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Up Topic Welding Industry / Technical Discussions / Argon/oxygen
- - By z5gxray (*) Date 03-22-2004 18:26
My manufacturing plant is currently welding GMAW with 86/14 argon- CO2. Our plans are to switch to GMAW-Pulse with 95/5 Argon- oxygen.
I have used this gas combination for over 15 years in other plants. I am now being told that with this gas combo will cause the weld area to be brittle. Can I get some feedback on this choice?
Parent - - By Sean (**) Date 03-22-2004 19:27
Dear Don:

The 95/5 Ar/O2 mixture has been around (as various trade names) for a while. Before commenting further can you tell us the base metals being welded? What do you define as brittle... keep in mind any time you weld something you are affecting the base material regardless of the shielding gas.

For mild carbon steel (CS) there should be no problems. Also, you will notice that because of the O2 the welds will wet better and the pool will be a little more fluid. You will also be able to achieve spray transfer at a lower voltage (for the same WFS) with the 95 Ar - 5 O2 than with the 84 Ar 14 CO2.

As for the mechanical properties there is going to be a difference in the mechanical properties due to the difference in the shielding gas.
Parent - By z5gxray (*) Date 03-22-2004 20:51
The engineer said the brittleness (CRACKS) is in the weld and the HAZ. To refine my question, we want to switch to pulse for the increased productivity, better weld appearance no spatter. Also we want to have more control of the weld puddle since most of the material on our equipment is made of copped round or oval 11 Ga. low carbon Tube and 75% of it is welded out of position. The problem with the brittleness was when argon/oxygen was used which is what we want to switch to. The welding is all manual
Parent - By Lawrence (*****) Date 03-22-2004 20:17
Hey z5,

I'm with Sean in wanting to get more data.

Manual or Robotic?

Why the change to pulse power sources in the first place? Out of position welds? Other than mild steel application?

That 5% O2 has the same oxidizing potential as 50% CO2, Soooo...While its technically true that the O2 gas may provide more fluidity its hard to imagine a situation that your current gas mix would produce an unacceptable effect in that regard. In spray transfer mode too much fluidity is more likely to be a problem.

This is a very interesting thread, please keep us posted on your findings.
Parent - - By GRoberts (***) Date 03-23-2004 01:15
For GMAW welding of mild steel, anyone who makes a generalized statement that a 86/14 mix makes the weld and HAZ brittle needs a little more welding knowledge. Unless the gas contains hydrogen, there is no way for a gas to make a mild steel HAZ brittle. Also, GMAW can be done with up to 100% CO2 without causing the weld to be "brittle" (which in itself is a very arbitrary term.) in most service environments. It is true that a higher argon mix will lead to a lower weld metal oxygen content which improves toughness, but with mild steel, thin walled tubing (I am guessing on the thin part), toughness is not degraded enough to be an issue. If you are welding thick tubing for cold service temperatures, then improving the toughness could be beneficial, but switching from 86/14 to 95/5 won't be that much of a difference. That is because the oxidizing potential (which is what determines weld oxygen content, and has an affect on toughness) of oxygen is about twice that of carbon dioxice (according to Linnert and my sometimes faulty memory- but I think Lawrence's factor of 10 might be a bit high), so the equivalent argon/co2 mix to 95/5 (Argon/ox) is 90/10 (argon/CO2). Not much different than 86/14.

Depending on your application, the main difference between the application of the two gasses is most likely that welding with 86/14 would put you in short circuit (dip) transfer, and welding with 95/5 pulsed would be spray transfer during the peak current. (there are always exceptions) Theoretically, on thin material, pulsed could give you a higher deposition rate, but welder skill, proper perameters for either transfer mode, fixturing, proper joint fitup, will make a bigger difference.
Parent - - By bmaas1 (***) Date 03-23-2004 02:41
I find the gas percentages interesting to say the least. 86/14?

Brian J. Maas
Parent - By jwright650 (*****) Date 03-23-2004 10:48
Hi Brian,
They probably have a in-line mixer to mix bulk gasses to whatever ratio they need.
John Wright
Parent - - By 357max (***) Date 03-23-2004 14:53
Eighty percent argon or greater with the remainder carbon dioxide will allow spray transfer. 80/20, 82/18, 83/17, 84/16, 85/15, 86/14, 88/12 or 90/10 will allow short circuit, spray and pulse spray transfer on steels. Check your gas distributors, different distributors will have a different percentage. Remember the gas is an essential variable. Increasing argon will increase tensile strengths and reduce ductility.
Parent - By dee (***) Date 03-23-2004 16:27
To expand and modify previous information, Spray transfer is indeed possible with C25 gas mix- it is done regularly. It will not provide a stable enough transfer with 035 to be called practical, but, with an 045 electrode provides a good, high energy stable spray transfer. It's not laws of physics preventing stable spray transfer with C25, its the power supply limitations... thus it MAY be correct to say an individual machine cannot, therefore in that limited context it cannot be attained.

As Ar ratio increases, the width of the HAZ decreases... I am not sure absolutely everyone likely to read this realizes that phenomenon and how it effects the penetration profile.

You may want to dig out JOURNAL volume 81 number 9 and refer to article:"shielding gas mixtures for semiautomatic welds" by Mr V. Vaidya.
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