耐蚀合金中TiN析出机制

摘要：TiN颗粒尺寸及其分布对耐蚀合金性能有明显的影响，因此有必要对TiN在铸坯中的分布及其析出行为进行研究。采用扫描电镜(SEM)、金相显微镜（OM）观察了TiN夹杂物在铸坯中的分布、尺寸及其形貌；基于热力学和动力学理论分析了耐蚀合金铸坯中TiN夹杂物的析出时机及其尺寸，结合试验结果和理论计算明确了TiN夹杂物在凝固后铸坯中的位置和尺寸与析出时机的关系，为控制TiN夹杂物提供理论指导。结果表明，冶炼过程中析出的TiN夹杂物尺寸较大，在凝固过程中被枝晶吞没，位于铸坯枝晶内和等轴晶内；微观偏析计算结果表明，在凝固分数为0.55时，TiN开始析出，最开始析出TiN夹杂物的逐渐长大，长大后的TiN易于被二次枝晶吞没，最终位于铸坯中的枝晶间和等轴晶内，后期析出的TiN则在枝晶间和等轴晶间。固相中析出的TiN夹杂物长大较慢，尺寸细小，最终位于奥氏体晶界。

Mechanism of TiN precipitation in corrosion resistant alloys

Shanghai University, Shanghai 200444, China)Abstract：Size and distribution of TiN particles have a significant effect on properties of corrosion resistant alloy. It is necessary to study distribution and size of TiN in slabs and understand their precipitation behavior. Scanning electron microscopy (SEM) and metallographic microscope (OM) were used to analyze distribution, size and morphology of TiN inclusions in the billet. Based on thermodynamics and kinetics, the precipitation timing and size of TiN inclusions in the corrosion-resistant alloy billet were analyzed, which are combined with experimental results and theoretical calculations to clarify the effect of precipitation timing on the position and size of the TiN inclusions, and then provide theoretical guidance for controlling TiN inclusions. The results show that the TiN inclusions which precipitated during the smelting process are larger in size, and engulfed by dendrites during solidification. The microsegregation calculation results show that TiN startes to precipitate when the solidification fraction is 0.55. In molten steel, the earlier-precipitated TiN inclusions, which are larger in size, are easily engulfed by secondary dendrites, and are finally located in the secondary dendrites in the slab; the later precipitated TiN inclusions are engulfed between the dendrites. The TiN inclusions, which precipitated in the solid phase, have a small size as a result of growing slowly and are finally located at the austenite grain boundaries.