Laser-Ultrasound-Based Grain Size Gauge for the Hot Strip Mill

Abstract

The paper summarizes the creation of a robust online grain size gauge for a hot strip mill. A method and algorithm for calculating the grain size from the measured ultrasonic attenuation is presented. This new method is self-calibrating, does not rely on a geometrical reference sample and can cope with the effects of diffraction on the attenuation. The model is based on 52 quenched samples measured with more than 23,000 laser ultrasonics shots and has a correlation coefficient R2 of 0.8. Typical online laser ultrasonic measurements from the hot strip mill and the calculated grain size versus length are presented for a couple of steel strips.

Estimation of Grain Size and Composition in Steel Using Laser UltraSonics Simulations at Different Temperatures

“…The scattering is considered to be in the Rayleigh regime (𝛾 = 4) and in the transition regime (𝛾 = 3), as can be seen from the area of interest in Figure 9. Since several experimental systems use a constant exponent 𝛾 = 3 [5,20,21,54], this same exponent has been chosen here as a compromise. This constant exponent 𝛾 = 3 has been used for the whole range of grain sizes.…”

“…is defined, based on [20,21]. Note that the signs of 𝑏 and 𝑏′ are the same, enabling a distinction between a positive and negative 𝑏.…”

“…Details on the physical background and practical applications of LUS techniques are described in several books and articles, e.g., [12][13][14][15][16]. Various LUS systems have been developed and used in offline systems [5,10,[17][18][19] or as inline systems in steel mills [20].…”

Compensated laser vibrometry using wavefront-reversal via a MEMS SLM integrated with a metasurface retro-array: a proposal

“…The present work concentrates on an area of continuing research in the field of compensated vibrometry, where shot-noise limited performance is sought under real-world manufacturing conditions, including in situ inspection diagnostics and process control of such recent in-factory applications as hot strip mill thermal processing 6 , and additive manufacturing processing 7 such as laser powder bed fusion scanning. A variety of techniques have been considered for the detection of laser surface vibrations, especially in the case of roughened (i.e., diffuse or non-specular) real-world workpieces, including metals and composites 4,5 .…”

“…Years ago, a second true-wavefront reversal device was also demonstrated 25,26 if a corner cube is physically attached to each piston element of a deformable mirror, all on a pixel-by-pixel basis, configured as an array 6 . Using such a 2x2 array in a closed-loop configuration, it was shown that compensation for wavefront distortions that involved both phase and tilt errors can be corrected.…”