There is a certain amount of oxygen in molten steel during steel smelting. Oxygen is supplied in the production process, because oxidation and the removal of P, S, Si and C all requires the supply of oxygen to molten iron. However, there are various steelmaking processes, the relationship between C and O of molten steel in the molten pool of the furnace has a common regularity. That is, with the gradual decrease of C content, O content is gradually increasing, and two elements have a corresponding equilibrium relationship.
Oxygen co-exists in the combined state and free state. Generally, the free state is very few, and mainly exists in the form of Fe2O3, Fe3O4, FeO, metal oxide inclusions, silicates, aluminates, oxysulfide and similar inclusions.
Oxygen,like hydrogen, has an adverse effect on the mechanical properties of steel. Not only oxygen concentration, but also the amount, type and distribution of oxygen-containing inclusions have important influence.Such inclusions are metallic oxides, silicates, aluminates, oxysulfides, and similar inclusions. Steelmaking requires deoxidation, because during solidification, the oxygen in the liquid reacts with the carbon to form carbon monoxide, which can create bubbles. In addition, oxygen can be removed from the solution during cooling as FeO, MnO, and other oxidizing inclusions, thus reducing its thermal or cold working properties, ductility, toughness, fatigue strength, and mechanical properties of steel. Oxygen, nitrogen and carbon can also cause aging or a spontaneous increase in hardness at room temperature.For cast iron, when the casting block is solidifying, the oxide can react with carbon, resulting in product porosity and product embrittlement.
