My first time and it did not work out. As you can see, the broken bolt, which had originally broken flush with the end of the nut is on the left and the new nut/bolt combo I installed are on the right. What you see on the end of the broken bolt is the sheared weld where I had welded on a 3/4-10 nut on to the end of the broken bolt. The bolt is 3/4-10 and had been in place undisturbed for 11 years and I am in the rust belt with a lot of salt used in the winter.
I first tried 7018 and wasn't getting good penetration, so I switched to 6010 and the broken weld you see in the pictures was done with 6010. As you can see I was able to achieve a good weld on to the end of the broken bolt but it still wasn't enough to spin the bolt. The seized bolt was subjected to being welded on four times, so it was heated up pretty well four times and it still did not break loose.
Any thing I could have done better? I started off soaking the rusted bolt with acetone/atf over a few days and it did not help. I tried heating the nut/bolt with a propane rosebud tip running off a bar-b-q tank and that did not help. I did not have my oxy-acetylene set up with me, the bolt might have come off had I heated the nut/bolt white hot.