Unusual precipitation and its effect on mechanical properties for Aermet100 steel during electropulsing ageing

The electropulsing assisted ageing is a newly developed method which could achieve the ultrafast hardening of Aermet100 steel by significantly accelerating the precipitation of secondary phases. However, the precipitation mechanism of Aermet100 steel during electropulsing ageing is hitherto unexplained due to the lack of understanding of the athermal effects of electropulse. In this paper, the precipitation mechanism of AerMet100 steel during electropulsing ageing was studied. The athermal effects of electropulses on precipitation thermodynamics and precipitation kinetics were discussed based on an investigation into the electropulsing ageing threshold. Results suggested that the ultimate tensile strength of the specimens after electropulsing ageing was nonlinear dependent on the increment in the electric current, that it rose first followed by a decline. The current density threshold that can influence dislocation density is approximately 1.5 A/mm². As the current density increased to a 3.5 A/mm², the dominative precipitations transferred from fine acicular (Cr, Mo)₂C phases to spherical (Cr, Mo)C phases. Furthermore, the energy at the nucleation site is significantly increased at current densities above 5 A/mm², resulting in a shortened time of peak ageing. This investigation sheds new insight into the regulation of the electropulse on precipitation behavior of Aermet100 steel via electropulsing assisted ageing. Moreover, the effectiveness of electropulses with low current densities in influencing the precipitation mechanisms was validated for the first time.