black steel

[junker]

what about the forge turns steel black? is it just a solid fuel thing or does propane do it too? is it an oxidation? :blink:

[southernforge]

Oxidation.

[fciron]

The black scale that forms in the forge is an iron oxide that forms at high temperature, as compared to rust, which forms more slowly and at lower temperatures. All that scale flaking off your steel is chemically the same as hematite, but those thin flakes are really hard to make jewelry with.

Since it's related to temperature it occurs in both gas and solid fuel forges. A lot of smiths feel that gas forges actually create more scale. Personally I don't think it's inherent to gas forges but a result of the material sitting longer at scale forming temperatures in the forge.

[ThomasPowers]

Well actually the black oxidation is Magnetite, Fe3O4, and the red is Hematite, Fe2O3.

Magnetite is essentially the same as the black sand smelted to make japanese swords, I'm collecting it for doing a scandanavian short stack bloobery run myself.

Gas forges can be anything from extremely reducing to extremely oxidizing depending on how they are constructed and tweaked. Aspirated ones tend to be more oxidizing as you can't choke them as well due to how they work, (and the more sloppily the burner is built the more "free air" it needs to work without messing up).

Since leaving your stock in a coal forge too long can result in it disappearing while you can tune your gas forge to let it sit all day there we may have a user perception issue---stuff gets left longer in the gas forge and so scales more and that's considered to be that gas is more oxidizing.

[MattBower]

Gas forges also tend to heat longer portions of the work, which probably results in more scale than you'd end up producing with smaller, localized heats.

[Wesley Chambers]

Gas forges also tend to heat longer portions of the work, which probably results in more scale than you'd end up producing with smaller, localized heats.

adding a lump of coke to burn in your gasser can reduce your scale buildup~

[Frosty]

short stack bloobery run myself.

When I read your reply Thomas I wanted to ask if you were going to put up a video but then I got this mental image of an old fart's short stack on a bloobery run and am so creeped out.

Seriously though you're pretty much right on the money once again. The only thing I have to add being, it doesn't matter what kind of forge you use if it has a reducing atmosphere it isn't going to scale IN the fire. As soon as you remove the iron/steel to open air it's going to start scaling, the hotter the faster.

Frosty the Silly.

[MattBower]

As soon as you remove the iron/steel to open air it's going to start scaling, the hotter the faster.

Yup!

[canada goose]

Interesting question!thanks

[canada goose]

And thanks for the answers.

[fciron]

Well actually the black oxidation is Magnetite, Fe3O4, and the red is Hematite, Fe2O3.

Ok, I just assumed it was the same stuff as the jewelry because of the similar color. Now I know what to do with my five gallon bucket of scale, too. :rolleyes:

[junker]

thanks for the info, just was kinda curious seeing as i've never had anything rust where the black stuff was intact lols, figured it was something that blocked the oxy from the steel :blink:

[ThomasPowers]

Actually you can have scale "rust". Often seen when folks forge on a concrete driveway in a damp climate, you will start getting rust spots from the scale that wasn't cleaned up all the way off the concrete.

I'd correct that typo If I could; but IFI won't let me edit the post anymore...