SUPERSATURATED SOLID-SOLUTIONS OF CARBON IN FE, CO AND NI - CORRELATION WITH CARBIDE STABILITY

Binary alloys of the systems Fe-C, Co-C, Ni-C with carbon content from 1 to 6 wt% were quenched from the liquid state with the use of CO2-la ser heating under a protective atmosphere. Cooling rates were in the r ange 10(4) to 10(7) K/s. The supersaturated solid solutions of carbon in Fe, Co and Ni formed during melt quenching have been investigated b y X-ray determination of lattice parameter. The maximum attained carbo n concentration C-m in all three systems was about 9 at.% C, that is, approximately equal to the equilibrium solubility C-g of carbon in fcc iron at the graphite eutectic temperature. The relative supersaturati on C-m/C-g decreases steadily in the sequence Ni, Co, Fe along with in creasing melting point of the Ni3C, Co3C and Fe3C carbides, i.e. incre asing thermodynamic stability of carbide phase. The observed tendency is in agreement with other published data.