Ultrafine grained steels managing both high strength and ductility

Abstract

Mechanical properties of the ultrafine grained (UFG) steels having mean grain sizes much smaller than 1 μm were systematically shown from the original experimental data. The UFG steels performed very high strength that reached to 2–4 times of the starting materials having conventionally coarse-grained structures. On the other hand, the uniform tensile elongation was commonly limited within a few percents when the materials have single-phased UFG structures. The limited uniform elongation was explained in terms of early plastic instability. On the basis of the understanding, the ways to manage both strength and ductility in the UFG steels were indicated. The effectiveness of making the UFG structures multi-phased was confirmed.