Phase determination in dual phase steels via HREBSD-based tetragonality mapping

Area of Science:

• Materials Science
• Metallurgy
• Crystallography

Background:

• Electron Backscatter Diffraction (EBSD) is crucial for material microstructure characterization.
• Distinguishing similar phases (e.g., body-centered cubic and body-centered tetragonal) in steels using standard EBSD is challenging due to subtle lattice distortions.
• Accurate measurement of tetragonality is key for phase distinction, but sensitive to errors in microscope geometry (pattern center).

Purpose of the Study:

• To develop and validate a novel strain minimization routine for precise pattern center determination in EBSD.
• To improve the accuracy of tetragonality measurement for reliable phase identification in dual phase steels.
• To assess the capability of the developed method for estimating local carbon content within steel microstructures.

Main Methods:

• Implemented a strain minimization routine for accurate pattern center determination across numerous grains in dual phase steels.
• Utilized both kinetically simulated and dynamically simulated EBSD patterns for tetragonality measurement.
• Generated tetragonality maps and subsequent phase maps for analysis and comparison with image-quality methods.

Main Results:

• The new pattern center determination method significantly improved accuracy in tetragonality measurements.
• Phase maps derived from dynamically simulated patterns achieved nearly 90% accuracy in grain phase identification, outperforming image-quality methods.
• Tetragonality measurement errors were approximately 1%, leading to a ~0.2% error in carbon content estimation, suitable for mapping localized carbon variations.

Conclusions:

• The developed strain minimization approach offers a robust solution for accurate pattern center determination in EBSD analysis of steels.
• Dynamically simulated patterns provide superior accuracy for phase mapping and local carbon content estimation compared to kinetically simulated patterns.
• While unsuitable for bulk carbon content, the technique is valuable for understanding carbon distribution in specific microstructural features like martensite in dual phase steels, aiding in microstructure design for enhanced properties.