Determination of the Fe-Ni and Fe-Ni-P phase diagrams at low temperatures (700 to 300 °C)

Abstract

The α + γ two-phase fields of the Fe-Ni and Fe-Ni (P saturated) phase diagrams have been determined in the composition range 0 to 60 wt pet Ni and in the temperature range 700 to 300 °C. The solubility of Ni in (FeNi)3P was measured in the same temperature range. Homogeneous alloys were austenitized and quenched to form α2, martensite, then heat treated to formα (ferrite) + γ (austenite). The compositions of the α and γ phases were determined with electron microprobe and scanning transmission electron microscope techniques. Retrograde solubility for the α/(α + γ) solvus line was demonstrated exper-imentally. P was shown to significantly decrease the size of the α + γ two-phase field. The maximum solubility of Ni in α is 6.1 ± 0.5 wt pct at 475 °C and 7.8± 0.5 wt pct at 450 °C in the Fe-Ni and Fe-Ni (P saturated) phase diagrams, respectively. The solubility of Ni in α is 4.2 ± 0.5 wt pct Ni and 4.9 ± 0.5 wt pct Ni at 300 °C in the Fe-Ni and Fe-Ni (P saturated) phase diagrams. Ternary Fe-Ni-P isothermal sections were constructed between 700 and 300 °C.