Re: [welding_group] Re: TIG welding mild steel, porosity problem
- The items below are good things to check. The quality of "mild steel"
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.
> 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 firstname.lastname@example.org, "Big Redbird" <totsuwa@y...>
> > Well, you're not alone on this one. I've tried tigging .125" Mild
> > steel and had the same problem, particularly on corner weld
> > It can drive you batty. I chalked it up to impurities in the
> > 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 email@example.com, "deklundpacbell" <deklund@p...>
> > wrote:
> > > I am wondering if I can get some advice from this list.
> > 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
> > 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
> > 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,
> YAHOO! GROUPS LINKS
> * Visit your group
> "<http://groups.yahoo.com/group/welding_group>welding_group" on the web.
> * To unsubscribe from this group, send an email to:
> * Your use of Yahoo! Groups is subject to the
> <http://docs.yahoo.com/info/terms/>Yahoo! Terms of Service.