Cooling down slooooooooowwww for an anneal

[Bühlmann]

Everywhere I read it says to put in vermiculite, but why can't I just let it hang in the kiln? I have an airbath that will still show above well over ambient after sitting with the lid down overnight. Am I missing a reason not to do this?

 

[DevinT]

It depends on the alloy.

Hoss

 

[Bühlmann]

How about any alloy that is recommended to be stuffed into vermiculite.

 

[12345678910]

Everywhere I read it says to put in vermiculite, but why can't I just let it hang in the kiln? I have an airbath that will still show above well over ambient after sitting with the lid down overnight. Am I missing a reason not to do this?

If you have an electronic controller, you can just program it to hold temp and ramp down slowly.

 

[DevinT]

If it cools at the same rate, you will get the same result.

Hoss

 

[weo]

Everywhere I read it says to put in vermiculite,

because most of the information about blacksmithing readily available to the general public is based on early-mid 20th century technology and materials understanding.

 

[Lorien]

I annealed some files years ago by putting them in a bonfire and grabbing them out once the fire burnt out and the coals were no longer hot

 

[timgunn1962]

It depends on the alloy and the cooling rate it needs. For some of the simpler Carbon steels, which are essentially water-hardening, sticking a hot blade in vermiculite will give a slow enough cooling rate, but for some of the air-hardening steels, the cooling rate needs to be *really* slow: not just switch-off-the-oven-and-let-it-cool slow, but ramp-down-over-several-hours-slow.

Note that the cooling rate is much greater when the oven is hot than when it is cooler. Conversely the heating rate is much slower at higher temperatures (which you are much more likely to have noticed).

If you don't have ramp/soak control on your oven, you can get it hotter than you'll need, switch it off and note the temperature every minute, plot it on graph paper and see what the maximum cooling rate is at the temperature you intend to anneal from. That'll tell you whether it's slow enough for any given steel.

 

[Bühlmann]

It depends on the alloy and the cooling rate it needs. For some of the simpler Carbon steels, which are essentially water-hardening, sticking a hot blade in vermiculite will give a slow enough cooling rate, but for some of the air-hardening steels, the cooling rate needs to be *really* slow: not just switch-off-the-oven-and-let-it-cool slow, but ramp-down-over-several-hours-slow.

Note that the cooling rate is much greater when the oven is hot than when it is cooler. Conversely the heating rate is much slower at higher temperatures (which you are much more likely to have noticed).

If you don't have ramp/soak control on your oven, you can get it hotter than you'll need, switch it off and note the temperature every minute, plot it on graph paper and see what the maximum cooling rate is at the temperature you intend to anneal from. That'll tell you whether it's slow enough for any given steel.

Thank you for that. I hadn’t really considered the variability in rates, just overall temp/time. That makes sense to me.