Fig. 1. (a) Machining cutting process of NG 304 SS. Cutting fluid was used to avoid overheat of the sample surface; (b) test samples. All the samples were cut from the same position of the machined plates.

Fig. 2 Three-dimensional morphology of the machined samples. (a)-(g) are the machined samples labeled #1 to #7 respectively. Machining characters like peak, valley and feed direction are denoted by arrows.

Fig. 3. (a)-(g) Cross-sectional metallographs of machined samples, with numbered #1 to #7 respectively. Machining-produced characteristics such as “peak”, “valley”, slip band, deformed GB, broken chip are all identified in the photograph.

Fig. 4. EBSD analysis of cross-sectional deformation of the machined samples, including (a) band contrast (BC) map, (b) inverse pole figure (IPF), and (c) kernel average misorientation (KAM) map. Samples from #1 to #7 are arranged in order from left to right.

Fig. 5. (a) Effect of feed rate on the distribution of the cross-sectional hardness. The cutting speed (Vc) is 140 r/min, the cutting depth (ap) is 1 mm, and the feed rate (f) is 0.50 m m/r, 0.20 mm/r, 0.15 mm/r respectively; (b) Effect of cutting speed on the cross-sectional hardness. The feed rate is 0.20 m m/r, the cutting depth is 1 mm, and the cutting speed is 450 r/min, 300 r/min, 140 r/min respectively; (c) Effect of cutting speed on the cross-sectional hardness. The cutting speed is 450 r/min, the feed rate is 0.20 mm/r, and the cutting depth is 1.0 mm, 0.5 mm, and 0.2 mm respectively.

Fig. 6. (a) Schematic diagram of sampling in different areas of Sample #5. Samples are taken from the surface, the deformation zone about 50 μm from the surface, and the substrate 300 μm from the surface; (b) The sample preparation process using FIB, where b-1, b-2, b-3 is the ion beam cutting process at three sampling positions.

Fig. 7. (a) Bright field (BF) micrograph of the microstructure of the machined surface; (b) Selected electron diffraction of the nanocrystalline region; (c) Dark-field micrograph of the nanocrystalline region; (d) Local BF micrograph of the nanocrystalline region and the corresponding SADP.

Fig. 8. (a) The bright-field micrograph of the FIB sample in the machining-affected zone (MAZ); (b) The corresponding selected area electron diffraction of the deformation bands; (c) Dark field image of the twin.

Fig. 9. Bright field TEM micrograph representative of 304 stainless steel substrate (operating vector g = 200).

Fig. 10. (a) FIB sampling of the surface of Sample #5; (b) TEM bright field scanning transmission micrograph of the corrosion sample with big oxide particle on top and SADP of the area below big particle; (c) Selected area electron diffraction of the big oxide particle and the corresponding EDS analysis; (d) TEM dark field scanning transmission micrograph of the corrosion sample; (e) EDS line scan analysis on the cross-section oxide film. In scanning transmission mode, the electron beam spot size is 1.5 nm, and the scanning step size is 2 nm.

Fig. 11. (a) Morphology and FIB sampling at the deformed area of Sample #5 after corrosion; (b) TEM bright-field scanning transmission micrograph; (c) TEM dark-field scanning transmission micrograph.

Fig. 12. (a) BF micrograph shows corrosion morphology of the grain boundary in the deformed area of Sample #5; (b) high magnification of oxides morphology at the tip of grain boundary corrosion front; (c) EDS mapping results of Cr, Fe, Ni, O elements in GB corrosion area.

Fig. 13. (a) TEM bright-field corrosion morphology at the deformed zone of Sample #5, with the inserted selected area electron diffraction pattern; (b) high-angle annular dark field (HAADF) image of the deformation twin corrosion area; (c) EDS mapping analysis of Cr, Fe, Ni, and O elements; (d) EDS line scan analysis across the corroded deformation twin. Under scanning transmission mode, the electron beam spot size is 1.5 nm, and the scanning step size is 2 nm.

Fig. 14. (a) Schematic diagram of FIB sampling of the cross-section of Sample #5; (b) the cross-sectional morphology after the FIB milling; (c)-(e) the high-magnification photo of the I, II, and III regions in (b).

Fig. 15. Comparison of the corrosion behaviors of different microstructure of Sample #5. A, B&E represent the general corrosion rate of the fine-grain region, plastic deformation region and substrate material respectively. C&D represent the localized corrosion rate along grain boundary, deformation bands in the same depth of deformation region.