Improving the Sheared-edge Formability of High Strength Dual-phase Steel

Dual phase steels are commercially attractive since they offer good formability at a high strength.These steels exhibit high n-values and high uniform and total tensile elongations. However,one limitation in the application of high strength dual phase steels is failure during sheared edge stretching.In order to develop high strength dual phase steels with improved sheared edge ductility,the amount and hardness of both the hard and soft constituents must be carefully controlled. The failure mechanism observed during stretching of the sheared edge is closely related to the microstructures(i.e.amounts,hardness,size and distribution of different phases),and the initiation of cracks were found to start at ferritemartensite interfaces which will be discussed in this study.In the present research,the effects of pre-annealing conditions(hot and cold rolling),different CGL processing paths and alloying elements on the sheared edge formability of dual phase steels have been studied. It has been found that all three of these variables can exert a strong influence of sheared edge ductility as determined in the hole expansion test.