On the effects of Mo versus Cr as microalloying elements in HSLA steels deformed in the ferrite

C. Ledermueller, H.I. Pratiwi, R. Webster, M. Eizadjou, S.P. Ringer, S. Primig
Materials & Design 185 (2020) 108278

This paper is part of Carina's PhD project and Sophie's Australian Research Council DECRA Fellowship. 

This research was conducted with the aim of implementing alloy design to invoke grain refinement in Nb HSLA steels coupled with strengthening arising from microalloying with Mo and Cr. Therefore, three model Fe-1.5Mn-0.4Nb-0.1C+0.5Mo/Cr steels were made to study the detailed microstructural evolution and hardness when subjected to thermo-mechanical processing in the ferrite.

We find that Mo leads to a significant increase in hardness of ~20% compared to the base alloy, whereas Cr provides only a minor hardening increment of ~4%. Our results show that Mo is more effective than Cr in delaying dislocation recovery during ageing at 600°C. We also report that Mo partitions into nanoscale Nb-C solute clusters, as well as precipitates of NbC and Fe₃C (cementite) during ageing, retarding the coarsening of these phases. Cr is found to partition only into the cementite, and does not contribute to the nature of the dispersion of clusters and NbC precipitates.