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Re: [welding_group] Re: TIG welding mild steel, porosity problem

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  • C. J. Frederick
    The items below are good things to check. The quality of mild steel varies a lot. There are many levels of impurities in the steel depending on the source
    Message 1 of 4 , Jul 27, 2005
      The items below are good things to check. The quality of "mild steel"
      varies a
      lot. There are many levels of impurities in the steel depending on the source
      and ASTM designation. Porosity and the "bubbling" mentioned is common. The
      best mild steel to weld is cold rolled as it is of higher quality stock. A
      couple of additional suggestions; make sure the surface and edges of the joint
      are super clean. The best way is to grind them lightly to remove any mill
      scale and other surface contaminants. Make sure you are using a triple
      deoxidized steel filler rod. Extra oxidizers (scavengers) are required to
      remove impurities in poor quality steel. The triple deoxidized filler wire is
      designated as AWS ER70S2. It is available in cut lengths for TIG and gas
      welding. As a last resort use SS rod. It usually eliminates the
      impurity/porosity problem. I use it for most mild steel welding but have the
      triple deoxidized rod for cleaner steel base metal. The SS alloy I use is
      ER308LSi. It is a common low carbon (the "L") high silicon ("SI") filler.
      silicon helps remove impurities and improve wetability. I just modified an
      pan using the SS rod and it worked fine with no porosity.

      C Frederick

      > Don,
      > This could be impurities in the metal, but I would check a few
      > things. I have had porosity during tig for seveal reasons.
      > 1) bad or lack of gas- not likely in your case since you can weld
      > other stuff
      > 2) Incompatible filler rod
      > 3) tightly adherent surface coating that some manufacturers put on
      > the metal to inhibit rust (likely in your case). I have had to use my
      > sandblaster or a wire wheel on this in the past
      > 4) Running too hot and/or too slow
      > --- In welding_group@yahoogroups.com, "Big Redbird" <totsuwa@y...>
      > wrote:
      > > Well, you're not alone on this one.  I've tried tigging .125" Mild
      > > steel and had the same problem, particularly on corner weld
      > joints. 
      > > It can drive you batty.  I chalked it up to impurities in the
      > parent
      > > metal.  I always stock .125" HRPO (Hot Rolled Pickled and Oiled)due
      > > to the finish, but that pickling and oiling could leave residual
      > > impurities behind.  I always clean the oil off wth a light solvent
      > > to prevent oil contamination, but still have porosity.  I've tried
      > > upping the shielding gas, used different DC polarities, but no real
      > > solution.  Fortunately, I also have a small wire feeder so it isn't
      > > a real difficulty, but if anyone knows WHY this happens, I'd also
      > > like to know.
      > >
      > > Totsuwa
      > >
      > > - In welding_group@yahoogroups.com, "deklundpacbell" <deklund@p...>
      > > wrote:
      > > > I am wondering if I can get some advice from this list.
      > Yesterday,
      > > I
      > > > hooked up my TIG machine to weld some brackets out of .125 mild
      > > > steel.
      > > > Something in my weld puddle was bubbling from time to time and
      > > > contaminating my electrode.  In these areas I was also getting a
      > > > porous weld.  I cleaned the steel with sandpaper first, so I am
      > at
      > > a
      > > > loss as to what was causing the trouble.  I ran a bead on some
      > > other
      > > > tubing I had laying around and it was ok.  Is there some kind of
      > > junk
      > > > in my new steel that would account for this? 
      > > >
      > > > Another thing, when I ground out the bad weld and tried to go
      > over
      > > it
      > > > again, I had the same problem, only more so.  I finally ended up
      > > > getting the Oxy Acetylene rig out and finished the job with that.
      > > >
      > > > Any help is appreciated.
      > > >
      > > > Don,
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