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Ti-IF鋼凝固過程中TiN的析出機理和規律

Precipitation mechanism and behavior of TiN during Ti-IF steel solidification

  • 摘要: 結合冶金熱力學和凝固偏析模型分析了Ti-IF鋼凝固過程中TiN的析出特點.Ti-IF鋼凝固前期鋼液中TiN夾雜無法生成,固相中TiN源自低溫固相析出;凝固固相分數達到0.64時,Ti、N組元在凝固前沿富集程度增加,凝固前沿固相中開始有TiN析出;凝固末期,Ti和N的富集程度進一步增大,固液相中均能有TiN析出.采用掃描電鏡分析了TiN在鑄坯中的分布,從鑄坯表層到中心TiN數量和尺寸存在顯著變化:從鑄坯表層向中心方向TiN尺寸不斷增大,平均尺寸從1-2μm增大到5μm,在距離表層70-80 mm處尺寸達到最大;在鑄坯厚度中間位置,TiN尺寸較大,平均尺寸為5μm左右;在鑄坯中心TiN尺寸又有所變小,平均尺寸為3μm左右;在鑄坯表層TiN密集程度較高,在鑄坯中間和中心TiN數量密集程度顯著降低.IF鋼鑄坯中TiN析出時機及其尺寸和數量與Ti、N組元偏析和凝固冷卻速度關系密切.

     

    Abstract: Characterization of TiN precipitation during Ti-IF steel solidification was analyzed by thermodynamics and the solidification segregation model. It is found that TiN inclusions cannot precipitate in liquid steel before solidification. In the earlier stage of solidification,TiN precipitates at low temperature in solidified steel. When the solid fraction reaches to 0.64,TiN can precipitate in solid steel around the solidification front at higher temperatures,due to the increased enrichment of Ti and N. However,at the end stage of solidification,TiN can not only precipitate in solidified steel,but also in molten steel,for the segregation of Ti and N is getting serious. TiN distribution in the Ti-IF slab was observed by scanning electron microscopy(SEM). The results show that the number and size of TiN precipitates vary a lot from the slab surface to the center. The TiN size is increasing from the slab surface to the center,from 1-2 μm to 5 μm,and it is maximum in the area of 70 to 80 mm from the slab surface. In the middle of the slab in thickness,the TiN size is large,with an average size of 5 μm; while in the center of the slab,the TiN size is getting smaller again,with an average size of 3 μm. The TiN denseness is high in the surface layer of the slab,but decreases significantly in the center and middle. The precipitation moment,the size and number of TiN precipitates are closely related with the segregation of Ti and N and the solidification rate.

     

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