The minimal x-ray radiation from airport scans shouldn't do anything to raw polymer clay, but those scans can set off the detectors for "explosives" since polymer clay is raw plastic (which can be used for bomb making) and some clayers have had a hard or impossible time taking it through security.
Not sure what could have happened to your clay since you said it was actually taken on board into the passenger comparment with you rather than checked in below where temp can be an issue (unless it was in some situation before or after that where the temp was higher).
And, the main versions of the Sculpey
brand of polymer clay are so soft that they usually don't get hard easily. Their makeup has more of certain ingredients to make those versions that soft compared to most other brands and lines of polymer clay, so perhaps that made a difference?
Still not sure how that could have happened though unless one of the machines (particularly the item-scan ones, not body scan ones) was malfunctioning enough to create 50-100 times the amount of radiation it should be using...and the DH-physics person who gave me that info also says that the machines and radiation levels are all pretty much standard throughout the world.
(If you want info on reconsistuting harder or even partly-cured polymer clay, check out this page at my site:http://glassattic.com/polymer/Conditioning.htm
... and if necessary, read the Old-Hard Clay
subcategory there too)
And btw, re microwaving polymer clay....it's not really that it's verboten except that the results can be uneven compared to "baking" with hot air (or even boiling in hot water). In fact, polymer clay can be softened a bit with just a few seconds in a microwave since the microwaves will heat up fats and oils.
But if you put an entire clay item into a microwave oven on High to cure it, even with a rotating tray the microwaves wouldn't be delivered equally and some some areas of the item would heat up more than others. And also any projecting areas would act as little antennas and absorb more microwaves. (If you use a Low setting in a microwave though, it's possible to cure polymer clay more easily but that's also because any heated areas will heat the areas next to them spreading the heat around more evenly...it's just very unreliable though.)
Polymer clay can be boiled in water in a microwave though if the item can stand that bumping around. Since polymer clay is a thermosetting type of plastic, the ratio of time-to-temp is what's important so even at boiling, 212 F, the polymerization will proceed--just slower.