A corrosion investigation was conducted to determine corrosion behavior and stress corrosion cracking (SCC) susceptibility of S30400 and S31600 stainless steel (sst) exposed to soldering flux paste containing 25 percent by weight (wt%) zinc chloride. Electrochemical test results indicated that soldering flux paste was not corrosive to S30400 and S31600 sst at room temperature. In the molten state, the wax phase (light phase) of soldering flux was also not corrosive to S30400 and S31600 sst because it was not an electrolyte. However, the heavy phase of solder flux was corrosive to S30400 and S31600 sst at elevated temperatures. In heavy phase, S30400 sst did not passivate, while S31600 sst passivated at temperatures up to 80°C while no passivity was observed at 85°C and above. AC impedance test results showed that S30400 and S31600 sst corroded at rates of less than 0.1 mpy in solder flux pastes at room temperature. In the soldering flux heavy phase, corrosion rates were about 2 mpy or less for S30400 at temperatures up to 75°C and S31600 at temperatures up to 70°C. However, corrosion rates of S30400 sst in the soldering flux heavy phase increased to 5, 8, 10, and 22 mpy at 80, 85, 90, and 95°C mpy while corrosion rates of S31600 sst in the soldering flux heavy phase increased to 4, 5, 7, and 11, and 30 mpy at 75, 80, 85, 90 and 95°C, respectively.

Constant Extension Rate Test (CERT) results revealed that no SCC susceptibility when S30400 and S31600 sst were exposed to soldering flux paste at room temperature and wax phase at 65 and 95°C. However, both test alloys were susceptible to transgranular SCC when exposed to the soldering flux heavy phase at temperatures of 65°C and above. Severity of SCC increased with temperature increase. SCC fractures were characterized by reduction of ductility and numerous SCC secondary cracks on the specimen gage length. The most severe SCC fracture was observed on a S30400 sst specimen partially submersed in the soldering flux heavy phase and partially submersed in the soldering flux wax phase at 95°C. The fracture was completely brittle. However, no similar cracking was observed on S31600 sst.

Subject
Scanning electron microscopy, Fluxes, Corrosion rate, Impedance, Transgranular stress corrosion cracking, Fractures, Wax, Mechanical failure, Pastes, Cracks, Corrosion potential, Stress corrosion cracking, Test specimen
Keywords:
Soldering flux, zinc chloride, stress corrosion cracking, susceptibility, CERT, heavy phase, wax phase, transgranular SCC, passivity, S30400 and S31600 stainless steels (sst)
© 1995 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).
1995
Association for Materials Protection and Performance (AMPP)
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