Overview
ISO 5949:1983 specifies a micrographic method for assessing the distribution of carbides in tool steels and bearing steels. It applies to steels with carbon between 0.1% and 1.5% and a total content of alloying elements ≤ 5%. The method uses a set of reference photomicrographs (annex) to grade carbide distribution by visual comparison and defines sampling, sample preparation, observation, assessment, result expression and test reporting. Use for other steels requires special agreement.
Key topics and technical requirements
- Reference photomicrographs: Series of 10 images (numbered 0–9) representing increasing carbide levels; images grouped into four series by morphology and condition: NA, NH, LE, LD.
- NA: carbide network in the annealed condition
- NH: carbide network in the quenched and tempered condition
- LE: enclosed carbide streaking (distinct lines)
- LD: diffused carbide streaking
- Field sizes and magnifications:
- Series NA: 0.08 mm field at ×1000
- Series NH: 0.4 mm field at ×200
- Series LE & LD: 0.8 mm field at ×100
- Slight magnification variation acceptable; the visual field diameter must match the series used.
- Sampling:
- Samples from rounds, bars and flats; polished area ~100 mm².
- Surface examined should coincide with the direction of greatest elongation (longitudinal) or transverse section where appropriate.
- Sampling method and number of samples to be specified in product standard or agreed between parties.
- Sample preparation and etching:
- Polishing per metallographic techniques; electrolytic polishing only by agreement.
- Etchants: picral for NA (and optionally NH); nital for NH, LE, LD (picral may also be used).
- Assessment & expression of results:
- Compare each visual field to photomicrographs; record the matching photomicrograph number.
- Characteristic number = series symbol + photomicrograph number.
- Results can be expressed as an average (NA & NH) or as the characteristic number for the predominant worst field (LE & LD).
- Test report must include steel grade, sampling details/position, number of fields examined (NA/NH), heat treatment conditions, and results.
Applications and users
ISO 5949 is practical for:
- Metallurgists and microstructural analysts assessing carbide distribution
- Quality engineers in tool steel and bearing steel production
- Materials testing laboratories performing acceptance testing
- Toolmakers, bearing manufacturers and heat-treat shops verifying microstructural quality
The method supports quality control, process validation (heat treatment and rolling), failure analysis and material specification compliance.
Related standards
Keywords: ISO 5949, tool steels, bearing steels, carbide distribution, micrographic method, reference photomicrographs, metallography, sampling, nital, picral.
Open preview (PDF)Tool steels and bearing steels — Micrographic method for assessing the distribution of carbides using reference photomicrographs
