Welding Tips and Tricks

A friend of mine stripped the threads (guide bolts) on a cast steel log splitter wedge. He asked me if I could weld the hole and drill and tap to 3/8-24. Without putting much thought into such a small welding job I MIG welded the hole, ground it flush. Next I went to center punch the new hole and realized it had become harder than my punch and drills. Oops, I guess the higher carbon content of the cast steel joined with the MIG weld. I tried to anneal the weld with a torch, it worked a little but not enough to drill through. Any ideas as to how I might resolve this problem would be greatly appreciated.
Tom

i have been in a similar fix, and i used a carbide spade bit that is made for drilling ceramic or glass . it is a funny looking bit that is just a shaped piece of carbide brazed to a drill shank: go slow and use cutting oil you should be alright. retapping the hole may be a little tricky too just remember to back the tap a quarter to half turn ti every two or three turns with plenty of oil , and if you have air handy blast out the hole a couple of times as you go.....ps... a standard masonry bit will also do the job but they are sharpened wrong for drilling metal and will need to be changed, witch can be done with the right grinding wheel if you are used to sharpening drill bits.. I hope this helps