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Determination of Free Energy of .DELTA.-Ferrite/.GAMMA.-Austenite Interphase Boundary of Low Carbon Steels by In-situ Observation.

1998; The Iron and Steel Institute of Japan; Volume: 38; Issue: 8 Linguagem: Inglês

10.2355/isijinternational.38.794

1347-5460

Hongbin Yin, Toshihiko Emi, Hiroyuki Shibata,

Metallurgy and Material Forming

Phase transformations of δ-ferrite/γ-austenite in low carbon steels containing 0.017 mass% phosphorus are observed in-situ by using a combination of confocal scanning laser microscope with infrared image furnace. Dihedral angles at triple points of one high energy δ/δ grain boundary and two incoherent δ/γ interphase boundaries are measured by holding the sample at temperatures where δ- and γ-phases co-exist in quasi-equilibrium. From the average value of observed dihedral angles, free energy of γ/δ incoherent boundary for a steel with low sulfur content (0.007 mass%) is estimated to be 0.450 J/m2 at ca. 1700 K. The effects of temperature and sulfur content on the dihedral angle and free energy of incoherent δ/γ boundary are also discussed.