On-line structure monitoring by laser ultrasonics for process control in rolling and heat treatment; CUSTOM
In thin sheet copper a more sophisticated approach was taken. Previous work aimed at assessing the structures in copper samples was carried out on relatively coarse grained materials. In the present work, fine grained copper sheets having grain structures more appropriate to commercial products have been investigated. Conventional analyses of attenuation would not be sensitive to grain sizes in this range using the 6 MHz interferometer so a new approach was attempted. The initial results look very promising. Overall, robust relationships between ultrasonic propagation parameters and microstructure have been shown for recrystallisation in thin strip steel, grain size in thick section steel and copper and, phase transformation in thick section steel. Within nickel, differences can be detected between treated and untreated alloy although the relationships at treatment temperature are less robust. Under mill conditions a working laser ultrasonic system for non-contact inspection has been produced and has operated successfully. Within annealing applications the system has proven to be reasonably robust and sensitive capable of operating for extended periods of time. The technology has also been shown capable of operation under the more severe conditions imposed by hot rolling applications although more sophisticated installation engineering will be required for routine on-line use in these situations.