Microstructures of lath martensite that contains bcc or bct martensite crystals in FeC alloys are known to depend on the carbon content of the alloys. The effect of nitrogen content on microstructure, however, has not yet been elucidated. This study elucidates the effects of carbon and nitrogen content on microstructures via local crystallographic analysis. We found that the packet sizes are similar when the nitrogen content in the alloys are the same as the carbon content, with the packet size decreasing with increasing carbon and nitrogen content. The block and subblock thicknesses in low nitrogen lath martensite are smaller than those in low carbon lath martensite, whereas those in medium and high carbon and nitrogen lath martensites are similar. Martensite lath thickness and dislocation density in the FeN alloy laths are lower than those in the Fe C alloys laths, and the distribution of misorientation angles between adjacent the blocks and sub-blocks in FeN alloys is similar to that in FeC alloys.
The surface patterns called Bamboo-leaf type, Pine needle type and Hexagonal type appear at around 1350°C on the molten iron. These patterns are known to be used to examine the condition of the molten cast iron in a cupola. In this study, the developing mechanism of the surface patterns was examined.The origin of the surface patterns is a surface SiO 2 film which formed by the oxidation of Si with CO. The difference in radiation rate between SiO 2 and molten iron makes the patterns visible. The addition of 0.02% mass% S reduces the surface tension remarkably. As a result, a complex Marangoni convection occurs beneath the surface and it generates the complex surface patterns. The characteristics of the molten iron get better in the order of Bamboo-leaf, Pine needle and Hexagonal pattern. The Hexagonal pattern becomes finer by the inoculation.
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