Sublattice alloy design of high-strength steels: Application of clustering and nanoscale precipitation of interstitial and substitutional solutes
Tadashi Furuhara, Yongjie Zhang, Mitsutaka Sato, Gorō Miyamoto, Masanori Enoki, Hiroshi Ohtani, Tokuteru Uesugi, Hiroshi Numakura
Abstract
Recent advances in high-strength steels for automobile applications or surface-hardened steels have attracted interest on controlling the nanoscale dispersion of alloy carbides/nitrides in ferrite. Particularly, B1-type carbide/nitride precipitation and metastable alloy clustering can be understood as the coupled ordering and compositional phase separation of interstitial alloying elements i and substitutional alloying elements s, i.e., "spinodal ordering". In this paper, the behavior of i–s clustering and alloy carbide/nitride precipitation is revealed by nanoscale characterization, theoretical calculations, and evaluations of mechanical properties. Physical measurements and density function theory-based analyses revealed that strong i–s attractive interaction is responsible for metastable i–s clustering, which clearly indicated "hidden" nanoscale inhomogeneity in solid solutions. Further, we discuss a concept termed interstitial sublattice engineering in bulk and at interphase boundary for strengthening of alloyed steels.