ブリッジマン法による一方向凝固片状黒鉛鋳鉄の試料移動速度または炉温の変化で生じる遷移領域について

抄録

  A study was conducted on the variation of the flake graphite spacing and growth rate of austenite-graphite eutectic in the transition zone caused by a sudden change in the driving rate of a specimen or the furnace temperature during unidirectional solidification by Bridgman method. When the driving rate of a solidifying specimen was changed, a transition zone appeared where graphite spacing gradually altered. The transition zone in graphite eutectic is considerably longer than that in ledeburite eutectic and other regular eutectics which means that it takes longer time for the graphite eutectic growth to attain steady state after the change in the driving rate. The long transition zone suggests that the growth rate and the undercooling at the solidification front changes gradually. The relationship between the solidified distance and the time after the change of the driving rate was in good agreement with that calculated by using the dependence of the growth rate on undercooling at steady state growth.
  When the furnace temperature was raised by 10°C during unidirectional solidification at the driving rate of 1.90 μm/sec, the specimen stopped growing for a while and attained a steady growing state after 30 to 40 min. In lowering the furnace temperature by 10°C, the growth rate increased rapidly and undercooled graphite structures appeared. The growth rate of the specimen became equal to the driving rate in about 20 min after changing the furnace temperature, and the specimen grew about 5 mm during that time.