Examination of Formability and Hardness Variation in Hydroformed Low-Carbon Steel Sheets

Production Engineering & Metallurgy College, University of Technology-Iraq, Baghdad 10066, Iraq

Published online: 24 June 2026

Abstract

Sheet hydroforming is a modern metal forming technique that employs hydraulic pressure to produce complex sheet components with enhanced dimensional precision and improved mechanical properties. In this work, the formability and mechanical behavior of AISI 1008 low-carbon steel sheets with thicknesses of 0.48 mm, 0.68 mm, and 0.88 mm were experimentally evaluated using the hydraulic bulge test and compared with the conventional Nakazima formability test. Circular specimens with a diameter of 180 mm were tested at a deformation rate of 10 mm/min. The Nakazima test results indicated maximum stresses of 4.6 MPa, 6.4 MPa, and 9.2 MPa for sheet 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. Conversely, the hydraulic bulge test exhibited improved forming performance, achieving burst pressures of 6.6 MPa, 9.58 MPa, and 11.58 MPa, along with dome heights of 32.633 mm, 30.45 mm, and 40.82 mm for the respective thicknesses. The failure thickness increased with the original sheet thickness, reaching 0.345 mm for the 0.88 mm specimen. Micro-hardness measurements performed at the pole region using a 200 g load (HV0.2) demonstrated pronounced strain hardening following hydroforming. In the case of the 0.88 mm sheet, the maximum formed height reached 37.16 mm, while the pole thickness decreased to 0.559 mm, accompanied by a micro-hardness value of 187.9 HV0.2. Overall, the findings demonstrate that sheet hydroforming provides better formability, higher load-carrying capability, and improved surface quality compared with conventional forming processes.