PRECIPITATES ANALYSIS BY SCANNING ELECTRON AND TRANSMISSION MICROSCOPY IN A BORON STEEL

Abstract

We studied the carbides precipitation of low carbon steel with boron austenitized at 870°C, 1,050°C and 1,200°C, oil-hardened by scanning electron microscopy (SEM) and transmission (TEM). We evaluated the nucleation sites and size of the precipitates, in addition to the microstructure obtained. The precipitates by TEM analysis was performed using the replica and carbon thin films. It was observed the presence of cementite, Fe3 C, and borocarbides, M23(C,B)6 at all test conditions. The cementite showed approximately equal sizes in all austenitizing temperatures, which was attributed to solubilization and reprecipitation during cooling tempering. It was observed the presence of borocarbides in all austenitizing temperatures, and at a temperature of 870°C the precipitation was coarser. This size distribution was not attributed to solubilization and coarsening of borocarbides to 870°C and the solubilization and reprecipitation during cooling tempering the other two temperatures. There was also a lesser precipitation in the grain boundary borocarbides to 1,050°C compared to 1,200°C.

Keywords

• Low carbon steel with boron; Precipitation; Quench.