There is one method of steel production that has been forgotten by history, but today people are still trying to replicate it: Damascus steel.
This is a close-up of a real Damascus steel knife
Here is a modern replica of the knife used to make it:
Damascus steel is very legendary because its manufacturing methods have been forgotten by history, because of its complex and beautiful patterns, but also because of its durability. Perhaps even more surprising is the traces of carbon nanotubes found in real Damascus blades. Now, this is clearly an unexpected by-product of the manufacturing process, but it does explain how the material has been so highly valued to the point of myth; it is said that a real Damascus blade can cut through the barrel of a gun.
The term "Damascus" itself has also caused a heated debate: what is really "Damascus"?
Interestingly, Damascus steel does not come from Damascus. It is actually thought to have come from India, although it is associated with the Persian and Arab worlds. In fact, it even reached Russia, where it was called "bulat". There are many theories about how they are called "Damascus", such as the Europeans who first encountered it discovered it in Damascus (one of the production centers of the sword at the time), or the corruption of the name of a famous Arab swordsman who made these, and so on. In any case, the Damascus people would not call this steel "Damascus". The truth about the origin of the name is also likely to be forgotten by history.
In the 19th century, "Damascus" was the term "patterned welded steel" used to make knives and barrels. Then in the 20th century, people began marketing their patterned knives as "Damascus" to maintain their fame, further adding to the chaos.
Scientists and engineers have been trying to reconstruct the material from the current sample, but so far they have only been able to approach, but not fully replicate, the process. In order to make them correctly, blacksmiths need the right knowledge of raw materials and procedures, both of which may never be found again.
However, by today's standards, damascus's power was not so special, just as japanese swords were no more than European swords or other types of knives. At that time, however, it must have been almost magical to see something so beautiful and durable.