Combined online microstructure sensor and model for a better control of hot strip rolling conditions and final products properties (MICROCONTROL) : final report

This project provides new knowledge in the field of non-destructive and non-contact laser ultrasonic technique to monitor steel microstructure during hot rolling. Various signal processing techniques based on ultrasonic waves velocity, attenuation, backscattered noise or Poisson's ratio are tested for evaluation of average grain size, grain shape, phase transformation and recrystallization: all methods could be used online except backscattered (grain shape) and velocity methods. Moreover, an all-fibered Laser UltraSonic (LUS) sensor is designed, manufactured and tested in laboratory, pilot and industrial hot rolling conditions with the capacity to measure the microstructure in multi-points along a hot rolling mill (though in this project the sensor was used in single point). Furthermore, the HSMM-Integ metallurgical model for prediction of microstructure evolution all along a hot strip mill and final mechanical properties is calibrated for AM Eisenhuttenstadt finishing hot strip mill on 2 different grades: final mechanical properties predictions match reasonably with measurements. Finally, rolling trials are performed with the laser ultrasonic sensor on AM Eisenhuttenstadt hot mill to measure for 22 coils austenite grain size in inter-stands and at last stand exit. The grain size values obtained by LUS analysis match reasonably with grain sizes predicted by model though some discrepancies exist between final microstructures predicted and measured by metallography, further work is needed to develop new models fine tuning procedures using these newly available austenite grain size measurements. As a conclusion, this work is a significant step to move a step closer to a fully automatic feed-back control of microstructure and product properties.