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对轴承钢连铸坯中夹杂物进行了检测,发现铸坯中存在大尺寸的Ti N夹杂物。从热力学和动力学方面研究了凝固过程选分结晶对Ti N夹杂物析出的影响。热力学分析表明,液相线温度以上不会有Ti N析出;凝固过程由于凝固前沿Ti、N富集,当凝固率达到0.65~0.75后会有Ti N析出;降低Ti、N含量可推迟Ti N的析出,减小Ti N夹杂的尺寸和数量。动力学分析表明,随着冷却速度的降低,凝固过程Ti N夹杂物的尺寸显著降低,当冷速高于50K/s时,Ti N的理论半径为2.4μm,当冷速低于5 K/s时,Ti N的理论半径在7.6μm以上;完全凝固后铸坯冷却过程析出的Ti N为纳米级。实际铸坯表层未发现等效半径大于2.5μm的Ti N,1/4和中心处观察到的最大Ti N等效半径分别为6.77μm和8.46μm,这表明铸坯中大尺寸Ti N夹杂物是在凝固过程析出的。
The inclusion in the bearing steel billet was tested and found to have large size TiN inclusions in the billet. The thermodynamic and kinetic studies of the influence of the selective crystallization in the solidification process on the precipitation of TiN inclusions were investigated. The thermodynamic analysis shows that no precipitation of TiN occurs above the liquidus temperature. The solidification process is enriched in Ti and N due to the solidification front. When the solidification rate reaches 0.65-0.75, TiN will be precipitated. Decreasing the Ti and N content may delay TiN Precipitation, reducing the size and number of TiN inclusions. The kinetic analysis shows that with the decrease of cooling rate, the size of TiN inclusions in the solidification process decreases significantly. When the cooling rate is higher than 50K / s, the theoretical radius of TiN is 2.4μm. When the cooling rate is lower than 5 K / s, the theoretical radius of TiN is above 7.6μm. The TiN precipitated during the solidification of the slab completely solidified is nanoscale. TiN with equivalent radius greater than 2.5μm was not found on the surface of the actual slab, and the maximum TiN equivalent radii observed at 1/4 and center were 6.77μm and 8.46μm, respectively, which indicated that large size TiN inclusions Is precipitated in the solidification process.