Chemical gradients across phase boundaries between martensite and austenite in steel studied by atom probe tomography and simulation

Abstract

Partitioning at phase boundaries of complex steels is important for their properties We present atom probe tomography results across martensite/austenite interfaces in a precipitation-hardened maraging-TRIP steel (12 2 Mn 1 9 Ni, 0 6 Mo 1 2 Ti, 0 3 Al, at %) The system reveals compositional changes at the phase boundaries Mn and Ni are enriched while Ti, Al, Mo and Fe are depleted More specific, we observe up to 27 at % Mn in a 20 nm layer at the phase boundary This is explained by the large difference in diffusivity between martensite and austenite The high diffusivity in martensite leads to a Mn flux towards the retained austenite The low diffusivity in the austenite does not allow accommodation of this flux Consequently the austenite grows with a Mn composition given by local equilibrium The interpretation is based on DICTRA and mixed-mode diffusion calculations (using a finite interface mobility) (C) 2010 Acta Materialia Inc Published by Elsevier Ltd All rights reserve