Development of a Model for Dynamic Recrystallization Consistent with the Second Derivative Criterion.

Area of Science:

• Materials Science
• Metallurgy
• Mechanical Engineering

Background:

• Dynamic recrystallization (DRX) is crucial in hot working for controlling material properties and reducing forming forces.
• The second derivative criterion (SDC) by Poliak and Jonas is a key method for detecting DRX onset via strain-hardening rate inflection points.
• Existing flow stress models, while used in finite element analysis for metal forming, lack verified consistency with the SDC.

Purpose of the Study:

• To identify inconsistencies between current DRX models and the SDC.
• To develop a novel, consistent strain-hardening model for DRX kinetics.
• To validate the proposed model against experimental data for alloy 800H.

Main Methods:

• Analysis of strain-hardening rate transitions in Kocks-Mecking space.
• Development of a new strain-hardening model for stages III-IV of DRX.
• Integration of the new model with consistent recrystallization kinetics.
• Experimental validation using alloy 800H at various temperatures and strain rates.

Main Results:

• Three sources of inconsistency in existing DRX models were identified.
• A new strain-hardening model was proposed, exhibiting linear variations in transition and inflection points for alloy 800H.
• The model demonstrated high precision in predicting the strain-hardening rate, leading to accurate flow stress predictions.

Conclusions:

• The developed model provides a consistent approach to modeling DRX kinetics, aligning with the SDC.
• Accurate flow stress predictions are achievable through this refined modeling approach.
• The findings enhance the reliability of finite element simulations in metal forming processes involving DRX.