The fracture toughness and tensile properties of Alloy 600, Alloy 690 and their welds, EN82H and EN52, were characterized in 54° and 338°C water with an elevated hydrogen content. Results were compared with air data to evaluate the effect of low and high temperature water on mechanical properties. In addition, the stress corrosion cracking (SCC) behavior of EN82H and EN52 welds was evaluated in 360°C water with high hydrogen.

Elastic-plastic JC fracture toughness testing revealed that the fracture resistance of all test materials was exceptionally high in 54° and 338°C air and 338°C water, demonstrating that fracture properties were essentially unaffected by the high temperature water environment. In 54°C water, however, JC values for EN82H and EN52 welds were reduced by an order of magnitude, and Alloy 690 showed a five-fold decrease in JC. Scanning electron fractography revealed that the degraded fracture properties were associated with a fracture mechanism transition from ductile dimple rupture to intergranular cracking that appears to be associated with a hydrogen-induced cracking mechanism. The fracture toughness for Alloy 600 remained high in 54°C water and microvoid coalescence was the operative mechanism in both low temperature air and water. Tensile properties for all test materials were essentially unaffected by the water environment, except for the total elongation for EN82H welds which was significantly reduced in 54°C water. At a strain rate of 5 x 10−6 sec−1 in low temperature water, there appears to be sufficient time for environmental interactions to restrict ductility in EN82H welds.

Constant-load testing of precracked weld specimens in 360°C water resulted in extensive intergranular SCC in EN82H welds loaded to KI levels between 35 and 55 MPa√m, whereas no SCC occurred in EN52 welds under comparable test conditions. A flutter fatigue load superimposed on a high mean stress (i.e., stress ratio = 0.9) did not accelerate cracking rates for EN82H welds in 360°C water.

Subject
Water, Materials, Intergranular stress corrosion cracking, Moduli, Fracture surfaces, Dimples, Stress cracking, Cracking resistance, Intergranular cracking, Fracture, Alloys, Stress corrosion cracking, Hydrogen
Keywords:
Alloy 600, Alloy 690, EN52, EN82H, welds, fracture toughness, stress corrosion cracking, tensile properties, water, hydrogen
© 1996 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).
1996
Association for Materials Protection and Performance (AMPP)
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