You always see those "do not weld on frame" stickers on big truck frames, but why? What is it that makes them so difficult to weld successfully? Could it be hydrogen embrittlement next to the weld? I realize that this material is usually some type of steel that is quenched and tempered to give it the hardness and strength it needs to get the job done. I also realize that when you weld on it, it changes the desired characteristics of the steel therefor creating weak spots.
I've seen some frames welded with GTAW, SMAW, and GMAW without any prob, but I have also seen some welded that have cracked again near or next to the weld. For example, I saw a crack in a frame repaired with GTAW, it didn't even penetrate half way through the frame and it cracked right next to the weld. This was obviously in a stressed area and you would of thought that if it was going to crack again, that it would have cracked through the PJP weld and not next to it. Well, I would of though that anyway.;-) In that particular instance, I was thinking Hydrogen embrittlement. So do you think a bit of preheat, weld it with a low hydrogen electrode, a good interpass temp, and an annealing process done afterwards might have given a successfull repair? This kind of stuff really interests me and I love to know why things happen.
Ray C.