No, I don't imagine I would end up with molten steel, though my boss would probably kill me if I did.

The kiln would slowly heat to 1250 or 1300 degrees and immediately begin to air cool after reaching the desired temprature, and unlike a torch there would be no risk of overheating. The silver braze would hopefully melt and spread enough to bond the lugs, but the frame tubing whould be about 1000 degrees away from liquifying. My fear is that heating the entire frame would significantly weaken the steel, but other than that I am fairly certain that it could be done without much difficulty.

I was aware of the Mercian process, not what I'm imagining exactly; my plan is to wrap very fine brazing wire tightly around the ends of the tubing, then to insert the tubes into the lugs, which would need to be heated enough that they would expand to accomidate the increased diameter. Perhaps bisque moulds could be used to hold additional braze-ons in place.

So ultimately my question is would heating Reynolds 531 or an equivlent steel to 1300 degrees make it weak?

This would just be a fun project for me, designing and building my own custom touring frame cheaply.

Thanks.