ISO 11408:1999 - Overview
ISO 11408:1999 specifies requirements and test methods for black oxide coating (a chemical conversion coating) applied to iron and steel - including cast and wrought iron, carbon steels, low-alloy steels and stainless steels. The standard covers intended uses such as reducing friction between sliding surfaces, decorative finishes and reducing light reflection. It notes that only very limited corrosion protection is provided, even when supplementary preservative treatments (oil, wax, lacquer) are applied. The standard does not set requirements for substrate finish or surface roughness.
Key topics and technical requirements
- Scope and ordering information: Purchasers must provide ISO 11408 reference, significant surfaces to be coated, substrate nature and condition, sampling plan and appearance criteria.
- Appearance and surface quality: Coating must be free of red oxide spots and not overall reddish-brown; wiping with filter paper must not produce reddish or green smut. Non-uniformity is permitted in locally treated areas (welds, hardened zones).
- Oxalic acid test: Detailed procedure - dissolve 50 g oxalic acid per litre of water, place ~3 drops (0.2 ml) on a flat coated spot; reaction must occur within 30 s to 8 min and be evaluated against reference images. This checks coating quality.
- Neutral salt spray (NSS) resistance: For austenitic stainless steels, the unpreserved significant surface must withstand 96 h in NSS (per ISO 9227) without visible corrosion.
- Heat treatment: Pre- and post-coating heat treatments to reduce hydrogen embrittlement risk are referenced (see ISO 9587 and ISO 9588). Surface-hardened parts require post-coating tempering between 190 °C and 220 °C for at least 2 h.
- Sampling and inspection: Lot sampling follows ISO 4519 attribute-based plans. Annex B describes test methods for neutral surface reaction (phenolphthalein) and porosity/continuity (CuSO4 immersion or droplet).
- Processing guidance: Informative Annex A provides typical processing procedures for various steel grades.
Practical applications and users
Who uses ISO 11408:
- Manufacturers and processors that apply black oxide coatings to fasteners, sliding components, decorative hardware and optical housings.
- Quality engineers and inspection personnel defining test methods (oxalic acid, NSS, porosity tests) and acceptance criteria.
- Purchasers and specifiers who need to include coating requirements in procurement documents and drawings.
Practical value:
- Ensures consistent appearance, basic surface performance and comparability between suppliers.
- Helps manage risks like hydrogen embrittlement via referenced heat-treatment requirements.
Related standards
- ISO 2064 - coating thickness definitions
- ISO 4519 - sampling procedures for inspection by attributes
- ISO 9227 - salt spray (NSS) corrosion testing
- ISO 9587 / ISO 9588 - pre- and post-treatment for hydrogen embrittlement prevention
Keywords: ISO 11408, black oxide coating, chemical conversion coatings, iron and steel, oxalic acid test, neutral salt spray, porosity test, hydrogen embrittlement, sampling, surface quality.
Open preview (PDF)Chemical conversion coatings — Black oxide coating on iron and steel — Specification and test methods