welding 4130 chromoly tubing

[swamper8]

hello,
Can anyone give me tips on welding 4130 chromoly tubing? I.E. best tungsten material, argon flow rate, cup size etc. Also, what is the best filler rod? I used the miller calculator but would be interested in someone's real life experience. I will be welding plate up to 1/4" and tubing up to about .05" wall thickness.
Thank you

[Bodybagger]

Use ER70-S6

A lot on this subject has been hashed out with the aircraft homebuilders. The consensus is that er70-s6 is the best filler for light tubing because it picks up enough of the 4130 alloy to do the job. You can obtain a 4130 filler, but you have to heat treat the whole assembly afterwards. Is the plate REALLY 4130?

[Laiky]

1st describe what it is your trying to do. The experts here aren't going to give general info on Chromoly since it is usualy in critical applications, and the reccomendations are a little specific and complex.

2nd do a search, this topic has been very well covered.

[swamper8]

Yes, the steel is definitely 4130. I am not doing anything quite 'mission critical'. I was going to build a recumbant bike frame out of 6061 aluminum but my TIG welder is flaking out in AC mode. So I have to switch my project frame to 4130 chromoly instead. I was just looking for some basics, I am a new TIG welder. I will do some searches under keywords 4130 or chromoly and read other posts............................................. .......

OK, looks like 1/16 to 3/32 2% lanthanated or cerated tungsten. Argon flow of 10-15 CFH. #6 or #8 cup size. And either ER760S-6 or ER70S-6 filler? I saw different references and i'm not sure if they're the same.

[Aerometalworker]

Right,
The subject has been hashed out to death

For what your working on, by the books I would suggest something along these lines.

Filler-ER70s-2 or -6
Tungesten-old standard is 2% thoriated....others will work though
Argon flow and Cup size depend on your joint configuration.
Cleaning-Clean ALLLLLLL oils from the base material and filler, use a non heavy hydrocarbon solvent of choice and be sure its all evaporated before welding.

now the following is more technical in nature, but by the books, proven and the safest. Absolutely required for what your doing? maybe not, but why risk it, its easier to do it right the first time then re-weld and paint later.

After welding, after the part has cooled, use use localized heating ( oa torch )to evenly bring the joint to around 1200 degrees F ( dark dull red in indoor lighting ). I suggest temp sticks to get the hang of it. Keep it there for about 1 hour per inch of metal thickness, ends up being only a minute or 2 on thin tubing. Slowly trail the torch off and let it cool in still air. Note that this is not normalizing, or true annealing...this is tempering. Places in your base material will have untempered martensite in them after TIG welding, this structure needs to be tempered to help prevent brittle fractures over time. This also helps hydrogen migrate from the material should it have been absorbed durring the welding process ( vaporizing oils on the metal and moisture in the argon are known sources of this ) and therfore helps prevent hydrogen embrittlement.

Sounds like a fun project!! Have fun and be safe!

-Aaron

[swamper8]

Thanks! I was going to post another question for a better description of annealing. I have a mapp gas torch and a acetylene torch. Will the mapp gas get to 1200 degrees? Also, is this process necessary for a simple recumbant bike frame? I will be gusseting each joint as well and I weigh under 200lbs.

[Aerometalworker]

Thanks! I was going to post another question for a better description of annealing. I have a mapp gas torch and a acetylene torch. Will the mapp gas get to 1200 degrees? Also, is this process necessary for a simple recumbant bike frame? I will be gusseting each joint as well and I weigh under 200lbs.

I would stick to the OA torch, the chemistry of the flame of a MAPP torch may not be a good mix for base material, ill have to dig to be sure though.

Is it necessary?? Thats entirely up to you to decide along with the design of the frame. The loading and fatigue applied to a portion of your frame might be the same as the engine mount for a jet turbine. Since loading is a function of both force and area, its easy to see how critical things become the lighter and smaller you make your frame. The old road racing bicycles were very light and very marginally designed, therefore every bit of joint ductility was needed. A heavily over designed joint may not have any fatigue issues, but how do you know its over designed? Its that giant "question mark" that leads me to doing all I can to improve weldment reliability. Unless I know for sure that the loading is light enough to not need every bit of the materials fatigue strength, I play it safe. Although if the part in question is that over designed....then its just wasted weight and material.

-Aaron

[swamper8]

Well I like to do things right so i will probably try my hand at annealing. Do I have to anneal the joint soon after welding? Or could I fab up my frame, assemble my components and fully test my design to make sure I won't be cutting/modifying any of my joints? It'd seem like a waste of time to weld and anneal a joint then possibly have to modify it later because my design needs tweaking.
Where can I get temp sticks? Would my local welding supply store have such a thing?
Thanks

[Aerometalworker]

Well I like to do things right so i will probably try my hand at annealing. Do I have to anneal the joint soon after welding? Or could I fab up my frame, assemble my components and fully test my design to make sure I won't be cutting/modifying any of my joints? It'd seem like a waste of time to weld and anneal a joint then possibly have to modify it later because my design needs tweaking.
Where can I get temp sticks? Would my local welding supply store have such a thing?
Thanks

Nope you can go through the joints after the whole frame is welded, no time limit. I buy my temp sticks from MSC ( www.mscdirect.com).

Another little tip, if you use a jig of any kind, dont make it too ridgid. If you restrain the parts while welding you can have "hot cracking" of the material as it cools. Allow some slop in the jig for expansion and contraction. For what your doing 1/8" allowance should be fine for most of the parts. Jigs that slip ( i.e. magnetic clamps) are fine as well as they allow the parts to move upon cooling.

Oh and be careful when using the term "annealing". Technically its tempering, but historicly its been called "Stress relieving" , " Torch annealing" , and "Normalizing". I too find myself using different names for it depending on the audience.


-Aaron

[swamper8]

OK,
So I went to my local welding store to pick up some ER70S-6. Not only did they not have it but no one thought that would be the right filler for 4130 anyway. They thought maybe ER80S-6 at first, but after asking around they think I should be using actual 4130 filler rod. So I got two lbs just to save a trip back. What does everyone think of this?

Also, they didn't have ER70S-6, however my local harborfreight retail store has a MIG spool of ER70S6 on sale. Can I buy this spool and just use the wire like it was a straight piece of filler? It does not have a flux core or coating.

Thanks

[Aerometalworker]

OK,
So I went to my local welding store to pick up some ER70S-6. Not only did they not have it but no one thought that would be the right filler for 4130 anyway. They thought maybe ER80S-6 at first, but after asking around they think I should be using actual 4130 filler rod. So I got two lbs just to save a trip back. What does everyone think of this?

Also, they didn't have ER70S-6, however my local harborfreight retail store has a MIG spool of ER70S6 on sale. Can I buy this spool and just use the wire like it was a straight piece of filler? It does not have a flux core or coating.

Thanks

First problem was asking a welding store a question like that. Anyway Per the real welding and engineering handbooks, normally 4130 filler is only used when the entire part will recieve an actual post weld heat treatement. I cant believe they didnt have ER70s-2 or -6 in stock. Yes you can use the -6 from a mig spool, just get the heaviest you can to avoid "tiny weld" syndrome. Note that there is one individual in this country pushing 4130 filler and TIG, cant believe everything you read in a Home Depot welding book. When looking at strengths of a weldment, it must be remembered that there is interalloying between base and filler material, so just because a filler is 70ksi , does NOT mean the weld itself will be 70 KSI.

-Aaron

[Laiky]

i would just mail order .045" or 1/16" filler from cyberweld.com or who ever. The mig wire always wan'ts to curl up and is never straight.

[ASKANDY]

Er80s-d2

Most of the 4130 tube chassis we do in Drag racing or 4130 suspension parts we use the ER80S-D2. The strength is closer to than the 4130 base metal and does NOT rely so much on base metal dillution with the filler to make up the strength loss in using the lower ER70S-2. The elongation percentages are great and it does not require post stress relieve like a full 4130 filler. Because 4130 is heat sensative, keep your tig arc lengths low but use enough amperage to properly tie in the toes of the weld. Higher arc lengths will cause the machine to have to put out more voltage to keep the amperage steady and since Volts X Amps = total watts and watts is heat, keeping the arc length lower will be better.

hope this helps.

A

[Bodybagger]

Wow.

Looks like another person has yet been led down the path of hassle of welding with 4130 filler rod by a good salesman even after being told by others that it is not the best choice.

I can't help but think of all the bickering on usenet in the 1990's on the homebuilt aircraft newsgroups about welding 4130 tubing, and how many people ended up eating humble pie over this after learning the hard way.

At least he's not building an airplane!

[Aerometalworker]

Looks like another person has yet been led down the path of hassle of welding with 4130 filler rod by a good salesman even after being told by others that it is not the best choice.

I can't help but think of all the bickering on usenet in the 1990's on the homebuilt aircraft newsgroups about welding 4130 tubing, and how many people ended up eating humble pie over this after learning the hard way.

At least he's not building an airplane!

Yeah tell me about it. That and people worrying about the strength of the filler. You can have a 150ksi fillet if you want, but there is an area outside of the weld thats annealed to about 75ksi anyway. Thats why the engineering books use the annealed strength of the material when doing weldment design.
-Aaron