The investigation of precipitation behavior of titanium compounds for high titanium steel based on in situ observation

PLOS ONE RESEARCH ARTICLE The investigation of precipitation behavior of titanium compounds for high titanium steel based on in situ observation Xiaolei Zhu1,2, Ji Yang2, Shuang Wang2, Shenchuan Bu ID1, Minggang Shen ID1*, Xincheng Miao1, Xiang Li1 1 School of Materials and Metallurgy, University of Science and Technology, Anshan, China, 2 Iron & Steel Research Institutes of Ansteel Group Corporation, Anshan, China a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Zhu X, Yang J, Wang S, Bu S, Shen M, Miao X, et al. (2023) The investigation of precipitation behavior of titanium compounds for high titanium steel based on in situ observation. PLoS ONE 18(4): e0275049. https://doi.org/ 10.1371/journal.pone.0275049 Editor: Arun Devaraj, Pacific Northwest National Laboratory, UNITED STATES * Abstract The effects of cooling rate, Ti content, and casting temperature on titanium compounds for high titanium steel were investigated. In-situ observation of high titanium steel during remelting and solidification was carried out by using a High Temperature Confocal Scanning Laser Microscope (HTCSLM), and the observed results were in good agreement with the thermodynamic and kinetic calculations. The observation and calculation results both show that the inclusions in high titanium steel first precipitate in the form of TiN, followed by TiC precipitates as temperature decreases, eventually forming TiCxN1-x type inclusions at room temperature. The initial precipitation temperature of the inclusions increases with the increase of Ti content in molten steel, whereas casting temperature has little effect on the initial precipitation temperature of inclusions. In addition, the size of TiN inclusions increases with the increase of Ti content in steel but decreases with the increase in cooling rate. Received: September 8, 2022 Accepted: March 17, 2023 Published: April 3, 2023 Copyright: © 2023 Zhu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper. Funding: The present work was financially supported by the National Key Research and Development Program of China (2017YFB0305100). the funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. 1. Introduction Compared with Nb and V, Ti is more abundant in resources and cheaper in price, which has attracted more and more attention in recent years [1, 2]. At present, researchers try to replace some expensive Nb with cheap Ti for microalloying, and adopt a high-purity smelting process and controlled rolling and controlled cooling process to achieve grain refinement and precipitation strengthening, to obtain high-strength and toughness steel materials [3]. However, for the smelting process of high titanium steel, Ti is easy to react with the N and C in the steel to precipitate the inclusions of TiN and TiC. However, in the smelting process, Ti is easy to react with the N to precipitate the inclusion of TiN in the steel, which reduces the effective titanium content. In addition, the precipitation of large-size TiN inclusions will be harmful to the material performance, and will also adhere to the inside of the submerged entry nozzle of continuous casting, resulting in the nozzle clogging [4]. The inclusion of TiC in high titanium steel has the characteristics of low density and high hardness, which can be used to improve the wear resistance of materials [5, 6]. In addition, if Ti and N in high titanium steel form stable titanium compound TiN during the solidification PLOS ONE | https://doi.org/10.1371/journal.pone.0275049 April 3, 2023 1 / 17 PLOS ONE Precipitation behavior of titanium compounds for high titanium steel process, it can hinder the migration of austenite grain boundary, further refine austenite grain and improve the strength and toughness of the steel [7, 8]. TiC precipitates in the form of a eutectic reaction in high Ti steel, so the size of the precipitate is large. Eutectic TiC has the characteristics of low density and high hardness, so it can be used to improve the wear resistance of materials [9, 10]. The toughness and plasticity of high titanium wear-resistant steel do not decrease but increase with the increase of strength, which is mainly due to the refinement and homogenization of large-size TiC during rolling deformation [11]. Yang et al. [12] found that the inclusions of TiN were square with sharp edges, which were not easy to deform, but would damage the toughness of steel. A similar conclusion was also proposed by Fu et al. [13]. Many researchers [14–16] had found that the precipitation and growth of TiN inclusions in steel could be controlled by reducing the content of Ti and N. Huo et al. [17] studied the behavior of precipitates in steels with different Ti contents and found that the size of TiN increased with the increase of Ti content. Because TiN and TiC had the same crystal structure of NaCl type, and the lattice constant was almost the same, the two inclusions usually completely dissolved each other to form Ti(NC) [18]. Cheng et al. [19] proposed that TiN would precipitate in the liquid phase, and its size was related to the content of Ti and N in the molten steel. Besides, the cooling rate was also an influencing factor for precipitating TiN. However, the precipitation behavior of titanium compounds is not only related to the cooling rate and element composition but also related to the casting process of continuous casting. At present, there is still a lack of systematic research on the precipitation behavior of TiN or TiC related to the continuous casting process. In this work, the HTCSLM experiment was used to observe the solidification process of the mushy zone for high titanium steel and the precipitation behavior of titanium compounds. The effects of Ti content, cooling rate, and casting temperature on the precipitation behavior of titanium compound high titanium steel were investigated systematically. The thermodynamic and dynamic calculations of titanium compound growth were carried out simultaneously. The influence of different Ti content, different cooling rate, and casting temperatures on the precipitation behavior of titanium inclusion in steel was investigated by using HTCSLM and thermodynamic kinetic theory. Furthermore, the experimental results were in agreement with the calculated results. 2. Experiment design and method 2.1 Material In this experiment, the high titanium steel was melted by a 200 kg vacuum induction furnace. The unit for supplying this material is the Iron & Steel Research Institutes of Ansteel Group Corporation. The intervention of a va (...truncated)