This research reports a distributed fiber optic high-temperature sensing system tailored for applications in the steel industry and various other sectors. Recent advancements in optical sensor technology have led to the exploration of sapphire crystal fibers as a solution for sensing in harsh environments. Utilizing a femtosecond (fs) laser, cascaded fiber Bragg gratings (FBGs) were meticulously fabricated within a multimode sapphire optical fiber. These FBGs endowed the system with distributed sensing capabilities and underwent rigorous testing under extreme temperatures, reaching up to 1800 °C. The study delves into the investigation of the FBG reflection spectrum, facilitated by the development of a sophisticated multimode demodulation system, which contributed to the attainment of precise temperature measurements with a performance accuracy of 99.9%. Demonstrating exceptional thermal stability, the sapphire FBGs endured temperatures of 1600 °C for a sustained duration of 22 h. Furthermore, this article explores the application of distributed temperature sensing employing multiple sapphire FBGs, showcasing their utility in temperature measurements related to molten steel studies.

Accurate measurement of interfacial heat transfer during casting solidification is crucial for optimizing metal solidification processes. The gap between the mold wall and casting surface plays a significant role in heat transfer and cooling rates. In this study, two innovative fiber-optic sensors are employed to measure real-time mold gaps and thermal profiles during the solidification of A356 aluminum in a permanent mold casting. The experimental setup consists of a specially designed mold system made of unheated, uncoated tool steel, which facilitates easy installation of the fiber-optic sensors. An Extrinsic Fabry-Perot interferometric (EFPI) sensor is utilized to monitor the evolving gap between the mold wall and casting surface. This method relies on the unique concept of using molten metal as the second reflection interface for gap measurements. The EFPI gap measurements exhibit high accuracy and precision, with a maximum error of only 2 μm when compared to physical measurements. Simultaneously, a stainless steel-encased fiber utilizing the Rayleigh backscattering (RBS) technique is deployed across the mold wall and cavity to achieve real-time temperature measurements with a spatial resolution of 0.65 mm. The study demonstrates that leveraging high-resolution temperature profiles and gap evolution measurements enhances understanding of heat transfer dynamics at the mold-metal interface, particularly valuable for complex-shaped castings and continuously cast metals. Additionally, the ability to measure the cast shape exiting a continuous casting mold during operation presents a novel tool for real-time product quality monitoring and process safety enhancement by detecting conditions that may lead to slab cracking and breakouts.

Extensive research has been conducted on Ti–Fe–Sn ultrafine eutectic composites due to their high yield strength, compared to conventional microcrystalline alloys. The unique microstructure of ultrafine eutectic composites, which consists of the ultrafine-grained lamella matrix with the formation of primary dendrites, leads to high strength and desirable plasticity. A lamellar structure is known for its high strength with limited plasticity, owing to its interface-strengthening effect. Thus, extensive efforts have been conducted to induce the lamellar structure and control the volume fraction of primary dendrites to enhance plasticity by tailoring the compositions. In this study, however, it was found that not only the volume fraction of primary dendrites but also the morphology of dendrites constitute key factors in inducing excellent ductility. We selected three compositions of Ti–Fe–Sn ultrafine eutectic composites, considering the distinct volume fractions and morphologies of $\beta$-Ti dendrites based on the Ti–Fe–Sn ternary phase diagram. As these compositions approach quasi-peritectic reaction points, the $\alpha$${}^{″}$-Ti martensitic phase forms within the primary $\beta$-Ti dendrites due to under-cooling effects. This pre-formation of the $\alpha$${}^{″}$-Ti martensitic phase effectively governs the growth direction of $\beta$-Ti dendrites, resulting in the development of round-shaped primary dendrites during the quenching process. These microstructural evolutions of $\beta$-Ti dendrites, in turn, lead to an improvement in ductility without a significant compromise in strength. Hence, we propose that fine-tuning the composition to control the primary dendrite morphology can be a highly effective alloy design strategy, enabling the attainment of greater macroscopic plasticity without the typical ductility and strength trade-off.