Aplicação de modelos estatísticos para verificar a influência dos elementos residuais (Cr, Ni e Cu) na usinabilidade de aços de corte-fácil

Abstract

Low carbon free-cutting steels are widely used for parts and components subject to moderate strength levels and relatively low shock loading, with machinability being the most important factor. Examples are hydraulic valves, keys, contact boards and other parts requiring rapid metal removal. These materials are especially designed for high machinability, that is, reduced tool-chip contact length, low coefficient of friction between the tool and the chip or the workpiece, production of easy handled chips, low cutting forces and power consumption, thereby providing long tool lives and/or high productivity by using high cutting speeds. Elements like Mn, P, S and Pb are generally present in their composition ensuring improved machinability. However, low carbon free-cutting steels also contain residual elements that often impair machinability such as Cr, Ni, Mo and Cu, which are difficult to be eliminated during the manufacturing process. This work investigates the influence of the trump elements Cr, Ni and Cu on the machinability of the SAE 12L14 low carbon free-cutting steel after testing in accordance with VOLVO STD 1018, 712 standard. The standard is based on tool life tests using HSS single point tools in face milling operation under special cutting conditions. The tool life results were treated statistically using ANOVA method, Student´s t distribution and multiple regression analysis. The results showed that the residual elements actually affect machinability of the SAE 12L14 low carbon free-cutting steel, with Ni and Cu being more significant.