Discussion on the classification rule for the nonmetallic inclusions measured by scanning electron microscope
ZHANG Shu-lan1, WANG Hui2, WANG Chang*1
1. Central Lab, Central Iron and Steel Research Institute, Beijing 100081, China; 2. Institute of Material Science and Engineering, Chongqing Univeristy, Chongqing 400044, China
Abstract：During the detection of inalusions by scanning electron microscope (SEM), there are few reports on the following settings: wether O and N are counted or not; the hardness of inclusions with different composition. However, these factors are very important for the classification of inclusions. The content of inclusions in low carbon steel was automatically measured and analyzed by scanning electron microscope. The changing law of composition (content) in various types of inclusions was investigated when the elements of O and N were counted and not counted, respectively. Some typical inclusions were selected for Mapping to analyze the distribution characteristic of O, N and alloying elements in inclusions. Finally, according to the content and distribution characteristic of elements, it confirmed that whether the elements of O and N should be counted and not, and confirmed the composition classification standard for various types of inclusions. The hardness of inclusions was tested by nanoindenter. The influence of composition change on the hardness of inclusion was discussed. The experimental results indicated that the elements including Mg, Al, Ca, Mn and S had high detection resolution. When the mass fraction was not less than 2%, the presence of such element could be confirmed and its classification could be conducted according to the detection results. The measurement error of N was relatively large and it was not counted in classification. In addition, the harness testing results of inclusions indicated that the hardness of inclusion was closely related to the composition. The hardness of oxide inclusion was highest, which was up to 25GPa. The hardness of MnS was in range of 3.5-4.5GPa. According to the quantitative analysis of composition in inclusion and Mapping results, the classification principle for various types of inclusions was proposed.
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