               Enikő-Réka, Fábián Bay Zoltán Foundation for Applied Research, Institute for Materials Science and Technology; H-1116, Fehérvári u. 130, Budapest, Hungary reka@bzaka.hu  enamel-grade steel, deformation, hydrogen, microstructure, dislocation, orientation.  The cold rolling effect on the hydrogen permeability (T H value) and on the microstructure have been studied on samples prepared from Al-killed low carbon steel sheets after several cold rolling levels. The T H values of the hot rolled strips were very short, but due to the cold rolling increase exponentially. The fragmentation of large cementite phase has a significant influence on the evolution of texture during the cold rolling process. The cold deformation effects on the T H value were studied on four annealed enamelling grade steel sheets also. Depending on the carbides sizes and carbides position in ferrite grains after annealing the T H values increase or decrease after low deformation degrees, due to the steel texture modification and dislocation character. Dislocations act as major tripping site for hydrogen, if deformation degree is higher than 30%.  The effect of H has been the subject of extensive studies to understand the mechanisms of degradation in mechanical properties of metals and alloys because industries often encounter failure of products due to hydrogen embrittlement. A well-known effect of hydrogen on mechanical properties is the reduction in ductility. The fish-scale formation on the surface of enamel coated steel products is caused by appearance and recombination of hydrogen at the sheet-enamel interface. The tendency for fish-scale formation in case of the cold rolled Al-killed low carbon enamel grade steel sheets is characterized by the hydrogen permeability [1, 2]. The hydrogen is not homogeneously distributed in steel, as it would be in perfect iron crystal. Various trapping sites exist in steel for hydrogen atoms. Trapping enhances the solubility of hydrogen but decreases the diffusivity. Despite extensive investigations for over a century, because of its complexity, the hydrogen caused failures remain an unsolved problem. For a long time there has been controversy over the extent of the effect of cold working, as discussed by Marandet [3]. There was reported that at unalloyed carbon steels plastic deformation usually increased the total amount of hydrogen occluded, but indicate a disagreement in the literature over the associated hydrogen embrittlement phenomenon, many investigator finding a deleterious effect, others a beneficial effect. After Szklarska-Smialowska and Z. Xia [4] the presence of dislocations is responsible for the hydrogen diffusivity in iron at room temperature. H. Huang et al. [5] examined hot rolled type 1020 steel (C=0.18-0.23, Mn=0.3-0.6). At this steel H diffusivity decreased with increasing cold work and levelled out when cold work reached 30% - 40%. Keth [6] observed that the dislocation density increased with cold work and levelled out when cold work reached 30% to 40%. Martinez-Madrid et al. [7] observed that in general the hydrogen content increased with the degree of cold work at cold worked iron, but there was a drop in the hydrogen content of specimens with 5-10% of cold work. They observed very little scatter in the result for hydrogen content for small amount of deformation, and as deformation increases there were greater variation in the hydrogen content. P. Alexandru [8] observed at cold rolled rimmed steel for deep drawing and enamelling type A3 (STAS 9485-80) (C ≤ 0.08, Mn=0.2-0.45, Si=0.03- 0.08) that after ε=20% thickness reduction appeared fish-scales, and maximum number of fish- scale/m 2 appeared at 30% deformation degree. Materials Science Forum Vol. 659 (2010) pp 7-12 Online available since 2010/Sep/13 at www.scientific.net © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.659.7 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: 78.131.14.51-15/09/10,19:50:03)