Over in rec.crafts.metalworking and alt.machines.cnc, we can't seem to come
to a conclusion regarding steel.
Is it a mechanical mixture, solution or compound? Or, is it two or more, or
something else completely?
Basically my metallurgy instructor said it was a "compound" and a "solid
solution". I suppose it is, but from what I've heard, it's not that simple.
I'm just a simple tool and die apprentice, so it's not _really_ important,
but I'm interested.
Thanks for any thoughts...
Hardenable normalized steel is a heterogeneous alloy consistig of
ferrite (solid solution) and cementite (compound).
When hardened, it is martensite (solid solution).
There are always additional inclusions (compounds) present.
Congratulations for having decided that you need more expertise than a
bunch of "fans" who can't decide the definition of "steel", and who
can't bring themselves to look it up.
It is composed of compounds (iron carbides) and mixtures at the atomic
level(dissolved carbon in ferritic or austenitic matrix of iron) and
mixtures at the microscopic level (the iron carbides and iron atomic
mistures forming things like the Pearlite regions in steel).
You might appreciate this reference site for many things metallurgical
and in more or less fairly plain English.
Just by reading a few things at this site, you may find out how
misinformed some "fan" posters can be.
Careful, you might find that you like actually knowing about the
That's just about the most belittling comment I've ever heard on a news
group, mostly due to the fact that it didn't appear induced. Do I sense an
What do you mean "fans"? I work for a heavy stamping die maker in the
automotive industry and many other folks on those newsgroups are cutting
metal for money as I type this message...
I think that's the issue. I don't understand how some of the carbon is in
solution, and some is in a compound. Or perhaps it's both at once. I'm used
to molecules having a specific number of one atom and a specific number of
another. However, I don't know very much about metallic bonding at all, so
it's just my ignorance.
Thank you. Very interesting.
Indeed! And what about the rest of the posters on this *professional* group
that gave the wrong answer?
I've always thought that once you see one mistake on a print, you don't
trust the rest...
Not sure where _that_ came from, but OK.
Some of the people are "fans" of materials as some people are "fans" of
Some people are "players" of either.
If the choice of the term "fans" irritates your rectum, you are
listening with the wrong end.
Players come in all skill and knowledge levels. Some get booed, sometimes.
Absolutely correct, and in simple terms I attempted to explain it.
Do you understand that salt is dissolved in water? And if you have
enough salt in water, some of it is dissolved and some of it is just a
physical mixture (the undissolved part).
There are many other examples that can be given.... including dirt and
water where some parts of the dirt dissolve into the water, and other
parts of the dirt swirl around as a mixture of fine particles. If you
fish on most rivers, you can see this as you fish.
Or that ethyl alcohol can be dissolved in water? The salt breaks down
into ions of sodium and chlorine. The alcohol literally dissolves or
mixes as an intact molecule.
If yes, then you should have no great difficulty in metals being
dissolved in another metal in the molten state.
Most of the understanding of metal mixtures in the solid state comes
from looking at chemically etched metals with microscopes and other
instruments, making some measurements, and then *thinking* about the
meaning of what it is that you saw. If you have done only the "big
picture" stuff of working with the metal mixtures with your hands,
machines and naked eyeballs, you have decreased possibility to readily
grasp what metal mixtures (alloys) are all about because you have no
experience approaching a fundamental behavior level.
There is something in the textbooks besides artfully arranged ink on paper.
Steel is a bit more complicated than a chemical compound made of
A simple model to think about might be coffee where you have stirred
in some sugar. (ie you have a solution of sugar in coffee). Then
keep adding sugar until there is so much that no more can dissolve.
Now you have got a mixture of two phases - one phase is sugary coffee,
the other phase is wet sugar. Sugar is present in both phases. The
wet sugar phase can have a number of different forms, ie small
crystals or big crystals, etc, depending exactly on how you mixed it
To apply the model, mild steel as you would normally use it consists
of two phases. alpha-iron (carbon dissolved in iron) and cementite (a
compound basically iron carbide). Carbon is present in both phases.
The cementite phase can have a number of different forms depending
exactly on how the steel has been made - and the physical form of the
two phases is a major factor in determining the properties of the
Why is top posting bad? Do you like to scroll through all of the previous
text? This is a serious question. I prefer top posting. Maybe it has to do
with your interface. Do you read news via an outlook type or on the web?
I did not top post. Ian Kemp quoted some of my post at the top of his
message, and then he quoted the rest of my message below his, including the
part he had already quoted.
After posting thousands of messages on various newsgroups over the past 5
years, I have gotten into the habit of not looking below someone's sig at
the bottom if there is basically more than two blank lines. I just assume
there's nothing there.
If you look back, I did bottom post and I did trim the quoted portion of the
message to which I was responding.
Anyway, thanks for the answers.
At a given carbon level, and assuming you're not quenching to
martensite, you will have a set percentage of cementite (Fe3C)
present. The distribution and size of the cementite can vary
depending upon cooling rate,etc, but the amount present will be fixed
due to the set amount of carbon that can be dissolved into solid
solution (0.005%?), and the set ratio of Fe and C in Fe3C. This can
be calculated using the Tie Line and Lever Law using an Fe-C binary
In the book "Model Engineering--A Foundation Course" by Peter Wright, on
page 47 while discussing the hardening of carbon steel, it is written:-
Steel which has 0.87 per cent of carbon is known as eutectoid
steel. Its structure comprises thin particles of cementite
alternating with similar particles of ferrite, in the ratio of
87 per cent ferrite to 13 per cent cementite. This particular
structure is known by the name Pearlite.
I have done a calculation of the amount of carbon in Pearlite and it
appers to be 0.43 per cent insteaad of 0.87 per cent. I present it here
and ask for comments:-
Cementite is Fe3C. The atomic weight of iron is roughly 56 and the
atomic weight of carbon is roughly 12 (the actual differences are very
small). Thus, the ratio of carbon to iron in cementite is
C/Fe = 12/168
Thus the proportion of carbon in cementite is 12/180 = 1/30
Because the proportion of cementite to ferrite is 13/87, we have
Fe3C = 0.13
C = 0.13/30
=0.43333... per cent
this is roughly half what the author says.
If my calculation is wrong, why is it wrong? If it is correct, I shall
apprise the author accordingly.
Software Engineer specialising in Algol 68
email@example.com (Sian Leitch) wrote in message
Right here at
"Thus the proportion of carbon in cementite is 12/180 = 1/30"
Acually 12/180 = 1/15, at least if you're working in base 10.
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