SEM AND HREM CHARACTERIZATION OF PRECIPITATION IN A BORON MICROALLOYED STEEL

Boron-rich precipitation in a boron microalloyed steel was studied emp loying high-resolution electron microscopy (HREM). A 200 ton melt of b oron microalloyed steel was fabricated employing a high-quality electr ic 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 particle s were formed along grain boundaries and also in ferrite or pearlite g rains. HREM, standard TEM and SEM techniques were employed to determin e 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 B1 3C2 or B4C. Fine precipitation of boron particles in ferrite or pearli te grains of Fe23(C,B)6 was also characterized with the HREM technique . Cuboidal particles of TiN, and other features of the microstructure are also reported.