What is cast iron?

wikipedia has a much better description than I could hope to duplicate. To my surprise, it turns out not to be unalloyed iron, as I'd always assumed: it's actually iron alloyed with carbon and silicon, with more carbon in it that steel has.

It's pretty unpleasant stuff to work with. It's really brittle, and it's hard to weld.

Cast iron is often described as an alloy of iron and carbon, but it also contains a significant amount of silicon. Typically it contains between 2 % and 4 % carbon and between 1 % and 3 % silicon. Oddly enough, this makes it a less pure form of iron than mild steel. Mild steel typically contains less than 0.2 % carbon and less than 0.6 % silicon. Historically, cast iron is not too far removed from pig iron, which comes straight from the blast furnace in which iron ore is smelted. The carbon in the pig iron comes from the coke which is burnt to heat the blast furnace. The silicon comes from silicon dioxide, which is a major component of rock which is mixed with the iron ore. Mild steel is formed by blowing air or oxygen through or over molten cast iron to oxidise the carbon and silicon, facilitating its removal.

The difference in carbon content is responsible for many of the differences in the properties of mild steel and cast iron. Cast iron is harder to weld than mild steel. It is less ductile than mild steel, so it tends to fracture rather than bend. Its high carbon content means that during machining, or when used as a bearing, a layer of graphite forms on the surface. As you will know if you've rubbed your finger against the end of a pencil, graphite is slippery, and this means that cast iron has better bearing and machining properties than mild steel. Sometimes mild steel has a small amount of lead added to improve its machining properties.

The higher carbon and silicon content of cast iron lowers its melting point and makes it less viscous when molten, which makes it easier to cast.

You should be able to buy cast iron in the form of stock intended for machining from a good metal stockist, although it is less readily available than mild steel.

Best wishes,

Chris

Thank you ,Joe and Chris... Do you know why cast iron pans are good for health?,some say its better than stainless steel . I thought more silicon and carbon is not good for health..am I wrong??

Yoshi.

Depending on what you cook in them, cast iron pans can be a source of dietary iron. If you eat as much meat as most people in modern industrial democracies do, though, you don't need it.

Sand and soot, basically. Won't hurt you; and in any event, they won't dissolve out of a cast iron pan into your food anyway.

I don't know I'm afraid. But I have a suspicion that most stories about the metals used for cooking pans and their effects on health are not based on fact. I would be very surprised if what pans you use makes any difference to your health.

Best wishes,

Chris

Carbon is, of course, necessary for health! The "worry" with stainless steel is that it has other elements in the alloy -- chromium (by definition), and normally nickel and some others. These are much, much nastier than anything in cast iron. But I've never seen any credible argument that this stuff actually gets transferred into the food, so I don't worry about it.

The advantage of cast iron in cooking is that it's really good at heat transfer, so you end up with a more even heat in your pan. When properly seasoned, it's also pretty much non-stick.

And one I forgot...

Cast iron is considerably more resistant to corrosion than mild steel.

Best wishes,

Chris

Nice post, Chris. Informative & succinct. Bob

There's a lot more to cast iron than the grey cast iron used for pans & woodburners

======== Cast iron has very good vibration dampening, and machines well. It is however "dirty" because of the included carbon. It is very hard to weld requiring special high nickel rods. Brazing is frequently used. Traditionally is has been used for machine tools, engine blocks and other heavy/strong items.

You can purchase cast iron rods and bars. One source is

There are many forms of cast iron including gray, white [harder than my head], (FWIW gray and white iron may be the same "alloy", white is simply cooled/chilled faster when casting), malleable, and ductile. Even today many components are made from cast iron such as turbocharger housings that would be difficult to make from any other materials.

Cast iron is THE basic material for any industrial society.

Unka' George [George McDuffee] ============ Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.

Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.

Do a little reading, then, and be surprised. In particular, cooking high-acid foods such as tomatoes or citrus fruit in aluminum pans is inadvisable: enough aluminum dissolves into the juice that it *can* be tasted. And aluminum in your diet ain't good for you. And cast-iron cookware can be a source of dietary iron, particularly if you cook stuff like tomatoes in it.

Especially when properly seasoned!

Most machinists hate to machine cast iron... besides being very dirty from the free carbon that gets all over the place, the carbides and other crap get on the ways and do a number on them if you dont constantly keep wiping them. Some cast irons have more free carbon than others.

John

If you know the techniques, cast iron is not that hard to do. In a pinch you can use stainless rod or even mild steel rod. The secret is to heat the cast iron until it stops expanding. This happens at about 900 degrees F. then do your welding, beat the crap out of it with a welders hammer and let it cool slowly under an insulating blanket that will allow it to cool very slowly. If you are welding a crack, stop drill a hole at the end of the crack so it does not keep getting longer. Do this before you heat it. The cast iron rods weld very easily, as a weldor friend says " it goes on like butter " The real secret is preheating.

John

Absolutely! Cast iron can be very complex.

Harold

Another good source of dietary iron is as follows: One shiny 16d nail. Poke a bunch of holes in an apple. Eat the apple. Due to the acid in the apple enought iron transfer takes place. Beats any iron supplement commercially available.

Ivan Vegvary

Food cooked in a cast iron pot always tastes better than in stainless steel pots, the reason is that cast iron is in fact porous, therefore it absorbs the particles of food, this does not necessarily mean that it is healthier to cook in cast iron pots, quiet the contrary.

Regards,

Joe

On Jul 12, 7:04 pm, john wrote:

Cast iron is indeed dirty stuff to work with. I used to weld a lot of it, with both stick and wire, and always did it cold, with long waits between very short passes. I didn't let the metal get much hotter than I could put my bare hand on, and peened the bead immediately after welding to expand it as it cooled. The weld metal is mostly nickel and shrinks much more than the cast as it cools and will pull away from the cast unless you peen it. Takes a lot of patience. Any machining after welding involves cutting through the hard transition zone, and that zone must be kept as small as possible, so very low amperages are used to avoid melting much cast. It's more similar to brazing than fusion welding. The cast must be very clean; cast is a little porous and will absorb large amounts of oil, and that oil will ruin the weld with porosity and excessive hardness. We used to bake the castings in a burnout oven at 750=B0F for three or four hours to get the oil burnt out. Back in the '70s I sold heavy truck wheels and brake parts. There were two American heavy brake drum manufacturers, and the one that made straight cast drums went on strike for about a year and the other outfit, which made steel-shelled cast iron-filled drums that cost way too much, couldn't meet the demand. We ended up having a plant in India make cast drums. The Asians have been masters of iron casting for a lot longer than we have, and those drums were cheaper and really popular with the truckers. They lasted twice as long. And they came packed two to a teak crate, wrapped in plastic with dessicant, whereas the American drums came straight out of the outdoor yard in Portland, paint faded and drum rusty. Until Kelsey-Hayes came out with their Gunite drums, we sold a lot of those Indian things.

Dan