The continuous casting of Ti-alloyed Al-killed steels traditionally experiences clogging in the tundish, impeding stable operation. We studied the microstructures and mode of formation of such clogging deposits in tundish skulls recovered after long cast series. We sampled the steel skull along the whole tundish bottom from under the ladle shroud (impact zone) up to the tundish well and nozzle. The microstructures imply that the steel solidifies to the refractory (gunning mass) and remains partially solid through the entire cast. Thus, a “mushy zone” of steel loaded with solid delta ferrites is present along the margins of the steel during casting. In this mushy zone, the widely observed clusters of variably sintered alumina (NMI) accumulate, along with a substantial amount of gas bubbles acting as inclusion scavengers. The clustered alumina particles show a lognormal particle size distribution (PSD) in all locations, which becomes more pronounced if correcting for the observable sintering. Sintering of alumina size distributions linearizes a PSD, and further evolution, once the deposit is locked in place, occurs by Ostwald ripening, introducing skewness to the distributions. The observed PSDs contrast with the established log-linearity of PSDs of individual floating alumina NMI in the bulk steel, and suggest that the source of the alumina in the clogging deposits is not the passing bulk steel. However, ubiquitous sedimentary features show that the alumina particles are also not grown by reoxidation in situ. An upstream source separate from the bulk stream must be inferred, which is also required by the consistent sporadic presence of oxidic materials which cannot be derived from local sidewall reaction. In summary, the development of clogging deposits in this type of steel is an example of “slurry casting” of partially solidifying steel over thermal loss surfaces of refractories in the nozzle area.

中文翻译：

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钛合金冷轧钢中中间包堵塞沉积物的显微组织和形成

钛合金铝镇静钢的连铸传统上会出现中间包堵塞，影响稳定运行。我们研究了长铸系列后回收的中间包头骨中这种堵塞沉积物的微观结构和形成方式。我们沿着整个中间包底部从钢包护罩（冲击区）下方到中间包井和水口对钢壳进行取样。微观结构意味着钢凝固成耐火材料（喷补料）并在整个铸件中保持部分固态。因此，在铸造过程中沿钢的边缘存在加载有固态δ铁素体的钢的“糊状区”。在这个糊状区域，广泛观察到的可变烧结氧化铝 (NMI) 聚集在一起，以及大量充当夹杂物清除剂的气泡。簇状氧化铝颗粒在所有位置均显示对数正态粒度分布 (PSD)，如果对可观察到的烧结进行校正，则该分布会变得更加明显。氧化铝粒度分布的烧结使 PSD 线性化，一旦沉积物锁定到位，Ostwald 熟化就会发生进一步的演变，从而导致分布偏斜。观察到的 PSD 与散装钢中单个漂浮氧化铝 NMI 的 PSD 建立的对数线性对比，表明堵塞沉积物中氧化铝的来源不是通过的散装钢。然而，无处不在的沉积特征表明氧化铝颗粒也不是通过原位再氧化生长的。必须推断与批量流分离的上游源，这也是不能从局部侧壁反应衍生的氧化物材料的一致零星存在所需要的。总之，这种钢中堵塞沉积物的发展是部分凝固钢在喷嘴区域耐火材料热损失表面上的“浆料浇铸”的一个例子。