KINETIC STUDY AND MECHANICAL QUALITATIVE CONTROL OF AISI 4140 BORONIZED STEEL FOCUSED ON THE ROLE OF THE AUSTENITIC TRANSFORMATION OF THE SUBSTRATE DURING THE PROCESS
Published: 18 Sep 2019
Abstract: In this study a series of boronizing experiments was performed on AISI 4140 steel’s surface in temperature and time ranges 1073 – 1273 K and 4 – 12 hours, respectively. The well known pack boronizing method was applied and a thick dense, verified with XRD characterization, Fe2B layer was formed, with thickness reaching 160 μm. The material showed a satisfactory response to the boronizing treatment, except for the long-lasting experiments (12 hours), in which the coating was significantly thinner in comparison to the theoretical expectation, due to adsorbed boron depletion. After applying a Fick’s Law-based model and extracting the kinetic parameters, we observed an alteration of the diffusion coefficient of boriding related to austenitizing crystallographic transformation of the ferrous substrate. Additionally, enhancing the results of the kinetic study, an evaluation of the quality of the boride coating was operated via micro-Vickers and Rockwell C (VDI 3198) indentation tests, complemented with optical and SEM imaging. Vickers measurements varied between 1500 HV and 2200 HV. Rockwell C qualification test results were excellent at specific boronizing conditions, proving that boronizing is one of the most advantageous superficially protective techniques for steels.
Keywords: coating technology, diffusion, kinetics, mechanical properties, scanning electron microscopy, x-ray diffraction, boriding, steels
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