Sir Harry Bhadeshia FREng, FRS, FNAE

### Tata Steel Professor of Metallurgy

Director, SKF Steel Technology Centre

#### BSc City of London Polytechnic

PhD University of Cambridge

+44 (0)1223 334301

hkdb@cam.ac.uk

www.msm.cam.ac.uk/phase-trans/

### Phase Transformations

There are so many phase changes in iron and its alloys that it is possible to generate a seemingly infinite variety of microstructures and properties. This complexity makes the alloys versatile but at the same time difficult to understand and design from first principles. Much of our energy is devoted to the development of solid-state phase transformation theory, and its experimental validation, in the hope of inventing new alloys and processes.

**Theory of transformations**

We deal mostly with phase changes which are thermodynamically of first order, i.e. they involve nucleation and growth with well-defined mechanisms of transformations and particular constraints to the achievement of equilibrium. In fact, most useful microstructures are far from equilibrium so we build kinetic theory to determine non-equilibrium states. There are complications when many different transformations occur together, complications which have stimulated new theory. Finally, the microstructure must be related to properties which are appreciated by technologists.

**Mathematical models**

We express the theory and empirical observations in the form of computer models which can be used to greatly reduce the vast number of parameters that have to be controlled during the creation of new alloys and processes. We also produce courses, books and algorithms in addition to research papers to help spread the word about this thriving science of materials.

- L. C. D. Fielding, E. J. Sung, D. K Han, H. K. D. H. Bhadeshia and D. W. Suh, "Hydrogen diffusion and the percolation of austenite in nanostructured bainitic steel",
*Proceedings of the Royal Society A*(2014) in press. - S. Nambu, N. Shibuta, M. Ojima, J. Inoue, T. Koseki and H. K. D. H. Bhadeshia, "
*In situ*observations and crystallographic analysis of martensitic transformation in steel",*Acta Materialia***61**(2013) 4831-4839. - C. N. Hulme-Smith, I. Lonardelli, A. C. Dippel and H. K. D. H. Bhadeshia, "`Experimental evidence for non-cubic bainitic ferrite",
*Scripta Materialia***69**(2013) 409-412. - E. J. Song, H. K. D. H. Bhadeshia and D. W. Suh, "Effect of hydrogen on the surface energy of ferrite and austenite",
*Corrosion Science***77**(2013) 379-384.

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