I have a 1" round bar that I got as scrap.  It was an old shaft from some manufacturing equipment.  It was more shiny than most scrap I get but I thought it was from polishing.  It had some rust on it but only in a few places.  I heated it up in my gas forge (which I don't use much).  After forging and quenching I noticed it was tinted green.  The water in the slack bucket was very old and has been outside for over a year.  I am hoping that the green tint is from the water but afraid it may be some kind of coating on the metal.  There was no noticable smoke when the piece was heated to forging temps.  I am half way into this project and don't want to scrap the pieces but also don't want to poison my self :). I know someone is going to say heat up some mild still and quench it.  I am not sure why that brilliant idea didn't come to me before I closed down the forge for the weekend but here we are.  Has anyone else seen something like this from very dirty water or a propane forge? 

is it magnetic?

Hey Thomas, 

The second I saw your response I started feeling kind of dumb.  Those bars are probably some type of Stainless.  As soon as I get back to the shop tonight I will put a magnet to them and report back.  

why did you quench it after forging, its normally best to allow a slow cool, not attempt to harden, after the stress of the forge.?

Some stainless steels are magnetic, even some of the "non magnetic" 300 series can have some magnetism

But it's a data point.  Some stainless alloys will be slightly magnetic after cold working; but hot working should fix that depending on alloy and temperature and amount of work and ...

plated shaft?

chromium oxide?

copper undercoat from eletroplating?

 

No simple answer here on found objects.

Ric

1 hour ago, Steve Sells said:

why did you quench it after forging, its normally best to allow a slow cool, not attempt to harden, after the stress of the forge.?

I believe he might simply meant a cooling off quench. That's one of the uses the slack tub is for. Not always just for hardening. Think non-knife here, Steve :D. We don't always want to wait for stuff to air cool so we can pick it up to work another end, examine for further work, measure etc. I don't generally douse yellow or even red steel (but have if I want to isolate heat for example); but cool off a black hot piece so I can lay it down without burning the surface or especially my fingers? Sure! All day long. Still a quench by definition.

Scott

Hey Steve, 

Dodge is correct.  I was just trying to cool the pieces down quickly before the next stage (twisting some heat isolated sections on the bars).  These are going to be pieces of a table that I am texturing to look like tree bark.  Not everyone makes pointy objects all day :).  Love the book by the way.  

The bars are as magnetic as mild steel.  

Copper sulphate contamination of the quench tub would turn everything green. Chromium oxide is green, it is what is used in some polishing compounds. The chromium atoms leaching from a stainless steel vessel is what turns egg yolks green if they sit too long.

47 minutes ago, John McPherson said:

The chromium atoms leaching from a stainless steel vessel is what turns egg yolks green if they sit too long.

Actually, it's iron reacting with the hydrogen sulfide that forms when the egg is held at too high a heat for too long. Scrambling eggs in a cast iron pan makes it worse, since there's more iron for the  H₂S to react with than is normally found in the yolk itself.

Is that the piece pictured above? It actually looks pretty good as it is. Almost like an actual tree. Get the water tested if it turns out you can give anything that color and add that finish to your portfolio. So long as you don't poison yourself, obviously.

Yeah, 

The piece to the left is one of the 7 almost finished legs and the piece to the right is what it looked like after pulling the stock out of the forge and quenching.  I thought they looked pretty neat as is but the wife wants it to be more gnarly so I am going to put a few slight twists in sections.  

is the water in your quench tank treated with anything?

Nope, 

I have quenched copper in it a few times.  It also got an organic mosquito killer disc in it.  I am not sure what was in that stuff but I can find out :).  Other than that nothing out of the ordinary.  

I'm wondering... if you've  quenched copper in that tank before , could there be copper oxides dissolved in the water that are attaching to your steel?

Wow that's green alright I thought it had a light tinge to it until I saw the pics

Skiter dunks contain a bacteria

Green tint after forging and quenching doesn't automatically point to a hazardous coating. Since the bar was originally used as a machine shaft and appeared more corrosion-resistant than typical scrap, stainless steel is definitely a possibility. Stainless alloys can develop unusual oxide colors after heating, and the exact shade depends on alloy composition, temperature, atmosphere inside the forge, and the cooling process.

Old water can also contribute to surface discoloration, especially if it contains minerals, algae residue, or dissolved metals from sitting outside for a long period. If the color is only on the surface, try lightly sanding or grinding a small area to see whether the green tint disappears. That can help determine whether you're looking at a surface oxide layer or something deeper.

The magnet test mentioned above is a good next step. Another useful check would be comparing a freshly heated piece of known mild steel in the same quench water when you get the forge running again.

Interestingly, surface coloration caused by heat treatment isn't limited to forged steel. [Commercial material removed.] In this case, though, the lack of smoke and the limited rusting history make stainless steel oxidation seem more likely than a dangerous coating.

Edited yesterday at 01:28 PM1 day by Mod34
Commercial material removed per TOS