含钛微合金钢凝固过程中TiN的析出行为分析

分别从热力学和动力学方面研究了低碳含钛微合金钢凝固过程选分结晶对TiN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TiN析出;由于凝固过程凝固前沿Ti、N元素富集,凝固分数达到0.377时,凝固前沿固相中开始析出TiN;凝固末期,Ti和N的富集程度进一步增大,固液相中均有TiN析出。动力学分析表明,随着冷却速度的降低,凝固过程TiN夹杂物的尺寸显著增加,当冷速高于50 K/s时,TiN的理论半径为5.5 μm,当冷速低于5 K/s时,TiN的理论半径在17.5 μm以上;固相中析出的TiN为纳米级别。铸坯中TiN析出物主要尺寸为1~5 μm,且大尺寸夹杂主要在铸坯厚度方向的1/4处和中心处析出,这表明铸坯中的大尺寸夹杂物是在凝固过程中析出的。

Analysis of TiN precipitation during solidification of Ti-containing micro-alloy steel

Effects of separation crystallization on the precipitation of TiN inclusions during the solidification process of low carbon Titanium micro-alloy steel were studied from the aspects of thermodynamics and kinetics respectively. Thermodynamic analysis showed that TiN could not precipitate out above liquidus temperature. Due to the enrichment of TiN in the solidification front during the solidification process, when the solidification fraction reaches 0.377, TiN begins to precipitate out from the solid phase in the solidification front. At the end of solidification, the enrichment degree of Ti and N further increases, and TiN is precipitated in both solid and liquid phases. The dynamic analysis showed that the size of TiN inclusion during solidification increased significantly with the decrease of cooling rate, When the cooling rate was higher than 50 K/s, the theoretical radius of TiN was 5.5 μm. when the cooling rate was lower than 5 K/s, the theoretical radius of TiN was above 17.5 μm. TiN precipitation in solid phase is nano-level. TiN precipitates mainly ranged from 1 to 5 μm in the billet, and large size inclusions mainly precipitated at 1/4 and center of the billet, indicating that large size inclusions were precipitated during solidification.