Effects of Bainitic Transformation Temperature and Stress State on the Formability of C-Mn-Si TRIP Steel

摘要

The effects of TRansformation InducedPlasticity(TRIP) phenomena on the plastic deformation of 0.2C-1.5Si-1.5Mn multiphase steel have been investigated at variousheat treatment and stress conditions. In order to estimate adeformation behavior under multi-axial stress state, the holeexpansion(HE) tests were carried out. It is shown that theformability evaluated from the uni-axial tensile tests was quitedifferent from the formability measured from multi-axial HE-tests because of different stress state. The formability in themulti-axial stress state decreased due to the extinction of thetransformable retained austenite at relatively earlier deformationstage and the production of irregular #alpha#' martensite. Thevoids of TRIP steel were initiated exactly at the interfacebetween transformed martensite and ferrite matrix regardless ofstress state. In addition, new form of experimental formula isproposed in order to predict the multi-axial formability of theTRIP steel from the results of uniaxial tensile test.