70s-2 works well if you don't harden it later. Personally I use er80s-d2 to more closely match the base. Base metal dilution brings the weld up to strength. Post weld stress relieve is recommended to stabilize the HAZ.

If you do harden it you would be required to use 4130.

 

If you want to do this right, here you go:

1. Find out what kind of "chrome-moly " the base material is. You need the ASTM number- to find out the relative amount of Cr and Mo in the base metal. ( 1.25CR/.5Mo, 2.25Cr/1.25Mo, etc etc.....................

2. When you know the answer to number 1, you can then choose the appropriate filler material.

3. Stress relieving may or may not be required depending on (1,2) above. With the relatively low thicknesses used for the components you are assembling, it is unlikely PWHT ( post weld heat treatment) will be necessary.

 

Good call. I was thinking of it as 4130. I think but I may be wrong, but 1/8" or less does not require stress relief after weld.

Er70-s2 should be fine as Flyswatter,,,,,I mean Zapster says.

 

Use the 70S-2 and call it a day already....



...zap!

 

http://www.millerwelds.com/resources/communities/mboard/showthread.php?15570-Best-welding-rod-(tig)-for-welding-4130-chromoly-tubing

Apparently there are differing opinions ...................Here is a discussion regarding 80s-D2 filler. ( The D2 refers to 1/2 Mo..... and the 80,000 psi tensile is more closely related to the properties of 4130.......)

I guess I took a more technical approach ( part of my job is to review welding procedures ) rather than a commercial/ shop approach.

Good luck!

 

If it were my stuff I'd go with er80s-d2. Huge debate regarding this subject.

 

80s-D2 is all I use as well I have it in.035, .045 and 1/16th. For a lot that I have seen prep and fit should be the most important, If it is a big snake hole It won't matter what filler you use. And I always warm the joint but then I live in the moldy NW.

 

I use er70s-2 for 4130. As has been said, there is a lot of debate over filler choice. For weldments that will not be heat treated (hardened) after welding, Lincoln suggests er80s-d2 as a first choice with er70s-2 and er70s-6 as perfectly suitable second choices. 4130 filler would only be used on weldments that will receive PWHT.

I have not seen a definitive rule regarding wall thickness about when to anneal. I have read and heard that anything thicker than 1/8" should be preheated. I'm nowhere near those thicknesses though.

 

70 S 2 and you are done !!!

 

Thanks everyone for your advice, opinions. I did a modification to a chrome moly stand last night at the client's request using 70s-2, 3/32" rod. Came out fine. The client wanted to check out my welding before putting me on his chassis. He was satisfied. The actual project will begin next week. I also picked up some 1/16" 80s-d2 to have on hand for periodic welding on chrome moly bicycle frames that come my way.

Thanks,

Tony

 

Tony, if you ever want to try some 0.045 or 0.035 filler on the thinner stuff, drop me a private message and I'll send you some. 1/16 is pretty thick for bike frame work. Have fun!

 

Hi Zank,

I'll pm you shortly on that. Interesting you mentioned this to me because the reason I braze chrome moly bike frames is because the first time I attempted to tig weld one, it poked a hole in an instant. Therefore I backed off and began brazing them. I've done several dozen either repairs or modifications on such frames. At what amperage would thin bike tubing be tig welded? Would I need thinner than a 1/16" tungsten to do it?

I picked up an .040 (I think that's the size) tungsten one day (gas lens and collet) at the welding supply just to have on hand for the day it becomes needed. I haven't yet had to use it but maybe that's the size to use for frame tube welding. What do you think?

Thanks,

Tony

 

I'm fairly new on here so you may dismiss my comments but here goes anyway,

Theres a company over here Robinson race cars who i consulted a few years back regarding welding chromemoly tube as they build a lot of pro-mod drag cars,
They always use A15 filler rod, known as Er70s-2 ?

I looked into it and that filler is approx 85% of the strength of the chromemoly base material so its recommended to make the weldpool 10-20% larger to compensate for the weaker filler material.

A Robinson race car recently crashed badly at nearly 200mph and the chassis was inspected afterwards and apparently no welds had torn apart, only a few tubes fractured in other areas.

 

I have welded a frame or two, and use a slightly different approach than Zank, though his sounds good too.

Using a Dynasty 200dx, I generally set the machine to somewhere between 120-145 amps, with a 1.5 % lanthanated 1/16" tungsten, and a pulse rate of 1.6-2.4 pps. I use 30% on, and 5% background amps. Obviously, you need to control final amps with the pedal, but once up and moving, I generally have it floored, or close to it. I use .045" ER70S-2 filler for most joints, but often use 1/16" rod in joint areas with acute angles, so there is a little less sharp transition between tube members (lower stress). Using this, I can pretty easily weld down to .6mm (.023") tubing without making holes. One benefit of doing this is that you get smooth weld toes without burning through.

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Man, such beautiful stuff. Do you work at Co-Motion? Awesome bikes.

 

I am not getting notifications so I wasn't aware there was more activity on this thread. I didn't end up getting the project on the frame as the client wanted me to miter the tubes, something I am not equipped to do besides trial and error fitting, grinding, filing, fitting again, filing, etc. , etc. I don't have a lot of experience with tubes beyond welding on them but not fabricating them. The welds on those bike frames look like a work of art. Nice work!!!

Thanks,

Tony