Machining-Induced Surface Deformation Layer and the Impact on Tensile Plasticity of 316L Stainless Steel

316L stainless steel is widely used in aerospace components because of its mechanical properties and corrosion resistance. Standard tensile specimens are commonly used to evaluate material behavior, yet their measured tensile response can be affected by the final turning process. This study investigated the effects of cutting speed and depth of cut on the surface integrity and tensile properties of small standard 316L tensile specimens. Cutting-temperature measurement, optical surface characterization, EBSD analysis, fracture observation, and quasi-static tensile testing were combined to evaluate the machined specimens. A cutting speed of 45 m/min produced the most stable thermal response after repeated tool–workpiece contacts, with a temperature variation of 40.3%. Lower cutting speeds suppressed vibration-induced micro-pits and improved the morphology consistency between Area I and Area II. At the maximum depth of cut, increasing the cutting speed from 15 m/min to 60 m/min reduced the tensile strength from 1136.02 MPa to 1082.75 MPa and the tensile elongation from 56.6% to 53.5%. These results show that the tensile properties of turned specimens are governed by the combined effects of thermal response, surface morphology, deformation-layer microstructure, and fracture behavior. Among the tested conditions, Vc = 15 m/min, ap = 0.4 mm, and f = 0.1 mm/rev are recommended when tensile properties are the main requirement