Kinetics of plasma paste boronized AISI 8620 steel in borax paste mixtures

Abstract

In the present study, AISI 8620 steel was plasma paste boronized by using various borax paste mix tures. The plasma paste boronizing process was carried out in a dc plasma system at a temperature of 973, 1023 and 1073 K for 2, 5 and 7 h respectively in a gas mixture of 70% H2–30% Ar under a constant pressure of 10 mbar. The properties of the boride layer were evaluated by optical microscopy, Xray diffraction, the microVickers hardness tester and the growth kinetics of the boride layers. The thickness of the boride layersvaried from 14 to 91 μm depending on the boronizing time and temperature. Xray diffraction analysis of boride layers on the surface of the steel revealed the formation of FeB and Fe2B phases. Depending on the temperature and layer thickness, the activation energies of boron in steel were found to be 99.773 kJ/mol for 100% borax paste.