IF钢铸坯厚度方向夹杂物分布及洁净度评估

Evaluation of cleanliness and distribution of inclusions in the thickness direction of interstitial free(IF) steel slabs

为了减少IF钢生产过程中冷轧板缺陷以及降低夹杂物对钢的成材性能的影响,重要的是明确IF钢铸坯厚度方向夹杂物分布规律,本文采用氧氮分析、扫描电镜和能谱分析、夹杂物自动扫描以及原貌分析等手段进行了系统的分析.结果表明,铸坯厚度方向T.O(总氧)和N的平均质量分数值分别为1.6×10-5和1.7×10-5,T.O在内弧表面1/8处最高,为2.0×10-5,内弧1/8~3/8区间N质量分数较高,为1.8×10-5;共统计1177个夹杂物,70%以上夹杂物的尺寸都在5μm以内,平均尺寸为2.8μm,内、外弧3/8处夹杂物平均尺寸较大,分别为4.0μm、4.4μm;铸坯中心Ti N析出量较多,内外弧表面以Al2O3和Al2O3-TiOx为主,尺寸在5~10μm之间,Al2O3-TiN在内外弧1/4处呈不规则状,尺寸在3~5μm;当凝固率0.646<f≤0.680时,凝固前沿液相以及δ相中开始有TiN析出,尺寸在3~6μm之间波动.

During the production of Al-killed titanium-alloyed interstitial free steel,to reduce defects in cold rolled sheets and decrease the influence of inclusions on the properties of the steel,it is important to clarify the distribution of inclusions in the thickness direction of IF(interstitial free)steel along the slab.In this study,standard metallographic techniques were employed to analyze the total oxygen and nitrogen by performing scanning electron microscopy,energy spectroscopy,automatic scanning electron microscopy,and original morphology analysis.The results show that the average mass fractions of T.O and N are 1.6×10-5 and 1.7×10-5,respectively,and the T.O for the 1/8 thickness from the inner arc is 2.0×10-5,while the content of N for between the 1/4 and 3/8 thickness from the inner arc is 1.8×10-5.A total of 1177 inclusions were counted.More than 70%of inclusions are within 5μm in size,and the average size of inclusions in the thickness direction is 2.8μm.The sizes of inclusions for the 3/8 thickness from both the inner and outer arcs are larger at 4.0μm and 4.4μm,respectively.The amount of precipitation of Ti N is large in the slab center,and there are mainly Al2O3 and Al2O3–Ti Ox near the inner and outer arc surfaces with sizes between 5 and 10μm.Al2O3–Ti N distributes irregularly in the 1/4 thickness from the inner and outer arcs,and the size fluctuates between 3 and 5μm.The size of Ti N during solidification fluctuates between 3 and6μm.Ti N precipitates in the liquid andδphase of the solidification front when the solidification rate is between 0.646 and 0.680,and the size fluctuates between 3 and 6μm.