Sebastian Waengler

Bio: Sebastian Waengler is an academic researcher from ArcelorMittal. The author has contributed to research in topics: Dual-phase steel & Deep drawing. The author has an hindex of 1, co-authored 2 publications receiving 552 citations.

Simulation of Evolution of Dual-Phase Microstructure

Abstract: Dual-phase steels, developed in the 1970’s, found until now wide applications related to their optimum combination of strength and ductility, in particular as flat semi-products used for further shaping by deep drawing and cold forming operations. Actually the need appears to manufacture long semi-products of dual-phase steels for further processing by cold forging, in order to obtain high-strength final products, like e.g. fasteners, without additional heat-treatment. An additional aim has been to explore the possibility of achieving from the same chemical compositions dedicated properties for particular applications. In this work a thermo-mechanical route was developed of modifying an originally bainitic-martensitic low-alloy steel to achieve a dual-phase microstructure. For this purpose physical simulation was used on Gleeble 3800 thermal-mechanical simulator, programmed to affect austenite in its dynamic recrystallisation range followed by separation of microstructures in the two-phase austenite-ferrite range. Observation of relaxation was used to monitor advancement of transformation / recrystallisation in subsequent stages of the processing. In the simulated hot-warm rolling process it appeared possible to convert the original bainitic microstructure, having prior austenite grain size ~15μm and the martensite-bainite laths of usual length throughout these grains, to the dual-phase microstructure containing well-recrystallised ferrite of an average grain size 1*1.5μm and fine second-phase islands of less than 1.0μm diameter. SEM and TEM analysis have been applied to describe details of the resulting microstructures.

Critical review of automotive steels spot welding: process, structure and properties

Abstract: Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.

Transformation-induced plasticity (TRIP) in advanced steels: A review

Abstract: The transformation-induced plasticity (TRIP) in advanced high-strength steels (AHSS) is reviewed, where the main concepts and the recent progress in the processing and properties of AHSS are introduced. The metastable austenitic stainless and multiphase TRIP-assisted steels, as well as the more recent third generation AHSS grades, namely the medium-Mn and quenching and partitioning (Q&P) steels, are critically discussed. These steels utilize the TRIP effect and the enhanced work-hardening rate through the transformation of (retained) austenite in their microstructures to martensite during plastic deformation for the improvement of strength-ductility balance, which make them especially suitable for the automotive industry to be used in the lightweight car body for addressing the safety, fuel consumption, and air pollution issues. The kinetics of strain-induced martensitic transformation (SIMT) as well as the effects of chemical composition, grain size, deformation temperature, strain rate, and deformation mode on the austenite stability are reviewed. The effects of holding temperature and time during the isothermal bainitic transformation (IBT) in TRIP-aided steels, during the austenite-reverted-transformation (ART) annealing in medium-Mn steels, and during the quenching and partitioning steps in the Q&P steels are critically discussed towards enhancement of the amount of retained austenite and optimization of strength-ductility trade off. The alternative thermomechanical processing routes as well as the modified grades such as δ-TRIP and quenching-partitioning-tempering steels are also introduced.