Overview
ISO 5490:2025 - "Steel - Rating and classifying nonmetallic inclusions using the scanning electron microscope" - specifies standardized procedures for detecting, rating and statistically analysing non‑metallic inclusions in steel using an automated scanning electron microscope (SEM) equipped with an energy dispersive X‑ray spectrometer (EDS), a backscattered electron detector (BSD) and automatic image‑analysis software. The standard defines two main approaches: morphology (shape/size) or chemistry‑based rating and a statistical analysis method for stereological measurements.
Key topics and requirements
- Equipment & software: automated, computer‑controlled SEM with EDS and BSD; light‑element detector required if analysing C, B or N. EDS performance must meet ISO 22309.
- Calibration & checks: magnification calibration per ISO 16700; periodic EDS performance checks (e.g. ISO 15632 / ISO 22309); beam current adjusted to keep dead time < 40%.
- Analysis modes:
- Morphology rating: automated image analysis classifies inclusions by shape/size (AR threshold of 3 suggested for elongated particles) and chemistry as auxiliary input to reproduce ISO 4967 ratings.
- Chemistry rating: classifies primarily by elemental composition (may yield different ratings from ISO 4967 if chemistry is primary).
- Statistical analysis: reports area fraction, number per mm2, size distributions and chemical classes without producing ISO‑style ratings.
- Imaging & measurement parameters: magnification and resolution chosen so minimum particle (e.g., 2 µm) has adequate pixels (pixel size ≤ 1 µm, preferably < 0.6 µm). Suggested accelerating voltage for EDS ~15–20 kV. Spectrum acquisition counts typically set high enough (example: > 3 000 counts) for reliable classification.
- Automated rules: grey‑level thresholds for separating inclusions from matrix, rules for connecting stringers across field boundaries, and criteria for peak significance in EDS spectra (document provides example peak/background criteria).
Applications and users
ISO 5490:2025 is intended for:
- Metallurgical laboratories and quality control teams in steel mills for inclusion rating and process control.
- Failure analysis and R&D teams requiring objective, automated inclusion quantification.
- Suppliers and OEMs specifying inclusion limits for critical components (bearing steels, structural steels, forgings).
- Accreditation and inspection bodies seeking standardized SEM‑based inclusion data.
Practical benefits include reproducible automated ratings, faster large‑area analysis, and flexible statistical reporting tailored to application needs.
Related standards
- ISO 4967 - Micrographic method using standard diagrams (sampling & rating)
- ISO 15632 - EDS performance parameters
- ISO 16700 - SEM magnification calibration
- ISO 22309 - Quantitative EDS analysis and detector requirements
Keywords: ISO 5490:2025, steel inclusions, SEM analysis, EDS, BSD, automatic image analysis, morphology rating, chemistry rating, statistical analysis.