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Up Topic Welding Industry / Technical Discussions / 4130 voids
- - By Tommyjoking (****) Date 04-19-2007 08:49
Hello all,

I am currently a welder on aircraft...(formerly pressure vessels, pipe work, heavy equipment field work).  My question is in regards to tig welding on chrome moly (4130) material.

I must regularly weld 4130 billet and tube extrusions together with fillets and butt joints...because the part is chrome plated many welds (butt joints) are ground and polished prior to plating.  Myself and others are experiencing very very tiny voids in the weld after grinding.....they look like microscopic pinholes.   We only see these on the welds that are ground flush and they interfere with the plating process....they definitely show thru if not reparied by spot welds prior to plating.  Please understand these "voids" only show up under magnyfiying and intense light.    

We have tried everything from diffuser cups to anal cleaning before welding.  Nothing has seemed to have any effect.   Is this common to the material or what??  Note: we have all passed strict kodaks bend tests etc. on this material!

ANY HELP would be greatly appreciated!!!!
Parent - - By awill4x4 (**) Date 04-19-2007 11:50
We also do a lot of 4130 welding mainly for the motorsport industry here in Australia. I am assuming (and please correct me if I am wrong) that the problem is occurring when you join the thinner tube section to the thicker billet section?
We have similar problems where we are joining 2.5" X .095 tubing to "cotton reels" 1 3/8" diameter with a wall thickness of approx 3/8" to 1/2" and we find we get better results when we preheat the "cotton reels" to the point where you can't hold them in your hand.
If we don't preheat you can sometimes see what appears to be little voids forming as we weld, it doesn't occur when welding thinner tubes together though, only when welding thinner tubes to thicker sections.
We use ER70 S2 filler wire on most of our welding and get very good results as a rule.
Regards Andrew.
Parent - - By js55 (*****) Date 04-19-2007 14:05
70S-2 will often show little pepper like void/inclusions when used in multipass applications. It is actully inclusions of Ti, Al, and Zr.
Parent - - By Bill M (***) Date 04-19-2007 15:26
Just curious - wouldn't 4130 fall into a high strength low alloy steel catagory vs. a chrome moly steel?
Parent - - By js55 (*****) Date 04-19-2007 15:37
Yes, it would. But using CS fillers on some low alloys is not unheard of. Especially when the weld metal may demonstrate greater strength or ductility than the HAZ. It depends on how its engineered and the service intended.
Parent - By Tommyjoking (****) Date 04-19-2007 22:58 Edited 04-19-2007 23:13
Your right  awill4x4 in that where the tubing and the billet are joined is the most problematic area.  The difference in thickness is .049 wall tube to .125 billet  (machined area from 1/2" stock).   The metal is cleaned with scotchbrite and then wiped with epoxy thinners.  We weld on both sides of this joint a fillet on one side with a butt weld on the oposite side.  The welds look fine everytime  ....until we grind the butt weld flush with the surface.....then we see the voids and the look like tiny pinholes.  I have tried a bit of preheating but i may not have the temp right.  Next time I will experiment more with preheating it and see what happens.   We have put backup gas in the tubes as well without any success.    BTW.  we are using AMS 6457   4130 filler, 2% thiorated tungsten and 100% argon. 
Parent - - By chuck meadows (***) Date 04-20-2007 02:09
Bill,
  Actually, a 4130 is an HTLA steel (Heat-Treatable Low-Alloy). HTLA steels are higher in carbon and lower in moly than the chrome moly steels. Electrodes comparable to the 4130, but with lower carbon, may be suitable for certain applications in which lower joint strength is allowed than the base metal. Matching electrodes for 4130 are covered in ASM specifications 6457A. Type 309 and 312 stainless steel, and nickel alloy ENiCrFe-3 filler metals can also be used if the lower joint strength is permitted. The lower strength filler metals can reduce the risk of cracking in some applications. Joint strength is dependent of the following:
1. electrode selection
2. base metal thickness
3. joint design
4. welding procedure
5. amount of uniformity and dilution
6. response of the weld metal to the applicable PWHT

Chuck
Parent - - By Tommyjoking (****) Date 04-22-2007 05:15 Edited 05-11-2007 07:19
ALrighty   I misspoke I am a bit lethargic and ignorant of my alloys....generally I just go with whatever the spec they ask for requires.

I heard it called that (chrome moly) and I went with it....its amazing how easy it is for ignorance to perpetuate but difficult for knowledge to survive intact.    However I am not alone in this:

http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp

http://files.aws.org/wj/2006/12/wj200612/wj1206-24.pdf

http://www.aircraftspruce.com/menus/search.php?sec=&s=4130

But I still need somone to shine some light into why this problem is occurring ....it is a real headache, slows us down a lot and it reduces the quality of the finished product.  I keep thinking the tube we are using is contaminated...I find a lot of pits in it from time to time....however my hands are tied on the material because it has been "certified".  I intend to experiment with some subtle preheat next week, but other stratigies and ideas are most welcome on this subject.
Parent - - By Tommyjoking (****) Date 05-11-2007 07:31 Edited 05-11-2007 07:49
awill4x4    THANKS MAN!!!!!

I went back and tried preheat on the thicker material till a got a light gold color..(400 degrees maybe:?)  And I have had great results so far!!!   About a 99% improvement!!!  After a bit of research it seems that preheat is highly recommended as well as strict cleaning and backup gas where possible  (all were already being applied except for preheat).  Applied the preheat to a .250 section that gets welded to the tubing and had good results there as well.

I am still having tons of trouble with the tubing and sheet stock  >(.049 tubing and .063 sheet).   Sometimes it comes out with almost no flaws sometimes many.  I will experiment with preheat on this as well but it will be trickier because the parts are much smaller and delicate....the welds always look perfect until they are ground away.   I wish we could switch to a 309 filler...somthing in my welding gut just says that would eliminate it entirely.  Trying to butt heads with engineering on that would be a hard row to hoe I figure.  I am not absolutely sure but I do believe that the parts get heat treated so I assume thats why we are using the 4130 filler.  Gonna do some checking on all that.  Heck at least I am learning somthing along the way.
Parent - - By reddoggoose (**) Date 05-17-2007 16:56
Tommyjoking,

Have you guys tried cleaning the filler with some scotchbrite right before welding? I would be curious to know if this would have any effect.
Parent - By Tommyjoking (****) Date 05-18-2007 06:43 Edited 05-18-2007 06:55
we normally clean the filler...with solvent or just a laboratory wipe before use....if it looks like it needs scotchbrite we chunk em.

As far as the problem goes I am considering it for at least the most part SOLVED.....Preheat of ALL the joints is having good effect.  Backup gas, and rigorous cleaning will still be used...but the preheat is eliminating 95% of the problem for me.   That really makes me think that its humidity and or mosture content in the metal itself.   That would help explain why the problem seems much worse at times then others...with the same lot#(batch) of material.   I have went from having maybe 35-50 spots to repair down to 3-4 max.

Thanks to everyone for the efforts and advice.
Up Topic Welding Industry / Technical Discussions / 4130 voids

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