The aztecs, or mexica, how they called themself, have had a rich culture but they never managed to use other metals for their work then silver, gold, or copper.
They never used Steel or Iron, so the hardest material they had was obsidian, vulcanic glas.
Why they havent been able to forge Steel Iron or even bronze?
Silver, copper, and gold all exist in the free state in nature, while iron only exists as various forms of iron oxide. All that ancient cultures needed to do was find the silver/copper/gold in nugget form somewhere in nature, and melt it. Bronze is made from copper and tin, but tin only exists as compounds with other elements, so like iron oxide, it doesn't look like metal. It's a pretty big technological leap to go from collecting stuff that already looks like metal, and melting it, to figuring out how to reduce the metal in an ore back to the free state. Turning crude iron into steel is yet another technological jump. I don't know if the Aztecs even had access to high quality iron or tin ores.