钇含量对铝脱氧含钛不锈钢中夹杂物的影响

 以T4003铁素体不锈钢为研究对象,采用热力学计算与实验室试验的方法,对钇质量分数为0、0.007 0%、0.014 0%和0.023 0%的不锈钢中夹杂物进行了分析,研究了稀土元素钇含量对T4003铁素体不锈钢中夹杂物的影响,总结了不同钇含量对钢中夹杂物影响的规律。首先通过计算夹杂物的生成吉布斯自由能变预测了钢中生成的夹杂物种类,总结了不同钇含量试验钢中不同夹杂物的生成吉布斯自由能变随温度的变化规律。计算结果与扫描电镜对钢中夹杂物的检测结果一致。研究表明,不含钇的T4003不锈钢中夹杂物主要为尺寸不均匀的均相TiN夹杂物及少量Al₂O₃、Mg-Al-O、Ca-Ti-O与TiN的非均相复合夹杂物,添加钇后钢中夹杂物主要为小尺寸的TiN和部分以Y₂O₃和Y₂O₂S为核心表面包裹TiN的复合夹杂物。随着钢中钇含量的增加,钢中夹杂物的总含量先增加后减少,夹杂物平均直径先减小后增大。夹杂物中氧化物的改性路径为MgAl₂O₄-CaO-TiO_x→MgAl₂O₄-Y₂O₃-(CaO-)TiO_x→Y₂O₃-TiO_x→Y₂O₃-Y₂O₂S及Y₂O₃和Y₂O₂S。试验钢中含TiN夹杂物的数密度与面积分数先增加后减少,平均直径先减小后增大。钇的加入使钢中小于4 μm的小尺寸含TiN夹杂物数量增多,但钇的加入量过高时,含TiN夹杂物的细化程度减弱。当钢中钇质量分数为0.007 0%与0.014 0%时,渣中含TiN夹杂物的尺寸明显减小,大尺寸的含TiN夹杂物数量显著减少。

Effect of yttrium content on inclusions in Al-killed titanium-bearing stainless steel

Taking the T4003 ferritic stainless steel as research object, the inclusions in the stainless steel with measured yttrium mass percent of 0,0.007 0%,0.014 0%,0.023 0% were analyzed by thermodynamic calculation and laboratory experiments. The effect of yttrium content on inclusions in the ferritic stainless steel was studied. The influence of different yttrium contents on inclusions in steel was summarized. The types of inclusions in the steel were predicted by calculating the Gibbs free energy change of inclusions that may be generated in the experimental steel, and the variation of Gibbs free energy change with temperature of different inclusions in the experimental steel with different yttrium contents was summarized. Then, the actual inclusions in the experimental steel were observed by scanning electron microscopy, and the observation results were compared with calculation results and they achieved consistent. The result shows that inclusions in the stainless steel without yttrium are mainly homogeneous TiN inclusions with non-uniform sizes and a small amount of heterogeneous composite inclusions of Al₂O₃, Mg-Al-O, Ca-Ti-O and TiN. After adding yttrium, inclusions in the steel are mainly small-size TiN and part complex inclusions with TiN wrapping around Y₂O₃ and Y₂O₂S. With the increase of yttrium content in steel, the total content of inclusions in steel increases first and then decreases, and the average diameter of inclusions decreases first and then increases. With the increase of yttrium content in the steel, the modification path of oxide inclusions is MgAl₂O₄-CaO-TiO_x → MgAl₂O₄-Y₂O₃-(CaO-) TiO_x→Y₂O₃-TiO_x→Y₂O₃-Y₂O₂S as well as Y₂O₃ and Y₂O₂S. The number density and area fraction of TiN inclusions in the experimental steel first increases and then decreases, and the average diameter first decreases and then increases. Due to the addition of yttrium, the number of TiN inclusions with small size less than 4 μm in the steel increases, but when the amount of yttrium is too high, the refinement of TiN inclusions decreases. Besides, when the mass percent of yttrium in steel is 0.007 0%, 0.014 0%, the size of TiN is obviously refined and the number of large-size TiN decreases remarkably.