The Study of Practical Adhesion of a Layer/Substrate System on an AISI 8620 Steel Exposed to Boriding and Borocarburizing

Novel results about the practical adhesion of the layer/substrate system on borided and borocarburized AISI 8620 steels exposed to a quenching-tempering post-treatment were obtained. The hardness (H) and Young modulus (E) were assessed by instrumented Vickers microindentation. Consequently, the residual stresses (σr) and elastic strain to failure (H/E) were estimated. The microstructural characterization of the entire experimental set was carried out by scanning electron microscopy (SEM). Finally, the practical adhesion of the experimental set was evaluated with a scratch test, using a progressive load from 1 to 150 N at 10 mm min–1, with a scratch length of 7 mm. The results indicated that the quenching-tempering treatment increased the practical adhesion of the layer/substrate system, due to the dissolution of the outer FeB phase on the boride layer. Furthermore, the borocarburized material showed an increase around 2 times of the critical load during the practical adhesion test, attributed to a greater depth of the compressive residual stresses along the boride layer and the carburized zone. The borocarburizing + quenching-tempering treatment provided a mechanical support to the AISI 8620 steel, reducing the brittleness of the layer, in comparison with the borided and borided plus quenching-tempering material.