In-line metallurgical process control in the steel industry

Abstract
The steel products manufacturing involves a long line of complex processes : liquid metal elaboration, solidification, hot and cold transformation by rolling surface protection by coating. The Process Control aims at improving global productivity and quality of the resulting products by optimizing each elementary process as well as management of tools or workshops interfaces. Complex processes, involving generally many variables, require for their control more or less sophisticated models. These process models are either analytical when physical and thermodynamical mechanisms are known or statistical or knowledge based, according to circumstances. In any case, it is necessary to have a reliable and precise instrumentation to adjust undetermined parameters during mode1 development and to be able to take into account external parameters variability during current working. This instrumentation concerns both running of machines and testing of manufactured materials under harsh environment conditions of Iron and Steel industry : temperature, dusts, steam, electromagnetic interferences, vibrations, ... . In this context, in-line Non Destructive Testing methods contribute efficienly because they may give directly and in real time products characteristics, integrating both drifts of machines and sensors due to their ageing and the abnormal spread of material entering the process. These methods induce the development of sophisticated inspection equipments whose strategic significance is such that their failure to operate can require production shutdown. The paper gives some representative examples of improvement of the accuracy of an in-line measurement or controlling of elementary processes or processes interfaces : temperature measurement by infrared pyrometry, thickness profile determination by X-ray array sensor, recrystallization control in continuous by X-ray and ultrasonic methods, automatic detection and indentification of surface defects by optics, cracks detection on as-cast hot slabs by eddy currents.