That cut with no apparent kerf can be formed at least a couple of ways

-cut the kerf (then file/polish inside the kerf) then forge the part together (pinch it) so that the kerf is reduced to zero clearance
-form and forge (fold) the material to the point where it's faces are essentially touching at the root of the 'kerf'

finish, harden/temper etc


Cheers
Tinker