Ultrasonic Effect on the Deformation Behavior and Microstructure Evolution of a TRIP-Assisted Steel

The effect of ultrasonic vibration on the deformation mechanism of a TRIP-assisted steel is comprehensively studied based on micro-tensile tests. Lower flow stress and work hardening rate are observed in ultrasonically assisted (UA) conditions. Digital image correlation (DIC) analysis reveals the change in strain distribution and formation of Lüders-like deformation bands under superimposed UA. Electron backscatter diffraction (EBSD) characterization shows that at the same strain, UA reduces the fraction of retained austenite that is transformed to martensite, indicating a delayed martensitic transformation process. Additionally, EBSD reveals less low-angle grain boundaries and geometrically necessary dislocations with UA. All these microstructure modifications contribute to reduced flow stress and the change of strain distribution during deformation.