,050 % N (high-alloy steels).
- Limitations: Excludes samples containing silicon nitrides or Si > 0,6 %.
- Reagents and preparations: Defines required reagent grades and preparations (e.g., HCl 1+1, fuming H2SO4, NaOH solutions, sodium phenoxide, sodium nitroprusside, standard nitrogen solutions).
- Apparatus: Requires class A volumetric glassware, a spectrophotometer capable of 640 nm readings with 10 mm cells, and a suitable steam distillation setup (examples provided in Annex A).
- Calibration and quality control: Procedure includes blank tests, preparation of calibration solutions from a nitrogen stock/standard, plotting a calibration curve and reporting results. Precision and interlaboratory data are documented in informative annexes.
Applications
- Quality control in steel production: Monitoring nitrogen content to meet material specifications and performance requirements (e.g., mechanical properties, welding behavior).
- Metallurgical laboratories: Routine chemical analysis of low- and high-alloy steels where accurate low-level nitrogen determination is required.
- Third‑party testing and certification: Use in conformity assessment, inspection and verification of delivered steel products.
- Research and development: Studies where controlled nitrogen levels influence microstructure or alloys’ properties.
Who should use this standard
- Steel producers and mills, heat‑treatment shops, analytical laboratories, metallurgists, quality engineers, and standards bodies responsible for chemical analysis of metals.
Related standards
Keywords: EN ISO 4945:2018, ISO 4945, nitrogen determination, spectrophotometric method, nitrogen in steel, steel analysis, CEN standard.