ISO/TR TECHNICAL REPORT 20491 First edition 2019-02 FastenersFundamentalsof hydrogen embrittlement in steel fasteners Fixations - Principes de la fragilisation par I'hydrogene pour les fixations en acier Reference number IS0/TR20491:2019(E) ISO @IS02019 IS0/TR 20491:2019(E) COPYRIGHTPROTECTEDDOCUMENT @ISO2019 All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either IsO at the address below orIso's memberbody in the countryof therequester. ISO copyright office CP 401 : Ch. de Blandonnet 8 CH-1214 Vernier, Geneva Phone:+41227490111 Fax:+4122749 09 47 Email: [email protected] Website: www.iso.org Published in Switzerland ii @ IS0 2019- All rights reserved IS0/TR20491:2019(E) Contents Page Foreword ..iv Introduction. ..V 1 Scope. ..1 2 Normative references ..1 3 Terms and definitions .1 4 Symbols and abbreviated terms ..4 5 General description ofhydrogenembrittlement .4 6 Hydrogen damage mechanism 7 Fracture morphology .5 8 Conditions at the tip of a crack .7 9 Conditionsforhydrogenembrittlementfailure .7 9.1 Root cause and triggers for hydrogen embrittlementfailure .7 9.2 Material susceptibility .8 9.2.1 General ..8 9.2.2 Defects and other conditions causing abnormal material susceptibility ..10 9.2.3 Methodologyfor measuring HE threshold stress .10 9.3 Tensilestress .11 9.4 Atomic hydrogen 12 9.4.1 Sources of hydrogen. .12 9.4.2 Internal hydrogen .12 9.4.3 Environmental hydrogen ..13 10 Case-hardenedfasteners ..13 11 Hot dip galvanizing and thermal up-quenching ..15 12 Stress relief prior to electroplating ..16 13 Fastenersthread rolled afterheattreatment ..16 14 Hydrogen embrittlementtestmethods ..17 15 Baking ..17 Bibliography .19 @ IS0 2019 -All rights reserved iii