Koreaki Tamaki

On Carbides in Cr-Mo-V Hot-Working Tool Steels

On Carbides in Cr-Mo-V Hot-Working Tool Steels. (Study on carbides in commercial special steels by electrolytic isolation-X) Tomo-o Sato, Taiji Nishizawa and Koreaki Tamaki. Synopsis: Chemical and X-ray analyses were carried out on carbides, isolated electrolytically from the as-annealed, as-quenched and as-tempered structures of chromium-base hot-working tool steels. Carbides found in the as-annealed structures are M23C6, M6C and MC, similarly to the carbides in tungsten-base hot-working tool steels. M7C3 and ξ carbide expected from the equilibrium diagrams for Fe-C-Cr and Fe-C-Mo systems were not observed in the as-annealed structures. Carbide reactions during tempering are complicated, but are regarded as the combination of four sequences, which proceed separately in chromium, molybdenum, vanadium and tungsten steels; that is (i) M3C→M7C3→M23C6, (ii) M3C→Mo2C→M6C, (iii) M3C →MC, and (iv) M3C→W2C→M6C+M23C6. The rate of the carbide reactions taking place towards equilibrium during tempering were very slow, owing to the low mobility of molybdenum atoms.