Tig welding EN8 Options

[Ashley37]

Hi . Having an issue tig welding EN8 boss to a mild steel plate. Easy enough to do but resulting boss is so hard I can’t drill it . What has happened. The boss the EN8 bit was 12mm diameter fitted through a 12 mm hole in 4mm mild steel, I welded round the diameter on the flush side. I have tried annealing but maybe not for long enough it made no difference the part where the weld bead is incredibly hard. I’m assuming it’s to do with carbon but both parts were easily workable before welding. I’ve remade the job with both parts from mild steel which are fine.
What have I done?

[Technic Al]

I assume you used mild steel filler....These days there are more or less two EN8s......One that is a CMn steel something like S355 that is reclassed as EN8 because it meets the mechanicals required....the other is poor quality steel pumped up with Carbon to meet the mechanicals (tensile really)
I suspect youve got some of the high(ish) Carbon stuff.....however, I wouldnt expect it to be un-drillable unless it was quenched. Could it be that your drill is a bit iffy as well.

If you anneal it. Get a magnet on it and heat it until the magnet drops off....then pack it sand to cool for as long as you can......unless youve got a proper annealing furnace that is.

[Ashley37]

Yes that’s what I had deduced. My drills are good I stuffed two new ones, good ones too and my center drill.From the other end of the boss you can drill up to the hard part then it just stops. Post welding the jobs were left to cool on the bench I didn’t quench them.
I’ve now remade the 4 items using all mild steel. I’m going to pop the old ones in the outdoor wood stove embers when it stops raining long enough to try, that should keep them at a red heat for longer and let them cool slowly. I don’t have annealing furnace but always fancied making one looks easy enough but for very occasional use probably not worth the effort. I’ve quite a lot of EN8 so I’d better find out how to use it, I bought it for a job that probably won’t need it now. It wasn’t that expensive so I guess it’s Chinese.