Effect of W, Mo and N contents on pitting corrosion resistance of 25Cr and 23Cr base duplex stainless steels was investigated using the ferric chloride test according to ASTM G48. The improving effect by W addition for pitting corrosion was found out, and the modified pitting resistance equivalent(PREW) of Cr+3.3(Mo+0.5W)+16N was determined by using the least-squares method. In addition, effect of W, Mo and N contents on pitting corrosion at heat-affected zone in weldment was studied to decide the proper chemistry of the base metal. From these results, 25Cr duplex stainless steel with 2mass% W(25Cr-7Ni-3Mo-2W-0.3N), and high Mo-23Cr duplex stainless steel(23Cr-7Ni-4.5Mo-0.3N) have been developed as high pitting corrosion resistance materials. Further, corrosion behavior of the new developed-steels was investigated in H2S containing CO2 environment and these steels showed the improved-corrosion resistance compared with conventional 25Cr duplex stainless steel. Finally, pitting corrosion resistance of the duplex stainless stainless steel with high N content was discussed based on the corrosion test results and the calculation result of PREW in each phase of α and γ, and it was indicated that the duplex stainless steel with 40-45% α content has the most excellent pitting corrosion resistance.

Subject
Materials, Precipitates, Thermal cycle, Welding, Partial pressures, Chemical composition, Base metals, Steel, Pitting, Corrosion resistance, Duplex stainless steel, Stress corrosion cracking, Chloride stress corrosion cracking
Keywords:
duplex stainless steel, sea water, hydrogen sulfide, carbon dioxide, pitting corrosion, stress corrosion cracking(SCC), flow line, oil country tubular goods(OCTG)
© 1993 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).
1993
Association for Materials Protection and Performance (AMPP)
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