Control of Microstructure during the Eutectoid Transformation in the As‐cast Spheroidal Graphite Cast Iron with »in‐situ« Dilatation Analysis and Quenching Experiments

Abstract

Transformation of austenite can proceed into ferrite and graphite (YFe--+UFe+G) and/or in pearlite (YFe --+ uFe+Fe3C), Investigation of the eutectoid transformation has been undertaken by evaluation of the "in-situ" dilatation curves in connection with metallographic examinations, DTA and dilatation analyses of the solid state. On a basis of numerous quantitative relations, such as the relation between ferrite and pearlite fractions in as-cast spheroidal graphite cast iron (SGI), the ratio between ferrite and pearlite in the microstructure is determined in a very short time. Thus the melt composition was corrected using the "in situ" dilatation analyses by addition of Cu and/or Mn or Si respectively. From the kinetics of austenite transformation and temperature dependence of the ferrite or pearlite growth, the following characteristic temperatures of the eutectoid transformation have been established: the ferrite nucleation n. the beginning of the ferrite growth Tao and pearlite growth T p , respectively. Both temperatures Tg and Tp are determined from the differential inflection point of the dilatometric curves. For mainly ferrite and pearlite SGI, the kinetic curves, which show the fraction of the single microstructure constituents in the microstructure in dependence of the transformation time, are well represented by the physical sigmoidal Boltzmann model. In case of the kinetics temperature dependence, however, pearlite growth does not follow the sigmoidal transformation course, which results from the recalescence of the pearlite reaction. The time of transformation is a more suitable criterion for the description of the transformation.

Determination of pressure in the extradendritic liquid area during solidification

“…Volume change measurement during the solidification of cast alloys is reported by only a few authors [9][10][11][12][13]. Some of the authors of the present paper have published a review on the problems of volume change measurement [14].…”