Assessment of forming limits and hardness distribution in hydroformed low carbon steel sheets with nanotechnology-enhanced surface and deformation mechanisms

Abstract

Sheet hydroforming is an advanced metal forming process that utilizes hydraulic pressure to manufacture complex sheet components with high dimensional accuracy and improved mechanical performance. In this study, the formability and mechanical properties of AISI 1008 low carbon steel sheets with thicknesses of 0.48 mm, 0.68 mm, and 0.88 mm are experimentally investigated using the hydraulic bulge test and compared with the conventional Nakazima formability test. All specimens had a diameter of 180 mm and are tested at a deformation speed of 10 mm/min. The Nakazima test results showed that the maximum stresses are 4.6 MPa, 6.4 MPa, and 9.2 MPa for thicknesses of 0.48 mm, 0.68 mm, and 0.88 mm, respectively, with corresponding dome heights of 30.205 mm, 29.05 mm, and 36.423 mm. In contrast, the hydraulic bulge test demonstrated superior performance, with burst pressures of 6.6 MPa, 9.58 MPa, and 11.58 MPa, and dome heights of 32.633 mm, 30.45 mm, and 40.82 mm for the same thicknesses. Thickness at failure increased with initial sheet thickness, reaching 0.345 mm for the 0.88 mm specimen. Hardness measurements conducted at the pole using a 200 g load (HV0.2) revealed significant strain hardening after hydroforming. For the 0.88 mm sheet, the maximum product height was 37.16 mm, with a pole thickness of 0.559 mm and a micro-hardness value of 187.9 HV0.2. The results confirm that sheet hydroforming enhances formability, load-bearing capacity, and surface integrity compared with conventional forming methods. In addition, nanotechnology-based approaches such as nanoscale grain refinement, nanoparticle-assisted lubrication, and nano-enhanced surface engineering can further improve deformation uniformity, reduce friction effects, and enhance strain hardening behavior during hydroforming processes.