Differential Tempering

Straw color on peen after tempering

This is a cabinetmakers hammer head I made with help from a few friends. It’s O1 tool steel.

We hardened it in a propane forge made from an old propane tank. For the hardening it was heated until bright glowing orange, then quenched in peanut oil. The most fun part of the whole process came next when I tempered it. The ideal for a hammer is that it be hard on the ends so nails won’t dent it, but be relatively soft (and therefor tougher and less brittle) in the middle where the handle goes through the head. For O1 our target was to heat it until the face and the peen were straw color. So by applying the heat from a torch to the middle of the head the middle got hottest. As the heat spread out to the ends I watched for the straw color and quenched it to stop the ends from getting any hotter.

A little darker on the head?

In the first two photos you can see the black and blue colors in the middle where it got hottest during tempering, and the straw/brown color on the face and peen. I think the brown colors got a little darker after quenching in the oil.

The last two photos are of the forge used for hardening.

Propane forge for hardening

A cold head inside the forge ready to be heated for hardening

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About johnjoiner

Computer nerd by day, Dad and woodworker by night. Woodworking blog at https://johnjoiner.wordpress.com/
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