Nanostructured bainitic steel obtained by powder metallurgy approach: structure, transformation kinetics and mechanical properties

Abstract

A PM approach is investigated in the context of extremely fine low temperature bainitic steels with a reasonable combination of ultimate tensile strength and uniform elongation. The strategy consists of three steps. First, ball milling is used for mechanical alloying and to create a large density of interfaces prior to sintering. In the second step, spark plasma sintering is used as a rapid consolidation process to retain a very fine and homogeneous structure after sintering. The isothermal heat treatment which leads to bainite can then be done at a low austenitisation temperature (860°C) for a few minutes, leading to a small initial austenite grain size. A fine grain size promotes the rapid transformation of the austenite into bainite. The characteristics of a nanostructured Fe–Ni–C bainitic steel obtained after mechanical alloying and nanostructuring of the powder, spark plasma sintering and final heat treatment are reported.

This work was supported by the European Union, Marie Curie Actions, the Marie Curie 7th Framework Programme and the Trentino Programme. This paper is based on a presentation at Euro PM 2011 organised by EPMA in Barcelona, Spain on 9–12 October 2012.