Análise da retificabilidade do aço Hadfield em relação ao aço Rápido

Abstract

Hadfield steel is widely used in applications that require high impact and abrasion resistance, such as in the mining, rail, crushing and mills industries. Despite its excellent mechanical properties, Hadfield steel presents challenges in machining, especially in grinding. During the grinding process, elevated temperatures are generated in the grinding wheel-workpiece interface region due to intense heat generation, especially when conventional abrasive grinding wheels are used, which have low thermal conductivity. In additions to that, chips have small dimensions a result of low radial depth of cut, which favors most part of this heat is transferred to the workpiece. This increases it susceptibility to occurrence of thermal damage in the workpiece, such as burning, high variation in hardness, microstructural changes and cracks, among others, compromising its functionality and durability. To mitigate this damage, it is necessary to select the appropriated cutting conditions, with focus on the grinding wheel and its proper dressing operation. In this sense, this work analyzes the grindability of Hadfield steel under different cutting conditions (3 values of radial depth of cut (ae) (10, 30 and 50 µm) and 2 work speed values (Vw) (2.7 and 7.5 m/min)), as well as dressing conditions (2 grinding wheel overlap ratios (Ud) (2 and 8)) aiming maintenance of the surface integrity of the component. Tests were also performed on high-speed steel (HSS) for comparison purposes. Surface roughness (Ra and Rz), microstructure, texture and quality of the ground surfaces and power consumed in the process were the output variables to access the grindability. In general, the roughness increased with radial depth of cut and when using the lowest overlap ratio. Especially when varying the ae from 10 μm to 50 μm with combination with condition Vw = 2.7 m/min and Ud = 2 about 10 % increase in the Ra value was recorded, while in the combination with Vw = 2.7 and Ud = 8, about 41 % increase was achieved. Machining with higher radial depth of cut resulted in surfaces with a higher incidence of visible burning. The Hadfield steel samples most affected by thermal damage were those grinding under conditions overlap ratio Ud = 8. In terms of productivity and visual appearance of the surface, the most suitable conditions for grinding the Hadfield steel are combination of ae = 10 µm, Vw = 7.5 m/min and Ud = 2. In terms of lower roughness and favorable visual appearance, recommended grinding conditions are ae = 10 µm, Vw = 7.5 m/min and Ud = 8. The Hadfield steel presented better grindability than the High-Speed Steel.