Microstructure characterisation of a low density steel by transmission electron microscopic study

The microstructure including precipitates in a low density steel containing 3.3Mn-6.6Al-0.18C (wt%) was investigated using transmission electron microscopy under two heat treatment conditions of annealing (850 degrees C, 1 min.) and annealing + ageing (400 degrees C, 10 min.). The phases identified by electron diffraction patterns were ferrite (alpha), austenite (gamma), kappa-carbides and M3C type compounds. Ferrite was the matrix of the microstructures. The x-carbides were found to contain on average 9.9 wt% Mn and have the following orientation relationship with ferrite: (2 2 0)alpha parallel to(2 0 0)kappa with [1 1 2]alpha parallel to[0 1 1]kappa and (1 1 0)alpha parallel to (1 1 1)kappa with [1 1 2]alpha parallel to[0 1 1]kappa. Coarsening of kappa-carbides was observed in the annealed + aged condition as compared to the annealed condition. The solubility of Al and Mn in bcc ferrite and fcc austenite were determined. The kappa-carbides consisted of a wide compositional range of Mn and Al. (C) 2014 Elsevier B.V. All rights reserved.