A Special Phase Transformation Phenomenon was observed in isothermal decomposition (200-250℃) process of High Degree of Supersaturation Nitrogenous (>2%N) Supercooled Austenite. The nucleus number of new phase increase constantly, but the maximum size of the nucleus is 0.1 μm magnitudes. The expanding of new phase depends on the increase of the existing nuclei amount, not the growth of their size. Finally the highly disperse structure can be obtained. This structure is not only different from needle, plate and lath pattern martensite but also common bainite. The dynamics characteristics of the phase transformation is the long incubation period and complete decomposition of austenite under the isothermal situation. This is different from the ceasing phenomenon of bainite transformation. The hardness of the transformation product is greater than 900HV and the application perspective are very good.
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