Nucleation, growth and coalescence of voids in dual phase steels: from model microstructures to microstructure based modeling

摘要

Dual phase steels, a composite made of ferrite matrix and hard martensite inclusions, are currently introduced as automotive structural parts owing to their excellent strength/ductility compromise while involving only small amounts of alloying elements. Nevertheless, these alloys suffer sometimes from limited damage and fracture resistance, for instance during forming operations, due to early void nucleation leading to small or moderate fracture strains depending mostly on the characteristics of the martensite phase. Several DP steels, presenting various amounts of martensite and C content, with or without additional tempering, are investigated by performing mechanical tests under different loading conditions, in-situ micromechanical tests, nanoindentation, and in depth damage mechanism characterization. A micromechanical model combining an advanced Gurson model and homogenization theory is validated by comparison to the experimental results and used to perform a comprehensive parameter study with the objective of guiding microstructure optimization.