This paper presents the results of experimental work carried out to study the influence of surface integrity, measured as hardness (HV) and roughness (Ra) on torsional properties of annealed AISI 1020 steel machined by turning using carbide insert tools. The results showed a reduction in ductility when hardness and roughness increase, caused by the plastic deformation induced after machining. It was shown that the shear yield strength increases, as a consequence of the material strengthening by work-hardening and the rise of stress concentrators. Further, the ultimate shear strength increases with surface hardness, having the opposite effect when the surface roughness caused greater stress concentration. RESUMEN:Este artículo presenta los resultados del trabajo experimental llevado a cabo para estudiar la influencia de la integridad superficial, medida como dureza (HV) y la rugosidad (Ra) en las propiedades a torsión del acero AISI 1020 recocido torneado con herramientas de corte con inserto de carburo. Los resultados mostraron una reducción de la ductilidad con el aumento de la dureza y rugosidad, causado por la deformación plástica inducida después del mecanizado. Se demostró que el límite elástico de cizalladura aumenta como consecuencia del endurecimiento del material y el incremento de concentradores de esfuerzos. Además, la resistencia máxima a la cizalladura aumenta con la dureza de la superficie, pero tiene el efecto contrario cuando la rugosidad de la superficie provoca una mayor concentración de esfuerzos. relevant parameter used for evaluating a machined surface. Many mechanical components require special attention on the surface roughness because it affects the appearance, reliability, and function of the product. Meanwhile, these components also need to have a high surface hardness to resist wear and plastic deformation during services. Therefore, an improved control of surface integrity is considered to be of importance.Several factors affect machined surface roughness, such as tool geometry, tool wear, coolant and cutting parameters. The influence of tool geometry by means of the nose radius has been previously investigated, proving that high radius values cause rough surfaces [2,3]. According to a previous experimental research cutting with a worn tool also resulted in worse roughness [4]. Works conducted to analyze the effect of coolant showed that higher surface roughness was achieved on components machined without coolant, as compared to those with a supply of coolant [5,6]. Finally, there is an abundance of literature describing the relation of cutting parameters on surface roughness. Results from these studies indicated that a higher feed rate and depth of cut increase the surface finish values while cutting speed had the opposite effect on aluminum [6,7], brass alloys [8], carbon alloy steels [9][10][11][12], EN-31 steel [13] and stainless steels [14].

In this work, the effect of the torsion process angle of twist and distance from the center of cylindrical bars on the microhardness profile of annealed AISI 1045 steel was studied. The results showed that the microhardness increase with the evaluated parameters and the hardening is related to the plastic deformation caused by the process rather than by microstructural transformations. Based on the experimental results, ANOVA-Pareto analysis was conducted proving that the angle of twist is the most influential control factor (59.35%) among the parameters investigated. Finally, a model to predict the microhardness profile from the torsion process is presented. RESUMEN:En este trabajo se estudió el efecto del ángulo de giro del proceso de torsión y la distancia desde el centro en barras cilíndricas en el perfil de microdureza del acero AISI 1045 recocido. Los resultados mostraron que la microdureza aumenta con los parámetros evaluados y el endurecimiento se relaciona con la deformación plástica causada por el proceso más que por transformaciones microestructurales. Con base en los resultados experimentales, se realizó un análisis ANOVA-Pareto que demostró que el ángulo de giro es el factor de control más influyente (59,35%) entre los parámetros investigados. Finalmente, se presenta un modelo para predecir el perfil de microdureza del proceso de torsión.