[jakeru]

I ran into something I thought really strange playing around in my shop the other day, while trying to kill off an argon bottle that was almost dead.

I had broken a harbor freight tailpipe expander tool, (like the one pictured here:)


The end cone shaped piece that rams the multiple pieces outwards had broke into two pieces, and so I tried to TIG weld it for kicks, just to see how it would weld. It fractured in a kind of brittle like manner, not much ductility. So the broken pieces fit together almost perfectly. I thought at first, maybe it was some kind of hardened, heat treated steel. But it didn't really look like it was machined... it had the appearance more of a "cast" part.

To prep for welding, I didn't vee anything out, I just wiped it with a little brake parts cleaner, scrubbed it by hand with a steel wire brush, and went to town with the TIG. Immediately the arc struck it reacted and seemed dirty and "contaminated", the metal was fizzing and popping sparks and smoking, but after a first "heat cleaning" pass, going over the same spot the puddle actually flowed quietly and welded nicely (and I dabbed in some E70S6 filler.)

What was really weird is that after the part heated up, I found it was sitting in a puddle of oil that had leaked out of the ferrous metal! There was quite a bit of oil that leaked out!

What kind of metal is this, that can have so much oil soaked into it? I've heard of things "migrating around grain boundaries" of certain metals, but I was totally surprised about that oil that came flowing out of the part when I heated it up. Might this piece have been made by sintering together steel powder?

I can add that it wasn't tremendously strong in service. I mean, I was kind of abusing it, but I was surprised when it did fracture. I wasn't even using it that far off from how it was intended to be used.

I should also add that I did get a halfway decent weld on it (I welded the nut together with it for more strength) and after dressing the flats with a flat file, I think its actually going to work as good or better than new! I already got a new replacement so it will be interesting to see if the new one works better than the old "repaired" one.

[ogorir]

It might've been cast with a porous alloy in oil-sand. porous alloy=cheaper, oil sand= finer surface finish (looks less like cast) and can be cheaper than green-sand(water bonded casting sand).

cheaper, less work, and cheaper are pretty well synonymous with harbor freight, so I'd recon it's probably that. all metal is porous, cast more so, and cheaply cast is like a sponge. I think the carbon content may have something to do with it, too.

[jakeru]

Interesting, I've never heard of oil sand before. But yeah, I'll bet economics dictated the manufacturing technique on this. Otherwise it wouldn't have fractured when I put the stress on it.

Anyhow, I was just amazed how much oil leaked out of it. Probably a teaspoon, which is perhaps 20% or more of the volume of the piece itself! That's a lot of liquid oil in there. And that is not even counting the oil that clearly was smoking out around the area I was welding, or all around the surface as I brake parts cleaned it, and before welding it, just handling it didn't seem to be oily on the surface.

I do wonder if its made with a "powedered metallurgy" process?
http://www.youtube.com/watch?v=--jK1-5V ... re=related
http://www.youtube.com/watch?v=xdOfJSjxrrE
Seems like if the powdered pieces weren't compressed tightly enough together, it would leave lots of voids where oil could hang. The porous structure may actually have some desirable qualities in this application, as it would help lubricate the sliding parts.