Ultrafine grained steels: industrial prospects

Ultrafine grained (similar to1 mum) steels are currently the subject of a great deal of research worldwide. They offer the prospect of very high strength with very high toughness from standard steel compositions, and recently it has been shown that such fine grains can be obtained from the hot rolling mill. rather than merely from specialist, small scale techniques. If such material could indeed be produced economically in bulk, it offers a step advance in ongoing issues for the industry, such as light weighting of structures and components, rationalising the large number of current steel grades by extending the property combinations achievable from select compositions, aiding weldability and recyclability, and reducing the alloy costs by meeting high specifications from more dilute grades and promoting a high tech image from offering an apparently exotic product. However, it has quickly become apparent that this material has its 'Achilles' heel' in that it tends to exhibit unstable plasticity upon yielding, severely restricting its potential applications. Possible ways around this problem are being explored, but at present the industrial prospects remain unclear. This paper explores these issues, and suggests that ultrafine grained steels are not going to sweep through all the major steel markets, but will find their place for certain applications. MST/4771.