Improving the plasticity of thin cold-rolled steel sheet for cold stamping

Abstract

Two methods of surface treatment are proposed to improve the technological plasticity of thin cold-rolled carbon-steel sheet: ionic bombardment by low-energy titanium atoms; and epilam coating. Both methods markedly increase the extensibility of the sheet (by a factor of 1.2–1.3), as estimated by the maximum crater depth without cracking in Erichsen tests (from the VG group to values exceeding those for the VOSV group, which corresponds to extremely complex extension, in State Standard GOST 9045–93). This is associated with change in the behavior of the sheet on deformation (with change in the properties of the material) as a result of two processes: the healing of surface defects; and the creation of hybrid nanocrystalline and submicrocrystalline structure in the surface layer. In epilam coating, only the first process occurs; in ionic bombardment, both are observed.