One possible set of developmental steps in the the use of iron.
If one is writing (alternative/)historical fiction, it’s important to get the technology developed in a believable sequence. Iron is a highly technical product and deserves attention in any fiction.
Iron ore is a chemical compound of iron (Fe), oxygen (O) plus impurities.
In this earliest step, air is forced through a mixture of iron ore and charcoal (think of the poor apprentice working a bellows for hours on end). One of the byproducts of the burning charcoal is carbon dioxide which reduces the iron oxide to iron. Typical bloomeries do not reach a hot enough temperature (only 1000 degrees or so) to actually melt the elemental iron. Hence it ends up as a spongy mass called a bloom. The pores of this bloom is filled with ash and slag. Pretty useless until it is reheated and repeatedly beaten to join the iron particles and force out the slag and ash. The result is called *wrought iron*. It was a very labor intensive process. But the early ironworkers probably developed a nice set of muscles.
Wrought iron was fairly malleable (soft) metal. Heating in contact with carbon (charcoal again) allowed carbon to migrate into the outer layer of the metal. Quenching in water (or oil…think more carbon) froze the carbon in that outer layer. Now one can get a hard out layer (especially a cutting edge) with a softer inner core (producing a less brittle tool or weapon).
The wrought iron, even if carburized, is still soft. If a mixture of wrought iron, charcoal and glass is encased in a clay crucible and heated, the carbon migrates into the iron and the glass forms a protective slag.
If the iron can be mixed with a lot of carbon and heated to 1140 degrees, the iron is liquid and can be poured into molds. The high carbon content however makes the iron brittle.