Reply by Gunney

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Posted on Hardening metal banding for making putty knives.

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14 posts in 1995 days

#1 posted 01-19-2013 06:12 AM

I don’t think you can heat treat crate banding. In order for heat treating to work, the metal has to have a certain amount of carbon content and I suspect the amount in the banding is too low. To make a putty knife, I would look for spring steel (I know that McMaster-Carr sells it), which can be hardened.

As far as the process of hardening, the metal is heated to a certain temperature that varies depending on the exact composition of the steel, usually somewhere in the 1500 to 2000 degree Fahrenheit range, and held there for a certain period of time. It is then quenched in a quenching medium that is again dependent on the specific type of steel, but could be oil, air, water, or brine. At this point, most all steels are too hard and brittle to be of much practical use and must then be tempered. Tempering involves heating the steel again, but to a lower temperature (400 to 1000 degrees depending on the steel), holding that temperature for a certain time, then allowing it to cool. After tempering, the steel will not be as hard and therefore not as brittle. The trick would be finding the proper tempering regimen that would leave it hard enough that it would spring back to its original shape, but not so hard that it would snap.

There is a process called “case hardening” which allows you to impart a thin, hardened surface layer to low-carbon steels, but it is more involved and I don’t know if it would work with something as thin as the banding.

-- Patrick, Mobile, AL

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