개량된 12% 크롬 합금강에서 응고속도와 첨가원소에 따른 응고 조직 형성 거동
(The) Behavior of Solidification Microstructures with Solidification Rate and Alloying Elements in the Modified 12% Cr steels
크롬 합금강 응고 발전설비재료;
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The influences of solidification rates and carbon contents and boron contents on the formation of the solidification microstructures were studied by directional solidification in modified 12%Cr steels. Directional solidification experimental results showed that solidification microstructure depended on solidification rate and carbon content and chromium equivalent and boron content. The length of the mushy zone increased and the dendrite arm spacings decreased as the solidification rate increased. The volume fraction of the δ-ferrite decreased with increasing the solidification rate and carbon content. The volume fraction of the ferrite showed much higher at low solidification rates with planar and cellular interfaces than that at high solidification rates with dendritic interface. It is expected that macro-segregation of C causes lower C content at the lower solidification fraction in the directionally solidified sample, where lower C results in higher volume fraction of the ferrite. The influences of solidification rates and boron contents on the formation of the borides were studied by DTA experiment and SEM observation in modified 12%Cr steels. Borides observed in conditions of addition under 1374℃, 0.025 wt.%B and 2.0 wt.%W. In order to estimate solidification microstructure in modified 12Cr steels, various solidification conditions, such as solidification rate, cooling rate, segregation, alloy composition, should be considered..