Carbide Tool

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Metallurgy, I want to soften an 8mm allen key so I can machine it , I have a Elec muffle , ideas?

You don't need to soften it if you have tungsten carbide cutting tools, burrs, drills, etc., you do need to slow down the cutting speed somewhat. Grinding with aluminum oxide grinding wheels also works. A Dremel hand-held grinder would work, or a bench grinder.

Typically the core of the allen wrench key is softer to provide toughness (the key will bend before it breaks, warning the user, rather than just snapping off in a brittle manner).

A question: a completely softened key will not serve as a wrench key anymore, because it will bend and the hex shape will be distorted beyond use. Is it true you don't want to use it as a wrench anymore?

An electric muffle will completely soften the entire key - alternatively you can use a acetylene torch to heat up only one section (use a 'reducing' flame) to RED hot (ORANGE hot is too high and not necessary for annealing purposes).

The typical alloy additions of chrome and moly are to control the depth of hardening during the initial heat treatment. The alloy content (and the quality of the key) would determine the exact hardening treatment that would give you the optimum hardness and strength properties, but you most likely don't know the alloy content (or carbon content), so re-hardening after machining is problematic.

Suggestion: use carbide tools to machine the key (this probably would work fine) and don't soften the key, or, use a acetylene torch to soften just a local zone of the key and machine only inside this zone. Heating a narrow zone to nice RED hot (900-1100°F) will soften the key without risk of hardening (you may quench from this low temperature). The chrome/moly alloys will resist this tempering, so you may need to experiment for how long you'll need to keep RED hot to get the desired degree of softening (allen keys are inexpensive).

If you heat to to a nice ORANGE hot (1600°F+), you're getting to the hardening temperature range, from which a quench WILL harden the tool. However, without a protective atmosphere or heating with a 'salt pot' (the commerical method of heating), a lot of oxide scale will form and the surface will look kinda ugly (which is why to avoid hardening if possible and just machine directly or temper locally).

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