GMAW shielding gas for Duplex??

Date 07-12-2007 23:54

A combination of 98% argon/2% oxygen is normally used, but an addition of 30% helium will improve fluidity and penetration. Some specifications will require a certain amount of nitrogen be added to the shielding gas (argon/nitrogen/oxygen) but no more than 3 % nitrogen is recommended because the nitrogen can possibly lower the austenite/ferrite balance to unacceptable low limits. Much success has been achieved by usiing the 98/2 combination.

Chuck

By js55

Date 07-13-2007 14:28

I don't necessarily want to make this too complicated because Chuck's suggestion is excellent, but I think this could generate a very interesting discussion.
Mixtures of Argon, Helium, CO2, Oxygen, and Nitrogen have all been used with success. Some however more in research type applications or exotic higher alloys. The variables to consider are: What alloy are you working with? What transfer method are you using? What is the diameter of the pipe you are welding? Or the wall thickness?
If 2205, keep it simple. Especially when starting out.
An industry literature review shows Ar/O2 is common with both spray and short circuit. N2, though not as common in GMAW as with GTAW roots, and not generally recommended, is added predominantly with higher alloys but also adds the complication of phase balance concerns, as Chuck said, as well as porosity if added in too large of quantities. Ar/He seems favored for pulsing, though it has been used with great success in spray ansd short circuit as well. And even CO2 in tri mixes, at 3% or less for spray and short circuit.
Understanding the basics of the gases is the best place to start. For example, the stabilizing effect of inert Ar, the energy and weight of inert He, the penetration pattern of active CO2, the transfer advantages and wetting of active O2, and the alloying capability of N2. And then use them to your advantage.

By jrupert (*)

Date 07-14-2007 01:47

We are using the 98Ar/2O2 and we are having problems with spray mode. It has been reported to me that the wire is birdnesting in the wire feeder. It seems like it happens mostly at the start of welding. I haven't seen it myself yet, but they tried it on several differnt machines. We are going to try 75He/25Ar to see what happens. I let you know what's going on next week.

By ssbn727 (*****)

Date 07-14-2007 04:26 Edited 07-14-2007 05:42

Hello jrupert and "weldcome" to the forum!!! ;)

A couple of questions to make sure we're on the same page... Are we talking about Duplex and if so, which grade??? Also, are we talking about GMAW solid wire and what diameter???

Are you sure that the birdnesting is'nt occurring as a result of the wire burning back and fusing to the contact tip instead, and if you made a slight adjustment in the wire feed speed, do you think one could solve the problem instead of changing the shielding gas mix? ;) Btw, are you sure you're not meaning a 75%argon/25% Helium mix instead for spray transfer mode which btw, is'nt really recommended either???

When I say recommended, I'm not talking about salesman recommendations because as you should know most of their recommendations when it pertains to welding gases are shall we say, ridicuously exagerrated towards one's overall welding performance, quality and budget - Capish???

You may just want to check out this webpage from Ed Craig called Weldreality:
http://www.weldreality.com/MIG_welding_gases.htm
While you're at it check this one out also:
http://www.weldreality.com/stainlesswelddata.htm
Last but not least:
http://www.weldreality.com/eds_training_materials.htm

Have you observed this approach yet or did you simply forget to mention that the birdnesting is occurring as a result of the wire burning and fusing back to the contact tip which would therefore impede the wire from feeding thru the conduit, regardless of any adjustments made to the wire feed speed or voltage, thus birdnesting being the result at the drive rolls??? :)

How does the arc plasma stream look like when you start??? Is it unstable & inconsistent, and does the droplet column wander - resulting in a very erratic metal transfer??? A 98% Argon/ 3-4% CO2 mix is a suggestion as are some of the other above mentioned mixes, and I would'nt worry about any carbon pickup from the CO2 since the percentage is so low and that most of it would be vaporized in the plasma stream anyway :) Ultimately it depends on what grade of Duplex Stainless you're welding together in choosing the correct shielding gas... Read the info @ the above listed webpages, and you cannot go wrong!!! Are you purging also??? If so, read up on Ed's recommendations above also :)

I'm presuming even though I really do'nt like to do so, that you already checked the wire feed tension @the drive rolls, and are using the correct conduit & contact tip diameters for the wire diameter being used, am I correct???
I await your clarification ;)

Respectfully,
Henry

By welder5354 (**)

Date 07-14-2007 05:30 Edited 07-14-2007 06:03

Welcome to the bird nesting problem. I was having the same problem this week with the STT process birdnesting. I switched gases back and forth, but it was still happening. I was also using .035 solid/SS wire; i then decided to switch to .045 solid/SS wire. Excellent results and no more birdnesting. In the meantime the saleperson told me sometime ago he had another similiar problem with birdnesting and they switched to a different brand of wire and that corrected the problem. I think myself the .035 wire was too soft (maybe the brand type) and any hesitation at all on the voltage or WFS would cause it to jump and then jam at the rollers.
In the meantime with switching gases, i found that 90% ar+7.5%co2+2.5%ni was getting better results on open root joints than with 75% ar + 25% co2.
Hope this will work for U 2.
Attached u will find a PDF file with STT process on SS Plate.
The top half of the weld was made with 75% ar+25% co2 and bottom half was made with 90% ar+7.5%co2+2.5%ni (no purging).
Thanks Stephan for your info on uploading documents.
P.S. The hole that you see on the diagram is where i stopped and switched gases and i never ground the stop/start.

Attachment: STTRoot.pdf (166k)

By ssbn727 (*****)

Date 07-14-2007 05:48 Edited 07-14-2007 05:56

Hi Welder 5354!!!

I agree to switch diameters as you have done since I also experienced the same situation previously...
what grade of Duplex were you welding??? In the .pdf attachment image, is that surface porosity I see or is that on the root side of the weld deposit?

Btw, did you get around to performing the tensiles on the stainless STT open roots without purging as you mentioned in an earlier post and if you did, would you mind sharing your results???

Respectfully,
Henry

By welder5354 (**)

Date 07-14-2007 05:58

No tensile, yet on the SS material. The guy who does my procedures was on vacation and so was the welding inspector and next week i will be off work for a few days. This time of year, it's hard to coordinate things with everybody trying to get in vacation time. Will inform you when it happens.

5354

By ssbn727 (*****)

Date 07-14-2007 06:00

Sounds like a plan ;)

Respectfully,
Henry

By Stephan (***)

Date 07-14-2007 20:41

Jeff,

I agree 100% with what you have said about Chuck's explanation. This is excellent.

But I agree also with you when you say that this topic could generate an interesting discussion, and...

Once again you were right when I can read what the other appreciated fellows have already stated and supplemented after Chuck's and your "boost". By the way, thanks a lot "5354" for appreciating my hints on "uploading documents". If you allow I would like to pass on your thanks directly to John Wright. Without him I would never have been able to upload any kind of document in the forum. ;-)

Honestly, Sirs, I must admit to have never had the luck to weld or process respectively, Duplex- or even Superduplex-Steels. Thus you can easeful call me a "droughty theorist".

Nonetheless I am very interested in these materials since - for me - they do represent a very specific and "non ordinary" group of metallic alloys, having truly superior properties by being a greatly sophisticated mixture of mainly two different metallurgical phases.

This again makes them not so very easy to handle for welding - which normally is a clue for making them interesting regarding weld-processing. Now in combination with the shielding gases to be used my interest is doubled, since the different properties of the shielding gases, just as already described by Chuck and you, have - from the physics point of view - surely a deep influence on the later welding result or microstructure.

I have busied myself a time back relative intensively with the effects of active shielding gas constituents in inert gases, mainly Argon, and their physical influences in welding aluminum and its alloys. That was the time when in Germany the Gas-suppliers have advertised their micro-doped shielding gases containing extremely low amounts of active constituents as in particular Nitrogen.

Basically, and only for a better understanding, I am meanwhile known for sometimes being a "savage dog" in technical discussions or arguing respectively, due to I do not agree to pay for somewhat what is only being good advertised without being proved by hard technical facts and thus to have a significant and technical measurable benefit for the user and/or the welder. Here I am - once again - 100% with Henry, when he says: (quote) "...as you should know most of their recommendations when it pertains to welding gases are shall we say, ridiculously exaggerated towards one's overall welding performance, quality and budget..." When the gas suppliers have developed the micro-doped shielding gases, e.g. Argon + 0.0025% Nitrogen for "...significantly improving the welding results in aluminum alloys (e.g. depth of fusion, reduction in porosity,...)..." I have asked myself if this could really be the truth when Argon is being doped with such as homeopathic values of active gases and thus I have tried to find an answer by having a closer look on the physical coherences when using shielding gases in Gas Metal Arc Welding. As you can surely imagine this is like - as "King Henry" (SSBN 727) stated in another post - "...opening Pandora's box..." - since the entire subject is so tricky that my head was truly aching that time. However, I could find out that there is an effect to be observed, since the mentioned coherences are so complex that also minimal contents of substances or elements are - by intricate interactions - truly able to change the physical behaviour, the composition of, and the effects being accomplished, by the arc-plasma. That was surprising for me and I had, nonetheless, doubts at that time. But intermediately there are newer investigations (methodologies have progressed) in the general field of shielding gases and their influences - also in the field of iron-based alloys - that these facts could be approved and solidified. The funny thing is again, that the physicists have also up to now no real idea what the welding arc - in particular in Gas Shielded Metal Arc Welding - actually is - exceptional the agreed and well known physical models! There are so many different questions, begging to be answered, that - I would like to cite Prof. John J. Lowke (my undisputed idol in arc physics) - "...there is more than enough work to be carried out for future generations of interested Researchers!"

Whole and short, I am sure that likewise and in particular in Gas Shielded Metal Arc Welding of Duplex-Steels or Superduplex-Steels shielding gases and their compositions can and will play an important role in the later behaviour of the base metal or weld-joint, respectively.

Well, my problem though is, now, after I have read what problems have occurred in processing Duplex (original post of jrupert), i.e. "birdnesting" was the initiation for the shielding gas question, I am no more sure to asking my questions about the coherences in GMAW Duplex-Steels with various shielding gases and the resulting outcomes to you - the experts being more than "droughty theorists" but being "practitioners + theorists" and thus universally experienced in processing these materials.

Anyway, although I have also my personal opinion on the reasons in charge for "birdnesting" (personal experiences), however please permit to "capture" the opportunity to making actually a sidestep off the original reasons for the topic of "jrupert" and ask some questions concerning the processing of Duplex-Steel(s) by using the GMAW-process and to honestly hope to be - once again - enlightened by you.

· As you have already stated I guess that it should be of great interest to basically know about the grade of Duplex-Steel to be processed. My latest information - and I beg your forgiveness if I am not fully informed about the actual progression in developing those steels but I honestly have had a look to the "www" - is, that there are meanwhile modified Duplex-grades available, compared with the well known "standard-grade" 2205. Now my question would be - in particular with regard to the United States of America and the specifications valid there - how are these different grades to be treated in Welding. As far as I have interpreted the procedures in welding different materials correctly, in the U.S. you have to prepare a WPS for each application and base/filler-material combination. How would e.g. the procedure "jrupert" has spoken of and being valid for a particular Duplex-grade be used for Duplex-Steels different to this particular grade? Has every specific grade/process application its own WPS to be prepared or are there some "intersections" possible? This means, does, for instance, a modified grade WPS (more complex in composition e.g. Superduplex) include applications of a "standard" grade e.g. 2205?

· Resuming. What about the material parameters to be considered beside the material composition, e.g. wall thickness, joint-preparation geometry, etc.? As far as I know in particular Duplex-Steels having a higher sensitiveness in regard to "heat input" and further on the respective cooling rate for achieving an adequate ratio of Ferrite and Austenite growth. Presuming the welding process and its specific parameters, representing important factors as heat input or thermal efficiency, were fixed. How are different parameters as mentioned above (wall thickness, different joint geometries and thus weld-metal volumes,...) taken into account in particular with regard to cooling rates? Would it, for instance, be possible to prepare a WPS for a specific Duplex-grade, having a specific wall thickness and joint geometry, and extend this WPS on base materials having the similar composition but different wall thickness, joint geometry, etc. by varying e.g. the heat input by "varying the welding speed appropriately", "using different droplet transfer modes",..., to achieve e.g. mechanical-technological, or corrosion testing-results being actually represented by and achieved through following the original WPS?

· Henry has asked for clarifying the "filler metal question". As I have heard once from a Spanish welding engineer being employed in shipbuilding and who has investigated the feasibility of using Laser-GMA-Hybrid Welding in joining pure Duplex-Steel (2205) and dissimilar material-combinations (2205/AH36 structural shipbuilding steel), this specific industrial sector has also specific requirements on the Ferrite/Austenite ratio. As far as I remember, they require a minimum austenite value of 30% in both weld-metal and Heat Affected Zone. Is this - from your experience - a value which can be generalized in welding Duplex-grades? Or have different industrial fields (Chemical processing,...) also different requirements on the Ferrite/Austenite ratio to be obtained after welding? How strong - to come back to Henry's question - can the choice of filler-metal (solid wire, slag forming flux cored wire) affect the mentioned ratio under otherwise similar conditions (e.g. chemical composition)?

· Coming now to the very interesting question of different shielding gases. As Chuck and you, Jeff, have already excellently explained the possible differences in using different shielding gases not only by achieving different arc- or droplet detachment/transfer behaviour, but also influencing directly or indirectly the austenite/ferrite balance, I guess that this issue is a very important one and worth for having a closer look upon. When I have busied myself with the shielding gas subject matter mentioned above, in particular the influence of Nitrogen in Argon, I had also a closer look on the influence of this element in welding austenitic nitrogen containing steels. And what I have found out at that time was the fact, that Nitrogen as a shielding gas additive can negatively affect the weld pool purity or solidification (porosity through supersaturation), the arc stability (through degassing) and the outer seam appearance (through slag- or oxide layer generation). These drawbacks again were to be observed in a not so easy to understand relationship basing on the different base metal nitrogen contents and the shielding gas nitrogen contents. Due to between the arc-plasma (gas physics) and weld-pool (solid-state or fluid flow physics) occurring interactions it was - at least at that time - impossible to calculate the later results from the point of equilibrium conditions. But what the most investigations have shown was, that Nitrogen as an additive in shielding gas mixtures (2- or 3 component mixtures) and welding Nitrogen containing austenitic steels can have not only positive, but also negative effects. O.k. to cut the long story short, my question to you, my appreciated colleagues and experts in the forum, is: "Due to Duplex- or in particular also Superduplex Steels containing higher and reasonable Nitrogen amounts and one can also suppose that - depending on the used welding-processes, fillers, welding conditions,..., - these - for the metallurgical microstructure - important and desired amounts of Nitrogen will be reduced by the process, higher Nitrogen contents in the shielding gas whereas can negatively affect the welding behaviour ("bubbling", spattering through degassing,...,), what is the major way to "compress" these reductions?" Is it only a higher Nickel content within the filler metal to balancing the base metals Nitrogen content and thus to ensure that both Heat Affected Zone and welding joint have sufficiently high amounts of austenitic phase for ensuring the corrosion resistance properties?" By the way, I do not know, therefore I request your understanding when I am asking. In regard to what I have mentioned above, "Boiling"- or "Bubbling" of the molten pool due to the physically-chemically reactions of dissociating molecular Nitrogen into monatomic Nitrogen and the further interactions between the molten metal and the gaseous constituents, I would like to cite once again Henry who has stated: (quote) "...In the .pdf attachment image, is that surface porosity I see or is that on the root side of the weld deposit..:". Could it be that the seam surface, to be seen on the pdf-image, is a result of such a "boiling-reaction" induced through Nitrogen, either in the base metal alone or in both base metal + shielding gas (90% Ar+7.5%CO2+2.5%N2)? Would be extremely interesting - "welder5354" - to hear somewhat about the arc- or process-stability when preparing the specimen!

Enough for now.

Please forgive me for asking such kind of bothersome questions but please believe me, where when not here would I find both friends and experts who could answer the queries I am honestly interested in!

Thanks a lot for reading and... responding, in advance!

Best regards to you and all,
Stephan

By welder5354 (**)

Date 07-15-2007 02:40

Stephan, there was no porosity in the root of the weld. Image #4 shows the best profile, just rotate it around and it will give you better views. The close-up pictures were difficult to get on SS because of the reflection from the SS material. What i found from changing gases was that the 75ar+25co2 (c-25) was much brighter on the eyes than the 90ar+7.5co2+2.5ni. Also, the latter produced a better root (from my viewpoint) than with the C-25 gas. All parmeters were the same, only the gas changed. Using the c-25 gas, u can notice the bead profile was wider and there was a slight concavity in the center of the weld. It's a little difficult to see from a bird's viewpoint.
DH

By Stephan (***)

Date 07-15-2007 16:57

DH,

thanks a lot for your answer!

It is understandable what you have observed when using 25%CO2 balanced by Argon.

Just as js55 has already explained in his response (quote):

"Understanding the basics of the gases is the best place to start..." ... "...the penetration pattern of active CO2, the transfer advantages and wetting of active O2..."

There must be differences when using higher amounts of Carbon Dioxide compared with the 90Ar+7.5CO2+2.5N2 shielding gas, in particular with the view on the outer seam shape and appearance.

"Normally" I would suppose that you could also measure different arc-voltage values when comparing both shielding gases and holding the other parameters (wire feed speed, contact tip to workpiece distance,...) constant.

This proves once again impressively the important role of the used shielding gas in Gas Metal Arc Welding.

Please allow me to ask two more questions.

As you are in the lucky situation to being able to, and being an expert in, processing Duplex-Steels.

- "Do these materials in general "create" such a bit "roughly" seam-surface-appearance - like those ones to be seen on your pdf-images - when using GMAW, or is this in particular depending to the droplet transfer mode (short- spray- or pulsed arc)?

- "Is it usual to utilize Ar+25%CO2 in GMAW of Duplex when simultaneously using solid wire electrodes?"

The latter is being asked since I have heard once that "normally" shielding gases containing higher amounts of CO2 are used commonly when welding flux cored stainless steel wire electrodes. It would be interesting to hear if the higher amounts of CO2 would have no negative influence on the material- or joint-properties after welding.

However, thank you once again for your additional explanations and your kind reply!

My best regards,
Stephan

P.S. I will start a tour for the next 14 days and thus I will have presumably no access to the Internet. So I kindly request to being not upset when I cannot reply immediately!

By js55

Date 07-16-2007 14:13

I have never known gases to influence birdsnesting problems, though given their electrical activity I suppose its possible. More often than not I see the problem manifest due to too much tension on the drive rolls or a trailing guide too far from the drive rolls combined with sloppy start technique-specifically too perpendicular a wire entry angle.
Changing wires brands and changing diameters can certainly solve the problem since larger diameters are generally stiffer, and not all manufacturers drawing and annealing processes are created equal. But if you wish to use the smaller wires or a particular brand these would not be ideal solutions. And sometimes just clipping your wire at an angle instead of perpendicular helps.

By js55

Date 07-16-2007 14:31

Stephen,
Your posts have generated enough discussion points to fill the forum for years. All potentially interesting I might add.
As for CO2 for duplex I have never known anyone to use higher volumes than 3%. And unless someone has experience to the contrary would not recommend it.
As for your qualification questions I would say in general that, as far as I remember, the bulk of DSS's are lumped into the same P-No. I welcome a correction if this is no longer the case.
Therefore, given the differing necessary regimes of the differing Duplex alloys the PQR and WPS would necessarily have to be more stringent than code requirements.
DSS's are intended for corrosive services and therefore WPS applications would tend to be very service-testing-regime specific. I thus far agree with ASME IX's tendency to stay away from getting to specific in their requirements for Duplex quals.

By jrupert (*)

Date 07-16-2007 23:38

Thanks for all the input so far. I had no idea it would generate this much discussion and I have to say I'm quite pleased. I'm sorry if I don't address all of the questions you had before. Just keep asking.

Here is some more detail. We are trying to qualify a duplex (2205, 10H) to duplex, 1/2" thick groove, spray mode, using 0.35" wire. The tech said the wire seemed real hard and didn't want to start properly. It sort of stubbed on the plate and that's what was causing the wire to bird nest. It doesn't happen every time. He tried four different machines and a few different guns as well.

I haven't actually seen it yet. Hopefully tomorrow or Wednesday. I will get the weld parameters at that time.

Here is what I am going to try:
buy a spool of 0.045"
buy a spool of 0.035" from a different manufacturer
Try the 75He/25Ar

By Stephan (***)

Date 07-31-2007 14:30

Jeff,

thanks again for your competent and complete answers and - your kind words.

In combination with Henry's (ssbn727) greatly appreciated private message I am fully informed and no more questions remained!

Once again you all have taken care for getting me a bit "wiser".

By the way, I agree 100% with you and Henry to what you have posted in regard to "birdnesting" and to what you have recommended in regard to "clipping the wire for receiving a sharp tip". Often - in particular in manually applications where it is easily possible to execute - this can be a real helpful measure to improve the arc ignition.

Would be interesting to hear how "jrupert" has solved the problem - as far as he may be able to inform us.

Best regards,
Stephan

By DaveBoyer (*****)

Date 07-17-2007 04:53

js55: I was wondreing if I am right or wrong. The tension on My MIG machine will let the rolls slip rather than birdnesting if for some reason [My carelesness] the wire gets stuck to the tip. This seemed to Me to be less of a problem than a birdnest, but then I am using .035 steel wire, and it is pretty stiff. Is it the usual practice to set the tension no higher than needed to get proper feed when things are right?

By ssbn727 (*****)

Date 07-17-2007 06:12

The short answer is:
Yes!!! :)

However, if the spool tension is too loose or too tight - you will have improper feed so, make sure that both the drive roll & Spool tension are synchronized in order to achieve consistent and smooth feeding provided that the other variables are adhered to also such as: the correct drive rolls & associated feed adapters (if necessary) for the type & grade wire being used, the correct conduit & gun liner for the type & grade of wire being used and finally, by using the correct size(dia) & process contact tips and gas cup. :)

Respectfully,
Henry

By js55

Date 07-17-2007 13:26

I agree with henry 100%.
Generally overtightening is not critical, except for flux cores. It just wears out the drive rolls faster. But in some situations it can be problematic. Yours seems to be one. I doubt changing the gas is going to help you. If anything the higher ionization potential of He over Ar may even make it worse since birdsnesting is actually an electrical problem, so to speak, i.e., not striking fast enough-though I suspect no noticable difference. A better idea might be to back off on the drive roll tension and try to keep the wire conduit as straight as possible. Use a 45deg gun instead of 90deg gun, if thats what you are doing, the idea being to reduce resistance.
And even annealed 2205 is a strong material. Try clipping your wire at an angle to give the ignition point a sharp tip. Make sure the gun has an angle when starting so the strike is not so hard when the wire hits the surface.
Oh, and one more thing I think, if you have time. Try changing one variable at a time to see if it works. This is the only way to learn what it is that is actually the cause of the problem, becasue I would like to know. Though in production environments this luxury is seldom possible.

By PhilThomas (**)

Date 07-17-2007 14:45

All of the earlier suggestions regarding proper setup of the wire feeder, gun, etc are great.

I just read through this thread (not sure why I missed it thus far) and it sounds like a wire without sufficient lubrication is as much the culprit as the equipment setup. I can tell you from experience that getting sufficient lube on non-ferrous wires during manufacturing is tricky. That may be why the problem went away when the OP switched to a standard S/S and to another vendors wire.

If you have a can of lubematic and an applicator, you can find out very quickly if that is the case. If so, you have to decide if adding the lubematic to the wire yourself is going to affect the deposit (usually not, but since the user is changing the wire, they need to be certain it is still attaining the desired properties).