|MadSci Network: Engineering|
Hi Jeremiah, Youíve asked a great question, and Iím glad youíre investigating information your friends tell you before you accept it as fact. The short answer is that your friend is wrong, but he has the right idea. The folding he is talking about is an ancient metalworking technique that was perfected by Japanese swordsmiths. They would fold a piece of metal hundreds, sometimes thousands of times, and this would result in a strong, flexible, yet hard sword that would be very good at keeping a sharp edge. There is quite a bit of metallurgical detail, history, and experimentation behind the process, but the short version is that they formed swords composed of super-thin layers of steel that had soft, flexible cores with hard, sharp edges. However, in the situation you describe, the density of the steel will not increase. (Unless during the folding process, you accidentally add carbon or make some other change to the material itself.) The crystal structure and the grain size (and thus the strength) will change depending on how quickly and to what temperature the material is heated (casting, tempering), how quickly the material is cooled (quenching), and how the material is mechanically deformed (peening, rolling, hammering, drawing, and folding). Folding the material many times under the right conditions will indeed make the steel stronger, but the density will not change. (in the real world, each time you heat up and hammer a piece of metal, you'll lose some material to slag and evaporation, so your bar of metal will not entirely fill the 1'X2'X3' volume but it will also have lost mass, so the density won'y have changed.) If youíre interested in learning more about metallurgy or Japanese swordmaking, try looking online. Here are some links. Metallurgy Heat treating steel Heating / Quenching Tempering Work Hardening Japanese Swordmaking History Japanese Swordmaking History Japanese Swordmaking History 2 How Stuff Works - Swordmaking I hope this helps. Keep asking questions! Jeff Yap Mad Scientist
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