Springback characteristics of a martensitic steel for warm U-shape bending: Experiments and FE simulation

Martensitic (MS) steel, a modern type of Ultra-high Strength Steel (UHSS), offers a significantly improved strength-to-weight ratio compared to conventional cold rolled steel grades. This is especially important for weight saving applications on crash-relevant automotive structures. However, it is challenging to conventionally cold form MS steel sheet into complex components due to the lower formability and excessive springback. In this present work, both experimental and finite element simulation methods have been used to investigate the springback characteristics of MS steel in U-shape bending at cold and warm stamping conditions. It was found that the amount of springback is greatly reduced by approximately 62.3% at elevated temperature compared to cold forming. Fast forming speeds were also found to be beneficial for reducing the springback. FE models were successfully developed for the U-shape forming process and close agreement between experimental data and FE simulation results has been achieved. (paper)