See query. The old trusty cast iron pan (nowadays almost always made by Lodge).
I was seasoning one (flaming the hell out of it for an hour before coating it with oil) and thought “if my stove was a forge that sucker would turn red, then white,” and then realized I don’t know why it is black at room temperature to begin with.
The seasoning on a cast iron pan is carbon. A new cast iron pan is iron gray. If you heated your cast iron pan to red hot, it would burn off all the carbon seasoning.
Carbon for strength? If then, it is integrated metallurgically throughout?
Or carbon as (“seasoning”) top layer, for surface roughness interactions with food?
BTW, the words “integrated metallurgically” surely if not redundant is an illiterate way of putting it.
What is the correct way of saying “made into a new metal x with a portion of this and that?”
That would be an alloy. Rarely is iron pure. It will contain some amount of carbon and other metals. When the carbon content is just right it is steel.
As Lemur866 said, it’s the seasoning that’s black. The iron itself contains some small amount of carbon but that’s not what makes it black. Unseasoned cast iron is gray. The black color is from the polymerized oil that coats it when you season it.
BTW, your comment “(flaming the hell out of it for an hour before coating it with oil)” suggests you may not be seasoning it correctly. You should oil it first, then heat it. For even heating, it’s best to heat it in an oven rather than on the stove top.
Cites:
From Lodge themselves:
http://shop.lodgemfg.com/use-and-care/seasoned-cast-iron-use-and-care.asp
Others:
Yes, you are right. I was, in fact, showing off to my wife about the “real way” to do it (and I didn’t`t feel like emptying out the oven, and I needed the pan in about half an hour) which I would get to later.
Not sure if I accomplished anything beyond being a fake to my wife talking about “the iron ‘pores’ expanding.”
Adding carbon to iron as an alloy turns it into steel. But that’s not what happens when you’re seasoning a cast iron pan. A cast iron pan isn’t steel (iron + carbon + sometimes CHEMICAL X), but iron, that’s why it’s called a cast iron pan instead of a steel pan.
The seasoning is a surface layer of carbon. If you sandblasted your seasoned pan you’d see grey iron underneath. You can remove the seasoning by scrubbing the hell out of the pan, by heating super-hot so the carbon burns off, or by caustic chemicals. And underneath is plain iron.
The cast iron is pretty rough, and food will stick to plain rough iron. The carbon seasoning fills in the rough spots and makes a smooth surface that food doesn’t stick too that easily, although it’s not nearly as nonstick as teflon.
It’s also sacrificial.
If you scrub it so hard that you remove the seasoning, you can always season it again. Not true of a coated pan, like Teflon or ceramic. If you scrub those hard enough to remove the coating you ruin the pan.
True, but to clarify, you remove carbon from pig iron to make it steel, since the cast iron is the first product in many cases. Cast iron has so much carbon (around 4%) that it is found in microscopic clumps throughout the cast iron. This gives it its characteristic self lubricating qualities.
To make steel, first you must remove most of the carbon in an oxygen rich melt, like the Bessemer Process. Oxygen is forced through the melt to burn out the carbon. Then the correct amount of carbon is left in (or added) to make the desired steel.
Low carbon steel is only .020% carbon, while high carbon tool steels have .040%. We often name steels by their carbon content, typical low carbon steels are 1018 or 1020 (.018 to .020% carbon). 1040 steel is a nice high carbon steel that can be hardened by heat treating. Most modern tool steels have other elements alloyed as well.
Dennis
so you are saying cast iron has MORE carbon than steel does? I’ve seen nickel, copper, and silicates added for various cast grades along with carbon.
I can attest the flaxseed oil seasoning is awesome and lasts a long time
I just wanted to say, yeah, cast iron isn’t as nonstick as teflon but it’s nonstick in a very different way.
I’ve used both frequently over the years and just about the only things I will use a teflon or similiarliy nonstick pan for would be eggs or pancakes or something along those lines.
The sear or crust you get from cast iron can’t be matched by anything else, much less teflon. But it has to be a properly seasoned skillet or pan. And the user has to know what they are doing.
Correct. So much that it precipitates out in nodules throughout the cast iron. In addition to giving the cast iron it’s self lubrication quality it also affects the machining properties.
When I machine steel on a lathe, I get long, stringy, wire-like chips. Machining cast iron is a mess, you just get black powdery dust. The carbon nodules break up the chips as the metal matrix is not continuous.
Here is a short history of iron and steel making, a good read:
http://www.anselm.edu/homepage/dbanach/h-carnegie-steel.htm
Dennis
I agree. Part of it is that I don’t need to be afraid about heating up my cast iron pans all the way - other forms of nonstick are great at what they do, but need careful handling.
The difference between iron and steel is that in steel, the carbon is dissolved into the iron matrix. As mixdenny notes above in pig-iron the carbon exists as separate nodules that are not integrated into the iron matrix.
Ignoring the complexities of carbidies…
The dissolved carbon exists as individual atoms in the steel. This brings about the single most important characteristic of steels. Where in the matrix of iron atoms do the carbon atoms sit? An iron metal matrix is a cubic lattice. Think lots and lot and lots of cubes, all the same size, all neatly stacked in 3D. The iron atoms can be though of as sitting at the corners of the cubes. So how do you fit the carbon in? There are two things to notice. You can’t fit a carbon atom in without distorting the matrix. Those iron atoms will pack as tight as they can, so the gaps are small. The next thing is that there are two places you can stick a carbon (or other alloying element) in the matrix. You can stick it in the centre of the cube, so that it is surrounded by the 8 iron atoms at the cube’s corners. Or you can stick it in the middle of one of the faces of the cube, so that it is surrounded by the four atoms that make up a face. Unsurprisingly these two arraignments are called body centric and face centric respectively.
You can’t get much carbon into the steel, the distortions of lattice reach some way. What matters is that this distortion of the lattice acts to stress it. And because of this, the overall properties of the lattice change. The body centric configuration is very highly stressed in comparison, and becomes much harder.
The really neat trick is that it isn’t hard to control where the carbon atoms are sitting. If you heat the steel up to a high temperature the carbon atoms become quite mobile and will rattle about all over the place. If you slowly cool it down, they will tend to settle in the minimum energy configuration, which is in the centre of the faces. So the steel is dominated by face centric carbon. However if you cool the steel down very quickly you can catch a lot of the carbon atoms in the body centric location, and get the steel cold enough that the carbon atoms remain trapped there. So you can make the steel have a range of mixtures of face centric and body centric configurations. These two configurations have different properties. Managing the balance of the two is a critical part of hardening and tempering steel.
It turns out that the two configurations are evidenced by macroscopic properties of the lattice, and inspection of the metal with a microscope will reveal different appearances of the crystal structure. This is how the two were first discovered. The usual name given to the two structures are named after their discoverers, Adolf Martens and Sir William Chandler Roberts-Austen. So we have Austenite (face centric) and Martensite (body centric). These terms have no become applied to pretty much any other metal alloy for which similar configurations are found. However the relative strength and hardness of the Austentic and and Martensetic states varies from metal to metal.
To get hard steel you need to get the carbon content up enough that the above manipulations make any difference. Hardening steels have more carbon. Or you can diffuse carbon into the structure. Cooking steel with carbon (and a reducing atmosphere) can allow carbon to slowly diffuse into the surface, yielding an object that can have its surface hardened. But it takes hours, has to be red hot, and you need the reducing atmosphere. So, no matter what you do with seasoning your pan, you won’t be doing much to the actual iron.
The cooks illustrated method is one of the few instructions I’ve seen that will actually work. The caveat is, the high heat required makes a fair amount of smoke and will be stinky. It takes several iterations to build up a layer of several coats. A lot of directions say heat to 200°F, this results in a rancid, sticky pan that will rust, because the fat never carbonizes.
I’m not so sure if I agree with the assertions that cast iron isn’t as slick or nonstick as teflon. If the pan isn’t seasoned correctly they are correct. Done right it’s a distinction without a difference, and teflon tends to degrade over time anyway. Isn’t teflon a form of carbon anyway??
No, Teflon is a fluoropolymer. It is chain of carbon-fluorine bonds, and the fact that C and F bond so well together is what makes it non-stick.
Well so are human beings.
PTFE - poly-tetra-fluoro-ethylene. It is the tetra-fluoro (as in four fluorine atoms) that makes teflon what it is. Two carbon atoms per unit make the backbone, but four fluorine atoms replace the hydrogens you would expect. This is a very tightly bound compound. It reacts with essentially nothing, has a high melting point, and very low surface energy. You can thank the fluorine for that.