The nature of the carbides in several cold-working die steels were studied by the electrolytic isolation, subsequent chemical analysis and X-ray examination, and the following results were obtained:
(1) The carbides in annealed high-C high-Cr die steel are M7C3, as reported in the previous paper. (Tetsu-to-Hagané, Vol. 42 (1956) p. 1118) While, the carbides in the steels, modified by the addition of W (3%) or Mo (1%), are principally M23C6. The high-C high-W die steel contains very large amounts of M23C6, accompanied some M6C.
(2) The most of Cr, W and Mo in the annealed steels are tied up in the carbides.
After usual quenching treatment of these steels, the considerable carbides are undissolved in austenite, so that at such a quenching temperature, C, Cr, W and Mo contents of the austenite are less than those of the steel as a whole.
(3) In the course of tempering of these steels, ε anld θ carbides precipitated in martensite change to another special carbides, depending on the time and temperature of tempering. That is, in the high-C high-Cr-W steel, carbide reactions proceed as ε→θ→M7C3→M23C6, and in the high-C high-W steel, as ε→θ→M6C→M23C6.