Hardened steels

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Hello GroupI am making an ebike delta trike, ( atomic zombie ) and need to weld a hardened free wheeling hub to a hardened sprocket, I have machined the sprocket so it is a loose fit in the hub, I am unsure of how to weld it, I have a mig and access to a tig, ( my stick welder was lost in a workshop fire and was replaced with a bigger mig ).The link below shows what I am comfortable with, can anyone suggest if it is weldable and how - or should I just get a welding professional to do it.http://weldingweb.com/vbb/showthread.php...ht=Ring+roller.Thanks, Ed
Reply:My 1st thought would have been to undersize the sprocket and heat it, freezing the hub and press them together so you end up with an interfearance fit..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I use Eutectic 680 for tool steels,but it's a stick rod. You could probably get by using ER309L TIG wire, but keep in mind that welding will affect the hardness.
Reply:I'm thinking that sprocket and hub may have been tempered after hardening,Welding them may reharden them,making them brittle(at least around the welds).Or maybe the heat would over-temper the parts making them wear faster.Depends on what type of steel,how much heat is applied and how quickly parts cool.Miller a/c-d/c Thunderbolt XLMillermatic 180 Purox O/ASmith Littletorch O/AHobart Champion Elite
Reply:Do you have any idea what steels were used? What about silicon bronze applied with the TIG? That would reduce the hardening effect, but still could cause some tempering near the junction,  probably causing no problem. Have any other similarly hardened steel to practice and do a test with to be sure? Perhaps a bolt-together-collar would be better. Just need enough strong fasteners to take up any side thrust; could increase the clearance between the two parts so a locating ridge of the collar fits in and through, and into a recess on the second part. Assembled cross section like an H  with the though bolts keeping the two parts from spinning wrt each other.
Reply:i would just bolt it to the hub... if you dont know what steels you used to make it its going to be tough to weld it correctly..  i have welded a bit of heat treated h13 toolsteel (around 44rc)with a filler rod called marweld made by eureka, its pretty forgiving material..   but if you dont know what steels your welding its pretty much a crap shoot if it works or not.... i've mainly used it when rebuilding die cast and plastic injection mold cores and cavities, to build up (tig weld) cracked and broken cores, cavities and cams..  it is some tough stuff. we also heat treat it.. i have also used it to weld 4140 prehard for myself and it worked fine, very good actually..   also alot of sprockets are just case hardened..  heres a copy and paste from eurekaweldingalloys.comEureka Marweld 250For the repair or composite fabrication of die casting dies, plastic molds, extrusion dies, mandrels, dummy blocks and cold heading dies. Also for repair of maraging steels in general. Excellent for overlay of axial cones for ring rolling.A nickel, cobalt, molybdenum, titanium, aluminum alloy which develops machinable deposits that are in the 30-32 HRC range as welded. The as welded deposits are in the solution treated condition. Further heat treatment (aging) at 950 degrees F increase hardness up to 49 HRC and yield strengths of 250,000 psi. Although the deposits possess an exceptionally high strength, they also exhibit a high level of toughness which lends themselves perfectly to heat checking and erosion type environments.Last edited by brucer; 06-20-2011 at 12:48 AM.tackleexperts.comwww.necessityjigs.comhttps://www.facebook.com/groups/mach...dingequipment/