Current processes for strengthening steels make them less flexible, which in turn makes them less applicable to wider industry.
Dr Rahnama, said: “Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. Lightweight steels are one of the candidates to address these concerns.”
Two lightweight steels were tested for their potential to achieve maximum strength and ductility: Fe-15Mn-10Al-0.8C-5Ni and Fe-15Mn-10Al-0.8C.
During production, two brittle phases can occur in these steels: kappa-carbide (k-carbide) and B2 intermetallic. These make the steels hard, but limit their ductility, making them difficult to process using traditional means such as hot or cold rolling.
Through simulation and then experimentation, the WMG researcher group found that at certain high annealing temperatures, the brittle phases become much more controllable, allowing the steels to retain their ductility.
Between 900°C to 1200°C, the k-carbide phase can be removed from production, and the B2 intermetallic brittle phase can become manageable, forming in a disk-like, nano-sized morphology, as opposed to the coarser product that forms at lower temperatures.
Dr Rahnama, said: “Most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off. This paper studies the kinetics and thermodynamics of microstructural evolution of lightweight steels through simulations and experiments and proposes a mechanism to achieve higher strength and larger ductility; a method that can be readily adopted by industry.”
The research, ‘Effect of Ni alloying on the microstructural evolution and mechanical properties of two duplex light-weight steels during different annealing temperatures: experiment and phase-field simulation’, is published in Acta Materialia.
It is co-authored by Dr Hiren Kotadia and Professor Seetharaman Sridhar.