Increasing the bending strength of hardened AISI 1045 steel by milling process

Surface characteristics play a critical role in initiating and propagating defects when metallic components are subjected to static or dynamic loading, directly influencing their mechanical performance and service life. Therefore, selecting an appropriate finishing process is essential for improving surface integrity and mechanical resistance. This study investigates the effects of cutting speed and feed per tooth on the flexural strength of AISI 1045 steel specimens subjected to hard machining using an 80 mm diameter end mill, with cutting speeds of 100 and 400 m/min. Specifically, it evaluates the influence of surface roughness and the resulting changes in surface hardness on the bending behavior of the material. The findings indicate that surface roughness significantly impacts bending strength more than the metallurgical alterations caused by the machining process. A reduction in maximum surface roughness from 4.66 µm to 3.02 µm, approximately 35%, resulted in a 51% increase in rupture stress and a 137% increase in deflection at fracture. In contrast, variations in surface hardness induced by machining were found to have a negligible effect on mechanical strength. Once failure is initiated, the material's hardness becomes even less relevant, as it does not influence crack propagation. These results highlight the importance of optimizing surface finishing parameters to improve the structural performance of hardened steels, particularly in the metalworking and automotive industries, where mechanical reliability and durability are crucial.