Clustering, nano-scale precipitation and strengthening of steels

Continuous innovations in design of advanced structural steels are essential for future progress in manufacturing, automotive and construction industries. Events taking place at nano and atomic scales play crucial role in controlling the strength of steels. Recently, strengths of 1–1.5 GPa were realised in nano-scale precipitation strengthened steels. With availability of modern characterisation techniques, such as high-resolution scanning transmission electron microscopy and atom probe tomography, it is now possible to gain insight into the mechanisms of solute atoms clustering and formation of nano-precipitates, as well as their interactions with dislocations and resulting contribution to strength. In this review, the focus is on cluster formation and nano-precipitation in low temperature body centred cubic phases (ferrite, bainitic ferrite and martensite) in a range of steels from high strength low alloyed to maraging ones. Experimental and modelling data on nucleation and growth of these features is presented. The possible strengthening mechanisms are reviewed. Finally, future research areas and challenges for these classes of steels are critically discussed.