The classic Katana is made from two grades of steel: High carbon steel is wrapped along one side with a lower carbon steel. It's then heated and pounded, folded and pounded some more. That has the effect of blending the two carbon levels so you get a gradient: Lower carbon along the spine for a springy, resilient blade, and higher carbon along the edge, making it harder there and more capable of taking and holding an edge.
It was not silver in Middle Earth. It was a metal that was lighter and harder than still and looked like silver, but didn't tarnish. That's why it was called true silver. It would not have worked on werewolves in the same way silver does.I think I remember True Silver coming up in D&D back in the 70's or early 80's. But no idea the source, canon, 3rd party, or Tolkien! Anyone know?
As for me, I hate material specific immunities and resistances. I find them cumbersome and annoying as a player. Lets see; my sword is silver, my mace is adamantine, my hammer is holy and then I have pair of daggers, one lawful and one anarchic! Now which weapon do I use when fighting an adamantine flaming skeletal Archer?
Mithril was called silver-steel, because of it's color and strength. It wasn't an alloy. Dwarves made a gate from mithril AND steel once, and the elves made and used a mithril alloy called ithildin.Also, in Middle Earth I think mithril was alloyed with steel. Tools were not made solely from mithril.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.