Sudden rust

[svincent]

Greetings!

I'm relatively new, to the community, and to blacksmithing -- so if this is a stupid question, please bear with me. :-)

I have a propane forge and am messing around, making tapers and leaves out of mild steel (new from Metal Supermarkets).

Strangely, the steel rusts suddenly as it cools -- like I get it orange-yellow hot, let it cool down, and a layer of flash rust immediately coats it.

I've not seen this happen in any of the online videos, and none of the books talk about it: the oxide scale, yes, but not brown rust.

Any thoughts/ideas? Is there something I'm doing wrong?

Thanks for any help!

-Shawn.

[Ten Hammers]

Tell us more about your gas forge please.

[Ratstomper]

Are you letting the pieces air cool or are you quenching them? I've seen steel rust pretty quick, but not as quick as it sounds like you're saying...

[Frosty]

Welcome aboard Shawn glad to have you.

I'm primarily a gas forge guy but I've never seen red rust form that fast, scale yes not red rust. Have you tried scrounged steel? With the world's markets being what they are I don't think new steel can be counted on to be any one analysis so it may corrode differently.

If it's causing problems you can flux the stock lightly as you remove it from the forge. I'm not a fan of quenching steel unless it's necessary to the process, say hardening or handling quickly but quenching may do the trick for you.

Frosty The Lucky.

[quint]

Just a new guy but was wondering could the forge be running to lean, I remember reading something about that but think it caused more scale or something. Just a thought.

[rockstar.esq]

I use a coal forge however if I stick the metal down low in the fire pot it scales much more rapidly. I've read this is because unburnt oxygen is oxidizing the metal. The coal solution is to put the metal higher in relation to the pot. I suspect you might have a means to adjust the air / gas balance. If so, it may need to go towards less air.

[Frosty]

If the forge is running lean it'll scale IN the fire. Any hot iron will scale in open air which is sort of what this problem is. I've just not encountered rusting, scale yes, not rust.

Frosty The Lucky.

[postleg]

I use a 3 burnner Diamond back forge and I've seen what you are talking about. It dosen't cover the hole piece but I get spots that seem to have a red rust on them as they cool. I just figured it happened to everyone.

[svincent]

I've got a 3 burner atmospheric propane forge. It's lined with kaowool, kast-o-lite 3000, and Plistix 900F. I can adjust the air mix (I'm sure it's not adjusted particularly well) -- I had assumed that this would cause more or less scale.

My red rust tends to be in spots as well, like you say, Postleg. I've been wire brushing it off, but it seems to keep coming back.

My anvil has rust on it in places -- could it be "contagious"? I don't know if it's an old wive's tale, but I've heard the phrase "rust breeds rust".

I also wondered about humidity in the air -- although I thought if that was the case that it would be much more common.

Frosty, when you say "flux the stock lightly", can you elaborate? What would I use to flux?

Thanks very much for your help! When I get back home, I will try adjusting the air mix and see if that makes any difference.

-Shawn.

[Frosty]

What I mean by fluxing lightly is to just sprinkle just enough borax on the piece to glaze it when it melts. The borax will prevent oxy from reaching the hot steel. This isn't something to do all the time, it's just to prevent rust or scale that's causing problems with the work.

About adjusting your air:fuel mix. If your forge has a little orangeish flame commonly called "dragon's breath" coming out the door it's not lean. (oxidizing) When I say a little orange I mean a LITTLE orange tinge, if it's more or less opaque orange or worse yet yellow it's WAY TOO RICH and dumping prodigious amounts of carbon monoxide (CO). While CO isn't actually toxic it will do you harm in no uncertain terms. First it'll replace oxy in your blood and because it has a stronger bond to hemoglobin it's very hard to get out of your blood, think hours in a hyperbaric chamber. It's odorless, colorless and it'll suffocate you by making it impossible for your blood to absorb enough oxy to support life.

Okay, if your forge isn't making scale in the fire it's running neutral to slightly rich which is good.

Oh yeah, no matter how your forge is adjusted it'll be generating CO so it's a REALLY GOOD idea to have some cross ventilation AND a CO alarm. They're cheap and can be found everywhere, our Safeway store carries a couple brands of fire and CO alarms.

I can't be more specific than this without more info and the best info for me is a picture or two. One looking right at the flame from the front will tell me a lot about your burner. One from the side in dim light so I can see the exhaust flames will tell me a lot about your air:fuel situation. Once I have an idea what's going on I can be more specific.

Oh yeah, only make ONE small adjustment at a time and see what happens. If you adjust more than one thing at a time you'll NEVER know what did what and you're likely to get farther from ideal than closer. Stick with methodical rather than poke and pray guesswork.

Well, I've probably babbled enough for one sitting. I just hope I was more clear than it looks right now. <grin> Any questions, just ask I'll do my far away best. Soon as I check my computer that is.

Frosty The Lucky.

[Frank Turley]

I have sometimes got a quick film of reddish rust on forged work, especially if the workpiece had already a deeper rust before I started heating and beating. I'll share something that a Japanese sawmaker sensei, Yataiki, told us at his workshop in Iowa. He said that when making a flat tool, to "wash it" preferably with rain water. He said to wet the anvil and wet the hammer and to hammer at a cherry heat down to a faint red, and to repeat this eight times. Yataiki said that doing so would get rid of present rust and would protect the tool from rusting in the future. He admonished us, "Don't worry about the science of it; just do it!"

The Japanese toolsmiths and bladesmiths have a small whisk hanging near their workspace, and they use it to dip into the slack water and apply to the anvil. As a Westerner, I was also shown the washing method when flatting forged ironwork to get rid of hammer marks. We use a blood red heat and water, as the thermal shock helps to pop scale and "clean the work."

[Alan Evans]

Greetings!

I'm relatively new, to the community, and to blacksmithing -- so if this is a stupid question, please bear with me. :-)

I have a propane forge and am messing around, making tapers and leaves out of mild steel (new from Metal Supermarkets).

Strangely, the steel rusts suddenly as it cools -- like I get it orange-yellow hot, let it cool down, and a layer of flash rust immediately coats it.

I've not seen this happen in any of the online videos, and none of the books talk about it: the oxide scale, yes, but not brown rust.

Any thoughts/ideas? Is there something I'm doing wrong?

Thanks for any help!

-Shawn.

Never stupid to ask questions...

Your description of the speed the red forms sounds unusual. Is it definitely appearing while you watch it out of the black oxide surface, or is it just there when the metal has cooled down? If its the latter it sounds more like a form of soot or other contamination than rust.

If you heat a piece of galvanised or zinc plated steel to red heat, the zinc burns off and can leave a white powdery residue. Is there any lacquer or rust prevention coating on this steel? does the colour continue to appear after the second or subsequent heats?

If you are sure it is rust (scrape a bit off onto a board and see if it will be picked up by a magnet) you may have discovered a new process we can all benefit from for patination! We will just have to reproduce the exact circumstances.

I have sometimes got a quick film of reddish rust on forged work, especially if the workpiece had already a deeper rust before I started heating and beating. I'll share something that a Japanese sawmaker sensei, Yataiki, told us at his workshop in Iowa. He said that when making a flat tool, to "wash it" preferably with rain water. He said to wet the anvil and wet the hammer and to hammer at a cherry heat down to a faint red, and to repeat this eight times. Yataiki said that doing so would get rid of present rust and would protect the tool from rusting in the future. He admonished us, "Don't worry about the science of it; just do it!"

The Japanese toolsmiths and bladesmiths have a small whisk hanging near their workspace, and they use it to dip into the slack water and apply to the anvil. As a Westerner, I was also shown the washing method when flatting forged ironwork to get rid of hammer marks. We use a blood red heat and water, as the thermal shock helps to pop scale and "clean the work."

The smith I worked with, Alan Knight used to spit on the anvil to make the scale pop off. The other time he would do it was with an evil grin, a wink to me, and a welding heat when he was fed up with whoever was hanging around bending his ear, a shower of sparks at crotch height seemed to be quite off putting to some people...can't think why!