Effect of Hot Rolling and Thermal Treatment on the Microstructure Evolution of Microalloyed Bainitic Steels for Pipeline

Abstract

Heavy plate for pipelines, which are used in earthquake-prone areas, must have among other a good ductility. The ductility is needed to prevent cracking in the case of local plastic deformation. The bainitic steels with retained austenite or martensite meet these requirements. The aim of this investigation is the determination of the thermo-mechanical treatment parameters with which such microstructures can be generated during the heavy plate production or an additional heat treatment. Experimental modelling of the production process for heavy plate was realized on a Gleeble HDS-V40 thermo-mechanical simulator. Moreover, the microstructure evolution processes during cooling on the round out table were investigated by dilatometry. The investigations on the formation of the microstructure during following accelerated cooling and heat treatment combination were carried out. All investigations were realized with two high-strength micro-alloyed steels, one of which was additionally alloyed with molybdenum. Results revealed that the decreasing of the temperature and duration of the heat treatment as well as addition of molybdenum reduce the size of grains and promotes the nucleation of the bainitic microstructure.