Tig welding chromolly with 4130 filler rod

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hi i have tig welded a roll cage made from 4130 molly and have used 4130 filler rod . i have just found out that i should of used ER70 S2 filler rod to prevent the weld from being too brittle .The 4130 rod is only used if you are heat treating the molly after it has been welded from what i can tell.would it be a safe cage and carry on with the build or not? any thoughts . i would't like to have to cut it out and start again !
Reply:The short answer is 4130 is direct hardening, and you may have quenched areas. The HAZ is similar no matter the filler. The real nasties show up when welding sections of different mass.If it were me in the car I'd at least try to draw back the welds with a large propane/air torch.Matt
Reply:No.  If the cage even held up through the vibration and chassis flex, it would almost certainly fail right at the weld on any sort of impact.
Reply:Matt has it right. Draw down (temper) the weldments. Bring them up to a dull (blood) red ( about 1200F ) evenly and keep it there for 15 min per inch of metal thickness. On most tubing structures its just a minute or so. Slowly back the torch off again keeping the heat even. Age old problem with 4130, and like Matt said, the effects of tig welding to the base metal is reguardless of filler metal selection. This is a BIG bit of information that for some reason is not common. You can pick any fancy filler you want, but the base metal next to the fillet will be affected the same, and thats where the majority of failures start. So as the old ( and wise ) saying goes, if your going to Tig it, temper it. Common guys, we have been using this material for 90 years, had it figured out once.....its not a mystery.
Reply:most people aren't used to the requirements of 4130 from a welding perspective. especially the home hobbyist type. For future reference:min preheat 60 degInterpass temp: 350-500f (i.e keep it above the PWHT temp)post weld heat treat 200-300 for 15 minutes (per inch thickness)we just hit them with a rosebud for a bit then throw a weld blanket over it for a slow cool.That's coming right from the mil spec aerospace GTAW spec. For thin wall it's not that hard.For already existing structures it's hard to say,  you can always make another mock up joint welded it exactly how you did then break it or take straps and bend them/ tensile pulls.  That can at least give you peace of mind that it's somewhat alright.Last edited by Metarinka; 05-25-2010 at 02:41 PM.Welding EngineerCertified Scrap Producer