Effects of local heating on formability of advanced high strength steel in U-bending operation

New grades of steel with high strength are being developed within the steel industry, of which, the steel of martensitic structure that has come to light recently with low ductility that is considered as the main concern in sheet bending operation. Indeed, bending has been researched extensively over the years since the application of bent parts varies widely. Yet, similar bending techniques are used to obtain the bent shapes of most ferrous and non-ferrous metals. In this study, a developed method was introduced to enhance the technique for bending the martensitic steel by heating the bending zone, bending in die, then cooling in air. A finite element model was built and validated by experiments to bend a sheet of MS1500 with a thickness of 2 mm into U shape at temperatures ranged from RT to 750°C. Optimal temperature distribution in the sheet was achieved, however, the percentage of martensite decomposing was increased with the temperature elevation resulted in decreases in the hardness of the bending zone. Likewise, the bending load and the springback were highly impacted by the bending temperature. Lastly, sheets with thicknesses of 1, 1.5, and 2 mm were studied using the built FEM to predict the springback, maximum load, and damage.