I am just wondering what is exactly cast iron ?
It is dark gray color and I have seen in cooking pan.
I also want to know where I can buy as raw marerial.
Are they weldable ,machineable,?
Thank you very much in advance.
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
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.
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.
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.
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
are many other suppliers.
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.
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.
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
In addition to that, I have successfully welded cracked exhaust
manifolds with my cheapy wirefeed and plain steel flux wire. Several of
these manifolds have years on them now with no weld failures.
Dweller in the cellar
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.
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.
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.