Properties of fine-grained steels generated by displacive transformation

It has been possible in recent times to make large quantities of steels in which the controlling scale is 20 nm or less, i.e., comparable to that of carbon nanotubes. The mechanical properties of such steels are abnormal. For example, in some cases the ductility vanishes as the strength increases, whereas in others the ductility almost entirely consists of uniform plastic strain. Some of the steels also can tolerate large fractions of brittle phases before fracture. These and other aspects of strong, nanostructured steels are critically assessed to arrive at a hypothesis which rationalises the odd observations.