> I question that. Wikipedia has an article about cast iron and
>> another one about steel. Though both kinds have iron plus
>> impurities, their properties are sufficiently different to earn
>> different names - and more important, different uses.
>>
> Iron may 'suffer' from impurities, whilst steel contains carefully
> controlled 'impurities' which are selected to give it the preferred > properties.
It’s quite a bit more confusing than that.
References to unqualified “iron” before the 19th century, and sometimes thereafter, almost invariably refer to wrought iron.
Wrought iron (which is no longer manufactured commercially, not since Thomas Walmley and Sons shut down the Aston Forge in Bolton in England in 01973) overlaps with mild steel in composition, but has a different macrostructure, with slag inclusions giving it a fibrous structure and reducing its susceptibility to corrosion.
In the specific case of *cast* iron, “iron” *also* "contains carefully controlled impurities which are selected to give it the preferred properties". In fact, the main impurity in both cases is carbon. Cast iron has quite a bit more of it (over 2%) than steel; low-carbon “mild” grades of steel can have as little carbon as wrought iron does. Roughly speaking, the usual ferrous grades are something like this:
- 0–0.1% carbon: wrought iron
- 0.05–0.3% carbon: mild steel
- 0.3–2.1% carbon: carbon steel
- 2.1–4.5% carbon: cast iron
- 3.5–4.7% carbon: pig iron (rarely seen outside foundries)
Also, if you have 10.5% or more of chromium, it’s “stainless steel”, even if it has no carbon.
Cast iron normally also contains silicon to improve its casting properties.
From the perspective of anyone who has studied this stuff, the above is a terrible oversimplification, since there are hundreds of grades of steels, with dramatically different properties, and different pieces of steel may even have the same composition but dramatically different properties due to heat treatment.
This is almost certainly off-topic for alt.usage.english at this point, but which of the still-active newsfroups would be best for it?
Kragen