What ball bearings used to be made of?

gt-arrowhead

I know ball bearings nowadays usually tend be made of high carbon stainless steel, and its not uncommon to find ceramic balls in higher end bikes and parts, like jockeys wheels, wheels, and bottom brackets, but what did they used to be made of say 15-20 years ago? For example i remember using perfectly nice and shiny bearings which i knew were brand new, but just old, and after about 6 months of commuter use they ended up looking like this:

rockmonkeysc

They've generally been made of the same steels since the second world war.
There are good bearings and cheap bearings. Just like there always has been. Cheap ones have a lower carbon content, less of some of the more expensive alloying elements and more impurities.
Most steel alloys in use now were invented during WW2.