Cast Iron Repair Question.

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Ok heres something ive run into too many times to count.  When repairing Cast iron, where i have to Drill/tap the repair area.  No matter what i try, i cant do it. I can drill and tap the weld, and the cast beside it, but where the weld and cast meet, its harder than a diamond.   For example, plug welding a stripped out threaded hole. Does anyone have a solution for this other than brazing?  Ive played around with pre and post heating, Sand, etc. but its always rock hard and will destroy a drill bit, or tap.
Reply:Yea thats a problem, drill area larger than needed and weld with ni99. Since you are not near the iron/weld boundary the nickel will be easy to drill and tap.PeterEquipment:2  old paws2  eyes (that don't look so good)1  bad back
Reply:Castweld is correct in that it would be easier to drill and tap the nickel.  For my cast repairs, which are nowhere near the quality of Castwelds, I use 309 filler.  I haven't tried drilling and tapping the weld metal to base metal boundary with that yet.
Reply:why not braze? it's easyIn the field: '06 Ram 3500/Miller PP350    '14 F-350/Lincoln Classic 300DIn the shop: MM252, Hypertherm PM-85, White face MM200