Adabavazeh Z, Hwang W S, Su Y H
Department of Materials Science and Engineering, National Cheng Kung University, No. 1 Tainan, 701, Taiwan.
Iron and Steel Research and Development Department, China Steel Corporation, Kaohsiung 812, Taiwan.
Sci Rep. 2017 May 9;7:46503. doi: 10.1038/srep46503.
Intra-granular Acicular Ferrite (IAF), as one of the most well-known desirable microstructure of ferrite with a chaotic crystallographic orientation, can not only refine the microstructure and retard the propagation of cleavage crack but also provide excellent combination of strength and toughness in steel. The effect of adding cerium on microstructure and controlling proper cerium-based inclusions in order to improve properties in low-carbon commercial steel (SS400) were investigated. The type of inclusions can be controlled by changing S/O ratio and Ce content. Without Ce modification, MnS is a dominate inclusion. After adding Ce, the stable inclusion phases change from AlCeO to CeOS. The optimum amount of cerium, 0.0235 wt.%, lead in proper grain refinement and formation of cerium oxide, oxy-sulfide and sulfide inclusions. Having a high amount of cerium results in increasing the number of inclusions significantly as a result it cannot be effective enough and the inclusions will act like barriers for others. It is found that the inclusions with a size of about 4∼7 μm can serve as heterogeneous nucleation sites for AF formation. Thermodynamic calculations have been applied to predict the inclusion formation in this molten steel as well, which show a good agreement with experimental one.
晶内针状铁素体（IAF）作为铁素体最著名的理想微观组织之一，具有混乱的晶体取向，不仅可以细化微观组织、阻碍解理裂纹的扩展，还能使钢具备优异的强度和韧性组合。研究了添加铈对低碳商用钢（SS400）微观组织的影响以及控制合适的铈基夹杂物以改善其性能。夹杂物的类型可以通过改变硫氧比和铈含量来控制。未进行铈变质处理时，硫化锰是主要夹杂物。添加铈后，稳定的夹杂物相从铝铈氧化物变为铈氧化物硫化物。铈的最佳含量为0.0235 wt.%，可实现适当的晶粒细化，并形成氧化铈、氧硫化物和硫化物夹杂物。铈含量过高会导致夹杂物数量显著增加，其效果不佳，夹杂物会成为其他夹杂物的障碍。研究发现，尺寸约为4∼7μm的夹杂物可作为针状铁素体形成的异质形核位点。还应用了热力学计算来预测该钢液中夹杂物的形成，计算结果与实验结果吻合良好。
