What is the molecular structure of the coating on cast iron cookware known as seasoning? When a piece of cast iron is repeatedly covered in fat and exposed to heat it develops a hard, black, non-stick coating referred to as "seasoning".

What exactly is this coating made of molecularly? How is it bonded to the cast iron substrate? What is the chemical process that transforms a liquid fat into this coating? And what if any characteristics of the fatty acids or triglycerides used have an effect on the final coating or how well the it bonds to the iron?
Some hints:


if you mean that "what exactly" in the original sense of the words,
then the answer is: nobody knows and will ever know. 
If you are content with some more vague answer, then 
look at the pyrolysis chemistry occuring from 150 °C 
up with fats, proteins and starch/sugars, and all that 
at once. This is a vast field of chemistry, and all 
is gives to a trained chemist is a idea of the structures 
of that coating. 
Bonds to iron will not occur, first because on cast iron and 
on steel pans there is always a layer of iron oxide, 
on cast iron  you find a glaze formed by fusion of the
molds finish layer (often containing graphite and clay)