Welding Tips and Tricks

Hi,
When tig welding 1020 and 4130 steels together with ER70S2 rod I get small spots of black glass like slag on the welds here and there and cadmium plating won't stick to this. Tried glass bead media to remove it and doesn't work. Any idea's or suggestions of what to use to remove this off the weld or possibly another rod that may be better suited ? The engineers are concerned that it could possibly rust under the slag where the cadmium plating will not adhere to. Any info would be appreciated. Thanks.

Welcome to the forum vmagnum.

I've gotten these, and I believe it comes from not cleaning everything enough. When people say "tig welding requires surgical cleanliness", it is not far from the truth. Make sure everything inside and outside is spotless, ground down to shiny bare metal, wiped down with acetone, run the filler rod up & down with a 3M scotchbrite pad just prior to welding, and do the same to the tungsten but with a separate 3M scotchbrite pad, and wipe them down with acetone as well. It is definitely from crud/impurities, and I've had to smack a couple spots with a small sharp chisel, and they do come off. Perhaps if a you have an air needle scaler you could take care of them much faster.

You can get rid of the "floaters" with a pencil grinder and high speed bit, then use a whit fibre bit to polish it up before playing. It will make everything smooth again and won't be able to tell.

vmagnum,
What you're seeing is the Silicon in the rod float to the top and harden. Actually the ER70S2 has the least amount of Silicon added for common steel Tig rods. It's there to flux out impurities in the base metal and carry them to the surface, hence the little glass like deposits on the top of your welds. They're a pain to remove but they can be mechanically removed with any of the methods already mentioned.

Len

vmagnum,

Len's description is dead on. However, you mentioned the deposits were black. If your material is prepped clean, this suggests the impurities in the steel itself are somewhat high. On clean steel, these floaters should be tan in color. You might consider going to ER70s-4 or s-6. This will give you more of these floaters, but they'll be easier to remove.

A light touch with a needle-scaler is the fastest way to remove them, if peening of the weld is not a problem.

Steve S

Hi guys,
First of all I liked to thank all of you for your help and suggestions in this matter. As far as cleaning I practice the three C's of welding, clean,clean,clean and that's whats led me to ask for you fine peoples help as I am not quite sure how to get this slag without damaging the appearance of the weld. I explained to the engineers that it doesn't physically effect the weld, but they don't like it on there. I'll have to give the pencil grinder a try. The needle-scaler might be a good idea also, but any peen marks wouldn't be allowed, that's why I have to be careful with even trying to chip it off. Going the different rod route might help also, so thanks for the rod suggestions. I knew that the 70S6 rod had more cleaning agent in it ,but didn't know the slag might be easier to remove. At work I have a couple other rods I thought of trying, they are a 4130 rod which you have to be careful with your heat at the end of the weld as to keep it from cracking and a M3800 rod which the materials lab fella tells me it's makeup is between the 70S2 and 4130 rods. What do you think? Again thanks and your help is greatly appreciated.

A wire wheel on an angle grinder works well too to get off all the scale it can reach if the wire finish is acceptable.

vmagnum,

I should have explained better, I suppose.

The darker the slag, the tighter it seems to tie to the metal. It seems to suggest incomplete cleaning. I have no evidentiary basis for this, it's based on experience, and your mileage may vary.

Since peening marks are a "no" on your weld, the higher silicon content combined with a wire-wheel cleaning may be the way to go.

The pencil-grinder approach will work wonderfully, but you must weigh the time factor into this. At some point, the effort you put in the cleaning will outweigh the money made on the weld.

Steve S

Thanks coldman, otto nobedder and everyone,
I have tried a fine stainless steel wire brush some, maybe as you suggest a 70S6 rod and a little heavier brush might work.
I believe some of the problem is as you suggested otto nobedder in that the one metal may have higher impurities in it.
I say this because where I'm welding the two parts made of 1020 steel the welds are clean and where I weld the 4130 steel to the 1020 that is where I'm getting the slag.
Thanks Don.