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在使用CSP工艺生产低碳或超低碳钢时,在铸坯中,特别是铸坯宽面的中心经常观察到相当数量的微米级碳覆夹杂物。通过对CSP流程不同的钢种铸坯取样,研究了这类夹杂物的结构特点和析出机制。指出碳覆夹杂物呈双层结构,外面包裹一层富碳层、中心为钙铝酸盐或含CaO的复合夹杂物。热力学计算结果显示这层富碳物质并非CaC_2。通过对比球墨铸铁中球状石墨的形成条件,指出CSP铸坯中存在冷却速度快、S元素含量低、加钙处理后促球化元素Ca、Mg含量相对较高,有大量夹杂物作为形核核心等促进碳覆夹杂物析出的有利条件。C为易偏析元素,在低碳或超低碳钢铸坯凝固过程中液芯中C含量的升高,能够析出球状的碳覆夹杂物。并指出由于碳覆夹杂物的析出,中心钢基体C含量降低,碳覆夹杂物析出能够减轻铸坯凝固过程中C元素的偏析程度。
In the production of low-carbon or ultra-low carbon steel using the CSP process, a considerable amount of micron-sized carbon inclusions are often observed in the slab, in particular at the center of the slab broad face. Through the sampling of steel slabs with different CSP processes, the structural characteristics and precipitation mechanisms of these inclusions were studied. It is pointed out that the carbon inclusions have a double-layered structure and the outer layer is covered with a carbon-rich layer, and the center is calcium aluminate or composite inclusions containing CaO. Thermodynamic calculations show that this layer of carbon-rich material is not CaC_2. By comparing the forming conditions of spheroidal graphite in ductile iron, it is pointed out that the cooling speed of CSP slab is high and the content of S element is low. The content of Ca and Mg in spherodizing elements after C-treatment is relatively high, and there are a large number of inclusions as nuclei And other favorable conditions for promoting the precipitation of carbon coated inclusions. C is easily segregated elements, in the low-carbon or ultra-low carbon steel slab solidification process C content in the liquid core can precipitate spherical carbon inclusions. It is pointed out that due to the precipitation of carbon inclusions, the content of C in the steel matrix decreases and the precipitation of carbon inclusions can reduce the degree of segregation of C during the solidification of slab.