The Ca-Fe phase diagram in [Massalski2] was redrawn from [1992Kah]. The Ca-Fe phase diagram near the Fe corner was reported by [1993Gla] partly based on [1960Kre] for the solubility of Ca in liquid Fe, as reviewed by [1994Oka]. This phase diagram is shown in Fig. 1. Formation of a γ loop was concluded in this study.

Fig. 1
figure 1

Fe corner of the Ca-Fe phase diagram [1993Gla] (composition scale may be wrong)

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Solid lines in Fig. 2 show the Ca-Fe phase diagram reported by [1987Sch]. The Ca corner of this phase diagram is enlarged in Fig. 3. The (γFe) phase was not shown in the diagram of [1987Sch]. This can be explained by assuming that the γ loop is so narrow that it is located within the line width of the pure Fe line. This is quantitatively consistent with the diagram of [1993Gla] (Fig. 1). However, the quantitative scale of Fig. 1 is questionable, as discussed below. Figure 4 shows the Fe corner of the Ca-Fe phase diagram calculated by [1994Ang]. The L1 + L2/L2 boundary was calculated based on the data of [1964Spo] and [1985Koh]. When Fig. 1 and 4 are compared, it is found that discrepancy in the solubility of Ca in liquid Fe is about 100 times. It is more reasonable to assume that the scale in Fig. 1 is questionable because the six 9 purity in the horizontal axis is very uncommon.

Fig. 2
figure 2

Ca-Fe phase diagram [1987Sch]

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Fig. 3
figure 3

Ca corner of the Ca-Fe phase diagram shown in Fig. 2

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Fig. 4
figure 4

Fe corner of the Ca-Fe phase diagram calculated by [1994Ang]

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The (γFe) phase was missing in the diagram of [1987Sch], as described above. However, the van’t Hoff relationship demands certain initial angle for the (αFe)/(αFe) + (γFe) boundary away from the 100% Fe line at both highest and lowest temperature limits (1394 and 912 °C). Because the L1 + (αFe)/(αFe) boundary is located very close to the 100% Fe line, the γ loop must cross this boundary. The temperatures at the crossing should not be much different from the allotropic transformation temperatures of γFe. Two dashed lines have been added in Fig. 2 to reflect this situation. After all, the overall Ca-Fe phase diagram looks like the one proposed by [1992Kah], but the behavior of the (γFe) phase must be clarified (tends to form a γ loop or not).

Ca-Fe crystal structure data are given in Table 1.

Table 1 Ca-Fe crystal structure data
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