An observation of micro-crack in transformation-induced plasticity-assisted multiphase steel

Abstract

In a transformation-induced plasticity (TRIP)-assisted multiphase steel, the phases around a micro-crack at the initial stage of cracking during wire drawing were observed by a focused ion beam (FIB), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). A novel FIB method, which is termed as "In-plane lift-out" technique, was applied to obtain an overall plan-view of the TEM specimen containing the micro-crack. The equilibrium concentration ratio of Mn in austenite and ferrite was calculated for the alloy and compared with the EDS line profile of Mn concentration across the micro-crack in the TEM specimen. The interface between the ferrite and martensite was identified as the crack initiation site during drawing of this multi-phase steel. © 2008 ISIJ.