STEEL - Distempering (Softening); and Re-tempering.
You will see that this is a very multidisciplinary lab exercise!

    Steel is obviously an important structural and utilitarian part of our civilization. Iron is thought to have been first extracted from rocks by the Hittites, who lived in central Asia Minor (today's Turkey) around the closing years of the Old Testament at just about the time of the Trojan Horse (about 800 BC).

    Iron carbide, or steel, was first invented most likely in sub-Saharan Africa. It is mentioned by Italian caravaners who crossed the desert in about the year 1200 AD and found that the warriors of the King of Mali in the capital city of Timbuktu possessed swords made of it. While this might be surprising to have occured in this most out-of-the-way community, it should be noted that Timbuktu at the time was probably the publishing capital of the world - its main export were handwritten books. In the December 2006 issue of the National Geographic Magazine, this publishing prowess is the subject of a complete article.

    We will not go into the processes of making steel. However, we will do our own blacksmithing today, following in the footsteps of some many of the pioneers in our country.

    Two years after gold was discovered in California and the Rush was on, a company in a Boston suburb shipped as much as 10,000 gross of hardened steel files to points west of the Mississippi River. Now who in the world would use all those files? Housewives in many cases! They converted the files into knives and spoons, and other implements for use around the house. It wasn't the filing property they were interested in, but the extreme hardness of the steel.

    Of course, you are wondering how they can do anything with a steel so hard that almost nothing can scratch or dent it. Molly Pioneer will tell you: "'Tis simple. Jest stick it in the fire and soften it. Then bang it into witchever shape ya desire, and then reharden it."

    Today for one part of the lab, you will take some extremely hard steel pieces, note just how hard it is by its ability to scratch various things. The iron atoms in this are in a face-centered cubic (FCC) arrangement that, for iron, is called Martinsite. When you build a model of FCC, you see there are spaces that may be filled. In the case of steel, which is a type of iron carbon mix, those spaces are filled to various degrees with small carbon atoms. The harder the steel, the higher the ratio of carbon to iron.

    Note, how it is attracted to a magnet. In other words, the steel is paramagnetic. This is because the magnet is able to cause a few of the electron orbitals in the iron to shift around from their random order and spin in the same direction. In a permanent magnet, so many of the orbitals are aligned that they don't randomize - and the sum of all the little electro-magnets add up to the whole piece's being a magnet. (Remember from physics, that electricity travelling through a coil of wire makes an electromagnet. Well, an electron that is whirling around its circular orbit is electricity going in a circle and thus producing a magnetic field. In permanent magnets its that lonely unpaired electron's unbalanced orbit that amounts to the magnetic field.

    Because you want to soften the steel so that you can "work" it, you need to allow the atoms to realign themselves into a softer crystalline form. Heating will make the atoms more mobile. So you'll take hold of the metal by one end with a pliers, and insert just the far end of it in a fire until it glows red, and loses its attraction for a magnet. This non-magnetic property indicates that the atoms are dizzily jiggling about so furiously that they cannot maintain their alignments and are somewhat fluid to move around a little bit. But so long as they are in this red heat, they really prefer the FCC lattice form.

    But if you allow the iron to slowly cool, more and more iron atoms will adjust themselves into a body-centered cubic (BCC) form. Once back at room temperature, do the magnetic test (attracts again!), and the scratch tests (softer).

    Normally a blacksmith would work with dull red-hot BCC steel (very bright red is FCC!). But you can bang on the end with a hammer and try to shape a screwdriver. (Just think of the rumors: "Chem students make screwdrivers in lab.")

    Once you have shaped your souvenire to the way you want it, grasp it again with your pliers and heat the worked end to bright red heat. Can you see the BCC turning back to FCC? Hold it at that high temperature for about a minute, and then plunge it with lots of violent swishing in cold water. You want to cool the metal as fast as possible. (Just holding it still in the water allows the red-hot metal to turn the adjacent water to steam and that hot gas coats the piece and slows the cooling process. Swishing it dislodges the bubbles allowing more liquid water to touch the hot metal and take away the heat.

    Why didn't it revert to BCC form? The cooling went so fast that the carbon atoms got trapped in the FCC lattice, couldn't move out of the way fast enough, and thus prohibited the iron atoms from moving to the BCC form before everything was too cool for any further movement. Thus the carbon atoms prevented BCC from forming and the resulting steel remained very hard. This is called by that fancy scientific word "hardening."

    Do some final scratch and magnetic testing. Satisfied?

    Next time you are camping and you happen to distemper a knife in the coals so that it is too soft to hold an edge, you know just what to do. Reheat it to red hot, and quench it in cold water to retemper it.