Oxygen content in cast iron

Although the atomic radius of oxygen is very small (0.66), it is a highly active element and can form compounds with many elements. Therefore, a certain amount of oxygen can only be dissolved in metals or alloys with weak oxidation.

Even in the process of steelmaking, although the content of C, Si and other oxidizable elements in the liquid steel is not high, the dissolved oxygen is also trace, and the active oxygen in the steel is basically dissolved in the steel in the form of FeO.

Cast iron contains a variety of elements with strong ability to combine with oxygen, oxygen is basically in the form of oxide, the content of dissolved oxygen and reactive oxygen should be negligible.

At the end of last century, the American Foundry Society (AFS) organized a special research on “W (o) content in cast iron”. Samples were taken from 20 foundries to determine w (o) content. The smelting equipment involved includes coreless induction furnace, groove type induction furnace and electric arc furnace, and the varieties of cast iron involved include gray cast iron, nodular cast iron and malleable cast iron.

In 2000, the American Foundry Association presented a preliminary report on this subject at its 108th annual meeting. The report only provides the amount of W (o) in various cast irons prepared by different smelting equipment, and does not involve the effect of oxygen on the properties and quality of cast irons. The amount of W (o) proposed in the report is also a vague concept, which does not distinguish between dissolved oxygen and oxygen in oxides, and should be understood as the total amount of W (o). Because there is little dissolved oxygen in cast iron, which is actually the amount of oxide. Under different conditions, the amount of W (o) in cast iron can be summarized as follows

(1) The amount of W (o) in gray cast iron was 3 ~ 16.5ppm, with an average of 7.08ppm, from 29 samples from 9 factories. Among them, the average value is 6.37 ppm for power frequency furnace and 8.43 ppm for medium frequency furnace.

(2) 358 samples were collected from 15 factories. The content of W (o) in nodular cast iron ranged from 3 ppm to 41 ppm, with an average of 9.33 ppm. Among them, the average value of power frequency furnace melting is 8.55 ppm; 59 ppm in medium frequency furnace.

(3) The amount of W (o) in malleable cast iron is 7.5 ~ 25 ppm, the average value is 13.12 ppm.

(4) W (o) content in cast iron melted by flume induction furnace and electric arc furnace

In the foundry where the samples were provided, only one domestic flume induction furnace was used to smelt gray cast iron. The amount of W (o) in the cast iron ranged from 5.5 ppm to 25.5ppm, with an average of 11.7ppm. The amount of W (o) in gray cast iron is 83 ~ 118 ppm, with an average of 102 ppm. The content of W (o) in ductile iron is 22 ~ 59 ppm, with an average of 37 ppm.

It can be seen from the above data that not only the amount of W (o) of cast iron melted by different manufacturers with different equipment varies greatly, but also the amount of W (o) of cast iron melted by the same manufacturer varies considerably.