Effects of Austenite Stability on Forming and Work Hardening Behavior of 1.2 GPa Gen3 AHSS

For this study, three 1.2GPa Gen3 AHSS grades with different steel designs were selected for an industrial stamping trial of a B Pillar part. Formability analyses were performed using an Argus system, the material work hardening was evaluated using sub-size tensile specimens sampled from different locations of the formed part and the TRIP effect was quantified using X-Ray diffraction. It was found that the strain distribution and strain localization are strongly related with the microstructural phase composition of the steel and with the mechanical stability of the retained austenite. The increase of the mechanical properties of the formed part represents a combined effect of strain hardening and transformation strengthening. The paint baking contribution to the increase of the yield strength of the formed panels decreases above certain percentage of induced effective strains. The remaining austenite after forming shows high thermal stability at the paint curing temperature. (paper)