too cold?

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tigging 1/2" ms..20 degrees in my work area...ta185 at 180amps..3/32 1.5% lanth, 3/32 er70-s2..tried to get a few tacks on a project because my usual  outside stick welding spot had snow falling..tacks cracked..i guess i needed to pre and post heat? Attached Images
Reply:If it were me and not too critical, I would just pre heat although a little post heat or something to slow the cooling would not hurt.1/2" is pretty thick and will draw the heat away form your welds fairly rapidly.Miller 185Lincoln Weldanpower 225Lincoln 225 buzz boxCheap-o C&H 110v (my first welder)
Reply:I would be concerned about your host material being that cold, let alone your welds.
Reply:bump over spamCo-Own CNC shop:Miller :1251 plasma cutter, MaxStar 700 TIG/Stick, & XMT 456 Multiprocess Welder.&  2 Hypertherm HPR260's Plasma CutterSorry I had a bad stroke but now I am back.
Reply:It could be that you're too cold or maybe try holding your post flow on your weld/tack a bit longer. If I was welding 1/2" material, I would probably run at least 250-275 amps. How this helps. Like I always say, "go hot or go home." Go hot, or go home!
Reply:I would definitely try to preheat that. I like stuff to be at least room temperature. If it is real cold like that the moisture in the steel can give you issues.
Reply:There was a thread on here a while back talking about this issue. The brittle regime for mild steel starts at around freezing, so you can have issues where your penetration ends and the cold part of the host metal starts. I think the prescription was a wide swath of preheating.
Reply:For that temp your working at and the thickness of that material, use pre heat.This looks like a job where a heavy duty stick welder with 7018-1 would shine.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:I would use at least 220 amps on 1/2", and I would also use 1/8" tung. I don't doubt that the cold plays a part in the failed tacks."SOUTHPAW" A wise person learns from another persons mistakes;A smart person learns from their own mistakes;But, a stupid person.............never learns.
Reply:Most likely cracked from too small of a tack in a restrained joint.  Several of them appear to initiate as crater cracks.
Reply:Warm it up with the gas torch first.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I would agree that it could use a pre heat, to at least bring it up to room temp, after that I would strongly recommend 250+ amps.
Reply:The metal is too cold.  Code calls for any ms 1/2 + be pre heated.  I'm not sure on the heat, but I would think atleast 350 - 450.  Get yourself a heat stick, a rose bud, and some 1/8 tungsten and you could have tacked that at 120 amps and been fine.
Reply:Preheat, don't worry about post heat.