Characterization of TRIP-assisted multiphase steel surface topography by atomic force microscopy

Transformation-induced plasticity (TRIP)-assisted multiphase steels have a complicated microstructure consisting of different phases, mainly ferrite, retained austenite, bainite and martensite. Atomic force microscopy has been used for the phase identification and characterization of the phases in this kind of steel. A series of tests has been made on a C-Mn-Si and a C-Mn-Al TRIP-assisted steel after two different heat treatments: intercritical annealing followed by quench, and intercritical annealing followed by aging. After the aging process, the C-Mn-Al alloy was tempered in order to make metallographic observation easier, except the samples for mechanical testing, XRD or Mössbauer spectroscopy. It has been possible to identify the different phases and their topographic characteristics and to study their morphology using atomic force microscopy. The fine and complex microstructures of TRIP-assisted multiphase steels require improvements of the existing observation techniques, like electron backscattered diffraction and atomic force microscopy. Results of these techniques are presented.