Hybrid experimental–numerical study on nanoindentation response of dual-phase steels: From macroscale to atomic scale

In this study, the elastic and plastic behaviors of the ferrite and martensite phases of dual-phase (DP) steels were investigated using nanoindentation data and the related constitutive equations. First, hardness (H) and elastic modulus (E) were determined to derive the monotonic yield stress (σ y ) and Hollomon's parameter and then for work hardening exponent (K) and work hardening rate (n).Next, the results obtained by the nanomechanical approach implemented herein were validated using the semiquantitative data computed by numerical finite element analysis (FEA) and molecular dynamics (MD). The difference between plasticity of ferrite and martensite can be attributed ti the geometrically necessary dislocations (GNDs), which stimulate work hardening. The elastic and plastic data of both the phases were incorporated into FEA to simulate the load–displacement curves and the projected regions. In addition, the load–displacement curves of the ferrite and martensite phases and the hardness and Young's modulus determined by MD were in good agreement with the nanoindentation test and FEA results. The strain-rate sensitivity of ferrite, which exhibited a lower hardness and greater indentation depth, was 0.0985, whereas that of martensite was approximately 0.087. Furthermore, the TEM images proved the existence of GNDs at the ferrite–martensite interface and their role in cell formation in the ferrite zone and interphase region.