水平连铸大直径球铁型材中夹杂物的研究

Analysis of Inclusions in Horizontal Continuous Casting Large-diameter Ductile Iron Bars

对大直径球墨铸铁型材中夹杂物的分布、尺寸、成分进行了研究。结果表明,主要的夹杂物聚集在型材中心线上方3/4R附近,多数呈丝状分布,且尺寸较大。SEM结果表明,几乎所有的丝状、块状及散落状的夹杂物都分布在铁素体中,且周围通常有退化石墨存在。颗粒状夹杂物则在铁素体和珠光体中都有分布。EDS和EPMA结果说明,由于RE-Mg球化剂与铁液中其他元素反应而导致的镁不足是促成多数夹杂物(尤其是丝状、块状和散落状夹杂物)形成的主要原因。夹杂物和退化石墨的存在对型材的力学性能不利。因此,选用合适的球化处理工艺及参数对防止夹杂物产生、保证大直径型材的组织与性能有重要的意义。

The distribution, size and composition of inclusions in large diameter ductile iron bars were studied. The results show that the main inclusions are clustered around 3/4R above the center line of the bar, and most of them are distributed in a filamentous manner with large size. SEM results show that almost all filamentous, massive and scattered inclusions are distributed in ferrite, and there is usually degenerate graphite around. Granular inclusions are distributed in both ferrite and pearlite. EDS and EPMA results indicate that magnesium deficiency caused by the reaction of RE-Mg spheroidizing agent with other elements in the iron solution is the main reason for the formation of most inclusions, especially filament-like,lump-like and scattered-like inclusions. The presence of inclusions and degraded graphite is unfavorable to the mechanical properties of the ductile iron bars. Therefore, the selection of appropriate spheroidizing process and parameters is of great significance to prevent inclusion and ensure the microstructure and properties of large diameter ductile iron bars.