1UglyFish (YES it is,what lake did that northern come from?) I'm not sure what your getting at, but a proper weld is stronger than the pieces it joins. the "overheated area" I think you are refering to is an annealed or heat treated area so to speak. it looks bluish in color and is approx 1/4 to 5/16" wide. this is for a gmaw (mig) welded joint on .083-.125 material. this area is slightly brittle compared to the base metal, but acts as a transition to the hardened weld.

the best way to attach two pieces is to plug weld through the base material. this is what I, and a few others have done. for maximum strength, the total contact area of the two materials needs to be figured out, then a 50% split of each to be welded. make sense??

My welds on the bottom of ZIPPY'S car don't look all that good, and I'm not proud of their show appeal, but they have great penetration.

have I ever said I hate welding on my back (inside joke)