Corrosion resistant alloy castings used in the Chemical Process Industries can experience premature failure or reduced service life as a result of carbon pickup from metal-mold reactions. Several case histories are presented confirming that carbon pickup can be a problem in many chemical plants. Laboratory test data are also presented to supplement the. field results. This work represents a continuation of studies first presented at Corrosion/72 and subsequently published.1  A short review of this prior work follows as background information:

It has been known for several years that lower carbon levels in corrosion resistant stainless alloys are beneficial for general corrosion resistance, weldability and resistance to intergranular corrosion. This realization has led to a substantial increase in the use of low carbon grade alloys by the Chemical Process Industries.

At the same time, the foundry industry has known for years that many mold environments contain substantial amounts of carbonaceous material in the form of organic binders and washes which contaminate an alloy with carbon during the casting operation. With full knowledge of this situation and the potential corrosion problems that could result from application of carbon contaminated castings, a study was initiated to evaluate the influence of carbon pickup on corrosion resistance and reliability of cast stainless alloys. Based on the results of chemical analyses, microstructural analyses and corrosion testing of contaminated and uncontaminated castings, it was concluded that:

  1. Stainless alloy steels cast in resin sand molds are subject to pronounced carbon pickup. The carburization effect is most pronounced in lower carbon grades and persists after a standard quench anneal heat treatment.

  2. Carbon pickup seriously degrades the corrosion resistance of stainless alloy castings.

  3. Carbon pickup, high general corrosion rates and intergranular attack can be avoided for stainless castings by employing ceramic (inorganic, noncarbonaceous) mold environments. Mold and core materials of this type become a necessity for low carbon alloy castings if corrosion resistance is to be unimpaired.

Subject
Acids, Materials, Stainless alloys, Sand, Metal surfaces, Valves, Castings, Nitric acid, Metals, Carbon, Corrosion resistance, Stress corrosion cracking, Resins
© 1975 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).
1975
Association for Materials Protection and Performance (AMPP)
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