Microstructure analysis of AISI 304 stainless steel produced by twin-roll thin strip casting process

The microstructure of AISI 304 austenlte stainless steel fabricated by the thin strip casting process were investigated using optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The microstructures of the casting strips show a duplex structure consisting of delta ferrite and austenite. The volume fraction of the delta ferrite is about 9.74vo1% at the center and 6.77vo1% at the surface of the casting thin strip, in vermicular and hand shapes. On account of rapid cooling and solidification in the continuous casting process, many kinds of inclusions and precipitates have been found. Most of the inclusions and precipitates are spherical complex compounds consisting of oxides, such as, SiO₂, MnO, Al₂O₃, Cr₂O₃, and FeO or their multiplicity oxides of MnO·Al₂O₃, 2FeO·SiO₂, and 2MnO·SiO₂. Many defects including dislocations and stacking faults have also formed during the rapid cooling and solidification process, which is helpful to improve the mechanical properties of the casting strips.