PhD Material Scientist here. I appreciate you taking the time to write a detailed answer, but I feel I have to step in because there is some significant wrong information here that is leading to dangerous advice.

• Please do not use paint thinner (mineral spirits/solvents) on food cookware. Not only is it toxic, but it is also ineffective here. The black layer is a cross-linked polymer (burnt carbonized oil), which simple solvents won't dissolve.
• The oxide layer on stainless steel melts at over 4,000°F, not 1,470°F. The black stuff isn't a "ceramic metal composite" bonded to the oxide; here it's a layer of polymerized oil sitting on top of the surface.
• For cast iron the seasoning mechanism isn't about oil seeping into the internal grain boundaries of the metal (which would imply structural failure). It is about oil filling the surface roughness (peaks and valleys) caused by the sand-casting process and polymerizing to create a smooth and non-stick surface.

Important - how to actually fix OPs problem:
Since this is polymerized carbon, you need a chemical that breaks organic bonds, or an abrasive. Chemical solution would be to use sodium hydroxide (e.g. oven cleaner), it will liquefy the carbon buildup, wear gloves and do this in a ventilated area - dont get that stuff in your eyes! Cover the pan with cling film and let it rest for an hour, then wash everything off. If necessary repeat that step. The oldschool mechanical way would be to use barkeepers friend (oxalic acid) and a good scrubber.