Adventures in Physical Metallurgy of Steels

During July 2013 I attended Adventures in Physical Metallurgy of Steels hosted by the Phase Transformations and Complex Properties research group of the Department of Materials Science and Metallurgy.

The programme looked like this, videos are appearing on bhadeshia123’s channel on youtube (links). There is also a playlist available.

Programme
Introduction to Adventure. H. Bhadeshia

Architectured Steels, T. Koseki

Magneto-structural coupling. I. Abrikosov

Quench and partitioning. J. Speer

Crystallographic variant selection. S. Kundu

Secondary hardened bainite, J. R. Yang

Welding of high carbon steel, K. Fang

Isotropy and Fatigue: P. Ölund

Atoms in bainite, atomic mechanisms. F. Caballero

Pulsed steels, R. Qin

Fullerenes & buckyballs in steel: I. V. Shchetinin

Boron: Type IV cracking, F. Abe

Low-density steel, H-L. Yi

Friction stirring of steel, T. Debroy

Flash Processing, G. Cola

Reliable first principles calculations for iron: A. Paxton

Steels composites for energy applications, C. Capdevila-Montes

Microstructures without contact, C. Davis

Pop-in deformation, H. N. Han

Plausibility of fine bainite, C. García-Mateo

Reduced Activation, K. Wu

Architectured microstructures, G. Anand

Flash microstructure, S. Babu

Energetic TWIP, D. Dye

Mass production of fine bainite: A. Rose

Voids and 30000 atoms, S. Munetoh

Soft Particles, T. Tsuchiyama

Mechanochemistry, F. Miani

Simplex and Kappa steels, I. Gutierrez-Urrutia

Innoculated high-speed steel, A. Chaus

Non-cubic ferrite, D-W. Suh

Montage of events

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Superbainite

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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Audi’s audacious aluminium advertising artifice

Audi’s advert for their A6 is really beautifully made…

Suppose you could make metal do anything you wanted,
use it in ways no one thought possible,
at Audi that’s what we do,
the new Audi A6 with Aluminium-hybrid body,
engineered for a lighter touch.

The way the metal forming is done in the advert is really nice, just shaping the parts by hand, just like the clay model can be formed when producing models of the car.

The technology is interesting, and challenging, a combination of aluminium and steel parts are used to make the car body. About 20% of aluminium by weight of the car body is aluminium, that means about 40% by volume. Non-load bearing parts such as body panels are aluminium (which benefit from good stiffness/weight ratio). All of the car body is made from cold formed and warm formed steels as in conventional car body. Interesting, aluminium sections seem to be present as side impact bars and bumper. From the advert you might be left with the impression that the whole body is aluminium, or that this is something that would be desirable, especially confusing since ‘hybrid’ is also now commonly used to refer to automobiles which use combinations of different power sources for the engine.

This video shows which parts of the car body are aluminium and steel.

However these cars overall are not much lighter due to the use of aluminium. From the previous model of A6 the weight saving is 30 kg, the weight if the total car is 1575 kg unladen or 2,155 kg gross weight (figures for 4 door 2.0 diesel). I want to look up the weight of Audio A6 since they are first introduced, that’s because in all cars there has been a trends towards increasing weight, despite all the advances in decreasing the weight of the car body.

Japanese Swords are medieval nanotechnology

During Japanese sword making the steel is folded repeatedly. Each time the steel is folded the structure is refined.

The folding is a key process in sword making. Folding and striking the metal forges the surfaces back together. This process of folding, then forge welding, can be repeated as many as 16 times. The process removes impurities and helps even out the carbon content, and controls the scale of chemical segregation, and it is this which results in alternating layers of hard and ductile material.

So how can folding the steel result in a nanoscale structure?

When the steel is folded the number of layers obviously increases geometrically. 1 fold result in 2 layers, 2 folds results in 22 = 4 layers, 3 folds results in 23 = 8 layers. By the time we get to 15 or 16 layers we have 32768 layers or 65536 layers. After that the sword is forged out to have a width of around half a centimetre.

5 mm divided by 65536 = 76 nm.
(5e-3/65536=7.629e-8)

So each layer is 76 nm. So we can legitimately argue that Japanese Swords are bulk nano materials, with structure controlled on the ‘nano’ level, for metallurgists this is just routine stuff.

Edo period Forge Scene

Edo period Forge Scene

Of course Japanese swords are not true examples of nanotechnology, despite the validity of the maths the folding doesn’t really result in a controlled structure on the nanoscale due to the changes that occur during the welding process… I plan to talk more about that in a later post.

As you can see below, the laminations are typically visible on the millimetre scale.

Lamination on Japanese Sword

Lamination on Japanese Sword

Breaking the Glass Ceiling Since 3000 BC

Archaeologists in Austria have found evidence that women were metalworkers during the Bronze Age:

The Museum of Ancient History says the grave originates from the Bronze Age, which began more than 5,000 years ago and ended 3,200 years ago.

In a statement on Wednesday, it said that although the pelvic bones were missing, examination of the skull and lower jaw bone shows the skeleton is of a woman.

The museum says tools used to make metal ornaments were also found in the grave northwest of Vienna, leading to the conclusion that it was that of a female fine metal worker.

It says such work had been commonly presumed to be in the male domain.

Perhaps discoveries like this will challenge conventional ideas about the division of labour in ancient societies. Metallurgy and metalworking have been male-dominated subjects for virtually all of time, so it’s interesting to see that women were still involved even at the earlier points in its history. This woman was identified as a metalsmith thanks to the grave goods that were buried with her: an anvil, hammers, flint chisels and some dress jewellery. In fact, it makes a lot of sense that Bronze Age women could be metalworkers. Materials like copper and tin* can be melted by a kiln without needing to pump a lot of excess air to feed the fire. Contrast this with ironworking, which requires a great deal of physical strength to pump air into the fire, and to shape the iron by hammering at arms’ length. When we think about smithing, the picture that comes to mind is a burly blacksmith in a forge, hammering away at a sword. Yet bronze was frequently used to manufacture household items like knives, needles, pins, mirrors, jugs, pots and cauldrons. Women were known to be exceptionally skilled potters. The question is: were they as good with metal as they were with clay, or did pot-making suddenly become mens’ work? Bronze is not particularly difficult to cast or grind and much of the early labour that is classed as womens’ work (cooking, pottery, childrearing, gathering unaccountably pink berries) involved a lot of working with fires and moderate physical activity. If a woman can grind corn, she can grind bronze.

Maybe women were also involved in the discovery of new metals and techniques. Gold was the first metal to be discovered and worked by humans, and early goldsmiths would collect gold nuggets from stream beds. If women did take on the role of gatherer in their societies, it could well have been a woman who found the first gold nugget, while collecting water from a stream or gathering fruit nearby. Meanwhile, archaeologists believe that copper smelting first took place inside pottery kilns (since campfires are not quite hot enough) – another domain of women. Tin and lead are more easily smelted, and this discovery was probably accidental, involving either a campfire or a cooking fire.

There is currently no way to know for sure whether this woman was an outlier even in her time, or whether Bronze Age societies routinely had female as well as male metalworkers. Some iconography does seem to imply that there was a division of labour according to sex but this is only a tiny snapshot of life at the time, and gender-specific artefacts are rare. Much archaeological excavation tends to focus on domestic locations within settlements, whereas typically ‘male’ activities like hunting and metallurgy would have taken place in other areas, so evidence of these practices is less likely to enter the archaeological record. The preconceptions of archaeologists must also be taken into account. It would be interesting to see how often a woman’s skeleton has been excavated, revealing that she was buried with weapons or tools, and the explanation provided was that the burial goods were purely decorative, and unrelated to the woman’s actual occupation. The issue of gender bias in archaeology is not a new problem, and only in the past few decades have archaeologists begun to recognise that this needs to be corrected, by becoming aware of their own inbuilt preconceptions and how these preconceptions might affect their interpretations of ancient life.

*Fun fact: the earliest bronzes were actually alloys of copper and arsenic. Tin came along much later. Unfortunately, the fumes created during the manufacture of arsenical bronze have some unpleasant side effects, one of which is permanent nerve damage. Some people have speculated that this is where the myths of Hephaestus – the lame Smith of the Gods – came from.

100 percent alloy

Great pedantic comment on the Amazon website.

100% alloy rant.

Component was made of “100% aluminium alloy”. If people don’t know what alloy means, why are they so keen to claim they are using it? Just because they think ‘alloy’ means it is good.

Is the World Cup solid Gold?