Phase equilibria in the Al-Fe-C system: Isothermal sections 1550 °C to 2300 °C

Abstract

Fe-C and Al-Fe-C systems were investigated over the temperature range of 1550 °C to 2300 °C by chemical analysis of alloys saturated with carbon within internally sealed graphite crucibles. The solubility of carbon in liquid iron agrees with accepted published values at 1550 °C, but was found to be slightly higher than published values at higher temperatures. Partial isothermal sections for the Al-Fe-C system at 1550 °C, 2150 °C, and 2300 °C and complete isothermal sections at 1700 °C, 1850 °C, and 2000 °C were constructed from the chemical analyses and from metallographic observations. The univariant point on each complete isotherm, at which the solid phase in equilibrium with the homogeneous liquid changes from A1₄C₃ (aluminum carbide) to carbon with increasing Fe-Al ratio in the alloy, was determined to be 55.OAl-37.6Fe-7.4C at 1700 °C, 61.2Al-29.4Fe-9.4C at 1850 °C, and 65.7Al-21.9Fe-12.4C at 2000 °C, where all concentrations are in atomic percent. The only solid phases observed at these elevated temperatures were A1₄C₃ and graphite.