Effect of surface-modified MgO nanoparticles on intragranular ferrite nucleated on inclusions in low-alloy steel. (15th November 2019)

• Record Type: Journal Article
• Authors: Guo, Hao; Yang, Shufeng; Zhang, Yanling; Li, Jingshe; Wang, Tiantian
• Is Part Of: Materials & design. Volume 182(2019)
• Publication Date: 2019-11-15
• Subjects: Surface treatment -- MgO nanoparticles -- Nanoparticle utilization ratio -- Inclusion characteristics -- Intragranular ferrite nucleation -- Critical inclusion diameter; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2019.108004
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: Despite extensive research into steel refining with nanoparticle addition, some aspects remain unclear, such as the low utilization ratio of the nanoparticles. In this study, application of surface-modified nanoparticles in the steel refining process was investigated. The effects of their addition amount on inclusion modifications and microstructure refinements were investigated and the mechanism of intragranular ferrite formation was clarified. Initial experiments were performed to determine the appropriate steelmaking holding time, and the utilization ratio of MgO@C nanoparticle was 65% from the calculated total oxygen content. After nanoparticle addition, the inclusions were mainly composed of MgAl2 O4 spinel or MgAl2 O4 –TiN-based composite inclusions. The inclusion size sharply decreased with nanoparticle addition. The number of sub-micrometer inclusions accounted for 77.2% of all inclusions in S2 steel sample, which contributed to inhibit the migration of prior austenite grain boundaries, and effectively induced acicular ferrite nucleation. Based on the theory that inclusions act as heterogeneous nuclei to induce ferrite nucleation, the results from thermodynamic calculations showed that the critical nucleation diameter for the TiN inclusions is 0.346 μm, which is consistent with experimental data of the minimum inclusion size for ferrite nucleation in actual steel samples. Graphical abstract: Unlabelled Image Highlights: Novel core–shell MgO@C nanoparticles were prepared for steelmaking and structurally characterized. The pre-experiment determined the appropriate holding time, and the MgO@C nanoparticle utilization ratio reached 65%. Modified nanoparticles had greater effect on inclusion modification and microstructure refinement than original ones. Theoretical calculations for the inclusion critical radius to induce ferrite were consistent with experimental results.