Effect of the origin of the modified surface layer on the structural strength of workpieces

Abstract

Changes in the deformation behavior of steel solids and their properties have been considered after different methods of surface treatment (carburizing, nitriding, bombardment with low-energy ions, epilam application). Distinctions between concepts “structural strength of a material” and “structural strength of a workpiece” have been illustrated. It has been shown that, at the same material structural strength, the metal mechanical characteristics of a finished metal workpiece (i.e., the workpiece’s structural strength) change cardinally depending on the genesis of the modified layer (features of the structure that arise at the surface) and its contribution to the general state of the workpiece. After ion bombardment (layer thickness less than 1 μm) for the same material with the full retention of its structural strength, we can obtain in workpieces of the material either a very high (25–40%) strengthening without reducing plasticity or huge growth in the plasticity (increase in the elongation by a factor of 1.6) with enhanced strength. The effect is due to the nondislocation mechanism of plastic deformation of the surface layer nanostructurized upon ion bombardment and competition between strengthening and plasticizing depending on the magnitude of its contribution. The effectiveness of the strengthening action of ion bombardment is shown on connecting rod bolts 10 mm in diameter; the plasticizing effect is observed on thin sheet cold-rolled steels (improved stampability).