Behavior of Carbides due to Heat-Treatment in High-W and Mo High Speed Steels.

The total amounts of carbides in the several heat-treated specimens of the high-W high speed steels and Mo high speed steels were determined by electrolytic isolation method in this 2nd report like thd 1st (Tetsu-to-Hagane, 1958, Vol. 44, p. 1186).Chemical compositions and crystalline structures of the isolated carbides were determined by chemical analysis and X-ray diffraction, and the shapes of the carbides were observed by an electron microscope, and the following results were obtained:(1) On the as-annealed states, the amounts of carbides in high-W high speed steel were about 30%, and in Mo high speed steel were about 23%, and about 95% of the W, 80% of the V in the steels, and 90% of the Mo in the Mo high speed steel were concentrated in the carbides, while the most portions of the Si and Mn were dissolved in the matrix.The carbides precipitated in these annealed steels were M6C, MC and M23C6, and the most portions of the carbides were M6C.(2) In quenched states, the amounts of insoluble carbides in these high speed steels were 10-14%, which was the same about 40-45% of the carbides in as-annealed state.The insoluble carbides in quenched high-W high speed steels were only M6C, but the carbide in quenched Mo high speed steel consisted of M6C and MC.(3) The higher tempering temperature, the more precipitated the carbides from the austenite. And, especially, the concentration percentage of the special alloy elements in the carbides increased suddenly by the tempering to 575°C.The M23C6 carbide, precipitated in the high-W high speed steel by the tempering to 750°C, and the amount of MC carbides in the Mo high speed steel increased by the tempering, and M23C6 carbide appeared by the tempering to above 575°C.