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Using laser ultrasonic (LUS) measurements, the microstructure of metal can be determined directly in situ. The measurement is non-contact and nondestructive, meaning it can be used for hot and moving samples, meaning microstructure can be determined in many parts of the steelmaking process where other techniques are not viable. The feasibility of inline LUS grain size measurements [1] as well as the utility of the captured data [2] have been demonstrated by an installed LUS instrument at the SSAB Borlänge hot strip mill.
In the ILUMHEAT project, funded by Vinnova as part of the “Swedish Metals & Minerals” program, we aim to bring a new LUS grain size gauge and microstructure probe to four Swedish steel mills. For each site, there are unique questions about the grain size and microstructure evolution, as well as unique challenges regarding the installation and use of the LUS probe. A modular design with a working distance of 1 meter has been developed as part of this project, and the preliminary results of the first on-site measurement will hopefully be presented.
[1] Malmström M, Jansson A, Hutchinson B, Lönnqvist J, Gillgren L, Bäcke L, et al. Laser-Ultrasound-Based Grain Size Gauge for the Hot Strip Mill. Applied Sciences 2022;12:10048. https://doi.org/10.3390/app121910048.
[2] Hoppe D, Haschke T, Sprock A, Hassel C, Hafer J, Bäcke L, Thorberg J-E, Jonsson C, Malmström M, Kneisel F, Bärwald M, New insights into the online LUS grain size measurements, in: Associazione Italiana di Metallurgia, Verona, 2025: pp. 227–234.