In real life steel isn't created by simply melting iron. Iron is melted in a furnace with other added stuff and Iron is created. This mod brings a bit more realism to the creation of steel in Minetest. In addition to adding another step to the creation of steel it adds a full set of pig iron tools, some blocks, and tweaks the strength of steel and bronze tools.
If you're really curious I found a post that describes the iron making process.