Objectives:

 

  • Investigate the very fine microstructure evolution during processing and in particular, the formation mechanisms of the morphology (size, shape and distribution) of second-phase constituents (martensite, retained austenite or martensite/austenite islands and carbides) in the bainitic matrix by means of modern, advanced microstructural characterization techniques. Develop or improve physically based or statistic models to describe the relationship between process condition and microstructural parameters. Appropriate thermodynamic and kinetic models will be applied. The thermo-dynamic based models of phase transformation will be coupled to micro-mechanical and crystallography based models.
  • Investigate the relationship between microstructure and mechanical properties by gathering and analyzing a complete set of data that associates the detailed microstructural characterization with the corresponding properties measurements as observed in a variety of mechanical tests that are of relevance to automotive applications, including tensile tests, hole expansion tests or bending tests. Crystal plasticity models will be applied to understand the influence of microstructural and textural variations of the bainitic matrix on the mechanical properties, whereas the effect of the carbon content in martensite/austenite and the morphology of secondary phases on mechanical properties will be taken into account by appropriate thermodynamic and kinetic models.
  • Investigate the impact of microstructural features in bainitic Advanced High Strength steels, and most noticeably the presence of secondary phases on damage properties. It is attempted to identify the critical microstructural parameters that play a role in damage initiation processes in those fine-grained steels. The effect of carbon content in austenite/martensite and the morphology of secondary phases (austenite, martensite and cementite) on damage properties during hole expansion and bending will be considered. It will be attempted to understand the damage process and mechanism using post-mortem observations and interrupted tests. This understanding should be materialized and contribute to improve damage models that can identify the critical microstructural features for damage initiation. With these models it will be possible to create guidelines to develop or optimize new bainitic Advanced High Strength steels.
  • Design and validate a workbench for industrial product development of high-strength – high-formability bainitic steels taking into consideration the limitations of industrial annealing plants.
  • Provide data suitable for the development of improved predictive models of mechanical properties and damage properties for bainitic matrix steels.
  • Develop guidelines for producing bainitic, Advanced High Strength steels with high elongation and high forming capacity (bending, hole expansion).