Evaluation of borides formed on AISI P20 steel

This study reports on an evaluation of borides formed on AISI P20 steel substrate. Boronizing was performed at 800, 875 and 950 °C for 2, 4, 6 and 8 h by using Ekabor 2 powders. The hardness of borides measured by means of Vickers indenter was about 1500 HVN. The depth of boride layers depending on temperature and process time was ranged from 10 to 180 μm. The presence of borides (e.g., FeB, Fe2B, MnB, CrB) was confirmed by X-ray diffraction (XRD) analysis technique. SEM cross-sectional examinations revealed that borides formed on AISI P20 has columnar morphology. Depending on the process time, fracture toughness of borides formed on the surface of AISI P20 mold steel ranged from 2.79 to 4.79 MPa m1/2. Kinetic studies show a parabolic relationship between layer thickness and process time, and the activation energy is calculated as 200 kJ/mol. Moreover, an attempt was made to investigate the possibility of predicting the iso-thickness of boride layer variation and to establish an empirical relationship between process parameters of boriding and boride layer.