A method for manufacturing a case-hardened ring gear/differential case assembly includes attaching a ring gear to a differential case. The case-hardened ring gear and the differential case are fabricated of materials each having differing properties of at least carbon content and melting temperature. The attaching includes placing a flange of the case-hardened ring gear in intimate contact with a flange of the differential case whereby a predetermined gap is defined between a remainder of the ring gear and a remainder of the differential case. The ring gear flange is attached to the differential case flange by a friction welding process. The predetermined gap defines an outflow channel that receives a carburized portion of the case-hardened ring gear as overflow material created by an upset forging step of the friction welding process. Differential assemblies and vehicles including such are described.