Formation of nanosized martensite particles in stainless steels

Martensitic transformations occur in steels and other metals when the mater ial is quenched or cooled. During the transformation, a metastable phase tr ansforms in an autocatalytic way into a thermodynamically stable phase. Thu s, it has been considered to be impossible to control the size of martensit e in the order of nanometers. Here, we report the formation and dispersion of nanosized martensite in stainless steels by controlling the dislocation density and temperature. Electron microscopy revealed that martensite parti cles of approximately 5 nm in diameter were dispersed. Since both work hard ening and precipitation hardening are effective in this material, this woul d be an additional, newly discovered strengthening mechanism for steels.