On the three-dimensional atomic scale characterisation towards understanding the sequence of nano-scale B2 phase evolution in Ni-alloyed Fe-Mn-Al-C low-density steel

Abstract

The enhanced mechanical properties of Al-alloyed Fe-Mn-C based multi-component steels are primarily derived from the different phases present in them in addition to their size, distribution, morphology, volume fraction and stability. Here we report on the thermal stability and the associated phase evolution sequence especially that of nanoscale precipitates in a hot-rolled 5Ni-alloyed Fe-16Mn-9Al-0.9C (wt.%) low-density steel. Systematic heat treatment studies were performed in the temperature range of 600-1200 °C. Bulk phase analysis using X-ray diffraction indicates the presence of three phases, namely FCC structured γ, L12’ structured κ and BCC phases in as-rolled condition which is in good agreement with the thermodynamic phase stability estimates. Combined microscopic analysis involving three-dimensional atom probe tomography reveals the presence of nano-scale κ and B2 precipitates, highly localized within the majority γ and banded BCC phase regions respectively. This presentation, therefore will focus on the temporal evolution of B2 nanoprecipitates and their localisation within the banded BCC phase regions along with their stability as a function of varied thermal treatments.