Overview
ISO 13520:2023 specifies procedures for estimating ferrite content in austenitic stainless steel castings (iron‑chromium‑nickel alloys) where a controlled amount of ferrite forms as a second phase. The standard describes three accepted approaches - chemical composition, magnetic response, and metallographic methods - and explains how to use Cr/Ni equivalents and the Schoefer diagram to estimate ferrite percentage. It also sets out ordering, acceptance, and certification information for suppliers and purchasers.
Key Topics
- Scope and purpose: Applies to austenitic castings balanced to produce limited ferrite (volume percent) and where ferrite content affects mechanical, welding and corrosion performance.
- Three measurement methods:
- Chemical composition method - estimation using chromium and nickel equivalents (Cr/Ni ratio) and the Schoefer diagram; depends on accurate chemical analysis of C, Mn, Si, Cr, Ni, Mo, Nb and N.
- Magnetic response method - instrument measurements calibrated for castings (reference methods such as ASTM A799 or BNIF 345); surface condition, probe placement, and heat treatment affect results.
- Metallographic examination - quantitative or point‑count methods (ISO 9042) on agreed specimen locations for the most accurate local ferrite fraction.
- Practical requirements:
- Element ranges applicable to the Schoefer diagram (e.g., Cr 17–28 wt%, Ni 4–13 wt%, plus limits for C, Mn, Si, Mo, Nb, N).
- Ordering details: alloy grade, required ferrite range (volume %), measurement method, and measurement locations.
- Acceptance criteria for magnetic measurements (average within limits; not more than 20% of individual readings outside limits) and precedence of metallography if disagreement occurs.
- Documentation and certification: manufacturers must report chemical analyses and ferrite estimates and sign inspection documents.
Applications and Who Uses It
ISO 13520:2023 is used by:
- Foundries and casting manufacturers for process control and supplier certification.
- Metallurgists and quality engineers for ferrite specification, testing and acceptance.
- Purchasing/specification writers and inspectors to define ferrite limits and test methods in contracts.
- Designers and fabricators who need to ensure mechanical, weldability and corrosion performance of austenitic castings by controlling ferrite content.
Practical applications include iron‑chromium‑nickel pump housings, valve bodies, pressure-containing components and other cast parts where microstructure impacts service behavior.
Related Standards
- ISO 4990 - Steel castings - General technical delivery requirements
- ISO 9042 - Manual point counting method for volume fraction estimation
- ASTM A799 and BNIF 345 - referenced calibration/guidance for magnetic ferrite measurement (moved to bibliography in this edition)
Keywords: ISO 13520:2023, ferrite content, austenitic stainless steel castings, Schoefer diagram, ferrite measurement, chemical composition method, magnetic response, metallographic examination.
