含バナジウム高マンガン鋳鋼の凝固組織

抄録

  The influences of carbon and vanadium contents on the solidification structures of high manganese cast iron were investigated using 12%Mn cast iron with 1.2% to 5.0%C and 0 to 7.5%V. Specimens were mainly cast into the exothermic mold to be solidified unidirectionally. The amounts of eutectic carbides and the secondary arm spacing of the primary dendrites were measured on the transverse planes at various distances from the chill surface. The distributions of solute elements in the carbide and matrix were analyzed with E. P. M. A. The freezing processes of the alloys were also investigated by thermal analysis and quenching method.
  The constitutional diagram on liquidus surfaces of primary γ, vanadium carbide and cementite, and the freezing processes of the alloys were elucidated. The amount of cementite decreased while that of vanadium carbides increased with the increase of the vanadium content. Eutectic vanadium carbides with fine granular or string-like shapes crystallized among primary dendrite arms in hypoeutectic irons, while primary vanadium carbides solidified dendritically and eutectic vanadium carbides grew radially around the periphery of primary vanadium carbides in hypereutectic irons. Secondary dendrite arm spacing of primary γ, became smaller with increasing carbon and vanadium contents. As the carbon content of the specimen increased from 1.2% to 3.0%, the distribution coefficient of manganese and vanadium of primary austenite decreased linearly from 0.80 to 0.70 and 0.55 to 0.30, respectively. These coefficients were little affected by the vanadium content.