Hot rolled steels are steel alloys manufactured through a very efficient direct rolling process following solidification above the recrystallization temperature. Hot rolled steels have a unique microstructure with relatively high contents of bainite and martensite phases continuously dispersed in a ferrite matrix. Hot rolled steels exhibit superior strength and moderate ductility. They are considered as a group of advanced high strength steels with very promising potential application in the automotive industry. Interest of these materials has seen a great increase in recent years.

In the present work, deformation behaviors of hot-rolled, stretch flangeable steels have been investigated. Tensile tests of circularly notched steel samples of different notch geometries are conducted to mimic the deformation condition during stretch flanging. A digital image correlation system is employed to record local strain distribution during the tensile test, while finite element simulations of notched tensile tests are performed to examine the stress state variation within the notched region. The stress-strain relations are derived from load-displacement history of tensile tests and digital image correlation analysis. Multi-particle unit cell models were built to simulate the effect of the distribution of bainite/martensite phases on the deformation behavior of hot rolled steels. The actual stress states experienced within the notched region were extracted from the finite element results and applied directly to the micromechanical models.