Formability Evaluation of TRIP-aided Steel Sheets with Different Microstructures: Polygonal Ferrite and Bainitic Ferrite Matrix

摘要

Recently, application of TRIP-aided steel sheets has been developed due to their good balance of strength and formability. In this work, a comparative study was performed on the formability of two different microstructures of TRIP-aided steel with different retained austenite characteristics. Microstructures along with their specific retained austenite characteristics such as volume fraction, stability and morphology were achieved by annealing of cold rolled sheet at fully austenite and intercritical region during subsequent isothermal treatment in the range of 350–410°C. SEM and XRD measurements were used to evaluate retained austenite characteristics. Formability and mechanical properties of sheets were determined by Erichsen test and tensile test, respectively. Results indicate that steel sheets with polygonal ferrite (PF) matrix present better formability. However, at identical volume fraction of retained austenite, sheets with bainitic ferrite (BF) matrix show better stretch formability due to high retained austenite stability.