Radial roller bearings outer races are heated up and pressed oval in a die when mounting the balls.
They would not crack with a hammer hit. The standard bearing material is 100Cr6 and has a surface hardness of around 60 HRC.
here are two interesting reports that gives a bit more insight in the materials used
https://www.google.de/url?sa=t&rct=j...,d.ZGg&cad=rja
https://www.google.de/url?sa=t&rct=j...,d.ZGg&cad=rja
And here it refers the material of the 332L2 planet gear outer race material:
Fractured Gear | Flight Safety Foundation
Subsequent testing determined that the particle was not silver or cadmium but 16NCD13 steel, planet gear outer race/gear material.