When to remove slag...

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All,Should slag be removed soon after the weld or allowed to remain for a while?  I know that certain types of heat treating, the heated metal is bathed in carbon dust to let the carbon diffuse into the material.  -Was wondering if a similar process is taking place when slag covers a fresh weld and therefore should not be removed right away..Thanks in advance...
Reply:I believe it is better to cool it with the slag in place. But the best beads will peel themselves....so...City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:RayC, interesting question, you are thinking beyond basic welding and questioning what may be happening metallurgically between the flux and weld metal.  As you said, there is a surface hardening treatment, known as carburizing that can be applied to items made of relatively low carbon steel which is easily machined, but which needs high surface strength and hardness.  This treament promotes the diffusion of carbon into the surface of the steel which is a function of temperature and time in furnace.  Depending on the steel compositon combined with the carburizing treament, the item is removed from the furnace and cooled at a high rate to form a hard martensite structure on the surface.  This then may need to be tempered at a lower temperature to reduce harness a bit and increase toughness.  I believe that for slag welding processes such as stick electrode, flux core, sub-arc, and electroslag, the  amount of time at elevated temperature is too short for continued interaction of the slag and the weld metal, and the flux composition is not intended to further react after weld solidification. The slag acts to provide protection to the solidifying weld from oxidation and nitrogen pickup from the atomsphere, but as mentioned above it is common and desirerable for the slag to self release and curl up a short distance behind the molten puddle.  Slag that sticks to the weld surface is undesireable since it can be difficult to remove and if not completely removed it will become entrapped in subsequent passes.  7014 and 7024 stick electrodes are famous for self peeling slag, as it should be.
Reply:I make it a practice never to remove the slag off a mild or low alloy until it no longer shows red. The slag aids the cooling rate of the bead. In some cases (medium or high carbon steel, tool steel and some types of cast iron and other alloys), I do not remove the slag until I can lay my hand on the work. If the slag peels off by itself, E7014, E7024 and low hydrogen SMAW and some types of FCAW, it has not proven to be a problem in my experience.
Reply:Thanks Guys...Being really new to welding, I get the urge to knock the slag off right away to inspect the weld before doing the next one.  That was really slowing me down.  Things are looking much better and now I can pretty much feel when the bead is going down right or not.And yes, I like the way 7014 just pops off and that happens to be my favorite rod -but it's probably over kill for the mild steel I'm working with...
Reply:I always let the weld cool for just a few seconds, then hit it with a wire wheel.Letting the flux peel off on its on will not work under certain applications - like welding uphill in a bevel.  Weld, wait for it to turn back its natural color (not red), wire wheel.
Reply:As long as it's not still glowing red, it is ok to remove the slag.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I was once told that slag chipping should be done as soon as possible after welding.The hotter the better.The idea was that the impacts of the hammer(peening) would help torelieve stresses created by welding.Anyone ever heard of this?Miller a/c-d/c Thunderbolt XLMillermatic 180 Purox O/ASmith Littletorch O/AHobart Champion Elite
Reply:Originally Posted by jpump5I was once told that slag chipping should be done as soon as possible after welding.The hotter the better.The idea was that the impacts of the hammer(peening) would help torelieve stresses created by welding.Anyone ever heard of this?
Reply:It's going to be difficult to cooridinate your welding and chipping of slag to perform any special metallugical or mechanical treament to the weld metal at any certain temperature.  As far as I know there is no practice of special timing to remove slag while the weld is at a special temperature.  Yes there is interpass temperature control on some high alloy, hardenable steels, but the common practice is to run the rod to the end, lift your hood (the old fashioned type), look at what you've done, then begin to remove the slag, and by that time the weld is certainly cooled way below the "red hot"  temperature.  Slag removal on a well made stick weld, one with a smooth surface, and smooth tie-in at the weld toes, will release easier than a coarse/undercut weld, and with rods like 7024 and 7014 that lay in on flat welds like butter, the slag self peels just behind the molten puddle.
Reply:Originally Posted by pulserIt's going to be difficult to cooridinate your welding and chipping of slag to perform any special metallugical or mechanical treament to the weld metal at any certain temperature.  As far as I know there is no practice of special timing to remove slag while the weld is at a special temperature.  Yes there is interpass temperature control on some high alloy, hardenable steels, but the common practice is to run the rod to the end, lift your hood (the old fashioned type), look at what you've done, then begin to remove the slag, and by that time the weld is certainly cooled way below the "red hot"  temperature.  Slag removal on a well made stick weld, one with a smooth surface, and smooth tie-in at the weld toes, will release easier than a coarse/undercut weld, and with rods like 7024 and 7014 that lay in on flat welds like butter, the slag self peels just behind the molten puddle.
Reply:yes, we could get 7-8" to curl up when goofing around at school.  Keeping it in one piece as proof is a whole nother deal.My name's not Jim....
Reply:If I am skipping around from side to side I like to run a few beads and wait till it cools because it always has a way of finding my bare skin! If I am running a continuous bead, I guess I wait about 10 to 20 seconds before chipping it. I don't know why, its just what I do."Where's Stick man????????" - 7A749"SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55"I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding"Stick-man"
Reply:I wait a little just because hot slag to the face does not feel any better than hot welding sparks to the face.
Reply:Slag?  What slag?  I love OA welding Hobart LX235Victor 250 Oxy-Acetylene Rig (welding and cutting)Bobcat 773F-350, 1999, 4x4, 16' 10K# trailerOutdoor Wood Burner - 10 cords/year
Reply:Only time I remove slag prior to paint prep is when I have to clean for another pass, or have intersecting beads on corners.  Otherwise it saves time to leave the stuff on until paint prep."Any day above ground is a good day"http://www.farmersamm.com/
Reply:I think peening for stress relief is more for cast iron.200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.
Reply:I weld a fair amount of carbon steel socket weld pipe fittings. I usually lightly chip the 7018 bead as soon as the glow stops, and then I get on it right away with a wire buffer. This leaves a beautiful bead and smooths the bead a little while polishing out a slight amount of undercut.
Reply:Unless its inside the bevel, my slag always falls off right off . I was told that if your amps are too high or your pipe is too hot, the slag will be a little harder to bust off. True ?
Reply:On hot and fill passes I leave it on but for the caps I remove it so my restarts are smooth. I hate to see lumps on restarts it shows poor craftsmanship and when I inspect a weld where I can't feel or see the restart I know they are good at what they do.