Overview
ISO 4499-4:2016 - "Hardmetals - Metallographic determination of microstructure - Part 4: Characterisation of porosity, carbon defects and eta‑phase content" defines standardized metallographic methods to detect, characterise and report porosity, uncombined carbon (graphite) defects and eta‑phase in hardmetals. The standard covers sample preparation, required apparatus (optical microscope, SEM), calibration, etching procedures and quantification/classification schemes used in quality control and microstructure evaluation of WC/Co and related hardmetals.
Key topics and technical requirements
- Scope: Methods for presence, type and distribution of porosity, carbon defects and eta‑phase in hardmetals.
- Apparatus & calibration: Use of metallographic optical microscopes and SEMs; image calibration against stage micrometre or certified grids (e.g., SIRA) traceable to national standards.
- Sample preparation: Grinding and polishing down to fine diamond paste (≈1 µm) and avoidance of particle pull‑out that can falsify porosity readings.
- Porosity classification:
- A‑type pores: up to 10 µm - examined at ×100 or ×200, reported as A02, A04, A06, A08 (A00 if below A02 level).
- B‑type pores: 10–25 µm - examined at ×100 and reported B02, B04, B06, B08; low counts in representative area are reported as B00‑# (pores/cm2).
- Larger pores: >25 µm are counted and reported per unit area in defined size ranges (25–75 µm, 75–125 µm, >125 µm).
- Carbon defects: Uncombined carbon (graphite) assessed at ×100 and reported as C02, C04, C06, C08 (C00 if none detected).
- Eta‑phase detection: Requires etching (commonly Murakami’s reagent):
- Large eta rosettes: light etch in 10% Murakami’s reagent for a few seconds, immediate water flush.
- Small eta particles: 5% Murakami’s reagent for ~20 min, then water rinse; dry with acetone or alcohol (do not wipe).
- Eta‑phase visual contrast varies (orange/brown after 10% etch; small white particles with 5% treatment).
- Reporting & uncertainty: Guidance on documenting location (top, rim, core), measurement uncertainty and test report contents.
Applications and users
ISO 4499-4:2016 is used for:
- Quality control and incoming inspection of hardmetal products (cutting tools, wear parts).
- Failure analysis and root‑cause investigations where porosity, graphite or eta‑phase affect density and mechanical properties.
- R&D and process control in powder metallurgy and liquid‑phase sintering of WC/Co and related hardmetals.
Primary users: metallurgists, materials engineers, QC laboratories, SEM/optical microscopy labs, hardmetal manufacturers and certification bodies.
Related standards
- ISO 4499-1: Metallographic preparation and photomicrographs
- ISO 4499-2: Measurement of WC grain size (normatively referenced)
- ISO 4499-3: Measurement of microstructural features in Ti(C,N) and WC/cubic carbide based hardmetals
Keywords: ISO 4499-4:2016, hardmetals, metallographic determination, porosity classification, uncombined carbon, eta‑phase, Murakami’s reagent, WC/Co, SEM calibration, metallography.