Superficial Grain Refinement of 316L Stainless Steel by Rolling with Rough Rolls

This study presents a novel approach to producing superficial micro- and nanostructures using a cold rolling process with rough rolls, followed by low-temperature annealing. The proposed technique attempts to recreate the superficial deformation occurring in the sandblasting process. It allows for the generation of an inhomogeneous network, or tangle, of high-deformation zones on the material's surface that act as nucleation centers during the subsequent annealing process. However, the proposed method has a significant advantage over sandblasting: it is a continuous process with high productivity. An austenitic stainless-steel sheet, previously normalized, was used as the raw material. The samples were cold rolled using rough rolls (rhombic-based pyramids of 2.08 mm, 1.04 mm, and 1.5 mm in length, width, and height, respectively) and annealed at temperatures between 200 °C and 400 °C for one hour. An optical and electronic microstructure analysis showed the presence of small, heterogeneously distributed surface grains of 200-300 nm in diameter. Finite element analysis revealed significant deformation that was inhomogeneous and likely responsible for the uneven distribution of the recrystallized grains. Additionally, surface nanohardness results showed a 20% increase with respect to the central zone of the material. Finally, wear tests of the treated samples showed lower wear than samples rolled with conventional rolls.