As we have pursued recently the formation mechanism about oxide inclusions formed in steels of the system Fe-Cr-O, we could summerize it from various experimental results obtained.
Those inclusions composed of mutual solid solutions between iron chromite (FeO·Cr
2O
3) and sesquioxide solid solution series (Fe
2O
3·Cr
2O
3), and appearance of iron chromite having tetragonal structure depend upon added chromium contents, oxygen potential and melting temperature.
According to our proposed diagram about the system FeO·Cr
2O
3-Cr
2O
3-Fe
2O
3, the formation mechanism of the distorted iron chromite is reduced to the ratio of Fe
+3/Fe
+2 and not related to the difference of valency of chromium as previously suggested.
The results induced from our diagram are as follows:
1) There are two sorts of existence ranges from FeO·Cr
2O
3 to iron chromite having axial ratio c/a=0.95 and from one having c/a=0.89 to 0.86, and these tendencies agree to theresult about the oxygen content dissolved in steels of this system from the equilibrium study. Under experimental conditions of oxygen potential given, two sorts of iron chromite will be formed, that is, one (Fe, Cr)
2O
3 dissolved in FeO·Cr
2O
3 and the other little FeO·Cr
2O
3 dissolved in (Fe
x, Cr
y)
2O
3.
2) In the case of the steel containing much chromium or electrolytic chromium, chromic oxide is formed at the moment, then as temperature falls, FeO·Cr
2O
3 will be dissolved into it and arrive to c/a=0.86 type iron chromite.
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