The project goal is to optimize the microstructures with a bainitic matrix in order to improve the cold formability and edge-cracking behavior of advanced high-strength steels with high yield strength. This will enable more efficient steel applications, like weight reduction without loss of formability, enhanced energy absorption due to high yield strength, higher elongation and favorable crash folding behavior due to improved bending properties.

 

Elongation vs strength banana v1

 

The project findings are expected to contribute to finding the right balance between high strength and sufficient formability of bainitic steels as well as to find productional and microstructural reasons for those outstanding properties. Including austenite as a secondary phase to a bainitic matrix may increase the formability (as a result of the TRIP effect), whereas including martensite as a secondary phase will increase the strength. Thus, it may be anticipated that by combining an appropriate volume fraction of the two phases, both strength and formability can be improved. On the other hand high shear stresses that will be involved by the existence of multiple phases will lead to worse damage behavior. The right balance of phases and production parameters is of fundamental interest to European steel industry in order to develop new extraordinary bainitic steels for automotive industry.

 

Expected benefits

  • Improved understanding of the process-microstructure and the microstructure-properties relations, in particular, what is the preferred fraction, carbon content, morphology and distribution of second-phase constituents (martensite and/or retained austenite) in bainitic matrix.
  • Integrated physical models allowing to simulate the thermo-mechanical process and the material performance in press forming operations.
  • Understanding of the mechanical behavior of bainite can be extended to many industrial Advanced High Strength steels grades containing bainite (Multiphase, Ferrite-Bainite or 1180 HF).
  • The knowledge acquired can be applied to the design of new products (3rd Generation Advanced High Strength steels like carbide-free bainite).
  • Understanding the mechanisms of the damage process in these microstructures.
  • Develop guidelines for producing bainitic Advanced High Strength steels with high elongation and high forming capacity (bending, hole expansion).