Overview
ISO/TR 22824:2003 is a technical report from IIW Commission IX published through ISO that gives expert guidance on specifying ferrite content (FN) for welding consumables used with nominally austenitic and duplex ferritic‑austenitic stainless steel weld metals. It addresses differences between predicted (calculated) and measured ferrite numbers, sets out measurement and calculation reproducibility considerations, and explains how welding practice and post‑weld heat treatment affect FN. Keywords: ferrite content, ferrite number (FN), welding consumables, austenitic stainless steel, duplex stainless steel.
Key topics
- Scope and intent
- Guidance for setting appropriate requirements on ferrite content in specifications, standards and contracts for weld metal.
- Measurement reproducibility
- Interlaboratory studies (ISO 8249 / AWS A4.2 methods) show 95% reproducibility typically about ±10% (with primary standards) or ±14% (with secondary standards) of the mean FN value. This impacts allowed tolerances on measured FN.
- Calculation reproducibility
- FN predictions depend on chemical analysis reproducibility. Small analytical variations (Cr, Ni, N) can cause large FN calculation differences (WRC‑1992, DeLong, Schaeffler diagrams).
- Comparison: calculated vs measured FN
- Constitution diagrams differ in accuracy and bias; WRC variants generally give better agreement than older diagrams (e.g., DeLong) in many datasets. Discrepancies can arise from analytical drift or diagram development data.
- Measurement location
- Ferrite is non‑uniform in welds. ISO 8249 and AWS A4.2 require FN measurements along the top axis of a weld pass; these give higher average FN and lower scatter than cross‑section or randomly sampled surface points. Acceptance decisions should be based on axis‑top measurements.
- Effect of post‑weld heat treatment (PWHT / TTAS)
- PWHT typically reduces ferrite in weld metal (transformation to austenite, intermetallics or other phases). Different FN limits may be needed for as‑deposited and PWHT conditions.
- Welding variables
- Procedure and multipass effects cause FN variation; specifications should allow for procedural variability.
Applications and users
ISO/TR 22824 is practical for:
- Welding engineers and metallurgists setting consumable and weld metal FN requirements
- Specification writers and standards committees drafting acceptance criteria
- Quality assurance / inspection teams interpreting FN measurements
- Consumable manufacturers and material suppliers advising on expected weld metal FN
- Designers and fabricators of austenitic and duplex stainless steel structures concerned with hot cracking and high‑temperature embrittlement
Practical takeaway: when specifying FN, account for measurement and calculation uncertainty, require standardized measurement locations (top‑axis), and use different acceptance criteria for as‑welded vs post‑heat‑treated conditions.
Related standards
- ISO 8249 (ferrite measurement methods)
- AWS A4.2 (ferrite measurement)
- WRC constitution diagrams (WRC‑1988, WRC‑1992)
- Schaeffler and DeLong diagrams
- ASTM E1086 (OES analysis) and ASTM E1019 (nitrogen analysis)
- Relevant ASME code guidance referenced in the report
Keywords: ferrite number, FN, ferrite measurement, welding consumables, duplex stainless steel, austenitic stainless steel, FN calculation.
Open preview (PDF)Welding consumables — Predicted and measured FN in specifications — A position statement of the experts of IIW Commission IX
