Fine evaluation of surface integrity of hardened 1.4418 stainless steel after finish dry turning

Abstract

Abstract1.4418 hardened stainless steel (SS) is widely used in mechanical engineering because of its high functional properties. They can also be enhanced by procuring improvements in the state of the surface layer (SL) and, above all, in the factors of its strengthening, among others the average size of coherent scattering regions (ASCSR), dislocation density (DD), residual stresses (RS) of first and second orders, and relative micro-deformations of the crystal lattice (RMCL). This study investigates the effect of cutting speed (vc) ranging from 100 to 250 m/min and feed rate (f) ranging from 0.005 to 0.25 mm/rev on the indicators of SL condition after finish turning the steel tested. A reduction in ASCSR values below 8 nm was obtained for vc = 100–135 m/min, while an increase of ~ 20% was obtained for 180–250 m/min and with the f ranging from 0.2 to 0.25 mm/rev. An increase in RMCL of ~ 90% was registered for vc = 170–230 m/min and f = 0.2–0.25 mm/rev. A decrease in DD below 109 cm−2 was obtained for vc = 180–250 m/min and its ~ 25% increase for vc = 100–135 m/min. A high correlation between ASCSR and DD was shown. In the deformed material, the dislocation’s resistance to motion increases in proportion to the increase in its density. A high linear correlation coefficient in the range of 0.8–0.9 is found between ASCSR, DD, and first-order RS on the one hand, and Sa and Sz surface texture parameters, which are used in the industry to assess product quality, on the other. Additionally, the effect of plastic side flow (PSF) was observed and described. When machining with vc = 119 m/min and f = 0.22 mm/rev, the intense plastic deformation of the material causes outflow and shearing of the surface micro-hills. Favorable compressive stresses (below − 100 MPa) were registered in the range of vc = 225–250 m/min at f = 0.005–0.05 m/rev and 0.2–0.25 mm/rev, as well as vc = 115–180 m/min and f = 0.05–0.17 mm/rev. The study proved the existence of a relationship between the cutting parameters and indicators of the thin crystalline structure of SL. This means that by proper controlling of these parameters, it is possible to obtain such a state of the SL workpiece, which will ensure its long-term use.