Characterization of complex phase steel using backscattered electron images with controlled collection angles

Area of Science:

• Materials Science
• Metallurgy
• Microscopy

Background:

• Complex phase (CP) steels require microstructural optimization for enhanced properties.
• Traditional scanning electron microscopy (SEM) characterization of CP steels often relies on etching, providing indirect topographic information.
• Distinguishing between ferritic (F) and martensite (M) phases in CP steels is crucial for microstructure control.

Purpose of the Study:

• To develop a novel, direct imaging technique for the martensite (M) phase in ferritic-martensitic (F-M) complex phase steels.
• To overcome limitations of indirect etching methods in SEM characterization.
• To enable precise structural information for optimizing CP steel microstructures.

Main Methods:

• Utilized scanning electron microscopy (SEM) with backscattered electron (BSE) imaging at 15-20 kV.
• Systematically varied the BSE collection angle (θ) relative to the specimen surface.
• Analyzed contrast variations attributed to electron channeling and defect density.

Main Results:

• Selective imaging of the martensite (M) phase was achieved at high BSE collection angles (θ > 60°).
• The bright contrast of martensite is attributed to its high crystallographic defect density, causing anomalous BSE scattering.
• Low-angle BSE imaging provided high-resolution microstructural details, while high-angle BSE enabled quantitative assessment of martensite distribution and volume fraction.

Conclusions:

• High-angle BSE imaging offers a direct and precise method for characterizing the martensite phase in complex phase steels.
• This technique bypasses the need for etching, providing more accurate microstructural analysis.
• The developed method facilitates the optimization of complex phase steel microstructures through quantitative phase analysis.