Tailored Blank of Ultra-High Strength Steel (UHSS) by Successive Forging: In-Depth Analysis of Geometry Changes and Transition Zone

Successive forging is a multi-stage process for tailoring ultra-high strength steel (UHSS) sheets thickness which normally done using rolling or welding process. Long transition zone and degrading of mechanical properties among the main problem when tailoring or reducing the steel thickness using these two processes. This study investigates the geometrical change and deformation at the transition zone at the thickness reduction area after the successive forging process. A 1.6 mm in thickness JSC1180YN UHSS sheet was subjected to a successive forging process using a 1500-kN servo press, aiming at achieving a thickness reduction of 0.8 mm. 20 forging steps were set with a constant feed rate of 5 mm. The punch was designed with chamfered edges to promote uniform strain distribution while the lower die is set to be flat. The results show that the process achieved a precise and consistent thickness reduction to about 0.8 mm with only a slight increase in width and length. The geometric control was followed by a great improvement in mechanical properties, where there was an increase in Vickers hardness from 415 HV to a stable 442 HV due to strain hardening. Successive forging can shorten the transition zone length with minimal impact on shape changes. Overall, successive forging proves to be a process which is well-controlled that can effectively modify both the geometry and mechanical properties of UHSS, providing many important data for predicting the characteristics of the final forged components.