mystery of the immovable heated teapot

Dopers - I need your help. Daugher and son-in-law ask me and I turn to you: they put a teapot (unknown metal) on the electric stove, turned up to high. Inadvertently, the pot was without water. They discovered their error and tried to take the pot off. No go. Stuck fast. Turned off the heat. When it cooled down, it lifted off easily. So, what caused it to stick? Induced magnetism from the coil? doubt it - magnetism works underwater, and why doesn’t it happen with just a little water in the pot? Heat, expansion, etc.? What stuck to what, and why? and how? Can we get a little speculation and proposition going here? I’m stumped.

Just a guess…
If the teapot had a slightly (concave? Convex?) bottom, a partial vaccum may have been the cause?

hmm - there may be something in your answer. In the absense of water, the bottom gets hotter than usual. Concave bottom changes shape from extreme heat, gets stuck on coils. hmmmm

hmm - there may be something in your answer. In the absense of water, the bottom gets hotter than usual. Concave bottom changes shape from extreme heat, gets stuck on coils. hmmmm maybe. …

Pot melted slightly while hot, and then the contraction of the metals during cooling broke the melted bonding?

You don’t need to have melting to get a cold weld. Two clean surface in close contact tend to diffuse into each other. The bond isn’t usually very strong, but it can cause real problems with overtightened bolts, or machines meant to work in a vacuum.
I’m having no luck finding a decent overview today, but this search at least brings up a wide assortment of information on cold welding

Alright. That makes sense. How about that for a good theory? While hot, a cold weld was created between the teapot and the stove. When cooling, the contraction rates for the burner and the teapot were different, which caused the cold weld to break.

The cold weld - meaning a bit of mutual diffusion? What other possibilities are there?

If it’s vacuum (suction), cooling it down shouldn’t have helped.

Is the stove top perfectly flat? My WAG is that the extra heat expanded the pot and lodged it in there, but this wouldn’t happen if it was flat.

Are you sure it doesn’t happen with a full pot? Normally there is no reason to try to move a full pot while the heat is on.