Springback-free Isothermal Forming of High-strength Steel Sheets and Aluminum Alloy Sheets under Warm and Hot Forming Conditions

Abstract

Quasi-isothermal sheet forming experiments of 300 mm square–1 mm thickness sheets are conducted using newly developed forming dies with a built-in heater and a 3000 kN hydraulic press, and the characteristics of springback reduction due to the elevation in forming temperature are clarified. The springback-free forming of high-strength steel sheets is realized in the warm forming temperature range. This result is confirmed by isothermal V-bending tests in a hot compression testing machine, where a marked decrease in springback is observed when the forming temperature of mild, precipitation-hardened, TRIP and dual-phase steels is higher than 750 K, which is approximately the critical temperature for the onset of ferrite recrystallization.