Other mods have changed iron and steel to be more realistic. Here's mine!
Both iron and steel can be made with, or without flux. Iron with flux is more ore-efficient and faster, but uses more fuel. Steel with flux is twice as fast, and uses the same fuel at a magma forge (less with a regular forge).
Iron can be smelted either in a bloomery, or a blast furnace.
Bloomery:
1 ore + [FUEL] = 1 sponge iron + 1 slag.
2 sponge iron + [FUEL] = 1 iron
4 slag + [FUEL] = 1 iron
Thus, 7 smelting operations will produce 3 irons out of 4 ores.
Blast furnace:
2 ore + [FUEL] + 1 fuel + 1 flux = 2 pig iron
1 pig iron + [FUEL] = 1 iron
Thus, 6 smelting operations will produce 4 irons out of 4 ores, 2 fluxes, and 2 extra fuels.
Then steel can be made either via blistering, or crucible.
Blister steel:
1 iron + [FUEL] + 1 fuel = 1 blister steel
1 blister steel + [FUEL] = 1 steel
Crucible steel:
1 iron + [FUEL] + 1 fuel + 1 flux = 1 steel
Thus, 1 steel can be from 1 iron using either 2 smelts and 1 extra fuel, or 1 smelt, 1 extra fuel, and 1 flux.
Finally, a higher grade of steel that I've yet to satisfactorily name, can be made from 1 blister steel + [FUEL] + 1 fuel + 1 flux. So 2 smelts, 2 extra fuels, and 1 flux turn 1 iron into 1 super-steel. Historically, that's how some people made their best steels--blistering, then the slag was removed via crucible and flux rather than beating.
I've left wootz out, as it was historically dependent upon specific ores containing vanadium and tungsten, and messing with ores to make different types containing different trace elements is way beyond the scope of what I want to do, which is just rebalance the game a bit so that iron and steel are both more labor-intensive and slower to make than bronze.
Any thoughts? Too complex, not complex enough? I was specifically trying to avoid randomness, as I really hate sacrificing ores to the Random Number God.