� TECHNOLOGY � the grain size of steel in realtime. Grain size is a crucial factor in determining the properties of high-strength steel and other types of steel. Traditionally, measuring grain size during the hot rolling process has been challenging due to the extreme conditions, with temperatures ranging from 800-1200 ° C and material moving at speeds of up to 10 m / s. The LUS-based grain size gauge is the only technique which overcomes these challenges, while providing accurate and reliable measurements.
How It Works: Simplified Explanation
The LUS-based grain size gauge operates by analyzing the frequency-dependent attenuation of ultrasonic waves as they pass through the steel. Here is a breakdown of the process:
1. Generation of Ultrasound: A laser pulse hits the surface of the steel, creating an ultrasonic shockwave.
2. Detection of Response: Another laser detects the response of the ultrasonic waves that travels inside the steel.
3. Frequency Analysis: The system analyzes the frequency-dependent attenuation of these waves. Higher frequencies are attenuated more than lower frequencies, and this
attenuation is related to the grain size of the steel.
4. Grain Size Calculation: Using a calibration curve, the system translates the measured attenuation into an average grain size value. This method allows for realtime monitoring of the steel’ s microstructure, providing valuable data that can be used to optimize the production process.
Impact on the Green Steel Transition
The introduction of the LUSbased grain size gauge is particularly significant in the context of the green steel transition. As the industry moves towards more sustainable
Figure 2( left) Image of the hot strip mill in Borlänge where the laser ultrasonic grain size gauge is installed, together with a graph of the measured grain size along the length of one of the strip.( right) photo of the device during a measurement looking up from underneath at the 900 ° C material passing overhead at around 6 m / s.
Green Steel World | Issue 17 | April 2025 13