An approach to microstructure quantification in terms of impact properties of HSLA pipeline steels

Several thermo-mechanical controlled processing (TMCP) schedules of a modern pipeline steel were executed using a laboratory mill to investigate both the TMCP parameters influence on the ductile properties and the microstructure and texture evolution during TMCP. Impact fracture toughness was evaluated by means of instrumented Charpy impact test and results were correlated with the metallurgical characterization of the steel via electron backscattered diffraction (EBSD) technique. It is shown that the ductile crack growth observed in the impact test experiments can be reasonably correlated with the Morphology Clustering (MC) and the Cleavage Morphology Clustering (CMC) parameters, which incorporate size, shape, and crystallographic texture features of microstructure elements. The mechanism of unfavorable texture formation during TMCP is explained by texture changes occurring between the end of finish rolling and the start of accelerated cooling.