Mechanical behavior of AISI 1045 steels subjected to powder-pack boriding

The mechanical behavior of AISI 1045 borided steels was evaluated in the present study. The diffusion of boron at the surface of the steel was achieved using the powder-pack method, and the following procedure was employed: a) boron diffusion was conducted at 1223 K for 1 and 3 h, b) boriding was performed at the aforementioned temperature and treatment times, and a subsequent heat treatment (quenching and tempering) was applied. First, the mechanical performance of AISI 1045 borided steels was established by conducting fatigue rotating bending tests in the 150 to 250 MPa range to verify the influence of the Fe₂B layer on the steel surface and to determine the effects of post-heat treatment on borided specimens. Likewise, the Young's modulus, hardness, and yield strength were estimated by performing Berkovich nanoindentation tests on the Fe₂B layer and diffusion zone, and applied loads of 500 and 100 mN were employed, respectively. Another set of indentation marks were produced under loads of 50, 100 300 and 500 mN to evaluate the hardness behavior of the Fe₂B layer as a function of the indentation load. Compared to steel that was not subjected to the diffusion process, the fatigue strength of AISI 1045 borided steel decreased. Moreover, the experimental results revealed that the post-heat treatment did not have an effect on the fatigue performance of the borided samples. In addition, the mechanical properties of the Fe₂B layer and diffusion zone, which were obtained by performing nanoindentation tests, were dissimilar, leading to higher tensile stresses in the layer/diffusion zone interface. Finally, the indentation size effect (ISE) was observed in the Fe₂B layer, and the elastic recovery (ER) model was used to obtain the apparent hardness of the coating.