Overview - ISO/TR 22824:2024 (Welding, ferrite in stainless steel weld metal)
ISO/TR 22824:2024 is a Technical Report that provides best practices for specification and measurement of ferrite in nominally austenitic and duplex (ferritic–austenitic) stainless steel weld metal. Prepared by welding experts (IIW in collaboration with ISO/TC 44), this second edition updates and expands guidance on the metallurgical behavior of ferrite, measurement methods, reproducibility, and handling of measurement outliers. It is explicitly not applicable to ferritic or martensitic stainless steels.
Key topics and technical content
The report summarizes expert judgement and practical guidance on:
- Metallurgical phenomena: solidification modes (A, AF, FA, F, and mixed modes), solid-state ferrite→austenite transformations, constitution diagrams, intermetallic phases, alpha-prime formation, chromium nitrides and secondary austenite, and effects of postweld heat treatment.
- Effects on performance: influence of ferrite variations on ambient tensile properties, toughness, chloride stress corrosion cracking (CSCC) resistance, general corrosion susceptibility and creep behaviour.
- Measurement methods: metallographic (optical) ferrite percent, EBSD, x‑ray diffraction (XRD), electrochemical dissolution, saturation magnetization, magnetic attraction, and magnetic permeability / magnetic induction. The report addresses Ferrite Number (FN) measurement (calibration per ISO 8249), correlations between FN and volumetric ferrite percent, and measurement location / volume (including weld heat‑affected zone - HAZ).
- Specification and tolerancing: best practice for setting contractual and standards requirements for ferrite content in weld metal (including duplex welds), non‑magnetic requirements, and considerations for cryogenic or high‑temperature service and dissimilar welds.
- Quality control: reproducibility of measurements, recommended approaches for dealing with outliers and unexpected results.
Practical applications and users
ISO/TR 22824:2024 is intended for professionals involved in welding metallurgy, quality assurance and specification of stainless steel fabrication, including:
- Welding engineers and metallurgists
- QA/QC and NDT personnel assessing ferrite in welds
- Standards writers and contract authors specifying ferrite limits
- Fabricators and inspectors working with austenitic and duplex stainless steels
Use cases include setting ferrite limits for weld procedure specifications, selecting measurement techniques for production or inspection, and interpreting ferrite test results for service-critical applications (e.g., chloride environments, cryogenic or high‑temperature service).
Related standards
- ISO 8249 - calibration of instruments for Ferrite Number (FN)
- ISO/TC 44 publications and IIW guidance referenced in the report
Keywords: ISO/TR 22824:2024, ferrite, stainless steel weld metal, Ferrite Number, ferrite measurement, austenitic, duplex, weld HAZ, welding specification, measurement reproducibility.
Open preview (PDF)Welding — Best practices for specification and measurement of ferrite in stainless steel weld metal
