The B4C system is a material for high performance applications like hard coatings, ballistic material and transmission windows for X-rays detectors. The aim of this work is the evaluation of the reaction sintering under pressure in the B4C+ amorphous boron system. Boron carbide have been obtained by pressureless sintering at 21502250ºC after the optimization of the powder processing steps. The microstructure of the sintered specimen has been observed using scanning electron microscopy (SEM) with Energy Dispersive X-Ray Spectrometer (EDS). The phase quantification has been determined by X-ray diffraction (XRD) patterns with Rietveld calculations using TOPAS software.