A new optimized post weld heat treatment (PWHT) of 347 type stainless steels has been developed and laboratory tested up to 1562°F (850°C) to address the needs of the petrochemical industry in stretching the upper operating temperature limits beyond 950°F (510°C). Experimentation focused on 347H, 347LN, and 16Cr11Ni2.5MoNb. The multi-step PWHT consists of stress relief and solution anneal, followed by a stabilizing stress relief. An optimized microstructure and substantial resistance to elevated temperature cracking was confirmed using a thermo-mechanical test simulator. Limitations associated with classical stabilization heat treatments, including sigma phase embrittlement and low ductility properties are eliminated. This PWHT provides high immunity to sigma phase embrittlement, reheat cracking, and stress relief cracking while retaining superior mechanical and corrosion resistance properties. Test results, mechanisms, and issues concerning alloy and nitrogen additions are discussed.

Subject
Sigma phase, Materials, Precipitation (solids), Precipitates, Niobium, Stress cracking, Stress, Stress relaxation cracking, Sensitization, Creep, Stainless steel, Heat treatment, Grain
Keywords:
post weld heat treatment, stainless steel, annealing, stabilization, stress relief, reheat cracking, sigma phase embrittlement, stress relaxation cracking
© 2004 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).
2004
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.