Boronizing and investigation of characteristic properties of AISI 7131

In this study, the 16MnCr5 steels have been subjected to the pack-boriding process. The samples were borided in an electrical resistance furnace at temperatures of 850, 900 and 950°C, during 2, 4 and 6 h. with Ekabor-II under atmospheric pressure. The studies on the boride layers were carried out by optical microscope, scanning electron microscope (SEM) and X-ray diffraction. The thickness of the boride layers was measured 24 to 159 µm as a function of boriding parameters. The hardness of boride layer was about 1940 HV0.1 after boriding for 6 h at 950°C, while the hardness of the matrix was only around 401 HV0.1. Tensile tests showed that both the yield strengths and the ultimate tensile strengths increase; however, the tensile ductility decreases with the increase of boron content. It was also observed that the rate of the boride layer formation was strongly dependent on boriding time, and had a parabolic character. Here, the activation energy and pre-exponential constant are estimated from the experimental results, and are 243.6 kJ/mol and 3.75x10-2 m2 /s, respectively. Key Words: Mechanical properties, Boriding, Boride kinetics, 16MnCr5 steel