Project A9: Experimental characterization and thermo-mechanical modeling of press hardening

Person in Charge: Rohith Uppaluri

Motivation and Objectives:
Hot stamping of steels is an efficient method for producing high strength automobile crash resistant components with minimal spring back. In hot stamping, the deformed austenitic state of the material is further quenched in the die to produce fully martensitic structure in the component. During this time, the microstructure is refined with a relaxed state of stress. This influences the martensitic start temperature and aids to predict the residual stress in the component accurately. In this work, a thermodynamically consistent approach is defined to address this issue and to account for its effects on the final properties of the formed component. The model describes the influence of prior austenite state of stress and deformation due to forming on the austenitic to martensitic phase transformations. The material model parameters are determined from the thermomechanical experiments on sheet samples using Gleeble.

Methods	Results
Experiments: (Themomechanical tests using Gleeble 3150) Tensile tests for different temperatures and strain rates Stress relaxation and creep tests Grain growth during austenization CCT diagram Modeling: Thermodynamic consistent finite strain plasticity theories Austenitic to martensitic phase transformations Hot stamping of a B-pillar component	Experiments: Strong stress relaxation behavior in austenitic state Martensitic microstructure relaxes even at room temperature Determined CCT is close with the results from literature Moderate Grain growth is observed for the recommended austenization temperatures Material model: Represents work hardening, dynamic/static recovery Inital studies on Hot stamping of B-pillar component