The resistance to sulfide stress corrosion cracking of special stainless steels, austenitic and duplex austenoferritic, was evaluated in various conditions, at temperatures up to 150°C under 1 to 15 bar H2S in the NACE TM-01-77 solution. The study of mechanical and electrochemical processes was undertaken in the duplex stainless steels: influence of mechanical twinning of the ferrite phase which causes strong local depassivations, and of the electrochemical processes, both anodic and cathodic. The first results seem to show the primary importance of the anodic dissolution process initiated by twinning of the ferrite phase, while cathodic hydrogen seems to exert a lesser influence, at least in most electrochemical situations studied here. Indeed, at this stage of the work, embrittlement by hydrogen cannot be ruled out, but it seems to play only a secondary role, at least at low pressures of H2S and in the electrochemical situations obtaining in the conditions investigated. Increasing the temperature seems to increase very much the relative influence of the anodic dissolution process, but at high pressures of H2S the participation of hydrogen can still be significant. In addition, one must take into account the complex influence of temperature increases on the mechanical twinning of the ferrite phase, which first becomes less important up to about 200°C, to augment again above. This can explain the better resistance of duplex stainless steels at 100°C and 150°C, whereas austenitic steels become very sensitive to cracking. Better knowledge of the several processes involved in the cracking phenomena made thus possible a more precise formulation and design of the duplex stainless steels in such a way that the resistance to cracking is much greater at room temperatures, up to about 80 % to 90 % of the yield strength. A more precise control of metallurgical factors and of fabrication procedures have been shown to improve very markedly the resistance of industrial products, castings, rolled plates and forgings.

In the last case, the resistance in the transverse direction becomes about the same as in the longitudinal direction whereas in more conventional common hot-worked material, the transverse direction can be very sensitive to cracking.

Subject
Composition, Yield stress, Wiring, Stress cracking, Cracking resistance, Heat, Steel, Corrosion resistance, Duplex stainless steel, Ferrite, Yield strength, Stress corrosion cracking, Hydrogen
© 1985 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1985
Association for Materials Protection and Performance (AMPP)
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