球状黒鉛をもつモリブデン-ニッケル系鋳鉄のS曲線

抄録

  The S-curves of Mo-Ni cast irons treated with various alloys or fluxes as graphite spherodizers, were studied. The behavioures of isothermal austenite transformation after austenization at 900°C for 30 minutes were investigated by microscopic examination in pearlite range and by dilatmetric measurement in bainite range. The results obtained were summarized as follows :
  1) The S-curve of the magnesium-treated cast iron was not so different from that of the iron treated with the mixture of 4%CaSi, 2%CaF₂ and 0.5%MgF₂. Thence, it was presumed that the behaviour of austenite transformation was unaffected essentially by residual magnesium.
  2) In case of the hypo-eutectic cast iron the pearlite reaction was accelerated slightly, and also the bainite reaction remarkably restrained.
  3) It was confirmed that in the nodular graphite cast iron containing high Mo with low Ni the pearlite reaction was retarded, while in iron containing high Ni and low Mo the bainite reaction was restrained remarkably.
  4) In the mishmetal-treated iron having quasinodular graphite, the isothermal pearlite reaction was retarded slightly, while the rate of bainite transformation was in the same oder as that of the magnesium-treated iron.
  5) By the addition of 6%CaSi together with 2%CaF₂, the rates of the second stage graphitization and pearlite reaction were remarkably promoted.
  6) When white cast iron treated with magnesium was annealed through the first stage white iron with was through the first stage graphitization, its S-curve moved to the right in pearlite range, but to the left in bainite range as a result of the first bainitic nucleation by very fine graphite.
  7) For the Mo-Ni cast iron containing a very small amount of silicon, the transformation product in bainite range was not aciculer ferrite, but similar to that in lower pearlite range.