Iron ingots are the most versatile metal, used extensively in crafting. It can be obtained by smelting Iron Ore, found underground. It is the third most common mineral after Copper and Tin that can be used to make tools and armor. Better than tin, it is perfect for your mass production of tools and armor.
Put iron nugs -> iron ingot recipe here
Put iron ore -> iron ingot recipe here.
Put the many recipes here.
Iron anvil and reforging station recipes here.