Among the three gas elements, the solubility of oxygen in liquid or solid cast iron is the smallest, but the activity of oxygen is the strongest, and it is easy to form oxides with other elements in cast iron, and the interaction and influence between them are also very complex.
In cast iron, oxygen does not precipitate as elemental gas, and the porosity defects caused by oxygen in castings are often caused by the reaction of FeO and C to form Co.
In the process of cast iron melting and heat preservation, a variety of oxides will be reduced by C. In the melting process of cast iron, due to the difference of temperature in different periods, the various reactions related to oxygen are different
(1) During the melting process, the temperature in the furnace is low and the oxidation reaction of various elements mainly takes place during the melting process;
(2) In the process of molten iron heating up, with the increase of furnace temperature, some elements continue to undergo oxidation reaction, while some oxides also undergo reduction reaction;
(3) When the molten iron is kept at high temperature in the furnace, some oxides are mainly reduced, and some elements are also oxidized.
In all kinds of cast iron, the amount of W (c) is quite high. The interaction between C and various oxides is very complex, and the influence on the quality of cast iron is also very important.