i work as a cnc gear grinder. after heat treating all the gears that come through our shop have a rockwell hardness of about 40 with a case hardening of around .0600 thick. this is almost impossible to drill through. i would guess that the handle of the razor, being thin is cased hardened completely through the entire tang. also the fact that the tang cracked so easily could indicate that during the manufacturing process the razor may not have been kept probably cooled leading to micro fractures in the steel. a nondestructive magpartical inspection would be able to eliminate this as a factor. also welding a heat treated piece of steel will distroy the case harding and the razors ability to hold as edge. if it were my razor i don't think i would invest any more money in it.