Development of 3rd generation steel combining high toughness and strength for automotive applications

Details

Supervisors

Jacques, Pascal

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux, à finalité spécialisée

Abstract

Weight reduction was always an objective to the automotive industry to reduce production costs and fuel consumption. Thus motivating the industry to develop new 3rd generation advanced high strength steels (AHSS) combining toughness, strength, and ductility. The obtained materials showed an outstanding potential to combine all the desired proprieties. It was also observed an excellent formability and interesting proprieties in comparison to the currently developing 3rd generation steels. The study presented here investigated the resulting microstructure on a medium manganese steel with high carbon content and silicon that was submitted to a full austenization at 1000 ͦ C and quenching, followed by Intercritical annealing at either 750 ͦ C or 700 ͦ C for 5 minutes and finally a bainitic maintain at 360 ͦ C for either 15 or 30 minutes. SEM observations were performed to observe the microstructure, succeeded by tensile tests to measure the mechanical proprieties, finally fractography and damage observations were made to evaluate the fracture mechanism and calculate the fracture strain. It was observed two main microstructures related to the annealing temperature, one containing ferrite, bainite and retained austenite (presenting TRIP effects) for 750 ͦ C and the other containing ferrite and cementite for 700 ͦ C. The steels presented remarkable mechanical proprieties such as an ultimate tensile stress up to 1327,23 MPa and uniform elongation up to 23,11%.