Nanostructured bainite

An alloy system based on iron is described in which it has been possible to create a high density of interfaces by heat treatment alone. The resulting structure consists of a mixture of slender platelets of bainitic ferrite, just 20-40 nm in thickness, embedded in a matrix of carbon-enriched austenite. The rate at which this structure evolves is slow by conventional standards, but this permits components to be made which are large in all three dimensions, with uniform properties throughout. The fundamental mechanisms behind this novel nanostructured steel are reviewed, along with the factors determining its strength, ductility and fracture toughness. It is argued that, although reasonable toughness can be achieved in the context of strength levels exceeding 2000 MPa, the impact toughness remains poor and that it may not be possible to improve this particular parameter.