Abstract: In this work, the effects of four kinds of La content on the microstructure and TiN precipitation behavior of high-titanium steel are studied by high temperature melting experiment, optical microscope (OM) and scanning electron microscope (SEM). It is intended to give scientific basis and experimental data for La treatment to refine the size of TiN and the microstructure in the center region of cast ingots of high-titanium steel. The results show that the solidification structures of all experimental steels are equiaxed grains when the solidification cooling rate is 0.17℃/s. La shows obvious ability of deoxidization, S and Al at low La content (0.0013wt%), so LaAlO3 and La2O2S are mainly formed in its steel. La just began to show obvious ability of deoxidization, S and Al at high La content (0.0052wt%, 0.0223wt%). With the consumption of a large amount of O atoms, the deoxidization and sulfur ability of La increased rapidly. Therefore, La2O2S is the predominant precipitate that forms in the steel, and some La2O2S particles will nucleate and grow on the surface of LaAlO3 particles that have previously precipitated. TiN mainly precipitates in the Liquid+δ two-phase region in this experimental steel. LaAlO3 and La2O2S precipitate before TiN, and their small lattice misfit with TiN are the primary cause of their propensity to act as the cores of TiN heterogeneous nucleation. When the La content in the steel is 0wt%, 0.0013wt%, 0.0052wt%, 0.0223wt%, the average axial grain size of each experimental steel is 354, 223, 154, 126 μm, respectively. The maximum size of TiN is 19.1, 11.7, 11.4, 10.4 μm, the TiN area density in each experimental steel is 42.2, 82.9, 86.3, 90.7 No./mm2, the maximum size of TiN is 19.1, 11.7, 11.4, 10.4 μm, and the average size of TiN is 7.8, 4.6, 4.5, 4.4 μm.

Key words: High-titanium steel, La treatment, TiN, E2EM model, Equiaxed grains

摘要： 本工作采用高温熔炼实验以及光学显微镜(OM)、扫描电镜(SEM)等方法，研究了四种La含量对高钛钢缓冷凝固组织及其钢中TiN析出行为的影响。结果表明，凝固冷速为0.17℃/s时，各实验钢凝固组织均为等轴晶。在低La含量(0.0013wt%)下，La体现出明显脱O, S, Al能力，因此其钢中主要生成LaAlO3, La2O2S；在高La含量(0.0052wt%, 0.0223wt%)下，La刚开始体现出明显脱O, S, Al能力，随着O原子的大量消耗，La的脱O, S能力快速增强。因此，其钢中主要生成La2O2S且部分La2O2S会依附于先析出的LaAlO3表面形核、长大。本实验钢中TiN主要析出于Liquid+δ两相区，LaAlO3, La2O2S优先于TiN析出且与TiN的错配度小是其易成为TiN异质形核核心的主要原因。当钢中La含量为0wt%, 0.0013wt%, 0.0052wt%, 0.0223wt%时，各实验钢中等轴晶粒平均尺寸分别为354, 223, 154, 126 μm，TiN面密度为42.2, 82.9, 86.3, 90.7个/mm2，TiN平均尺寸为7.8, 4.6, 4.5, 4.4 μm。

关键词: 高钛钢, La处理, TiN, E2EM模型, 等轴晶