Stronger, Lighter Steel in a Flash

As mentioned in a previous post on a new gelatinous material created by synthetic nanospheres, one of the great drivers of society is materials. And as such, one of the most important discoveries in the materials world over the past few hundred years is the creation of steel. Harder, stronger and lighter than iron, steel makes a lot of what we see in the world today possible.

One of the great drivers of chemical reactions is simple heat. It causes phase transitions such as closely bonded water molecules to become loosely bonded and reorganized into gas. Similarly, heat plays a role in how molecules are aligned in many other materials, including iron.

Imagine a cube with an atom at each of its corners. When this configuration is repeated over and over again in a material, it is said to have a primitive crystalline structure. Each atom is shared between eight cubes, so a single crystal cube unit has one total atom.

The simple cubic system (P) consists of one lattice point on each corner of the cube. Each atom at a lattice point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom (1⁄8 × 8). The body-centered cubic system (I) has one lattice point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell (1⁄8 × 8 + 1). The face-centered cubic system (F) has lattice points on the faces of the cube, that each gives exactly one half contribution, in addition to the corner lattice points, giving a total of 4 atoms per unit cell (1⁄8 × 8 from the corners plus 1⁄2× 6 from the faces).

The next form of structure adds another atom to the center of the box and is called body-centered. Because it has one atom in its center that is completely its own, each cube unit has two atoms.

Finally, face-centered crystalline structure adds an atom in the center of each of the cube’s faces. Each of these atoms is shared between two different cubes. Though it does not have an atom at its center (it wouldn’t fit), the configuration creates a total of three atoms in the cube, making it the most densely packed of the three.

When iron gets above 1,674 degrees Fahrenheit, its molecules undergo a configuration transformation from a body-centered crystalline structure to a face-centered one. Besides creating a denser material, this allows for more room for other elements to be dissolved into the iron’s structure. The most popular of these is carbon, which is what is used in most of the common forms of steel. Once the crystalline structure is in place, the new substance is rapidly cooled –or quenched – by soaking it in water. The rapid cooling process traps the crystalline structure where it is and does not allow it to go back to a less-dense formation.

By controlling how much carbon is in the steel, what other elements are added to the mix (nickel, tin and copper being common), how long the steel is heated and how high of a temperature it is brought to, steel can be given many different properties. All of these contribute to how hard, strong, ductile and brittle the final material is.

As you can imagine, there is a wide array of steels that can be made in this fashion. However, making steel is an old science. It’s been around for a long ass time. All of the different combinations and heating temperatures and times have been explored and documented. There isn’t much left to learn.

Or is there?

That’s where all of this is going. Recently, an entrepreneur from Detroit approached Ohio State material science engineer Suresh Babu with a startling discovery. In a science where just a percent or two of added strength would be a major breakthrough, Garry Cola claimed to have made steel a full seven percent stronger than the strongest on record.

Not only that, he claimed the new steel could be drawn (thinned and lengthened) 30 percent more than typical steel without losing its enhanced strength.

Surely not, is what Babu thought. So he took some students up to investigate. And sure enough, the claims were true. So Babu and graduate student Tapasvi Lolla began investigating the process Cola had invented and how it affected the steel’s structure.

Typical industry practices create martenistic steel (the strongest known steel because it has a completely uniform,  face-centered crystalline structure) by heating the substance at around 1,650 degrees Fahrenheit for a few hours – or even a few days – before quenching and hardening it.

Cola’s process took 10 seconds.

His process at his proprietary lab setup at SFP Works, LLC., carried steel sheets through flames as hot as 2,000 degrees Fahrenheit before being quenched.

By investigating the new steel’s microstructure with an electron microscope, the Ohio State team discovered a mostly martenistic crystalline structure, but with a number of bainite structures scattered with carbides.

Carbides are little packets of carbon-rich compounds and were found in the steel because of the quick heating process. The team believes that due to the shortness of heat exposure, not all of the carbon dissolves into the steel, creating these little pockets. Bainite is another type of crystalline structure located lower on the heat scale that is not as regular as martensite and contains irregularities.

But it is apparently these irregularities and pockets of carbides that gives the new steel its incredible qualities. The new steel is stronger and more ductile, meaning it can crumple a great deal before breaking.

This makes the steel a potential gold mine for the auto industry. If they can create the same steel, they could use it in cars to make them 30 percent lighter with a greater ability to absorb impacts without breaking.

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About bigkingken

A science writer dedicated to proving that the Big Ten - or the Committee on Institutional Cooperation, if you will - is more than athletics.
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