Abstract：The nanoscale precipitated phases play the role of precipitation strengthening in steel. They are also used as the inhibitor of grain growth to obtain microstructure with specific orientation. Therefore, the systemically analysis of precipitated phases is very important. At present, the statistical analysis of precipitated phases with size less than 50 nm was hardly realized by scanning electron microscope(SEM) and transmission electron microscope(TEM). In the study, the Feature software package in SEM for statistic of inclusions was applied to the energy spectrum control software of TEM, realizing the direct statistical analysis of nanoscale precipitated phases in steel by TEM. Meanwhile, the main factors influencing on the statistical analysis of precipitated phases by TEM, such as sample preparation method, acquisition parameter, classification method and large-area statistic method, were systemically studied. The results showed that the optimal experimental conditions were as follow: the new complex method was adopted for sample preparation; the single-point acquisition time of energy spectrum was 5 s; the image resolution was 2 048; the continuous map collecting statistics mode was adopted; the terminal condition was that when the statistical quantity of precipitated phases exceeded 100. The detailed implementation method for classification rules of precipitated phases was obtained. Combining the experimental statistic results of non-oriented electrical steels W800 and WH470, the type of precipitated phases was core-shell composite precipitation of CuS2 and MnS+CuS2. The minimum size of precipitated phases in statistical analysis by experimental method was 10 nm.
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