Steel in Japanese Swords

Steel is an alloy of iron and carbon and is widely recognised as one of the most practical strong materials for use in construction and in a huge variety of tools.

Application Durability is very important in Japanese swordsmithing, a sword will need to be able to stay sharp after have been used many times. This does not work in soft metals because they undergo permanent deformation with little stress which would be no good in battle where swords would be subjected to many powerful impacts. Furthermore large scale manufacturing did not exist in feudal Japan (12th to 16th century) so making just one sword could take up to a week. This meant that a sword costed a lot of money and were difficult to replace so they had to be built to last. Iron was used as a primary material because of its strength and availability. Nowadays the mass production of steel wares and more advanced tools have eliminated the need for such strong swords.

Macroscopic property Strength is a much needed property for a sword so strong materials like steel are used. It is an extremely important property because when a sword was used in combat, the life of those using it would often depend on the blade. It would also often have to withstand large stresses. It must also be resilient, a sword is no good if it can only be used once, they need to keep the shape for many years without deformation, however it is unlikely for creep to occur since the sword is not subjugated to continuous stress throughout its usage.

Microscopic structure Iron which is the main constituent of steel is a lattice of positive iron ions held together by delocalised electrons, these bonds are strong but on its own they easily undergo plastic deformation because all the atoms in the lattice are the same size so slip very easily across planes. In the high carbon steel in Japanese swords there are larger interstitial carbon atoms within the lattice, they cause a large compressive force on the smaller iron atoms while they...