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Metallurgy of Stainless Steel Alloys - Welding and Corrosion

Author(s)/Editor(s): Wayne E Reitz PHD

Pages in Print Edition: 26PP

Published: 03/08/2006
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Stainless steels are well known for their corrosion resistance, which is established by having sufficient chromium present to form an impervious oxide on the surface. Another equally important characteristic is strength, which requires understanding the iron-carbon phase diagram that aides in describing the effects of composition and thermal processing on performance. Schaeffler diagrams also predict the resulting microstructure after welding based on composition, as described by "equivalents." One should recognize that welding is another form of heat treatment that can degrade properties, strength and corrosion. Embrittlement occurs via three mechanisms: 475° C embrittlement, sigma phases and high-temperature embrittlement. Loss of corrosion resistance can occur in ferritic and austenitic stainless steels when least expected. Usually, this unexpected corrosion develops after exposure to moderately high temperatures. Sensitization, weld decay and knife-line attack are three of the most common problems. Weldability is usually defined as the material's resistance to cracking during fabrication and can be measured via several test methods. Weldability is a function of mechanical properties while maintaining excellent corrosion resistance. Author: W. Reitz (Reitz Consulting Ltd.)