Does anybody know? They are some sort of steel, but they don’t rust easily, like the ones on my Ford Focus? And do all manufacturers use the same material for their discs? Any metallurgists out there?

stainless steel (not sure what grade, probably a fairly good one seeing as they’r invariably hot/wet)

car ones are steel, as it has a higher coefficient of friction, but it does rust.

raceing cars/bikes used to have cast iron braking surfaces as it gave the highest coefficient of friction, problem was they had to be hot to work, and carbon/ceramic disks are a lot lighter.

I think car ones are still cast iron.. Stainless for bikes..

hope ones are made from the tortured souls of screaming banshees