preheating to prevent hardening of mild steel?

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I'm welding mild steel up to 16 gauge, with 3/32 6013 rod at 55 amps. No burn through and using flattened brass pipe for a backer.After air cooling ,the steel surrounding each weld is 3 times stiffer, to the point of possibly being brittle.Will pre-heating and post-heating reduce this "tempering" effect? Will hammer peening the weld sites when still glowing also reduce hardening? (Hammering does reduce the stress in each weld, but the heat tempering is stubborn.)(Each weld is a small button woven in c-pattern, there are no beads being run)
Reply:Are you certain of your base material?  Low carbon steel does not see any appreciable hardening through welding.
Reply:I agree with Supe. Any pictures available? Maybe the new geometry of the part just makes it seem ( or actually be) stiffer. Stiffer does not necessarily mean the metal is harder.
Reply:No pictures yet, sounds like I'm just misinterpreting thingsCould it be simply be local heat warpage that gives the sheet metal that  stiffness?I've got to try this on a carbon steel, like a spent hacksaw blade, for comparisonI was really surprised with the dramatic stiffness after stick welding mild sheet. Up to this point I've only done O/A hammer welding and the metal from oxy welding stayed buttery soft if never quenched.
Reply:On a high carbon steel like the hacksaw blade, it will likely snap fairly easily.More than likely, the buckling affect and distortion is providing this additional rigidity that you're referring to.
Reply:Mild steel does not have enough carbon in it to harden through heat treatment.Welding mild steel 16 gauge sheets with 6013 will not have or add enough carbon to make the steel hardenable through heat treatment.Just what weld are you making or trying to make?Lincoln says 3/32 6013 (Fleetweld 37) electrode runs AC at 75 amps for a lap joint on 18 gauge material, 70 amps for a flat (1F or 2F) fillet on 18 gauge material.Brittle?  As in it shatter-like-glass if you whack it with a hammer?  Or do you have something else going on there?A picture (photo or even just a sketch on some paper or the computer) might help us help you.  The best laid schemes ... Gang oft agley ...
Reply:low carbon mild steels won't appreciably harden as mentioned.  However they will get harder than the annealed condition to a noticable degree.yes preheat and a slow post heat will help keep them in an annealed condition. It could also be that since your welding thin material the extra thickness of a weld bead is increasing their stiffness. Similar in the way to folding a sheet of 16 gauge makes it significantly stronger.  Also residual weld stress can put things in tension or compression making it harder to cold work.My guess is this is more an issue of residual weld stress and changed geometry than work hardening.300 f preheat,. Slow cool with a blanket. If you still have trouble then it's not a work hardening problem.
Reply:The difference between your O/A weld and your stick weld, besides being a matter of heat input, could also be due to the filler material you're using. If you were using 45R for O/A welding, it's lower tensile strength could have been a contributing factor to the metal being easier to work. The 6013 has a higher tensile strength, so could possibly make the metal stiffer, depending on the geometry.
Reply:I've seen 2 "brittle" posts recentlySimply put.....................you're welding thin guage A-36 steel (36k tensile strength), with a rod that develops 60k tensile strength.  The weld will always be less flexible than the parent metal.I don't know crap about TIG, just what I read here, but a fusion weld might be what you're looking for to preserve the ductility of the metal in question.  No filler in a fusion weld.Same with spot welds on thin sheet metal."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Oops, same thread, different day Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:All of these replies are excellent input. There is unique metallurgy in every weldThe weld metal is indeed harder than parent metal, maybe harder than the 6013 electrode itself, before meltingIt's that ring of "bluing" around a stick weld, where the nearly molten steel oxidized outside the shielding gas, that's where something funny is happening. I've got to try TIG with argon!
Reply:Originally Posted by StickLandingI'm welding mild steel up to 16 gauge, with 3/32 6013 rod at 55 amps. No burn through and using flattened brass pipe for a backer.After air cooling ,the steel surrounding each weld is 3 times stiffer, to the point of possibly being brittle.Will pre-heating and post-heating reduce this "tempering" effect? Will hammer peening the weld sites when still glowing also reduce hardening? (Hammering does reduce the stress in each weld, but the heat tempering is stubborn.)(Each weld is a small button woven in c-pattern, there are no beads being run)
Reply:Amperage is so low your rod may not be producing enough shielding gas. Also, If you are moving to slow even at a lower amperage you can still increase the heat affect zone (see joule input*) and cause a migration of delta ferrite into the slowest cooling area. I would suggest using a smaller diameter rod (1/16th) and see how it does, I think you'll find it works a lot better. Common mistake is to try and use the biggest rod you can burn to increase weld deposition; but, there are significant dues to pay. *Go to this URL for more info on heat input: http://www.kobelco.co.jp/english/wel...les/v3n4,7.pdf
Reply:Originally Posted by farmersamm...I don't know crap ... but ...  No filler in a fusion weld....
Reply:Originally Posted by Lefty LucyIf I welded steel, brass, ice, wax, aluminum, glass, titanium, or anything else that I could fuse together, do you mean that it wouldn't be welded if I used a filler?  Am I wrong or is "fusion weld" about the opposite of a oxymoron?  Is not "fusion weld" redundant?Sorry, I'm just playing around.
Reply:Originally Posted by stampif, for example, you braze 2 pieces of cast iron together, or silver solder a joint, then you use a filler but they are not fusion welds, its more like they are chemically glued together.but you're right, if you use any process where you get a molten pool and mix the parent metal with the filler then its a fusion weld. i'm not sure what farmersamm means.
Reply:There have been many heated arguments over fusion welds on this board"Any day above ground is a good day"http://www.farmersamm.com/
Reply:There have been many heated arguments over fusion welds on this board
Reply:i've heard the term "autogenous"  tp describe a weld  of parent metal with no filler added. such as is possible with oa or tig.