Effect of Cu on the boron segregation at grain boundaries and vacancy-type defects in ultra-low carbon micro-alloy steels

By thermal neutron irradiation particle tracking autoradiography (PTA) technique, the development of boron segregation at grain boundaries in ultra-low carbon micro-alloy steels was investigated during cooling from 1150°C to 850°C, and the effect of Cu on boron segregation at grain boundaries was discussed. By positron annihilation lifetime(PAL) technique, the changes of vacancy-type defects with temperatures and the effect of Cu on vacancy-type defects in the cooling process were discussed. Results show that, the concentration of boron at grain boundaries increases rapidly at the beginning of the cooling; after that, it begins to decrease; and then, it increases gradually again. The addition of Cu not only increases the concentration of boron at grain boundaries but also speeds up the development process of boron segregation at grain boundaries. During the continuous cooling process, the addition of Cu significantly affects the change of vacancy-type defects with temperatures in ultra-low carbon micro-alloy steels.