ISO 23749:2022

Overview

ISO 23749:2022 - "Microbeam analysis - Electron backscatter diffraction - Quantitative determination of austenite in steel" specifies standardized procedures for using electron backscatter diffraction (EBSD) to quantify austenite in low- and medium-carbon steels and alloy steels. The standard governs specimen preparation, EBSD acquisition, data processing and statistical reporting to deliver reliable measurements of retained austenite content, morphology and distribution. ISO 23749:2022 is intended for austenite grains larger than 50 nm; it is not suitable for reliable quantification of grains below this limit.

Key technical topics and requirements

• Scope and limitations: Applied mainly to low/medium carbon steels; detectable austenite grain size > 50 nm (instrument- and parameter-dependent).
• Specimen preparation: Surface polish must produce high-quality EBSD patterns; avoid over-etching and deformation. Electropolishing recommended; ion milling not recommended for austenite.
• SEM/EBSD setup:
  • Specimen tilted 70° to the EBSD detector.
  • Maintain conductivity (carbon coating not suitable).
  • For iron/steel, acceleration voltage not less than 10 kV is recommended (balance pattern quality and resolution).
• Scanning parameters:
  • Scanning step size ≤ 1/5 of average austenite grain size (estimate grain size with a quick EBSD scan per ISO 13067).
  • Minimum 6 fields at 1000× magnification; total scanned area > 0.065 mm² (Annex A explains derivation).
• Indexing and data quality:
  • Define critical indexing reliability: mean angle difference (MAD) ≤ 1° or confidence index (CI) > 0.1.
  • Required hit rate: ≥ 85% for martensite-containing microstructures, ≥ 90% for martensite-free microstructures.
  • Data cleaning and handling of non-indexed/misindexed points are specified.
• Data analysis and reporting:
  • Calculation of austenite fraction, grain-size/shape metrics (ECD, aspect ratio), 95% confidence intervals and relative accuracy.
  • Test report requirements and examples (e.g., TRIP 590) are provided.

Practical applications and users

ISO 23749:2022 is valuable for:

• Materials scientists and metallurgists quantifying retained austenite in TRIP, TWIP and Q&P steels.
• Automotive and structural steel manufacturers for process control and mechanical-property optimization.
• R&D labs, failure analysis and quality assurance units requiring standardized EBSD-based austenite quantification.
• Certification bodies and testing laboratories aiming for interoperable, reproducible results.

Quantitative EBSD per ISO 23749 helps link retained austenite content and morphology to mechanical performance (e.g., the TRIP effect), supporting material design and production control.

Related standards

• ISO 13067 - EBSD measurement of average grain size
• ISO 22309 - EDS quantitative analysis (elements ≥ Na)
• ISO 22493 - Scanning electron microscopy vocabulary
• ISO 24173 - Guidelines for orientation measurement using EBSD

Keywords: ISO 23749:2022, EBSD, austenite quantification, retained austenite, steel, TRIP steel, grain size, electron backscatter diffraction.