镁钛复合处理对不锈钢凝固组织的影响及机制

摘要：TiN是铁素体不锈钢有效的异质形核剂，但钢中大尺寸的TiN颗粒会对不锈钢板材表面质量带来不利影响。为此，提出依靠镁钛复合处理来细化TiN颗粒及控制宏观晶粒的方法。通过良好气氛保护的电阻炉试验，研究了添加Mg和Ti元素对于铁素体不锈钢宏观铸态组织和TiN颗粒细化效果的影响规律，并对其细化机理进行了详细分析。经研究得知，向铁素体不锈钢中添加了微量Mg和Ti元素后试样宏观等轴晶比例由37%提高至50%，TiN颗粒平均尺寸由处理前的5μm细化至2μm。镁钛复合处理后，钢液中形成的MgO和MgAl2O4与TiN之间的晶格错配度很低，分别为1.14和5.29，均属于有效形核范围，可以成为TiN异质形核核心，促进在晶内均匀析出更多的TiN。同时基于TiN与铁素体相之间的良好的晶格匹配关系，其进一步促进了δ-Fe形核，从而有效细化了铁素体宏观组织，这将有利于提高铁素体不锈钢力学性能和表面质量。

Effect and mechanism research of Mg Ti treatment on solidification structure of ferritic stainless steel

TiN is an effective heterogeneous nucleating agent for ferritic stainless steel. However, excessively grown TiN particles deteriorate the surface quality of the slab. Therefore, to refine TiN particles and control grain size by adding Mg and Ti elements is proposed. Through the experiment in resistance furnace with protective atmosphere, the refining effect of Mg-Ti addition on the microstructure of ferritic stainless steel and the refinement mechanism of TiN particles were theoretically analyzed. It was found that due to adding Mg and Ti elements, the equiaxed crystal ratio increased from 37% to 50%, and average size of TiN particles reduced from 5μm to 2μm. After Mg Ti treatment, the lattice misfit of MgO and MgAl2O4 with TiN was quite low, 1.14 and 5.29, respectively, which were all in the effective nucleation range. It proved that MgO and MgAl2O4 could become the heterogeneous nucleation core of TiN, which promoted the precipitation of TiN in the crystal. At the same time, based on the good lattice matching between TiN with ferrite phase, it further promoted nucleation of ferrite and effectively refined the macrostructure, which would be beneficial to improve mechanical properties and surface quality of ferritic stainless steel.