Re: "steel" vs "iron" [was:Re: Competing unions [was: Re: Native English]]


Paul Wolff wrote:
In message <dvgdb5$ggo$1@xxxxxxxxxxxxxxxxxx>, Father Ignatius
<FatherIgnatius@xxxxxxxxxxxxxxxxxxxx> writes
In news:OU+EJzVJogGEFwb7@xxxxxxxxxxxxxxxxxxx,
Paul Wolff <bounceme@xxxxxxxxxxxxxxx> typed:

Concrete may be only 20 percent cement; most of it is aggregate. The
sort of steel that is corrugated for sheeting is probably at least 95
weight percent iron, and fits the coffee test. Cast iron may have
less iron than steel has. Calling an iron alloy 'steel' rather than
iron only signifies that it has been processed to a more controlled
condition than the crude metal, though it must have some carbon or
metal alloy to differentiate it from soft iron.

I'm a bit troubled about the term "soft iron" in this context as, IIRC,
cast- and wrot-iron are harder than steel, in the sense (of no other) or
being brittle. AFAIK, "soft iron" means orin that loses its magnetism
quickly, i.e. inapposite here.

By 'soft iron' I meant nearly pure iron, saving one word, as I thought
at the time. Cast iron is quite carbon-rich, a reason for its
potentially having less iron than steel does. Wrought iron doesn't have
any particular composition range by definition, but is likely to have
one in practice. Soft iron has very little carbon and very little of
anything else. Its magnetic properties are consequently similar to
those of elementary iron. They don't bear on the discussion of iron
versus steel nomenclature.



I think you understand the concepts here, but perhaps not all do.
Elemental iron is, as you've stated, relatively 'soft', and highly
susceptible to oxidation. (Which is why iron-rich soils are so
characteristically red: it's iron oxide, or rust.) Elemental iron is
not what people would think of as "iron" in the sense of the wrought,
cast or forged iron or steel seen in use around the world--until it is
combined the proper alloying ingredients and processed in various ways
to produce the things we use daily. When alloyed with carbon (for
hardness) and other elements (in trace amounts only) the alloy takes on
very divergent characteristics, for hardness, ductility, corrosion
resistance, etc.

Cast iron doesn't refer only to how much carbon is included in the
alloy, but also to how the metal was formed and processed, which
affects its molecular grain structure to give it the properties it has
for holding a shape and retaining its hardness. The amount of carbon
involved in the alloy is tiny; we're talking less than 0.5% or so. The
molten compound is poured into molds that create the shapes desired.

Structural steels involved in building construction and piping are
created using a different process. The near-molten steel alloy is
forged by extruding it under pressure through shaped dies to create the
structural shapes needed, from I-beams (and W, H, C and L shapes), to
pipes (or O-beams, as we joke about them in construction). The steels
needed for this type of application need to be more ductile (malleable)
than cast iron, so the alloy has less carbon (typically around 0.3% or
less). The strength required for building construction is not in
"hardness" so much as ability to maintain tension and withstand
compression and shear strength.

In steel pipe and tube shapes, depending on the elements to be
transported inside the pipe and the environment outside the pipe to
protect it from, plus the pressures to be withstood (inside and out)
the materials range from "simple" carbon steel (where "high carbon" is
still less than 0.3% of the alloy) to "stainless steel" and other
high-alloy compounds. High-alloy steels containing, for example, up to
2.25% chromium, 1% molybdenum, and trace amounts of various other
elements, AND strict control of the processing temperatures and heat
treatments given to the finished shapes, so that the desired
characteristics are retained and enhanced, are suitable for
high-pressure steam inside furnaces (for superheatered steam to drive
power generation turbines, for example), while lower carbon steels are
suitable to make the water and lower-temperature steam furnace walls
themselves.

On the other hand, "black iron" carbon steel pipe also works for low
pressure, low temperature water (non-potable) delivery for use in
agriculture and processing, and for waste disposal.

Plate steel is formed with the same alloying and processing as descibed
above, but run through massive rollers to achieve the desired
thicknesses, and *** steel is just run through more and more rollers,
successively closer together, to produce the finished product that ends
up in car bodies, kitchenware and appliance panels, for example.

Wrought iron is something I don't know much about (composition and
primary production), but the iron shapes are heated in forges and then
pounded and twisted into shapes for (mostly) ornamental and light
structural uses.

.