Key Takeaways & Executive Findings
- •• A two-stage austenite growth model incorporating second-phase pinning and δ–γ transformation accurately predicts grain sizes in Ti microalloyed steel slabs, with average error within 5%. • Increasing Ti content from 0.02wt% to 0.04wt% significantly refines austenite grains, especially at the slab center, achieving a 27.14% average reduction. • High-temperature ferrite growth follows parabolic kinetics, but higher Ti content slows grain boundary migration during initial solidification. • The model provides a robust tool for optimizing continuous casting parameters to enhance slab quality and reduce crack defects.
Abstract
The microstructural characteristics of austenite in Ti microalloyed steel during continuous casting significantly influence the thermoplasticity, thereby affecting the quality of the slab. In this work, a prediction model for two-stage austenite growth under varying cooling rates was established by incorporating the effect of second-phase pinning and high-temperature ferrite–austenite phase transformation and growth theory. The results indicate that with 0.02wt% Ti, the high-temperature ferrite growth exhibits typical parabolic growth characteristics. When the Ti content increases to 0.04wt%, the high-temperature ferrite grain boundary migration rate significantly slows during the initial solidification stage. The predicted austenite grain sizes for 0.02wt% Ti microalloyed steel at the center, quarter, and surface of the slab are 5592, 3529, and 1524 μm, respectively. For 0.04wt% Ti microalloyed steel, the austenite grain sizes are 4074, 2942, and 1179 μm at the same positions. The average error is within 5%. As the Ti content increases from 0.02wt% to 0.04wt%, the austenite grain refinement at the center is most significant, with an average grain size reduction of 27.14%.
1. Introduction
During the continuous casting process of slabs, the evolution of microstructure is a critical factor influencing the quality of continuous casting steel [1–3]. Specifically, the coarsening of austenite grains significantly reduces the thermoplasticity of continuous casting steel [4–5]. This coarse grain size often accompanies the precipitation of primary austenite films [6–7] and carbonitrides [8] at austenite boundaries, potentially leading to crack defects during the bending and straightening processes in continuous casting. Therefore, a thorough investigation into the evolution and refinement control strategies of austenite microstructure in continuous casting processes is of paramount importance.
Currently, using activation energy of grain growth to describe grain growth behavior has become a widely adopted approach [9–12]. However, this model does not directly reflect the growth rate of grains, thereby limiting its accuracy and effectiveness in practical applications. Consequently, Hu and Rath [13] and others have further proposed models concerning grain growth rate. While these models can effectively describe the laws of grain growth, they do not fully consider the influence of precipitation of microalloying second phases during the grain growth process. Therefore, Andersen and Grong [14] combined the thermodynamic driving force of grain growth derived from experimental studies by Patterson and Liu [15]. Additionally, models developed by Eskandari et al. [16] and Nes et al. [17] describe the drag effect of microalloy element precipitation on grain growth, forming a comprehensive mathematical model.
In subsequent model developments, Yoshida et al. [18] and others proposed a two-stage growth model for low-carbon steel austenite. This model delves into the dynamic changes during grain growth, accurately describing the evolution of austenite growth in low-carbon steel. However, the model simplifies initial austenite grains as secondary dendrite arm spacing and does not consider the influence of δ–γ phase transformation on austenite grain size. In this model, the initial austenite grains are simplified as secondary dendrite arm spacing, without considering the influence of δ–γ phase transformation on austenite grain size. These models have been widely applied in describing the isothermal growth behavior of grains, particularly in the solidification and thermal processing of metallic materials [19–20]. However, they still fail to accurately depict the microstructural evolution under the cooling and reheating conditions during continuous casting. Furthermore, studies on second phase pinning typically rely on scanning electron microscopy to observe the size and precipitation amount of the second phase [21–22], neglecting the dynamic process of second phase growth and its impact on grain size.
Loading authentic research manuscript (Pages 1–5)...
Tianci Chen, Cheng Ji, Jianhua Yang, Yunguang Chi, Miaoyong Zhu (2025). Grain growth kinetics model of high-temperature ferrite and austenite in Ti microalloyed steel during continuous casting. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-2991-8
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the main objective of this study?
The study aims to develop a prediction model for two-stage austenite grain growth in Ti microalloyed steel during continuous casting, incorporating second-phase pinning and high-temperature ferrite–austenite transformation, to accurately predict grain sizes and improve slab quality.
How does Ti content affect austenite grain size?
Increasing Ti content from 0.02wt% to 0.04wt% significantly refines austenite grains, especially at the slab center, with an average reduction of 27.14%. Higher Ti content slows high-temperature ferrite grain boundary migration during initial solidification.
What is the accuracy of the proposed model?
The model predictions show an average error within 5% compared to experimental measurements, indicating high accuracy in predicting austenite grain sizes at different slab positions.
Why is austenite grain size important in continuous casting?
Austenite grain coarsening reduces thermoplasticity and can lead to crack defects during bending and straightening. Controlling grain size is crucial for ensuring slab quality and preventing surface cracks.
What are the key innovations of this model compared to previous ones?
The model incorporates the dynamic effects of second-phase pinning and δ–γ phase transformation, which were often neglected. It also accounts for varying cooling rates, providing a more accurate representation of microstructural evolution during continuous casting.
Related Technical Papers & Translations
Direct Repair of the Crystal Structure and Coating Surface of Spent LiFePO4 Materials Enables Superfast Li-Ion Migration
The rapid accumulation of spent LiFePO4 (LFP) cathodes from retired lithium-ion batteries necessitates the development of effective and environmental-friendly recycling strategies. In this context, direct regeneration has emerged as a promising approach for reclaiming LFP cathode materials, offering a streamlined pathway to restore their electrochemical functionality. We report an integrated regeneration protocol that simultaneously repairs the degraded crystal structure and reconstructs the damaged carbon coating in spent LFP. The regenerated cathode material had superfast lithium-ion diffusion kinetics and a stable cathode–electrolyte interface, giving a remarkable rate capability with specific capacities of 122 mAh g−1 at 5C and 106 mAh g−1 at 10C (1C = 170 mA g−1). It also maintained capacities of 110.7 mAh g−1 (5C) and 84.1 mAh g−1 (10C) after 400 cycles. It could be used in harsh environments and could be stably cycled at subzero temperatures (−10 and −20 °C) and in solid-state electrolyte batteries. Life cycle assessment combined with economic evaluation using the EverBatt model reveals that this direct regeneration approach has high economic and environmental benefits.
Oxide Semiconductor for Advanced Memory Architectures: Atomic Layer Deposition, Key Requirement and Challenges
Oxide semiconductors (OSs), introduced by the Hosono group in the early 2000s, have evolved from display backplane materials to promising candidates for advanced memory and logic devices. The exceptionally low leakage current of OSs and compatibility with three-dimensional (3D) architectures have recently sparked renewed interest in their use in semiconductor applications. This review begins by exploring the unique material properties of OSs, which fundamentally originate from their distinct electronic band structure. Subsequently, we focus on atomic layer deposition (ALD), a core technique for growing excellent OS films, covering both basic and advanced processes compatible with 3D scaling. The basic surface reaction mechanisms—adsorption and reaction—and their roles in film growth are introduced. Furthermore, material design strategies, such as cation selection, crystallinity control, anion doping, and heterostructure engineering, are discussed. We also highlight challenges in memory applications, including contact resistance, hydrogen instability, and lack of p-type materials, and discuss the feasibility of ALD-grown OSs as potential solutions. Lastly, we provide an outlook on the role of ALD-grown OSs in memory technologies. This review bridges material fundamentals and device-level requirements, offering a comprehensive perspective on the potential of ALD-driven OSs for next-generation semiconductor memory devices.
Laser powder bed fusion of biodegradable Zn-4Cu alloy: Processing, microstructure and properties
Zn's natural degradability and biocompatibility make it a promising candidate for implants, however, its mechanical properties remain insufficient for bone applications. In this study, the performance of Zn was enhanced by developing Zn-Cu alloys via laser powder bed fusion (LPBF). Optimal LPBF parameters for forming stable tracks were achieved by adjusting laser power and scanning speed. Under optimized conditions of 100 W and 100 mm/s, high-density (99.58%) Zn-Cu alloys with improved hardness (68.2HV) and yield strength (160 MPa) were achieved. These improvements are attributed to solid solution strengthening, segregation strengthening, and grain refinement. The Zn-Cu alloys also demonstrated favorable degradation behavior, with a rate of 0.16 mm/year. This degradation is primarily driven by micro-galvanic corrosion between the CuZn5 phase and Zn matrix, along with refined grains and increased grain boundary density. This work demonstrates a viable strategy for fabricating Zn-based implants with enhanced structural integrity and mechanical performance via LPBF.