Alloy and process development of partial press hardening utilizing advanced bainite transformation models
Primary Shaping and Reshaping Technology, Additive Manufacturing
Final Report Abstract
A precise understanding of temperature-dependent material properties is crucial for accurate numerical predictions of complex phase transformations and forming processes in modern high-performance steels. As a foundation, an inverse solution method for determining Young’s modulus of ferritic and austenitic steels at elevated temperatures provides essential input data for calibrating finite element (FE) simulations. By accounting for temperature gradients in the sample, this non-destructive method accurately characterizes the elastic behavior and ensures reliable simulation parameters over a wide temperature range. Building on these parameters, a comprehensive study investigates the kinetics of bainitic ferrite formation through experiments (dilatometry and Gleeble tests), FE analysis, and thermodynamic modeling. Empirical data from Dilatometry test are used to calibrate the Bhadeshia and Hensel-Spittel models, while a modified Bhadeshia approach incorporates the influence of applied shear stress on activation energy. Rigorous validation of the predicted temperature fields against experimental measurements, coupled with EBSD analyses, confirms the simulation's reliability and highlights the importance of precise temperature-dependent properties for modeling phase transformations. Finally, these validated material models and parameters have been applied to the recently introduced BQP (Bainitizing, Quenching, and Partitioning) process. This process enables the formation of multiphase microstructures—martensite, bainitic ferrite, and retained austenite—offering a wide range of strengths (1150–2000 MPa) with improved ductility in a single steel alloy. Omega profiles produced on a BQP pilot plant demonstrate how variations in bainitizing holding times and forming conditions (e.g., temperature, friction) influence phase fractions and dimensional accuracy. Optical measurements verify the formability of the components, and XRD analyses show increased retained austenite at extended bainitizing durations. These findings showcase how robust temperature-dependent material data, coupled with advanced FE-based phase-transformation models, can drive the development of nextgeneration press-hardening and BQP processes for automotive lightweight applications.
Publications
-
“Design and processing of next generation press-hardening steels for car body applications,” presented at the 6th Int. Conf. Steels in Cars and Trucks, Milan, Italy, Jun. 21, 2022
A. Hatscher, C. Ostwald, U. Diekmann, P. Becker, M. Löcker, A. Ademaj, O. Schauerte & R. Thomas
-
An accurate method for determining Young's modulus for ferritic and austenitic steel at high temperatures using acoustic emission tests and inverse solution. Journal of Materials Research and Technology, 26, 4526-4533.
Faraji, Towhid; Irani, Missam; Korpala, Grzegorz & Prahl, Ulrich
-
„Herausforderungen und Potentiale einer neuartigen bainitischen Warmblechumformung“, In M. Merklein (editor), Warmumformung von höchstfesten Vergütungsstählen: Tagungsband zum 18. Erlanger Workshop Warmblechumformung, p. 27-46, 14th November 2023
A. Hatscher, C. Ostwald, R. Thomas, J. Hermann, M. Löcker, U. Diekmann, J. Dlouhy, A. Ademaj, E. Ince, N. Günther, J. Krost, M. Otto & P. Suikkanen
-
bainite transformation in macro scale, Conference Forming 2024, Szklarska Poręba-Poland
T. Faraji, G. Korpala & U. Prahl
-
Modeling the influence of bainite transformation on the flow behavior of steel using a macroscale finite element analysis. International Journal of Plasticity, 184, 104189.
Faraji, Towhid; Irani, Missam; Korpala, Grzegorz; Ostwald, Christoph; Hatscher, Ansgar & Prahl, Ulrich
