Project Leader: Otmar Kolednik

Steels with the transformation-induced plasticity (TRIP) effect exhibit phase transformations of austenite into martensite triggered by plastic deformation. This transformation enhances strain hardening, which leads to a combination of excellent strength and ductility. In spite of the fine microstructure of the material investigated, the deformation induced phase transformation of single austenitic grains can be studied using high-resolution scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The accompanying transformation strains in the surrounding matrix can be quantified by local deformation measurements.

Undeformed microstructure. The austenite grains (γ) exhibit phase transformation. From R. Kasberger, O. Kolednik, Verformungsinduzierte Phasenumwandlung einzelner Austenitkörner. In: XXXII Verformungskundliches Kolloquium Planneralm, B. Buchmayr, Ed., Lehrstuhl für Umformtechnik, Leoben, 2013.
Microstructure after 2.5% global strain. The austenite grains (γ) exhibit phase transformation. From R. Kasberger, O. Kolednik, Verformungsinduzierte Phasenumwandlung einzelner Austenitkörner. In: XXXII Verformungskundliches Kolloquium Planneralm, B. Buchmayr, Ed., Lehrstuhl für Umformtechnik, Leoben, 2013.

Local deformation measurements are based on a system for digital image analysis which finds identical points on SEM-micrographs captured at different deformation stages. The method provides, with high accuracy and resolution, the local in-plane strains that occur in the loading step considered. A similar digital image analysis system has been applied for quantitative fracture surface analysis.

Deformation- and fracture behavior of advanced materials

SEM micrograph of a region around a single austenite grain at 2.5% global strain. Parts of the y-grain have experienced phase transformation to austenite.
Map of local strain in the loading step between 0 and 2.5% global strain. Positive values (blue) indicate y - α phase transformation. From R. Kasberger, diploma thesis, Leoben 2012.
Map of local strain in the loading step between 2.5% and 4.5% global strain. Positive values (blue) indicate y - α phase transformation. From R. Kasberger, diploma thesis, Leoben 2012.