Effect Of Chromium/Iron RatioA sample of corrugated 304L panel was exposed to a chloride-containing environment. The chromium/iron ratio and the sample appearance are shown. A lower Cr/Fe ratio results in more corrosion.
The right iron spectrum was obtained from a sample that had undergone experimental passivation, while the left iron spectrum was from a standard passivation treatment. XPS demonstrated there is more metallic iron present on the surface of the experimentally passivated material, resulting in subsequent rust formation. Step 3. Depth Profile The third step in the analysis includes a depth profile to determine the concentration of the primary elements (C, O, Cr, Fe, and Ni) as a function of depth. This also yields the Cr/Fe ratio as a function of depth and the oxide thickness. As an example, for the polished sample (below, left graph), the iron concentration is always higher than the chromium concentration. For the passivated sample (below, right graph), the concentration of chromium is greater than the concentration of iron in the near-surface region. Step 4. After-profiling composition of all elements (for quantitative comparison) Susan Kerber of Material Interface has been actively involved with ASTM International on the development of a new stainless steel passivation standard. The new standard is currently undergoing round-robin testing. Please contact our office for additional information or for a quote. C. What is Rouge and how is it removed? Rouge is a surface deposit and discoloration on stainless steel surfaces, with various colors and textures. It generally appears after exposure of stainless to high-purity water and steam at elevated temperatures and often reappears after removal. Rouge is composed of various chromium and iron oxides. These forms are designated as Class I, Class II, and Class III Rouge. Class I Rouge is orange/reddish-brown and is primarily iron oxides and hydroxide. It is only loosely adhered to the base metal and is therefore migratory. The base alloy underneath the rouge is not affected by this deposit. It can often be removed by passivating processes. Class II Rouge is typical of rust formation, often from the presence of halides like chloride. It is active surface corrosion with a low chromium/iron ratio. Removal often requires abrasion and re-polishing. Class III Rouge forms in high temperature situations, including clean steam. It is dark blue to black in color and is chemically very stable. It contains iron oxide in magnetite form and is tightly adhered to the base alloy. In some cases, strong acids can remove this layer. In other cases, the surfaces much be mechanically repolished. Sematech, 2706 Montopolis Drive, Austin, TX 78741, Specifications 90120403B-STD and 91060573B-STD SEMI Global Headquarters, 3081 Zanker Road, San Jose, CA 95134, Specifications F30-0306 (XPS), F72-1102 (Auger), F73-1102 (SEM).