双稳定化铁素体不锈钢凝固过程形成含氧化物复合核心获得细小等轴晶组织机理研究

Great attentions have been paid on the investigation of dual stabilized ferritic stainless steel due to its several advantageous properties. And its cold formability and surface quality are well concerned by customers. Ridging as one of defect forms is commonly found in cold deformation process, which is closely related to as-cast solidification structure of ferritic stainless steel.This proposer puts forward a new method to promote the formation of fine and dense equiaxed grains by producing a large amount of fine and effective nuclei during solidification of this dual stabilized ferritic stainless steel.The basic principle for this new method is firstly to form a great amount of TiOx particles in the early stage of solidification. And on these particles, complex nuclei in the form of (Ti, Nb)x(C,N)y precipitate, which can promote nucleation,prevent grain growth and are beneficial for the formation of fine equiaxed grains as well as the depression of alloy elements segregation. This idea has already been proved reasonable in laboratory experiments. The aim of this project is to identify the characteristics and composition of the complex nuclei mentioned above, and clarify the formation mechanism of such catalysts. As a result, the optimized composition as well as the cooling condition of this ferric stainless steel will be proposed. Moreover, a high proportion (more than 80%) of fine equiaxed grains structure in the continuous casting slab will be achieved in practical production. Few investigations were reported in literature so far. Therefore, this research is of importance to the improvement of cold formability and ridging formation for dual stabilized ferritic stainless steel. ???.

含钛、铌双稳定铁素体不锈钢近年来受到广泛重视。其冷成形性和表面质量是用户极为关注的性能指标。冷成形过程中常见的皱折缺陷与凝固组织密切相关。本项目申请人提出通过采用在凝固过程生成大量核心获得细小致密等轴晶组织的方法来有效改善双稳定铁素体不锈钢皱折缺陷的科学思想。其基本原理为：控制钢液中的碳、氮、氧、钛和铌含量，使其在凝固初期形成大量特定的钛氧化物，并以此为基底，在该氧化钛外围形成(Ti,Nb)x(C,N)y复合核心，起到形核和对晶粒的钉扎作用，达到细化凝固组织和降低成分偏析的效果。实验室探索证明这种方法可行。通过本项目研究，阐明有效复合核心形成机理；确定核心的特征和成分；提出优化的钢液成分和相应的冷却条件。并在工业性生产中能较为稳定地获得80%以上细小致密等轴晶比例的连铸坯。该课题的研究对这类钢冷加工性、抗皱折性能的改善具有重要的理论和实际意义。这方面的研究目前尚无见到报道。

本项目通过采用在凝固过程生成大量细小的核心获得致密等轴晶组织的方法来有效改善双稳定铁素体不锈钢皱折缺陷。其基本原理为：控制钢液中的碳、氮、氧、钛和铌含量，使其在凝固初期形成大量特定钛氧化物，并以此为基底，在该氧化钛外围形成(Ti,Nb)x(C,N)y复合核心，起到形核和对晶粒的钉扎作用，达到细化凝固组织和降低成分偏析的效果。本项目执行过程按照计划稳步进行，进展顺利，取得了一系列研究结果，为提高铁素体不锈钢等轴晶率提供了理论依据，在实践过程中获得初步应用，主要研究结果包括：①复合核心形成所需的热力学及动力学条件，②钢液成分以及冶金工艺对核心类型及分布的影响规律，③核心的数量及分布对凝固组织的影响规律，④本研究在实验室以及工业生产条件下生产的铸件组织特点及核心分布，⑤提出适应于本研究的凝固组织预测模型并有效预测凝固组织。在国内外学术期刊上发表学术论文14篇，在国内外学术会议上发表学术论文8篇，培养研究生6人，在工业生产中获得了80%以上等轴晶比例的铁素体不锈钢连铸坯，相关技术成果形成2篇发明专利。完成了项目的研究内容，达到了项目的预期目标。