Analysis of mechanical property distribution in multiphase ultra-fine-grained steels by nanoindentation

Abstract The strength characteristics of microphases in ultra-fine-grained steels were analyzed using nanoindentation and AFM. It was found that there were fine ferrite grains ( 1–2 μ m) formed by a strain-induced dynamic transformation in ultra-fine-grained steels. They had equiaxed and polygonal grain shape, and higher hardness and elastic modulus than coarse ferrite transformed statically. Strengthening factors of strain-induced dynamic transformation ferrite were analyzed in terms of cementite particles and dislocation density.