places I have dealt with in the past that make bearings ( I have ball bearings up to about 4" diameter ) make them from many materials.
in the past I have had bronze and brass, stainless, high and medium carbon steels and some tool steels, also ceramics
magnetic indicates a steel
spark test may help
case hardened or through hardened may help.
I have used the inner and outer parts of ball races in the past and some of them are even quite hard when hot and still ring when hit at yellow.