The microstructure and phase transformation behavior of high Cr ferrite heat resistant steel used in ultra super critical power plants were studied using differential thermal analysis(DTA), scanning electron microscope(SEM) and X-ray diffraction(XRD). The results show that the steel generates magnitic transformation, austenite formation, M23C6-type carbide dissolution and transformation from austenite to δ-ferrite, successively, at 600-1100 ℃. The starting formation temperature of austenite is 853 ℃. The ma...