Face hardened was more common in European production but most British and US was homogeneous. The US were more willing to try welding than the British, Sherman went over to fully welded by mid 1942, Cromwell wasn't welded until early 1944 and then only some models, old habits die hard!
Though White used face hardened, IHC used homogeneous in their halftracks. Early US armour was quite soft, 1943 saw some improvements I understand.
As long as the welding is chrome or nickel based, cracking is not a problem. There is a heat affected zone adjacent to the weld but the ductility of the cooling weld metal allows for this.