Formability of Bimodal Steel Strips Subjected to Heavy-reduction Controlled-rolling Process

Erichsen and deep drawing tests were performed to examine the formability of 0.2% carbon steel sheets containing the bimodal microstructure fabricated by 70-75% heavy-reduction controlled rolling process with a range of heating temperatures from 700-1000°C. The formability of steel sheets was analyzed and discussed in terms of the microstructure, the crystallographic texture, the strain-hardening exponent, and the anisotropy coefficient, which are obtained from the tensile test. In Erichsen test, Erichsen Index (EI) of 900- and 1000°C-heated specimens with a bimodal structure of submicron-sized grains (< 1 μm) and micron-sized grains (2-5 μm) is similar to that of as-received specimen with an average grain size of 41 μm, meaning superior formability. In deep drawing test, failure took place in all 700°C-heated specimens, while others could be drawn with a drawing ratio of 2.0. 900- and 1000°C-heated specimens were uniformly deformed without ears.