Structure of superbainite. Inset is a same-scale image of a carbon nanotube. [1]

Structure of superbainite. Inset is a same-scale image of a carbon nanotube. [1]

According to archaeologists, the Iron Age began in 1300 BC and lasted for around two millennia. Today, steels (alloys of iron and carbon) comprise 95% of global metal consumption and this trend shows no sign of declining.

Glancing at the media, however, one would be forgiven for assuming that steel is now a has-been. We are bombarded with stories of novel materials: carbon nanotubes, metallic glasses, graphene, carbon fibre, nickel superalloys. . . all of which are “stronger than steel”.

“Now we can construct space elevators!” claim the articles. “Let’s build a climbing frame to the moon! We’ll use this stuff to make everything!”

The observant among us, however, will note that most cars, trains and buildings still don’t feature superalloys, metallic glass or magic nanotubes. Neither are they invisible; nor do they fly; nor do they do any of the other things that journalists tend to ‘predict’.

Instead, steels somehow remain the best — and cheapest — materials for the job. Also, they are stronger than steel. This is because ‘steel’ is a vague construct used by sensationalists, with an unspecified strength guaranteed to be less than that of a novel material. Metallurgists rarely refer to ‘steel’, just as the Inuit have fifty words for snow, not one of which is ‘snow’.

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Density of Iron Carbide (Fe3C)

There are 4 molecules of Fe3C per unit cell. The cell is orthorombic, typical lattice parameters at room temperature are given below from Mehl etal, Trans AIMME, 1933.


m = mass of 1 mole of unit cells
= 12 x FeRAM + 4 x CRAM
= 12 x 55.845 + 4 x 12.011 = 670.14 + 48.044
= 718.184 g/mol

Fe3C unit cell is 718.184 g/mol

v = volume of 1 mole of unit cells
= AV x a x b x c
= 6.0221415 × 1023 x 4.518 x 5.069 x 6.736 x 10-30
= 9.2901×10-5 m3

d = density
= m/v
= 0.71814 kg / 9.2901 x 10-5 m3
= 7730.14 kg/m3