The effects of C, P, S, and N on the transpassive corrosion of high purity(HP) Fe-18Cr-14Ni alloys were studied in 13 kmolm−3 [0.36 kmol/ft3] nitric acid(HNO3) and 13 kmolm−3 HNO3 containing ceric(Ce4+) ions. Alloy specimens of 99.99 % purity were fabricated by a cold-crucible method in argon(Ar) gas atmosphere to prevent contamination and used to isolate the effect of each target element. The results showed that C and P were the responsible elements for transpassive intergranular corrosion in 13 kmolm−3 HNO3. The critical concentrations, preventing intergranular corrosion, were less than 500 ppm for solution annealed HP18Cr-14Ni alloys. The addition of only 50 ppm of each impurity caused deep intergranular corrosion in HP18Cr-14Ni alloys corroded in 13 kmolm−3 HNO3 with Ce4+ ions. Thus the responsible elements and the critical concentrations for intergranular corrosion were different in both the test solutions. Aging treatment at 973 K for 1h degraded the corrosion resistance of all the impurity doped HP18Cr-14Ni alloys. Especially, 500 ppm C showed a detrimental effect on the corrosion resistance of the alloy in 13 kmolm−3 HNO3 through sensitization.

Subject
Transpassivation, Corrosion resistant alloys, Corrosion rate, Nickel based alloys, Purity, Commercial alloys, Nitric acid, Impurities, Elements, Grain boundary, Alloys, Intergranular corrosion, Aging
Keywords:
austenitic stainless steel, carbon, impurity, intergranular corrosion, nitric acid, nitrogen, phosphorus, segregation, sulfur, transpassive corrosion
© 2001 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).
2001
Association for Materials Protection and Performance (AMPP)
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