Experimental and Numerical Analysis on Dual Phase Steel (DP780) Sheet Forming Limit and Effect of Microstructure Evolution on Formability

The application of dual phase steel in the automotive sector is increasing due to its high strength-to-weight ratio and good shock absorption capacity. The formability of dual phase steel is complex due to its multiphase microstructure which results in inaccurate formability prediction using numerical methods. The present study is aimed at analyzing the forming behavior and microstructure evolution of a dual phase steel, DP780, at different strain paths. The forming behavior of this steel was analyzed in terms of forming limit diagram (FLD) using Nakazima tests and finite element method. Various necking criteria were used to construct the FLD. Samples deformed at different dome height for three principal strain paths and strain levels were subjected to detailed microstructure and texture investigations. The microstructure and texture study was mainly focused on analyzing the development of deformation texture, misorientation development and orientation hardness. These studies showed that the formability of DP780 steel is largely affected by the development of γ fiber texture. Also, the evolution of other microstructure and texture quantifiers such as texture intensity, misorientation and relative orientation hardness at different strain paths was correlated with the formability of the material.