Harder Stainless Steel
THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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THE WEAR RESISTANCE, galling and seizing characteristics of austenitic stainless steel nuts and bolts can
be improved by a process known as carburization.
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THESE DATA show how
S31600 stainless steel treated by the plasma carburization process developed by Tanaka
Ltd. does not significantly change the corrosion resistance of the stainless steel.
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PDF of this article (180 kB)
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A new plasma carburization process hardens austenitic stainless steel.
Nickel magazine, March, 2004 -- Tanaka Limited of Osaka, Japan, has developed a plasma carburization treatment that hardens the surface of austenitic stainless steel nuts and bolts.
Carburization of austenitic stainless steel is typically a challenge: at high temperatures of 550 to 850°C, chromium carbides are generated in the metal, and these are then precipitated at grain boundaries where they can lead to intergranular corrosion.
However, because the process developed by Tanaka operates at a much lower temperature of less than 500°C, the carbon provides solid solution strengthening without the formation of chromium carbides.
"For austenite-stable materials, such as S31600 and S31700, the process has a beneficial effect," says Tsunenari Murakami, general manager of Tanaka.
The new carburization process improves the wear resistance, galling and seizing characteristics of stainless steel in nut-and-bolt applications.
Harder nuts and bolts produced by this process can be used in food and beverage processing equipment, in which lubricating oils are not allowed, and in medical equipment applications, where hygiene is essential, says Murakami.
Carburized stainless steel has been used commercially by a major manufacturer for a threaded lid on a beverage processing vessel. The hardened lid prevents galling and seizing, which would result in wastage of the product being processed in the vessel.
The anodic polarization curve for treated and untreated S31600 is shown in the accompanying diagram. They show that corrosion resistance is not significantly changed by the process.
PHOTOS: Tanaka Ltd.
Tanaka Limited |
