Overview - ISO/TS 5486:2025 (Metallographic determination of ferrite)
ISO/TS 5486:2025 is a Technical Specification from ISO that specifies a metallographic method to determine the maximum local ferrite content within an austenitic matrix of stainless steel. The document covers sampling, specimen preparation (grinding, polishing, etching), microscopic examination and three accepted evaluation methods (comparison chart, image analysis, and point counting). It is intended for laboratories, manufacturers and inspectors who need a repeatable, standards‑based procedure for ferrite determination in austenitic stainless steels.
Key topics and technical requirements
- Scope and sampling: Sampling location and number are defined by the product standard or agreement between parties. Clause 4 gives specific guidance for bars, billets, tubes and plates to ensure representative test planes.
- Specimen preparation: Standard metallographic grinding and polishing techniques are required; avoid deformation or contamination. Final surface cleanliness is mandatory (see ISO/TR 20580 for preparation guidance).
- Etching: Table 1 lists six etchants and procedures to reveal ferrite contrast reliably for microstructural inspection.
- Microscopy parameters: Typical magnification range is 200× to 500×. The standard reference field for comparison is a square with side 0.24 mm (area 0.0576 mm²).
- Evaluation methods:
- Comparison method - compare the field with the normative reference images in Annex A. Ferrite is classified into six grades with these content ranges:
- Grade 0.5: 0 ≤ V < 2 %
- Grade 1.0: 2 ≤ V < 5 %
- Grade 1.5: 5 ≤ V < 8 %
- Grade 2.0: 8 ≤ V < 12 %
- Grade 3.0: 12 ≤ V < 20 %
- Grade 4.0: 20 ≤ V < 35 %
- (Report >35 % when observed)
- Image analysis - grayscale thresholding (flicker method) and certified software can be used for automatic quantification.
- Point counting - applies ISO 9042 procedures using a single image of the highest‑content field; minimum 100 grid points advised.
- Test report: Required items include method reference (ISO/TS 5486:2025), steel grade/cast number, specimen sampling details, magnification/field area/etchant, results (grade or %), operator ID, report ID and date.
Applications and users
ISO/TS 5486:2025 is useful for:
- Metallurgical quality control and acceptance testing of austenitic stainless steels
- Welding inspection and post‑weld metallography
- Steel mills, component manufacturers and independent testing laboratories
- Procurement and product compliance where maximum local ferrite limits are specified
Keywords: ISO/TS 5486:2025, ferrite determination, austenitic stainless steel, metallographic method, ferrite content, image analysis, point counting, comparison chart.
Related standards
- ISO 9042 - point counting method (normative reference)
- ISO/TR 20580 - preparation of metallographic specimens (referenced for polishing guidance)