Welding Chromoly to DOM Tube....?

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Hello, its been a long time since ive been on this forum.  With that said, i did a good search around here and i really did not find a suitable answer for what i need to know in this application.I am a machinist by trade, and have been doing it for 10 years now, im a self tought welder over those years as well, and i mainly MIG and TIG weld.I machine some suspension parts that require being welded into some DOM tube.  I have allways just made these parts from regular 1018 steel in the past, and never had a problem.  Well, since my shop has grown i have aquired numerous new tools and some of them being CNC equipment.   Well, this part i make is a threaded bung that drops into the end of some DOM tube, and gets welded in place.  I have recently been wanting to make these bung parts from chromoly material because of how nicely it cuts on my machines.  However, im worried that the customer may have issues with welding these into standard DOM tube.So, my question is, will the average person have a problem MIG welding a chromoly bung into a piece of DOM tube?  What problems could arrise?   Assuming these customers are plenty capable enough to weld other parts of their frame, will these people be able to weld the chromoly bungs to the DOM tube safely, and use their standard MIG wire ER70S-6thanks for your input.
Reply:A bike frames builder weld chromoly a lot this the one i would talk to  http://www.strongframes.com/
Reply:If you are thinking 4130 with MIG, the parts likes to be warmed up even when you're using E90-E100 wires that are intended to be used with it, a post weld stress relief would be mandatory if the bung has any section to it.Using 8620 for the bung the material cost and toughness go up, but the welding parameters are not as fussy. It will machine much the same.Matt
Reply:You will be fine with the 70S-6.  I always used 70S-2 if the parts were not to be heat treated.  If they are heat treating these components afterwards, use 4130 filler.Its not necessary to pre-heat tubular parts with a wall thickness under 0.095", although it doesnt hurt.  I have routinely made 4130 suspension and frame components with the above mentioned methods for years.The use of 90-100 series filler is unnecessary IMO, the yield strength of normalized 4130 is ~65 ksi, so you arent gaining a whole lot using the higher tensile filler.  The ultimate tensile for 4130 is around 100 ksi which is why some people go with that.  the link below is to Lincoln Electrics FAQ about 4130http://www.lincolnelectric.com/knowl...hrome-moly.aspMechanical Engineer
Reply:Well the DOM tube will be .125 wall , and the chromoly insert will be like a standard bung, about .375 thick at the neck.I guess what im most worried about is my customers having any problems welding this with their standard MIG welding machines, running ER70S-6 wire.   They are not going to be willing to buy a special wire or attempt any special welding process that is out of their normal welding routine , while welding their regular 1018 mild steel.With what i have listed there, does anyone think that if they were to attempt welding these bungs into the DOM tube, that they will have any issues with anything failing because of the Chromoly being welded to the DOM tube?
Reply:without knowing the stresses involved I cannot say for sure that it will hold up.But like I said earlier, you should be just fine with the 70S-6 and MIG...Mechanical Engineer