基于B竞争偏聚抑制钢中残余元素Sn的晶界偏聚机制

It’s difficult to remove the residual elements in steel. And even a little amount of them can significantly deteriorate properties of steel. Thus, it has become a common problem to hinder reuse of the steel scrap resource efficiently. Sn, one of the main residual elements, it can worsen hot ductility of steel greatly when segregation at grain boundary. To eliminate this harm, a new idea of suppressing Sn grain boundary segregation by the competition grain boundary segregation between B and Sn is put forward, which aims to change the behavior of grain boundary segregation of Sn in steel without changing its contents. And then the control mechanism of grain boundary segregation of Sn in steel will be studied. During thermoplastic deformation process, grain boundary characteristics (GBCs), the evolution rules and the interaction between GBCs and Sn grain boundary segregation will be illuminated. The relationships between GBCs and Sn grain boundary segregation will also be established. The rules and impact mechanisms of grain boundary segregation of B will be revealed during thermoplastic deformation process. The relevance among B content, GBCs, thermal deformation parameters and Sn grain boundary segregation will be studied. Moreover, the response rules and mechanisms among them will also be clarified. These research results will provide basic data and theoretical support for eliminating the harm of residual element Sn, guiding the production of steel containing Sn and making the steel scrap resources utilize economically, efficiently and environmental-friendly.

钢中残余元素难以去除且微量时即能显著恶化钢的性能，已成为限制废钢资源高效、循环利用的共性问题。Sn作为钢中主要残余元素之一，其在晶界偏聚能够显著恶化钢的热塑性。为消除其危害，本项目旨在研究在不改变残余元素Sn含量的前提下，提出利用B竞争晶界偏聚，改变Sn在钢中晶界偏聚行为这一新思路，达到抑制Sn晶界偏聚，消除其危害的目的，开展钢中残余元素Sn晶界偏聚调控机制研究。阐明热塑性变形过程中，晶界特征及其演变规律以及对Sn晶界偏聚的交互作用，建立其与Sn晶界偏聚间的相关性；揭示热塑性变形过程中，B晶界偏聚规律及其优先晶界偏聚的影响机制；研究B含量、晶界特征以及热变形参量与Sn晶界偏聚的相关性，明晰Sn的晶界偏聚行为与晶界特征、B含量以及热变形参量之间的响应规律及机制，为消除残余元素Sn的危害，指导含Sn钢生产，实现废钢资源经济、高效、环保利用提供基础数据和理论支撑。

本项目针对残余元素Sn在连铸等热塑性变形过程中易向晶界偏聚，降低晶间聚合力，恶化铸坯的热塑性这一共性问题，项目组研究了热塑性变形过程中，钢中残余元素Sn的晶界偏聚行为调控机制，研究表明，随着B含量的增加，实验用钢退火后的晶粒尺寸先增加后降低，布氏硬度则先减小后增大。B含量在34ppm时，退火后实验用钢的晶粒尺寸最大，平均尺寸高达216μm，硬度也最低，为59.8HB。当B含量超过60ppm时，退火后实验用钢的晶粒尺寸逐渐降低，硬度则逐渐提高。此外，随着钢中硼含量的增加，实验钢的相变起始温度逐渐减小；硼含量在34-91ppm时，相变温度下降了3-5.8℃。随着变形温度的降低、应变速率的增大以及应变量的增大，实验用钢中低ΣCSL晶界含量降低，Sn、B的晶界偏聚量逐渐增加。另外，热塑性变形过程中，硼发生了显著的晶界偏聚，能够优先占据晶界偏聚位置，抑制钢中Sn的晶界偏聚。随着硼含量的增加，钢中低ΣCSL晶界含量逐渐增加。热塑性变形过程中，Sn5B0钢中Sn的晶界偏聚最严重，晶界处Sn的原子百分比为0.63%，硼的添加能够抑制钢中的Sn的晶界偏聚，随着硼含量的增大，Sn的晶界偏聚量逐渐减少，在本试验条件下，当硼的添加量为91ppm时，晶界Sn的原子百分比下降至0.2%，晶界Sn含量减少了68.3%。另外，随着硼含量的增加，热塑性变形过程中晶界B的偏聚量也逐渐增加。不含硼的实验用钢中{111}<110>、{110}<110>织构组分最强，而{001}<110>织构组分最弱。随着硼含量的增加，{111}<110>、{110}<110>织构组分强度下降，而{001}<110>织构强度上升。通过上述研究工作，本项目揭示了热塑性变形过程中，钢中残余元素Sn的晶界偏聚行为调控机制。为消除钢中Sn的危害，实现废钢资源经济、高效、环保利用以及指导含Sn钢生产提供理论依据。发表学术论文5篇，培养研究生2名，申请发明专利2项。此外，由于新冠疫情的影响，部分实验数据出的较晚，目前还有1篇学术论文处于已录用待发表阶段，2篇学术论文处于审稿阶段。