Abstract
When steel, especially chrom-steel. is super-carburized, its case becomes so brittle that it often suffers danger of flaking or cracking in heat treatment or mechanical working. There are a few methods to prevent super-carbarization. The most effective one is mild carbarization by the use of any suppressor by adding to the carburizer consistsing of charcoal and such a promotor as BaCO3 or Na2CO3 There is also anothr mild carburization method which is to use a carburizer containing a weak promotor or decayed carbuized by repeated using. In view of reactions between suppressors and promotors, we classified the former into three systems; Silica-. Alumina-, and Phosphate-. In the first the mechanism of mild carburization in Silica- system was investigated, and it was found that silica reacts with promotor BaCO3 or Na2CO3 forming BaO•SiO2 at carburizing temperature, and since such a product has little effect for carburizing, the strong promotive power of BaCO3 or Na2CO3 decreases in using it together with silica. Si on Fe-Si as suppressors suffers oxidation in carburizing atmosghare, and then the produced oxide, SiO2 reacts with the promotor as above.
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