W-Cr-V熱間ダイス鋼中の炭化物について

実用特殊鋼中の炭化物の電解分離による研究-VI

抄録

In the present study, the carbides isolated electrolytically from two kinds of W-Cr-V hot-work die steels were examined by X-ray and chemical analyses, and by electron-microscopic observations.
The carbides in the annealed steels are M₆C+M₂₃C₆(+MC), and by austenitizing treatment, M₂₃C₆, the so-called heat-treatable carbide, preferentially dissolves into the matrix, leaving a part of M₆C(+MC) as undissoloved carbides. In tempering of these steels, a transitional carbide ₂C appears, as reported by K. Kuo (J.I.S.I. vol. 174, 1953, p. 223), and the carbide phase changes in the 4th stage of tempering are as follows;
θ→W₂C(+MC)→M₆C(+MC)→M₆C+M₂₃C₆(+MC)
W concentration in the precipitated carbides increases with the rise of tempering temperature, but V and Cr concentrations in the carbides take the maximum values in the course of tempering. This fact is considered to be due to the increase of the amount of W-rich carbide M₆C, resulting in the dilution of V-rich carbide MC and Cr-rich carbide M₂₃C₆.