Your steel may not be vegan?!

Did you know that some steel may not be vegan?

Case-hardening is a method of giving surface strength to a specific material. Hardening can only take place under conditions where there is a carbon content in the steel. In the case of some wind turbines, the gear wheels are made of a special, low-carbon, chrome-nickel steel. After the teeth are machined, the gear wheels are packed into large boxes full of bone flour or some other form of high carbon-content powder. The boxes are placed in an oven and heated for about 24 hours to a red glowing temperature. During this baking process, some of the free carbon will be transferred from the surrounding carbon-rich powder in the boxes to the gear wheel teeth surfaces.

I thought that was interesting and funny.