SEM and HREM characterization of precipitation in a boron microalloyed steel

Abstract

Boron-rich precipitation in a boron microalloyed steel was studied employing high-resolution electron microscopy (HREM) A 200 ton melt of boron microalloyed steel was fabricated employing a high-quality electric arc furnace where strict control of deleterious elements such as N, S, P, O and H was possible. The melt was continuously cast, forming a basaltic type of ferrite pearlite microstructure. Boron-rich particles were formed along grain boundaries and also in ferrite or pearlite grains. HREM, standard TEM and SEM techniques were employed to determine the nature and morphological characteristics of these precipitates. The boron-rich particles in the grain boundaries were found to be the largest (100 nm or more), and are likely boron carbides of the type B 13C 2 or B 4C. Fine precipitation of boron particles in ferrite or pearlite grains of Fe 23(C,B) 6 was also characterized with the HREM technique. Cuboidal particles of TiN, and other features of the microstructure are also reported.