porosity in P-20 tool steel!

by Mike
(Mount Dora, Fl.)

Hi, I was just wondering if you might know why I am getting porosity on a mold that I am welding!
This mold was repaired years ago, with what I don't know
but it was so hard that it had to be ground out, carbide wouldn't touch it! but did get it all out!
With this said I pre heat with a rose budd as best I could
to about 350 to 400 deg. (mold is about 24" dia. with a
tapered hole about 12" deep) the area to be welded is about
1 3/8" wide and 10" dia. all the way around.
I got the right tig rod from a Mold Welding Company.
Everything was going good until I had about 3" left to weld then I started to get porosity in my weld.
I used a carbide burr to grind out all that I could get
out but I could not get them all HELP PLEASE!!!

PS I am not a certified welder I had about 30 hrs of welding classes, been welding on and off for 40yrs.Thank You Mike

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Mike, you probably went over a sub surface pore and pressure increased and created the porosity. Its probably a flaw from the previous repair that caused it but you will probably keep getting pores unless you dig all the porosity out....bad news , I know, but it is what it is.