Kinetics of Deformation Processes in a High-Alloy Cast TWIP Steel Determined by Acoustic Emission and Scanning Electron Microscopy

Abstract

High-alloy cast CrMnNi steels exhibit depending on the chemical composition either transformation induced plasticity (TRIP-effect) or twinning induced plasticity (TWIP effect). Whereas the TRIP effect is caused by a martensitic phase transformation from the f.c.c austenitic phase into the b.c.c α-martensite phase via the formation of deformation bands with high stacking fault density the so-called ε-martensite, the TWIP effect is the result of mechanical twinning during plastic deformation. The occurrence of both effects as well as the underlying microstructural processes are strongly affected by the austenite stability, the stacking fault energy and/or the test temperature. However, the onset stress and the kinetics of these deformation processes are still unknown. The in-situ measurement of acoustic emission signals during the plastic deformation of materials is a powerful tool for the investigation of such dynamic microstructural processes and their kinetics. In the present study acoustic emission measurements were performed during tensile deformation at room temperature on a high-alloy cast TWIP steel. The AE investigations were completed by SEM investigations on the deformed specimens. The statistical and cluster analysis of acoustic emission signals reveals different patterns of acoustic emission signals, which are correlated with underlying microstructural processes.