On Carbides in Mo- and Co- High Speed Steels

The nature of carbides in Mo high speed steels (0-9-4-2, 6-5-4-2) and in Co high speed steel (18-4-1-20) were studied by electrolytic isolation method, with a view to clarify the role of Mo and Co in high speed steels. Carbides present in Mo high speed steels were M6C, M23C6 and MC, likewise in the case of W high speed steels.The density of the carbides in Mo high speed steels was smaller than that of the carbides in W high speed steels, and so the percentage of carbides by weight in the former was smaller than that in the latter. By austenitizing treatment, the carbides in Mo high speed steel were dissolved into matrix readily than the carbides in W high speed steel.Co high speed steel contained only a kind of carbide, M6C. This carbide was usually hard to be dissolved into austenite. But the addition of Co in high speed steel had the effect of enlarging the solubility limits of W, Cr, V and other carbide forming elements in austenite, and served to promote the dissolving of M6C during austenitizing.