J. Phys. IV France
Volume 104, March 2003
Page(s) 499 - 502

J. Phys. IV France
104 (2003) 499
DOI: 10.1051/jp4:20030131

In situ observations on the mechanical stability of austenite in TRIP-steel

S.O. Kruijver1, L. Zhao1, J. Sietsma2, S.E. Offerman3, N.H. van Dijk3, E.M. Lauridsen4, L. Margulies4, 5, S. Grigull5, H.F. Poulsen4 and S. van der Zwaag6

1  Netherlands Institute for Metals Research, Rotterdamseweg 137, 2628 AL Delft, The Netherlands
2  Materials Science and Technology, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, The Netherlands
3  Interfaculty Reactor Institute and Materials Science and Technology, Delft University or Tecnnology, Mekelweg 15, 2629 JB Delft, The Netherlands
4  Materials Research Department, Riso National Laboratory, 4000 Roskilde, Denmark
5  European Synchrotron Radiation Facility, BP. 220, 38043 Grenoble cedex, France
6  Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands

In-situ tensile deformation tests have been performed on a high Al TRIP steel (composition 0.26 wt. % Si, 1.5 wt. % Mn, and 1.8 wt. % Al) displaying the transformation-induced plasticity (TRIP) effect, while monitoring the phase transformation by means of X-ray microdiffraction in transmission geometry. Due to the small beam size ( $\rm 25 ~\mu m \times 25~\mu m$) every retained austenite grain appears as a discrete spot on the diffraction patterns. The diffraction patterns are treated like a powder pattern for different $\eta$-angles, with $\eta$ representing the angle between the tensile direction and the normal direction of the diffracting {200} planes. The disappearance of austenite {200} reflections is analyzed during as a function of the imposed stress and orientation. Grains with $\eta = 0$ or 90 $^{\circ}$ tend to transform to martensite more easily. A unique feature of this microdiffraction experiment is the possibility of detecting the average carbon concentration of the retained austenite as a function of stress. Direct proof has been obtained that austenite with a lower carbon content $\rm x_c$ transforms at lower stress levels. The average $\rm x_c$ increases from 1.0 to 1.05 wt. %. This increase indicates a relatively narrow distribution of the carbon content.

© EDP Sciences 2003