The dependence of the iron–carbon eutectic transition temperature on thermal history and its implications for thermometry

The melting behavior of the eutectic Fe–C fixed point was investigated as a function of the thermal history prior to melting using degassed and non-degassed Fe–C cells. The liquidus temperature and the melting range depend on the preceding growth rate: slower freezing entails a higher liquidus temperature and a smaller melting range. Annealing at temperatures just below the eutectic temperature has similar effects. The inflection point of the melting plateau and the maximum temperature of the freezing plateau showed a linear variation with the square root of the growth rate during the (preceding) freeze and this variation is approximately five times smaller for the melt than for the freeze. No clear evidence of the effect of gaseous impurities could be detected on the shape of the melting plateau obtained in conjunction with the lowest growth rate. However, both the inflection point of the melting plateau and the maximum temperature of the freezing plateau showed a larger dependence on the growth rate for the degassed cell.