To those who live their lives with weapons of wood and stone, bone and antler, metal is a mysterious and terrible substance. It defies the imagination that stone can be changed from a hard but brittle substance that is seldom sharp and strong, into something that holds a cutting edge, or a piercing point, that doesnt not shatter like stone.
Even in our enlightened day and age, the arts of metallurgy are often lost on the common populace. What is in steel? Iron and carbon, yes, but what is the process, and most people dont know that there are other trace elements added to create different varieties of steel. Vanadium, Chromium, Molybdem, nickle, all of these are added in varying amounts for different effects and products.
Bronze and Brass
Infinitely easier to create than iron, these metals are unfortunately not as strong, nor as durable as iron, but contrary to gaming opinion and 'game fact' they are not the incredibly heavy, and soft metals that they are often made out to be. Cannons were made of brass long before they were made of iron, and if it was soft and heavy, it would have never been made into weapons and armor, but it was.
Creating these materials is a simple matter of smelting copper ore (malachite, serpentine, most any strongly green stone is a likely cantidate) with tin, an equally easy to find soft white metal. Heated, the slag burns off and the two metals are mixed into an alloy, creating the material. The timing and mixings are important, and the laws of low sorcery can be applied for the counting of time, the shaping and forging of the metal as well as its quenching, or cooling.
Iron
Perhaps the greatest weapon of man is iron, shaped into the plow to cut the soil and raise farms, turned into weapons and armor to defeat foes, as the Egyptians learned from the iron spear wielding Hittites, and for making stronger nails, horseshoes, locks, hinges, and barrel bands. Black iron is the first step, made by hammering iron ore until the slag is literally beaten out of it. This is cold iron, as it was made by strength of arm alone and is not heated in a forge.
Wrought iron is similar, but it heated before being hammered. The impurities in the metal give it its matte black color. The metal is strong, but is also brittle as it still contains an excessive amount of carbon in it.
Cast Iron is likely the most advanced mass produced iron available in a typical fantasy setting, as the iron is smelted at higher temperatures in crucibles that let the molten iron be drawn off from the bottom, leaving the crust of impurites on the surface of the metal. Cast iron is still brittle.
Steel
The word should cause shivers, as there are precious few materials superior to steel in the fantasy world. The steel sword is the tool of the paladin, symbol of the king. It is strong, somewhat flexible, and resistant to snapping and shattering as iron is. This is the metal that shines in the dark, and is the fear of orcs and things fell and evil. There are secrets to the making if steel that are carefully kept, with lethal force if need be.
Each smith who learns the arts of making steel does so in a slightly different fashion from his peers, as there are no limits of conformity, no standards and measures commities to ensure equal quality. Japanese steel, folded and hammered dozens of times is revered for its powerful cutting edge (often to ludicrous extremes) just as the Europeans held damascus steel in high regard.
Exotic Metals
Mithril, orichalum, soulsteel, adamant, and the plethora of other exotic materials exclusive to fantasy are the realm of the master smith. It takes the secrets of steel, and mixes it with the secrets of magic and sorcery to craft these rare materials. The logic, if the blade cannot be harmed due to its material, how in the world was it forged, if not from the generic wizard made it formula? Iron is soft, until you mix carbon, perhaps mithril is the same, until you mix a certain amount of silver, or of some other certain element.