For blast furnaces, direct reduction corresponds to the reduction of oxides by the carbon in the coke. However, in practice, direct reduction only plays a significant role in the final stage of iron reduction in a blast furnace, by helping to reduce wustite (FeO) to iron. In this case, the chemical reaction can be trivially described as follows:
          FeO + C → Fe + CO            consuming 155,15 kJ/mol
However, "in the solid state, there is virtually no reaction in the absence of gases, even between finely ground iron ore and coal powders. In other words, it seems certain that the reaction takes place via gases". This means that direct reduction most probably corresponds to the following chain of reactions:
          FeO + CO → Fe + CO       producing 17,45 kJ/mol              (reduction by CO)
          CO + C ⇌ 2 CO                consuming 172,45 kJ/mol          (Boudouard reaction)