Effect of Dynamic Recrystallization on Microstructural Evolution in B Steels Microalloyed with Nb and/or Mo

Area of Science:

• Metallurgical Engineering
• Materials Science
• Physical Metallurgy

Background:

• Understanding dynamic recrystallization (DRX) is crucial for optimizing steel properties.
• Boron-microalloyed steels offer high strength but require careful processing control.

Purpose of the Study:

• To investigate the DRX behavior of ultra-high strength boron-microalloyed steels.
• To evaluate the influence of niobium (Nb) and molybdenum (Mo) on microstructure evolution during simulated plate rolling and direct quenching.

Main Methods:

• Multipass torsion tests to simulate plate rolling conditions.
• Electron Backscatter Diffraction (EBSD) for microstructural analysis.
• Direct quenching to study phase transformations.

Main Results:

• Partial DRX occurred in Nb-microalloyed steel, forming fine equiaxed grains within a pancaked austenite structure.
• Mo addition effectively suppressed DRX, promoting fully martensitic microstructures.
• Recrystallized austenite transformed into softer phases post-quenching.

Conclusions:

• Mo plays a dual role: enhancing hardenability and suppressing DRX.
• Controlling DRX is essential for achieving desired martensitic microstructures in direct quenching processes.
• Alloying elements significantly interfere with DRX phenomena.