Carbon is used in steel IRL, so maybe an alt steel recipe including carbon could be a thing?
i have two ideas: it could either take less iron plates to make, or make more steel for each 5 iron plates
1x Carbon + 3± Iron Plates = 1x Steel
1x Carbon + 5 Iron Plates = 2±x Steel

Already a thing in the mod. It uses iron ore and carbon, I believe.

ahh, no wonder i haven't seen it, it's in the 'unsure' category.
fair, since i thought of the idea on a whim seeing a lot of carbon in a chest and thinking "isn't carbon used to make steel irl?"