铝对稀土耐热钢中非金属夹杂物的影响

 稀土能够显著提升钢材的性能,是高品质钢中常见的合金元素之一。然而,由于稀土与O、S等杂质元素之间存在极强的亲和力,加入钢中后形成的高熔点、大尺寸夹杂物对浇铸工艺的顺行及产品质量均有严重危害。为了探讨不同铝含量对稀土耐热钢中非金属夹杂物类型及尺寸分布的影响,在利用优化的热力学模型进行模拟计算的基础上,设计并开展了高温试验。热力学计算结果表明,增大铝含量能够抑制钢中Ce₂O₃夹杂物的析出,同时促进CeAlO₃和Ce₂O₂S夹杂物的析出,根据钢液中Ce、Al、O及S含量的变化,总结了夹杂物转变的临界热力学条件,当铝质量分数为0.025%～0.065%时,满足w(Al])/w(Ce])为270,Ce₂O₃变质成CeAlO₃;当铝质量分数为0.065%～0.17%时,满足w(S])/w(O])为10,Ce₂O₃转变为Ce₂O₂S。试验结果表明,在铈加入量一定的情况下,随着铝质量分数在0～0.3%范围内增大,不同试验钢中典型夹杂物的变化趋势为Ce₂O₃→Ce₂O₃+CeAlO₃→CeAlO₃+Ce₂O₂S,相应地,夹杂物的平均粒径由4.69 μm降低至2.73 μm。由夹杂物类型与尺寸之间关系的统计结果可知,尺寸较小的Ce₂O₂S的形成是导致夹杂物尺寸减小的主要原因之一;适当增大稀土耐热钢的铝脱氧强度,能够通过改变夹杂物类型的方式,有效细化钢中夹杂物的尺寸,有望改善稀土耐热钢的水口结瘤问题和产品质量。

Effect of Al content on non-metallic inclusions in heat-resistant steel containing rare earth element

As a common alloying element in high-quality steel, rare earth is widely used to improve the properties of steel. However, due to the strong affinity between rare earth and impurity elements such as oxygen and sulfur in steel, the formation of inclusions with high melting point and large size after rare earth addition are seriously harmful to casting process and product quality. In order to investigate the effect of different Al contents on the type and size distribution of non-metallic inclusions in heat resistant steel containing rare earth, high temperature experiments were designed and carried out according to calculation by optimized thermodynamic model. The results of calculation show that increase of Al content can inhibit the precipitation of Ce₂O₃ inclusions, but promote the precipitation of CeAlO₃ and Ce₂O₂S inclusions in steel. The changes of Ce, Al, O and S in molten steel were calculated, and thereby obtaining the critical thermodynamic conditions of inclusion transformation. When w(Al]) was 0.025%-0.065%, and the w(Al])/w(Ce]) value was 270, Ce₂O₃ transformed into CeAlO₃. Ce₂O₃ converted to Ce₂O₂S with Al content ranging from 0.065% to 0.17% and w(S])/w(O]) value up to 10. The experiment results show that inclusions variation trend is Ce₂O₃→Ce₂O₃+CeAlO₃→CeAlO₃+Ce₂O₂S with the increase of mass percent of Al from 0 to 0.3% under a certain Ce amount in different test steels, and the average particle size of inclusions reduces from 4.69 μm to 2.73 μm accordingly. Based on the statistical results of relationship between inclusion type and size distribution, it is found that the formation of Ce₂O₂S with small size is one of the main cause for decrease of inclusions size. Therefore, increase of Al contents in rare earth heat-resistant steel appropriately can effectively refine the size of inclusions in steel by modifying the inclusion types, which is expected to improve the nozzle clogging problem and the product quality.