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Ask the Experts Metals

Can I determine where the oxidation on my heat treated parts is coming from within my furnace?

Mark Lanham
Applications Engineer

When checking a continuous furnace, oxidation in the preheat section has a matte or frosted appearance and is usually caused by air infiltration from the entrance of the furnace. Hot zone oxidation may cause scaly or blistered parts. This generally occurs from elevated moisture or oxygen levels due to improper atmosphere balance or water/air leaks in the cooling zone. Cooling zone oxidation typically results in a smooth, sometimes shiny discoloration—poor curtain design, excessive belt speed, water leaks, or insufficient atmosphere flow rates are possible causes.

In batch furnaces, start by identifying the oxidant causing the problem. Flowing nitrogen and measuring the oxygen and moisture levels can give an indication of the oxidant involved. Then a review of typical leak sources, such as seals, fittings, unions, and weld joints, usually leads to discovery of the leak source.

For help determining the oxidation causes or for atmosphere composition monitoring assistance, call 800-654-4567.
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