Residual stress and surface microhardness post-milling in 2205 duplex steel

The improvement of mechanical strength and corrosion in duplex stainless steels can be maximized when the fractions between phases (α) and (γ) are balanced. Machining operations may compromise surface integrity through microstructural deformations. In this study, surface milling of a 2205 duplex steel was performed under Vc conditions between 298 and 651 m/min and fz between 0.04 and 0.18 mm/tooth. The microstructural evolution characteristics, mechanical properties and residual stresses were investigated by optical microscopy, SEM, MFM, XRD and Vickers microhardness. After milling, microstructure was found to be deformed by shearing of the cutting tool, and the volume fraction of austenite and ferrite was altered, as determined by Rietveld refinements because of the transformation of austenite into martensite (α') induced by plastic deformation. The samples also exhibited variations in phase-specific microhardness, associated with strain-induced martensite formation and the presence of tensile residual stresses.