This reaction accounts for around half of the transformation of wustite FeO into iron, and removes 30% of the total oxygen supplied, mainly in the form of iron oxide FeO. This mode of wustite reduction is highly endothermic, whereas the reduction of iron oxides by CO is slightly exothermic (+155.15 kJ/mol vs. -17.45 kJ/mol), so it is essential to keep it to a minimum.
This reaction concerns all the iron oxides present in a blast furnace, but also manganese(II) oxides (Mno), silica (SiO), chromium, vanadium and titanium, which are partially reduced in blast furnaces. These chemical reactions are described below:
          MnO + C → Mn + CO    consuming 282,4 kJ/mol à 1 400 °C (begins above 1,000°C and involves half of the manganese present in the charge)
          SiO + 2 C → Si + 2 CO  consuming 655,5 kJ/mol          (begins above 1 500 °C)
Chromium and vanadium behave like manganese, titanium like silicon. As for the other iron oxides, their direct reduction is of negligible importance. This can be written as:
          3 FeO + C → 2 FeO + CO       consuming 118,821 kJ/mol
          FeO + C → 3 FeO + CO             consuming 209,256 kJ/mol
In non-steel blast furnaces, dedicated to the production of ferroalloys, direct reduction is fundamental. For example, for ferronickel production, both direct reduction reactions are used:
          NiO + C → Ni + CO          above 445 °C
          FeO + C → Fe + CO          above 800 °C
So, although nickel reduces slightly more easily than iron, it cannot be reduced and cast independently of iron.