This doesnt apply (really) to your type of material, but in heavier plate to avoid re-drilling & tapping in weld filler, it is a good idea to bore the hole out oversize (be generous), turn a tight fitting plug and weld it in. Now you have "clean" material to drill in.
In some cases with blind holes and a tight plug just beating (it must be about 0.05 long to start with) it good with your ball peen hammer this peens it into place quite permenantly. In most cases if you throw a surface grind in it you wont know the plug exists.
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