Comparative study of the prediction of microstructure and mechanical properties for a hot-stamped B-pillar reinforcing part

Automobile manufacturers have been increasingly adopting hot-stamped parts for use in newly designed vehicles to improve crash worthiness and fuel efficiency. However, the hot-stamped parts require extreme mechanical properties with ultimate tensile strengths as high as 1500 MPa (∼450 Vickers hardness) while still maintaining adequate formability during the stamping operation. The ultra high strength of hot-stamped components is attributed to the martensitic phase transformation that occurs after the part has been formed at temperatures corresponding to the austenite phase field where formability is enhanced. In the present study, a computer-aided design method incorporating Kirkaldy and Venugopalan type phase transformation models has been implemented following a thermo-mechanical coupled finite element analysis to predict the mechanical properties of hot-stamped parts made with a boron-modified steel. Three empirical models which are typically used for hot stamping analysis are employed and the prediction capability of the models is compared using continuous cooling dilatometry and forming experiments of a modified B-pillar part.

► Numerical phase transformation models were compared associated with an FE simulation for hot stamping of boron steel.
► Transformation models were the Kirkaldy–Venugopalan model and its variations (Li, A–O model).
► Hardness of the stamped part was predicted based on the quantity of calculated phase fractions and experimental phase hardness.
► Li model showed the best predictability in comparison.