Effect of Surface Nanocrystallization Induced by Supersonic Fine Particles Bombardment on Corrosion Fatigue Behavior of 300M Steel

Although 300M steel is one of the preferred materials for aircraft landing gears and other key load-bearing components in aviation because of its ultra-high strength and excellent ductility, its susceptibility to corrosion fatigue fracture during service in "high temperature, high humidity, and high salt" marine environments is a significant safety hazard. Surface strengthening can effectively improve the corrosion fatigue resistance of materials, thereby improving the reliability of components and extending their service life. Hence, the surface nanocrystallization of 300M ultra-high strength steel via supersonic fine particle bombardment (SFPB) and its effect on the corrosion fatigue behavior of the material in 3.5%NaCl solution was systematically investigated and the surface morphology, microstructure evolution, and residual stress relaxation of 300M steel after corrosion fatigue were characterized. After SFPB, the grain size near the surface was observed to have reduced to the nanoscale, forming gradient nanostructures and high amplitude residual compressive stress. The SFPB treatment effectively improved the corrosion fatigue life of 300M steel at the same loading-stress level. After corrosion fatigue, the grain size of the SFPB-treated 300M steel remained at the nanoscale near the surface, and the increase in the loading stress level caused a significant increase in the dislocation density in the subsurface layer and the number of deformation twins. During the corrosion fatigue loading, the residual compressive stress induced by SFPB in the surface layer of 300M steel relaxed to various degrees, with the degree of residual stress relaxation being significantly higher for higher loading stress levels.