Mechanical behavior on Cr base steels surface treatment

The surface treatment by diffusion of boron atoms enhances mechanical properties depending on the condition under which a hard coating is formed during a pack boriding process. In the present work, a slow bending test was performed for evaluating the mechanical behavior with hard coatings on surface Cr base steels. The formation of a hard coating was carried out by a surface treatment by diffusion of boron atoms at temperature 1173 K for time periods of 4, 6 and 8 h. The presence of the hard coatings was confirmed by scanning electron microscopy (SEM) with saw-tooth morphology and X-ray diffraction analysis surface revealed peaks of FeB, Fe₂B, CrB. The evaluation of the effect of each experimental conditions was determined along the depth of the hard coatings. The mechanical properties were determined by depth sensing instrument indentation along the depth of the hard coatings at a constant load of 150 mN to determine the hardness gradient and Young's modulus. A three point bend test was carried out on specimens with hard coatings, the result showed an increase of strength with respect to the untreated Cr base steel. The fracture surfaces of bend tested samples were examined using a SEM, and showed a morphology of brittle cleavage and columnar character of the microstructure which contributes to the brittle character of failure.