         P.R. Calvillo a  P. Bernárdez and Y. Houbaert b Department of Metallurgy and Materials Science, Ghent University, Technologiepark 903, B*9052 Gent, Belgium a Pablo.RodriguezCalvillo@UGent.be, b Yvan.Houbaert@UGent.be  electrical steels, hot dipping, diffusion annealing, aluminium*coating, intermetallics  The addition of aluminium (and of silicon) to steel increases its electrical resistivity and reduces therefore the power losses in electrical devices. There is also a favourable effect on magnetostriction. Nevertheless, these additions make the steel extremely brittle and very difficult to process through a conventional thermomechanical route. The authors developed an innovative processing route, avoiding the rolling of a brittle steel sheet. The used process consists of the hot dipping of a steel substrate in a pure aluminium bath, followed by a diffusion annealing treatment. In order to study the reaction of the aluminium with the substrates and the diffusion process during further annealing, two substrates (ultra low carbon steel (ULC) and a Fe + 3.4 m.’% Si steel) were used for immersion in a pure aluminium bath. Dipping times and temperatures were varied in the range of 700 to 750 °C and 5 to 1000 sec., respectively. The different surface layers formed during dipping and after annealing were characterised with an Elcometer, by Scanning Electron Microscopy (SEM) and by Energy Dispersive Spectroscopy (EDS). The results show that the chemical composition of the layers obtained is strongly dependant on the initial substrate composition. Diffusion gradients of Al and Si in the steel after hot dipping and diffusion annealing are shown and discussed. Samples with a concentration gradient of Si and Al over the thickness have been produced. There is only a light reduction of the power losses for the substrate with 3.4 m.’% Si. The ultra low carbon substrate presents worse power losses after the processing. Further improvement of the processing is still required.  Electric steel is a soft magnetic material used as core material for equipment for electric power generation, distribution and consumption. Electric steel does not convey electric energy, but the magnetic flow that circulates in the core of electric equipment. Although modern electric equipment is highly efficient, the losses that occur in the core material represent not only a waste of energy, but also a poor performance of the electric equipment. An important part of the total core losses are the so’called “Eddy current losses” caused by the currents induced in the core material, which is electrically conductive. What is needed, then, is a method of increasing the resistance of the core to current flow without inhibiting the flow of magnetic flux. In mains transformers this is achieved by alloying the iron with about 3 m.’% of silicon, lifting its resistivity to 4.5×10 ’7 [9 m]. Electrical steel with a Si’content up to 3% can be produced by conventional thermo’mechanical processing, but higher Si’contents increase considerably the brittleness and make rolling very difficult [1]. Also aluminium is an alloying element strongly increasing the electric resistivity of the steel and it could be used to produce electric steel. An innovative production scheme for high silicon and/or aluminium electrical steel was developed at Ghent University: after hot dipping a conventional or specific (e.g. with increased Si’content) steel substrate into a Si’ and Al’rich bath, a diffusion annealing treatment is applied to diffuse Si and/or Al into the substrate and to obtain an increased Si and/or Al’content, which may be homogeneous over the sheet thickness or may present a concentration gradient [2]. Defect and Diffusion Forum Vols. 273-276 (2008) pp 63-68 online at http://www.scientific.net © (2008) Trans Tech Publications, Switzerland Online available since 2008/Feb/11 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 147.83.80.143-04/03/08,10:13:05)