Overview
EN ISO 13520:2023 - Determination of ferrite content in austenitic stainless steel castings defines standardized procedures for estimating the ferrite content (volume percent) in austenitic iron‑chromium‑nickel alloy castings. The standard covers castings whose chemistry is intentionally balanced to form ferrite as a controlled second phase. It describes three accepted measurement routes - chemical, magnetic and metallographic - and provides guidance on sampling, ordering information, and interpretation of results to support quality control and specification compliance.
Key topics and technical requirements
- Scope and significance: Explains how ferrite fraction affects tensile/impact properties, weldability and corrosion resistance, and why controlled ferrite content is specified for many castings.
- Three methods of determination:
- Chemical composition method - estimation from heat or product chemical analysis using chromium and nickel equivalents together with the Schoefer diagram to predict ferrite percentage. (ISO provides the required calculation approach and diagram references.)
- Magnetic response method - non‑destructive magnetic measurements to estimate ferrite; notes sources of error such as other ferromagnetic phases, surface condition and instrument probe geometry.
- Metallographic examination - point‑counting and quantitative metallography on prepared specimens; Annex A gives normative guidance for magnetic and metallographic procedures.
- Measurement uncertainty and limitations: Discusses precision issues for each method (segregation, thermal history, etching technique, grid size, chemical analysis accuracy) and the need to set realistic specification limits.
- Ordering and documentation: Specifies information to be included in purchase orders: product specification, alloy grade, required ferrite range (volume %), chosen test method and measurement locations.
- Normative and informative annexes: Includes Annex A (normative methods) and Annex B (notes on the Schoefer diagram).
Practical applications
- Process control during melting and casting to achieve target ferrite levels.
- Incoming inspection and acceptance testing of austenitic stainless steel castings.
- Failure or root‑cause analysis where ferrite fraction impacts mechanical behavior or corrosion performance.
- Weld procedure qualification and design checks where ferrite‑to‑austenite balance is critical.
- Contractual specifications between manufacturers and purchasers to define allowable ferrite ranges and test methods.
- Foundries and steelmakers (material production and melt control)
- Quality and inspection engineers (NDT and metallography)
- Materials and corrosion engineers (selection and design)
- Procurement and compliance teams (specifying acceptance criteria)
- Welding engineers and fabricators concerned with microstructural balance
Related standards
- ISO 4990 - Steel castings - General technical delivery requirements
- ISO 9042 - Manual point counting method for estimating volume fraction
- EN ISO 13520:2023 replaces EN ISO 13520:2019 and is published by CEN in collaboration with ISO/TC 17.
Keywords: EN ISO 13520:2023, ferrite content, austenitic stainless steel castings, ferrite determination, chemical method, magnetic method, metallographic method, Schoefer diagram, chromium equivalent, nickel equivalent.
