Glenn Posted June 13, 2008 Share Posted June 13, 2008 I know if you wait till the slag cools, when you hit it the slag will fall free of the weld. But if you quickly chip this away will the cold air harden the weld causing problems later? Quote Link to comment Share on other sites More sharing options...
racer3j Posted June 13, 2008 Share Posted June 13, 2008 Glenn- while I am no expert on stick welding, I have always allowed welds to cool at their own pace. With the shock of any quick cooling, there is usually a risk of weld embrittlement- especially at the margins. But, I recall that the issue is less crucial when you are talking of removing the slag from such a weld. A quick heat-up with a torch and natural cooling will stress relieve the weld in most cases. When tigging chrome-moly(4130) chassis welds, I would mark with Tempilaq and bring the joint to kickover-then allowed ambient cooling. The need for all of that is dictated by critical use.jet Quote Link to comment Share on other sites More sharing options...
arftist Posted June 13, 2008 Share Posted June 13, 2008 Another good reason to let the weld cool, is that hot chips of slag landing on your eyelid hurt more than cool chips. The slag also serves to protect hot metal from oxidation. Quote Link to comment Share on other sites More sharing options...
HWooldridge Posted June 13, 2008 Share Posted June 13, 2008 The slag has little insulating ability. It is there simply to prevent the molten metal from taking on harmful gases from the atmosphere so by the time you stop and chip, it has already done its job. Better to preheat the weldment if chill hardening is an issue. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted June 13, 2008 Share Posted June 13, 2008 Preheat/postheat the mass has other benefits as well as heat is pulled away from the weld by the surrounding steel *much* faster than by the surrounding air. To be really sure you should cut the weld area out from the surround steel and let it cool slowly---then you can weld it back in, grin... This is an issue in blacksmithing/bladesmithing as well when people find to their dismay that a nice cold vise or anvil can "quench" a hot high carbon piece with nary a visit to the oil or water bucket! Quote Link to comment Share on other sites More sharing options...
Joe H Posted June 14, 2008 Share Posted June 14, 2008 In general this isn't really an issue when welding mild steel. The base metal, nor the filler metal have enough carbon to harden appreciably. The slag does chip off much more easily after the weld has cooled though. The weld shrinks as it cools, and the slag doesn't. With a good weld and a rod like a 6013, 7018, or 7014 the slag will curl up like a scorpions tail and fall off by itself as the weld cools. Quote Link to comment Share on other sites More sharing options...
Ten Hammers Posted June 16, 2008 Share Posted June 16, 2008 My experience with slag has been that with prep ( removing mill scale and rust ) the weld cleans up nicer. Some rods will state letting the weld cool prior to chipping is what the mfgr wants. In multi pass flux cored welding a needle scaler is sure nice for cleanup. OTOH, the thread was about weld imbrittlement and I'm not really the guy to talk about that other than to say that I was taught to pien welds for stress relief sometimes. Quote Link to comment Share on other sites More sharing options...
racer3j Posted June 16, 2008 Share Posted June 16, 2008 An un- stress- relieved front axle tig weld on a 4130 broke my back. King pin spud snapped off in mid- corner, front wheel and the rest folded under and like a pole vault, right into a wall and several barrel rolls later, it was over. I didn't even know about the flips until 7-8 tears later when my wife and daughter told me about it. The weld failed right at a margin.jet Quote Link to comment Share on other sites More sharing options...
KYBOY Posted June 20, 2008 Share Posted June 20, 2008 Ive never seen evidence as to where it hurts. Like someone said already the flux is just a shield to keep out the atmosphere. When you get a good burn you dont even have to hit the slag. Just hit near it and it will jump off. Curl up by itself ect..I passed my stress tests while taking the slag off quickly. It never hurt those welds, thats for sure. Quote Link to comment Share on other sites More sharing options...
racer3j Posted June 20, 2008 Share Posted June 20, 2008 As I noted in my first response- I have never heard of consequences from chipping a stick weld while it is still hot. However, weld margin embrittlement is a real phenomenon,in electric welding. It is only relevant to critical joins. For instance, we did not stress relieve all tig welds on 4130- just at critical cage welds and axle welds and a few heavily loaded running gear attachment points. One advantage to torch welding is that the wider heat distribution beyond weld bead margins stress relieves if allowed to cool at its own pace. It does not matter on the vast percentage of welds. It is one of several good reasons why teaching/learning welding covers "undercut" in detail- the metal there has been thinned and carries a much higher risk of embrittlement- it knocks off points in welds examined and tested. But the risk levels in critical welds have to be recognized and that reality is demonstrated by certification at various levels of welding skill and knowledge.jet Quote Link to comment Share on other sites More sharing options...
Hillbillysmith Posted June 27, 2008 Share Posted June 27, 2008 The slag protects the weld from the outside atmosphere, cleaning purposes, and on some rods part of the slag goes into the weld. By the time that you are done welding a part, the underlying weld metal will be totally solidified and chipping away the slag will not cause any problems. I would let it cool just so the slag comes off easier and it won't hurt as bad when it hits your eye. Now if you quench your weld, THAT is a completely different story...... Quote Link to comment Share on other sites More sharing options...
arftist Posted July 11, 2008 Share Posted July 11, 2008 Hillbillysmith, I am sure you meant to say part of the fluxe goes in the weld, right? Quote Link to comment Share on other sites More sharing options...
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