I've never seen anything like that on a gasoline engine, but some Diesels use various alloys in the crown area of the piston as a heat dam to isolate the combustion above the rings. I have a feeling that the alloy isn't exactly steel- - - -possibly something with a lot of nickel in it, maybe? Some versions of the old 2 stroke Detroit engines used a 2 piece piston- - - -cast iron crown with an aluminum skirt- - - -held together with the wrist pin!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!