So Factorio's steel making is actually pretty accurate, when done in the first two tiers of furnace. If a smith is working with steel, but it doesn't have enough carbon in it, they'll stick it in their fire, if it's a coal, coal coke, or charcoal fire, as these fuels will release some carbon, to add carbon to the metal.
...
Lotta carbon in that sentence.
Also, I did the math wrong for the copper. It only takes 10K.
Subnautica?