The effect of boron powder on surface AISI W2 steel and growth kinetic of the boride layer is studied. Boron powder mixture was used in the powder pack boriding; this process was carried out in the temperature range from 1173 to 1273 K with exposure times ranging from 2 to 8 h. The presence of boride was confirmed by optical microscopy, X-ray diffraction, and the distribution of alloy elements in boride layers with energy-dispersive spectrometry using scanning electron microscopy. A mathematical model of the growth kinetics of the single layer was proposed and boron diffusion coefficient was determined by mass balance equation. The morphology of Fe2B layer was smooth and boron activation energy in W2 steel was estimated as 187.696 kJ·mol−1. The kinetic model was validated with two experimental conditions, a contour diagram describing the evolution of Fe2B layer as a function of time and temperature parameters for industrial application.
The present work studied the characterization of boriding coatings without and with exposed hydrogen permeation on AISI 8620 through microstructure and mechanical behavior. A dehydrated paste pack process was carried out for the formation of boride coatings on AISI 8620 at 1173, 1223, and 1273 K for 6 h of exposure time for each temperature. After boronizing, hydrogen was introduced into the borided steels by in situ cathodic charging using an H2SO4 acid electrolyte. Specimens borided without and with hydrogen were characterized by scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction. The experimental techniques of the Vickers microhardness and three-point bending were used. As a result, the hydrogen diffusion on steel AISI 8620 borided shows a significant increase in microhardness. Furthermore, three-point bend tests showed an increased strength on 8620 steel borided. However, the ductility and strength value on 8620 steel borided surfaces presented a drastic reduction due to hydrogen permeation. The results revealed that the borided coatings provided strength and reduced the hydrogen embrittlement index on AISI 8620 borided.
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