Solve this metal mystery. Clues provided.

[MeltedSocks]

This is a 1" diameter linear bearing shaft.  It has been leaning in a corner of my shop--not always air conditioned--for about 10 years.  There is sparse and minor pitting with a little rush, but it is still 99% shiny.  Even the cut ends show little rust.

It is strongly attracted by a magnet.  Soaking in a 14% HCL acid solution causes the formation of a greenish-blue film on the shaft and causes the acid itself to turn blue-green.  Where I sanded off what appears to be a shiny coating on the shaft, the acid doesn't appear to have any effect; no greenish-blue film.  I only soaked the shaft in the acid for a couple of minutes.

Here are the pictures taken just after pulling the shaft out of the acid.

I'm wanting to make a hammer eye drift out of this metal, but I'm trepidatious about breathing some noxious metal oxide (although my forge is basically outside with good air flow).  Years ago, I took a piece and forged my first knife.  It was very resistant to being forged.  Worse than S7, IIRC.

Those are you clues.  Let the SWAG-ing begin. Grok3 led me to believe it might be 440 stainless steel, until I stuck it in acid and got the blue-green film.  Why would stainless steel be plated?

[JHCC]

If you have access to one, see if you get it tested with an XRF gun (ask your local scrapyard if they have one), preferably on the spot where you removed the surface coating. That will give you the exact composition, which you can compare against known steels.

The blue-green color is odd, and may be the result of the surface being contaminated with copper.

[Mike BR]

It could also be a chromium compound. Stainless resists rust because of a chromium oxide layer that forms on the surface. That might have reacted with the acid, even though the base metal didn’t. 

[MeltedSocks]

20 minutes ago, Mike BR said:

It could also be a chromium compound.

Grok3 says that one of the resulting compounds would be chromium (III) chloride in the hydrated form (CrCl3 6H20) and it often exhibits a blue-green hue.  But why would the manufacturer chrome-plate a stainless steel shaft?

I guess the same reason that ball bearings are chrome-plated:  smoother and harder surface.

[Mike BR]

I’m positing that it wasn’t chrome plated. Rather, the chromium oxide layer that naturally forms on the surface of stainless steel (and is crucial to resisting further oxidation)  reacted with the acid. Maybe. 

[JHCC]

Regardless, I wouldn't be forging with it.

[BillyBones]

We make parts all the time out of stainless that we send out to be plated. It could be for any number of reasons other than corrosion. Wear being one for example. 

[Florida Man Metals]

Has anyone suggested tantalum?

[Florida Man Metals]

 Tantalum and its alloys are highly valued in demanding applications, including those involving bearing shafts, where high strength, wear resistance, and corrosion resistance are essential. 

Here's why tantalum alloys are well-suited for bearing shafts and some specific examples:

Exceptional Corrosion Resistance: Tantalum is highly resistant to corrosive chemicals, including strong acids like sulfuric and hydrochloric acid, and even molten metals like lithium and sodium. This makes it ideal for shafts operating in harsh chemical environments.

High Melting Point and Strength at Elevated Temperatures: Tantalum is a refractory metal with a melting point of approximately 3,017°C. This allows tantalum alloys to retain their strength and integrity in high-temperature applications, such as jet engines and nuclear reactors.

Wear Resistance: Tantalum and its alloys, particularly those with tungsten, offer high hardness and wear resistance. This is critical for bearing shafts that experience friction and abrasive forces.

Biocompatibility: Tantalum is biocompatible, meaning it doesn't react adversely with bodily tissues. This property makes it suitable for medical implants and devices, which may include bearing components, according to www.edgetechmat.com. 

Specific tantalum alloys for bearing shafts

Tantalum-Tungsten (Ta-W) Alloys: These alloys are particularly known for their extreme hardness and strength, making them suitable for high-wear applications, notes Quest Metals. The addition of tungsten further enhances the alloy's ability to resist wear and endure mechanical stress.

Ta-10W: This alloy, containing 10% tungsten, offers high strength and wear resistance and is suitable for aerospace and defense components that need to withstand high mechanical stress and operate in harsh environments.

ULTRA 76 Plus Tantalum Alloy (Ta-2.5W-0.15Ru): This specific alloy is recommended for applications requiring higher strength and superior corrosion resistance in acids like hydrochloric and sulfuric acid, even at elevated temperatures. It's especially useful in situations requiring excellent resistance to hydrogen embrittlement. 

While tantalum alloys offer a promising solution for demanding bearing shaft applications, it's crucial to acknowledge the challenges associated with them. The high cost of tantalum and its alloys, along with the difficulty in machining and the limited global supply chain, are important factors to consider during material selection. 

 

[Florida Man Metals]

I guess it all comes down to where you got it from.

I would go with John's advice and shoot it with an xrf gun. Tantalum is worth good money.

Tantalum is most often used in electronics for capacitors. There are companies on line that you can send them to. They only buy capacitors thou because they know exactly how much tantalum is in them.

[MeltedSocks]

Thanks for the replies!

JHCC, why?  Noxious gases or just too difficult to work with?  It's a bummer because I've got four feet of it.  Are those XRF guns common?  Sound too high end for NW Florida.

Florida Man, I can't remember where I got it, but if I had to guess, it was eBay.  Ever tried Florida Man IPA?  Brewed by Cigar City Brewers.  9% and very hoppy.  It's my favorite, but not an everyday drink.

Mike BR, if the places that I ground off produce that blue-green after some time, that would confirm it.  Don't know how long it takes for that oxide coating to reform.

[JHCC]

Both. Just because you have it doesn’t mean you have to use it. 
 

XRF guns are really expensive, so not something most individuals would have. However, a scrap metal yard (or “material recovery facility”) can improve their profitability by sorting out the various alloys, so it’s worth the investment. 

[Florida Man Metals]

The scrap yards around me don't use xrf analyzers but one of the pawn shops does.

The guy that owns the pawn shop use to own the second largest scrap yard in town. He wasn't worried about a few dollars. The moment he opened the pawn shop he bought one and graciously allows me to use it.

Let's just say that with the price of platinum and gold it doesn't take many mistakes to pay for one. 

Not sure if you guys know much about white gold? White gold can be made one of two ways. You need a white metal to mix with the  gold. You can use either nickel or platinum to alloy with the gold.

Platinum used to be called the rich man's gold. It use to be twice as valuable as gold. 

You only get paid for the metal content of one of the metals, either gold or platinum. Just like when you sell say 14kt yellow gold you only get the value of the gold and none of the silver value that is alloyed with it to make it 14kt.

I haven't tried that IPA. I try to stick to hard liquor. Plus I don't really trust the Tampa municipal city water supply. I read something a while back that they tested a whole bunch of beers for forever chemicals and found the highest levels of pfas in beers from the south.

[Goods]

Chromium 3 is high toxic and carcinogenic. Dust/fumes etc, just avoid it!
My guess it that this is hard chrome plated. I run into that often on linear shafts. Base material of those shafts are pretty good stock (but I’ve run across one that wouldn’t harden), but it not worth the health risks to remove the plating.

Keep it fun,

David

[MeltedSocks]

Okay.  I'll order 1" round bar for my drift and put this shaft back in the corner for another decade. 

[JHCC]

That's the wisest choice. 

I once got permission to remove the scrap metal from a construction site at the college, which ended up including some really significant pieces of steel. However, these were all heavily galvanized, and there was no way I could use them for anything. I ended up taking them to the scrapyard and turning them into cash, with which I bought new, clean steel. I may have ended up with less metal, but I also ended up with fewer headaches.

Smiths tend to be packrats, but sometimes things have greater value as something to sell, when the money allows you to buy other, more useful things. This is why I'll be bringing (inter alia) my chop saw and some W1 drill rod to Quad-State to sell.

[Mike BR]

I once confiscated some cadmium-plated aircraft bolts a member brought for our guild raffle.