抄録
The S-curve of cast iron is affected by graphite structure and also by special elements such as Ca, Mg, O etc. in it. In order to study the latter factor, the authors investigated the effects of Mg-treatment, vacunm-melting and an addition of Fe3O4 on the S-curve for 0.5%Mo-1.4%Ni cast iron. The behavior of isothermal austenite transformation was studied by the same methods as described in the 1st report. The experiment results obtained were summarized as follows. :
1) The second stage graphitization through direct reaction was remarkably accelerated by Mg-treatment, but restrained by Fe3O4 addition. The indirect graphitization was slightly accelerated by vacunm-melting.
2) The begining point of the upper pearlite transformation was almost unaffected by these various treatments of melt. The ending point was considerbly shortend by Mg-treatment, and prolonged by vacuum-melting as the result of restraining the transformation in matrix of fine eutectic graphite.
3) In the lower pearlite transformation range, the time for begining the transformation was prolonged by Mg-treatment and the time required for its completion was equal for all samples in this work.
4) It was confirmed that Fe3O4 addition showed a strongest tendency to shorten the incubation period and to promote the formation of isothermal bainite in all samples. In the case of vacuum-melting iron, bainite transformation started earlier, but it was found from the dilatation curve that amount of transformation was reduced. By Mg-treatment, the begining line of the S-curve for bainite tranrformation above 300°C was moved remarkably to the right, and also, the Ms-temperature was lowered relatively.
