Ultrasonic backscattering model of lamellar duplex phase microstructures in polycrystalline materials

Area of Science:

• Materials Science
• Non-destructive Testing
• Metallurgy

Background:

• Pearlitic heat-resistant steels (carbon and low alloy steels) are vital for high-temperature pressure components.
• Long-term high-temperature service causes material degradation, including spheroidization, graphitization, and thermal aging.
• Degradation affects the lamellar microstructure, impacting mechanical properties and component integrity.

Purpose of the Study:

• To develop a theoretical model for ultrasonic backscattering in pearlitic lamellar structures.
• To analyze the influence of pearlite area ratio and interlamellar spacing on ultrasonic signals.
• To validate the theoretical model using finite element analysis and experimental data for material degradation assessment.

Main Methods:

• Development of a theoretical model for ultrasonic backscattering from lamellar pearlite.
• Construction of a 2D finite element (FE) model using Voronoi diagrams to simulate lamellar structures.
• Experimental preparation of spheroidized steel samples and ultrasonic testing to collect backscattering signals (RMS maximum values).

Main Results:

• The theoretical model and FE analysis accurately predicted the effects of pearlite area ratio and interlamellar spacing on backscattering signals.
• Experimental results showed trends consistent with the theoretical and FE models.
• The model demonstrated good agreement with experimental data, despite minor errors, confirming its utility.

Conclusions:

• The proposed ultrasonic backscattering model effectively correlates microstructural changes in pearlitic steels with signal characteristics.
• The model can be utilized to evaluate performance degradation in metallic materials exhibiting lamellar pearlite structures.
• This approach offers a promising non-destructive method for monitoring the health of high-temperature steel components.