Rust + heat = no problem, but why?

Put this in the OT forum 'cause I just didn't know where else to ask something like this.

In my (limited) experience any connection that is rusted shut can be opened with some heat. It works so well that I reach for the torch before the socket set when I see the red stuff all over. I saved a found pair of visegrips this evening with the torch. They were rusted so hard that the wouldn't even budge and now they're in my toolbox.

My theory is that the steel expands *and* the rust actually gets burned away when things get hot enough. I know this is totally frivolous, but are there any other theories about why this works so well?



Thanks