American Welding Society Forum
I have read that copper-coated (steel) rods are bad for use in TIG as they can cause pitting of the weld and give off harmful gasses. Is this true? It is all my local welding place stocks... On a related note, I am new to the world of TIG and have been practicing laying beads on 3/16 mild steel. Sometimes I get little craters in my weld bead -- it is almost certainly due to my beginner's technique, but I would love to either blame the rod or find out what I am doing wrong. Am I giving it a bit too much heat? Thanks for your help -- this newbie certainly needs all he can get!
Copper coated wire reduces oxidation and is pretty normal and in most cases standard. This is fine for beginners practice.
The indications you call pitting; are they only at the end of the welds? If so this could be related to reducing heat too quickly.
Other causes for pitting in the weld bead could be contaminated (dirty, rusty, oily) work or wire or poor shielding gas coverage.
Tell us a bit more about your practice welds and the answers will be more clear.
I would just like to add on more note concerning copper coating of GTAW wire. Another reason that the manufactirers coat the wire is because it aids in the drawing down process.
I am using 20 cfh 100% argon, so I don't think that's the problem. I have been cleaning the metal with a grinder/stainless brushes, but perhaps I need to use solvent as well (?). This is just stock mild steel from Home Depot -- come to think of it they probably oil pretty heavily it to prevent discoloration. The pitting is typically not at the ends, but forms in the middle of the bead, at the top of a "beadlet".
At first I thought I was accidentally hitting the bead with the tungsten, but having now done that a few times that's not it. Pitting normally results from impurities or overly rapid cooling? I wonder if I might be blasting it by stomping the pedal too hard...
I suspect your guess that your using to much amperage (heat) is correct. How wide are you weaving your beadlets. Quite often it is suggested that 3 times the diameter of your filler metal is the widest weave that should be used. Also try making a butt weld or fillet and see if it still occurs. It may be the steel itself if it's of low quality considering it's origin. Also you can remove the Cu with a piece of scotch bright or steel wool, a common practice when pipe welding.
My guess would be dirty base metal.
The 3x and 4x weave width limts are frequently imposed when it is desired to limit heat input, such as for notch-toughness properties, to minimize sensitization in stainless steels, prevent brittleness in Carpenter 20, prevent hot cracking in nickel-base alloys, and other similar problems. Otherwise, the weave width does not have any significant effect on weld quality or properties in carbon and low alloy steels. I have routinely made manual GTAW weave beads as wide as 1 inch with 1/16 inch diameter wire with no trouble at all. We had a method of making socket weld when I was in the Navy where we would put in a root pass, then weld the remaining a "t x 2t" fillet in a single pass. I'm sure Gerald and Curt remember doing that as well. I have also seen mechanized GTAW weave beads made with 0.035 inch diameter wire with similar widths produce excellent quality.
I once watched a boilermaker weld a 1-1/2 inch thick mild steel plate in the vertical position in a single pass by weaving in and out across the weld bevels and back and forth across the groove width. The plate passed tensile and guided bend tests when it was finished. There was no practical reason for using such a technique, he just wanted to prove it could be done.
Its amazing how red a 1/2" CS Socket weld can get !
All -- thanks for your input. I think my problem was basic bad technique-- too much heat, cooling the puddle too quickly with the rod, etc. The welds are beginning to look better!
The craters you are experiencing are probably from welding on steel that has not been fully deoxidized. This is very common on many cheaper grades.
You will be welding along, and a crater or bubble will form. Your first guess is that the gas flow is too low or contaminated. You also may think you have applied to much heat as the puddle will appear to "boil". This is just not the case.
What to do? Not much in this case. You have bad steel-grinding or cleaning will not help. This comes from the chemical composition of the steel.
The only deoxidizers we have in the tig process is in the filler metal itself. Be sure to use a deoxidized wire such as ER70S-6 (double deoxidized) or better yet, ER70S-2 (triple deoxidized) on this type material.
When a crater or bubble starts, jab a little more filler in there.It may help. It may not, if the steel is really bad.
Keep in mind, too, that there is carbon steel of such poor quality out there that tig welding can be very challenging.
As far as the copper coating-this is an argument that seems to go on forever. The copper coating you see is really nothing more than a "flash coating". It is so thin that the amount of copper volitized (especially with tig) is very minute and of little consequence. If you examine your rod under a microscope or similar, you will see that the copper often does not cover the steel entirely.
Yes-there are non-copper coated fillers out there, but they are rare and expensive. The bulk of the welding industry still uses copper coated fillers.
Hope this helps-
What, Home Depot doesn't sell the highest grade metal stock? What a surprise! I picked up a bunch of this because I thought it would be easy to learn on... Now I am pretty convinced that some of the pitting is the metal's fault -- not my own! My biggest mistake seems to have been moving too quickly, allowing the previous "beadlet" to cool too rapidly, but sometimes I get that pitting despite what seems to be good technique.
I am curious how quickly one moves along a bead with TIG -- I mean, I can blast the heat and move quickly (up to the point of pitting) or I can slow down... I've been using 120A on 3/16 steel -- does this seem about right (I think I saw it on a chart somewhere)...
See my previous post.
GTAW does not weld very well over even a slight amount of mill scale.
Mill scale is what occurred to me too. I'm not an expert but keep practicing several times a week and do some artmetal as well. I noticed immediately the same kind of pitting on mild steel. When I carefully and completely removed the mill scale the pitting problem resolved. Here is an additional observation. If you make a weld, let it cool while repositioning etc. then resume welding there is a new layer of scale and while not as heavy as the original mill scale it still has an effect on the arc and weld. I sometimes use a wire wheel on my flex-shaft to remove the new scale.
Hope this helps.
Thanks for all your responses. I believe that mill scale and bad technique were the culprits. When I cleaned the surfaces really well with a grinder I was OK.
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