Pig iron isn't even steel, so thats by definition not too good for swords.
Yeeeeaaah about the "Pig Iron" part... I wasn't thinking when I wrote that part but my point still stands, the steel used in the making of a Katana was only folded over because it was full of carbon which makes it horribly brittle. Even when folded over, the katana can easily break if swung in the wrong way. Being one sided, the katana is horrible in actual battles although it can be effective in one vs one fights which works fine in that case.
In regards to the Samurai they never really used katanas, during the Sengoku period (which was when all the fighting was until Japan was united in the early 17th Century), the use of a katana was thought to be dishonourable unless it was greatly needed and the Samurai themselves much preferred to use bows and/or spears in battles. This doesn't mean they didn't carry them, but they wouldn't use them unless it was vital, however at the end of the Sengoku Period when Japan was united and the Edo Period began, there was no longer much need for Samurai warriors in the new stable and peaceful Japan. As a result of the peace during the Edo Period, the Samurai mostly settled down and became local administrators, it was during this time that the Katana finally became popular as a status symbol.
In regards to the production of the Katana it wasn't anything special, as I said above the process of folding the Katana was to work out the carbon in the steel which was a process used by the Vikings much earlier to make their weapons. By this point in other parts of the world, nations had moved onto using better steel for their weapons and their swords were largely double-edged which made them a lot more practical in battle. The higher quality steel of their weapons meant that the weapons could take a lot more punishment in a battle without breaking and were a lot more effective for wielding in a battle against large groups of enemies.
Although I will admit that unsheathing a katana looks so much better than unsheathing another type of sword.
I feel all that needed to be said. Goodbye.