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High manganese (HMn) steels as part of the second generation of high strength steels are characterized by an excellent combination of mechanical properties, such as a high yield strength and ultimate tensile strength combined with a high ductility. These outstanding properties are a suitable basis for their application in light weight automotive body parts and especially for passenger safety components. However, concerning the sheet metal forming of high manganese steels a large amount of springback after forming due to elastic recovery is a common problem. The high yield strength of high manganese steels in combination with a low elastic modulus introduces high reversible elastic strains during cold forming that will partially recover after forming. Beside the mechanical properties of the material also process parameters e.g. blank holder force in U-profile draw bending have an influence on springback. Therefore, a thorough understanding of the factors influencing springback behavior after forming operations is crucial to establish high manganese steels for industrial sheet metal forming processes. As a first step this paper investigates springback of three different high manganese TWIP steels after U-profile draw bending in comparison to a conventional dual phase steel DP800. Draw bending is an economical characterization method for assessment of springback, because the collective load is comparable to simple deep drawing operations and only a fair amount of experimental effort is needed. The comparison of bending angles of U-profiles after springback of the different steel grades shows a significant higher springback than expected for the HMn steel grade without aluminum, which can’t be explained by specific strength, Young’s modulus and sheet thickness. Springback is also influenced by microstructure in high manganese steels visible in the comparison of the grades X60MnAl23-1 and X60Mn22 because latter shows more twinning in tensile testing. Additionally it is shown, that the variation of the blank holder force can be used to reduce springback in an HMn steel effectively without damage of the sheet.

Investigations on Springback in High Manganese TWIP-Steels using U-Profile Draw Bending