Effect of Retained Austenite Characteristics on Deep Drawability of TRIP-aided Steel Sheet

Microstructure of TRIP-aided steel sheets has been recently attracted much interests in improving their formability through different forming processes. Their performance can be successfully controlled by designing an optimum balance in the volume fractions of ferrite, bainite and retained austenite. The retained austenite is considered as the main key to achieving the desired final properties. Against this background, the effects of retained austenite characteristics, such as volume fraction, carbon concentration, size and shape, on the behavior of TRIP steels have been studied. In present study, deep drawability of cold rolled TRIP-aided steel sheets has been evaluated using swift cup test. The steel sheets had two different matrices; Polygonal Ferrite (PF) and Bainitic-Ferrite (BF), and different retained austenite characteristics (volume fraction, morphology and carbon content). Deep drawability of sheets was evaluated and compared in term of limiting drawing ratio (LRD). The results revealed that steels with PF matrix provide better deep drawability due to their higher volume fraction of retained austenite, better stability of retained austenite against deformation and higher difference between hardness of matrix and strain-induced martensite.