Powder-Forming Tendency of Nonequilibrium Phases in Fe-C-X (X=Cr, Mo, W, Al or Si) Alloys by Comminution and Microstructure and Hardness of Their Sintered Compacts

概要

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Among the nonequilibrium phases of χ, ε, amorphous, γ and κ in Fe-C-X (X=Cr, Mo, W, Al or Si) systems, the χ Phase dissolving C and Cr, Mo or W as much as about 20 to 65 at% was found to be readily comminuted into irregularly polygonal powders of a desirable size range by a hammer milling treatment as a consequence of the extreme brittleness of the nonequilibrium supersaturated solid solution. The χ Phase was easily consolidated into bulk form by conventional techniques of powder metallurgy, e. g., press and sintering. The resultant consolidate materials in Fe-C-Cr and Fe-C-Cr-Mo systems consisted of the duplex phases containing finely and uniformly dispersed M_7C_3 or M_<23>C_6 carbide in ferrite (or martensite) matrix and exhibited hardness as high as H_<RB>〓100. The formation of the uniform and fine structures without macrosegregation and the achievement of high hardness are interpreted to originate from the result that the phase decomposition of the χ Phase to fine aggregate of α+M_7C_3 or α+M_<23>C_6 occurs homogeneously at lower temperatures owing to highly unstable state of the χ phase. Thus, the use of the thermodynamically unstable χ phase produced by melt-quenching as a raw material in powder metallurgy seems to be very effective for the preparation of high-concentrated alloy material containing a uniform dispersion of ultrafine precipitates in finely recrystallized matrix phase.
1985-03-26