Microstructure and properties evolution during annealing in low-carbon Nb containing steel with high strength and electrical conductivity: an experimental and theoretical study

Based on the experiment and first-principles calculation methods, the evolution of microstructure, mechanical properties and electrical conductivity of low-carbon steel were investigated at various annealing conditions. The results show that with the increase of annealing temperature, the morphology of ferrite matrix grain undergoes a transformation from narrow and long fibrous to, accompanied by the continuous growth in size. The strength of alpha-fibre texture is reduced continuously while the strength of gamma-fibre texture increases evidently. The tensile and conductivity testing results indicate that with the increase of annealing temperature, both the yield strength and tensile strength of the steel decrease, while the elongation exhibits an opposite tendency due to the continuous growth of ferrite grains and dissolution of tertiary cementites. Additionally, the electrical conductivity increases because the reduction in the number of grain boundaries weakens their scattering ability to electronic waves. The first-principles calculation results indicate that with increasing distance to the interface, the segregation energy of Nb atom in ferrite matrix is reduced, as well as the interfacial energy of the structure is also decreased. The interface segregation preference of Nb atoms induces the transfer of charge, which is beneficial to enhance the conductivity of the ferrite matrix.

Automated summary

This study investigates the evolution of microstructure, mechanical properties, and electrical conductivity of low-carbon steel under different annealing conditions using experimental and first-principles calculation methods. The results show that annealing temperature affects the morphology of ferrite grains, resulting in changes in strength, elongation, and conductivity. First-principles calculations provide insights into the underlying mechanisms of these changes.