Porosity in a weld; what caused it

[ericher69]

I had a buddy ask me to help him fix a broken steering part for his lawn mower. Piece appeared to be cast steel.

Attached is the repaired part. (Deleted broken pic oops)

Anyway tried with Nomacast rods (tacks didn't even hold) and then used the mig.

First bead; arc was erratic almost wandering. The bead was also full of porosity.

Ground off some of the coating a little more and seemed to help. (Maybe a nickel Zinc coating)

Grinded the porous beads down and rewelded max amperage and it seemed to lay down a great bead! Turned up the75/25 to 35 CFH.

Would have tried 6013 or 7018 but was not at home so limited on rod selection.

What caused the porous welds??

TIG probably would have been the way to go as I have watched Jody from WTAT struggle with cast aluminum pieces.

Ps: I did tell him that I was not happy with it but he said that I worry too much! He will buy another part if it fails again.

Do not need any input from the safety police. This is a low speed riding mower on level ground.

 

[tcartwri]

Did you pre-heat the part? welder at work has an old BBQ in the shop just for those occasions.

 

[ericher69]

Did you pre-heat the part? welder at work has an old BBQ in the shop just for those occasions.

No

Thought about using the torch to pre-heat but just beveled the part and burned it in as hot as the MM210 would go.

Maybe pre-heating would have removed some impurities out of the cast steel?

 

[yomax4]

Normally the porosity issue is gas related but in this case it could also be a contaminated part. With anything cast, it's usually got some oil or worse soaked in..Pre heating can boil some of it out but welding usually pulls more. Sometimes you will have to weld, grind and then re-weld. Looks like you found that out..Good work..

 

[ThomasH]

Pre-heating can help with post-weld cracks and other metal fatigue properties, but it won't help with porosity. Porosity is either caused by the base material containing contaminants (common with cast aluminum and cast steel) or the base metal is not clean (surface contaminants); or slag inclusions(poor stick rod control)/lack of gas (mig/tig)/ or wrong or bad rod(stick). At least, that's all I can think of.

Tom

 

[LD1]

I second the contaminated part. Cast is like a sponge, It sucks up all kinds of contaminates.

Weld once to get most of the contamination out, grind and weld a second time for good.

 

[Gary Fowler]

Most likely culprit was grease soaked into the porous metal. Heating it up with the welding boiled it out as a vapor that got trapped in the weld metal. Grinding and rewelding usually lessens the amount. It looks like a good job and should hold.

 

[weldermike]

It may be manganese. Typical symptoms without correct filler and preheat.

 

[ericher69]

It may be manganese. Typical symptoms without correct filler and preheat.

Thanks for all the replies and help

I forgot to mention that the part was on fire once welding was complete!

Prob cast steel soaking up some oil or other junk

 

[Arc weld]

On a garden tractor probably a very low grade casting. What makes you think it is cast steel? Figuring out what it's made off is the most important thing to know in order to repair it. Cast steel is much easier to weld than cast iron and cast aluminum is an entirely different animal so comparing how it welds is a moot point. Too much gas flow can also cause turbulence which can cause porosity. TIG is best for cast aluminum but for cast steel, I'd use stick 7018 but MIG would also work. 6013 is the last thing I would use on just about anything. Preheat is good on anything that's cast.